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Volume 65, 1936
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Metamorphism of the Te Anau Series in the Region North-west of Lake Wakatipu

[Read before the Otago Institute, November 20, 1934; received by the Editor March 24, 1934; issued separately, December, 1935.]

Contents.

  • Scope of Investigation.

  • Previous Work.

  • Petrography of Least-Altered Rocks.

    • General Features.

    • Breccias.

    • Greywackes.

  • Petrography of Partially Reconstituted Rocks.

    • Meta-andesite.

    • Semischists.

    • Slates and Phyllites.

    • Crystalline Limestones and Calc-phyllites.

  • Petrography of Completely Reconstituted Rocks.

    • General Features.

    • Chlorite-epidote-albite-schists.

    • Actinolite-epidote-albite-schists.

    • Sericite-schists.

    • Ferruginous schists.

    • Quartz-albite-schists.

    • Calc-schists.

    • Stilpnomelane-schist.

  • Zones of Progressive Metamorphism.

  • The Significance of Actinolite.

  • Relation to Schists of Central Otago.

  • Acknowledgements.

  • Locality-list of Specimens Cited.

  • Literature Cited.

Scope of Investigation.

During the past five years the writer has paid a number of visits to the country which lies between the head of Lake Wakatipu and the Hollyford and Eglinton Valleys some fifteen miles to the west. The region is rugged, mountainous, and for the most part covered with dense beech forest; no attempt has therefore been made to map it in detail, and observations have been confined to the more accessible localities close to the tracks which follow the Greenstone, Routeburn, and Hollyford Valleys and to the new Eglinton Valley road.

Throughout the central and southern portions of the area there is an extensive development of green greywackes, breccias, slates, and rare intercalated limestones belonging to the Te Anau Series, the age of which is generally considered to be Permian, though only imperfectly preserved fossils have ever been recorded from this district. These rocks maintain a strike of 5° to 10° W. of N. and a steep though variable dip throughout.

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The Te Anau Series is flanked both eastward and westward by semischists, fine-grained, rather imperfectly foliated schists and phyllites, to which names such as Cecil and Walter Peak Series, Kakanui Series, and Lake Harris Schists have been applied by various earlier writers in the belief that their metamorphosed condition implied a pre-Te Anau age. There appears, however, to be perfect transition from the rocks of the Te Anau Series into the adjacent schists, and the writer therefore regards the two units as stratigraphically equivalent and differing from each other only in metamorphic grade.

In the north-western portion of the map the north-eastern corner of the great intrusive complex of Fiordland abuts against the greywackes and schists of the Te Anau Series. The actual junction is almost certainly determined by a profound fault, but there is nevertheless evidence which indicates that some at least of the Fiordland igneous rocks are intrusive into the Te Anau Series (Park, 1921, pp. 42, 43). These latter rocks are also invaded at a number of points in the Caples, Routeburn and Hollyford Valleys by small lensoid masses of greatly altered ultrabasic rocks which are doubtless to be correlated with the great peridotite intrusion of the Red Mountain-Cascade Valley region, some thirty-five miles to the north. These are believed to be younger than the granites, diorites, norites, and related rocks of the Fiordland complex, and are almost certainly Lower Cretaceous in age (Turner, 1933, pp. 276, 277).

With the exception of the Pleistocene moraines and stream gravels which here and there superficially mantle the older rocks, the youngest rocks in the district are a series of Tertiary conglomerates, arkoses and feldspathic sandstones which have been involved by faulting among the Te Anau rocks around Lake Fergus in the south-western corner of the map. These are rather poorly fossiliferous and are a remnant of a northerly extension of the great series of Tertiary beds which covers extensive areas in the lower part of the Eglinton Valley and around the head of Lake Te Anau (Park, 1921, p. 53).

The succession of rocks in the Wakatipu-Hollyford region may be summarised thus:—

(5)

Pleistocene gravels and moraines.

(4)

Tertiary conglomerates, arkoses and fossiliferous feldspathic sandstones.

(3)

Lower Cretaceous ultrabasic intrusive rocks.

(2)

Fiordland plutonic rocks (granites, diorites, norites, etc.).

(1)

Te Anau Series and equivalent associated schists (? Permian).

The purpose of the present paper is to give an account of the petrology, mutual relationship, and metamorphie history of the Te Anau Series and the adjacent associated schists.

In the near future it is hoped to publish a summary of the main features of the Fiordland plutonic rocks as developed along the western border of this area, while the ultrabasic intrusives of the Caples and Routeburn Valleys are still in process of investigation by Mr C. O. Hutton.

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The main papers dealing with the Te Anau Series and associated schists in the Wakatipu-Hollyford region are those of Hector (1864), Cox (1878, 1879), Hector (1881), McKay (1881), Park (1887), Hector (1892), and Park (1921).

In Hector's paper of 1864 his east-to-west section across the province of Otago shows the Te Anau Series of the Greenstone Valley as occupying a syncline, on the flanks of which an underlying formation of altered rocks is exposed. Later the same writer (Hector, 1881) gave a more detailed account of the distribution of the Te Anau Series, based upon McKay's field observations, and clearly stated the view that these rocks are exposed in the core of a southward-pitching syncline from Lake Gunn to beyond the Routeburn, and are flanked on either side by underlying metamorphic rocks.

In 1879 Cox published a good section across the Te Anau Series as exposed in the lower part of the Greenstone Valley. He recorded a downward (eastward) transition with perfect conformity into finegrained schists, which he believed to lie unconformably above the more strongly metamorphosed mica-schists of Hutton's Wanaka Formation.

The only comprehensive account of the geology of the district west of Lake Wakatipu is McKay's report of 1881, in which five main formations are recognised as occurring in the present area, viz.:

  • (1) Crystalline schists;

  • (2) Lake Harris schists;

  • (3) Cecil and Walter Peak Series;

  • (4) Te Anau Series;

  • (5) Maitai Series.

The “crystalline schist” group includes the gneisses and plutonic rocks of the Fiordland complex. The “Lake Harris schists” and the “Cecil and Walter Peak Series” include the fine-grained rather poorly foliated schists on either side of the Te Anau Series, but in the map (p. 128), section (p. 132) and accompanying text, the application of these two terms is somewhat confused. McKay noted that the rocks which he mapped as “Maitai Series” are “not stratigraphically distinct” from those of the Te Anau Series. In the present paper all these relatively unaltered rocks are grouped together as the Te Anau Series. McKay's map is very useful in that it shows clearly how the grade of metamorphism rises both eastward and westward of the central area of almost unmetamorphosed rocks.

In his report of 1887, Professor James Park, in dealing with the region immediately north of that now under discussion, has recorded important data bearing upon the nature and distribution of the Te Anau Series. The close association and possible stratigraphical connection of the latter with the fine-grained schists (“Kakanui Series”) is fully recognised, and intrusion of massive granitic dykes into the Te Anau rocks is mentioned (Park, 1887, pp. 133, 134). It is also shown that the western strip of schists is itself flanked on its western side by a second strip of unaltered Te Anau rocks which continue along the Bryneira Range into the

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Red Hills country. Rock specimens recently collected in this area by Mr C. Yunge, of Stewart Island, and presented by him to the Geology Department, University of Otago, confirm this interesting observation.

In Professor Park's latest bulletin (Park, 1921) the rocks of the Te Anau Series are classed as indistinguishable from those of the Maitai Series; the occurrence of (?) Permo-Carboniferous fossils in limestones of this group on the Livingstone Range is recorded, and reference is made to Hector's earlier record of “Permian fossils like those found south of Nugget Point” near Lake Harris Saddle (Hector, 1892).

Petrography of the Least-altered Rocks.

General Features.

None of the rocks of the Te Anau Series collected by the writer is entirely unaltered; the effects of incipient reconstitution are to be seen in every specimen on microscopic examination. Nevertheless, throughout much of the area, e.g., in the Greenstone and Caples Valleys, the coarser rocks show no trace of schistosity, the microstructure is still dominantly clastic and metamorphic recrystallisation has only just commenced.

These relatively unaltered rocks are for the most part greywackes and greenish breccias. Argillaceous rocks, being more susceptible to metamorphism than the associated coarser-grained greywackes, have been converted to slates and phyllites which may be considered more appropriately with the metamorphosed rocks.

Breccias.

The breccias of the Te Anau Series are hard compact rocks made up of well cemented subangular rock-fragments which in most specimens range up to 2 or 3 cm. in diameter, though this dimension may be greatly exceeded in some instances. Typically the rocks are green in colour owing to the presence of secondary epidote and chlorite, but not infrequently red fragments of jasperoid slate are conspicuous against the general green background.

In thin section, the chief constituents are relatively coarse heterogeneous fragments of igneous and sedimentary rocks accompanied by simple mineral grains also of clastic origin. All are enveloped in an interstitial matrix of secondary minerals resulting from incipient metamorphism.

Among the coarse constituents of the breccias, basic and semibasic igneous (mainly volcanic) rocks are well represented, though in many of these the structure is the only indication of igneous origin, for alteration-products are so extensively developed as to render it impossible to do more than conjecture as to the initial mineral composition. Essential petrographic details of typical examples are given below:—

(a) Epidote-rich altered basalts (e.g., 1493*, 1945, 2301). The main constituent is granular, yellow, ferruginous epidote which often exceeds 50% of the total composition. Small ragged flakes of pale

[Footnote] * Numbers refer to specimens and sections in the Geology Department, University of Otago.

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green, pleochroic, negatively elongated chlorite (showing yellowish-brown anomolous interference tints) are always plentiful though greatly subordinate in quantity to epidote. Sphene, quartz and (?) albite are constant minor constituents, while granular magnetite and carbonates were sometimes noted. The structure of the initial rock is sometimes well preserved in that the feldspar laths though greatly altered have retained their original form (e.g., 1493); but in the more altered fragments the traces of the initial structure are destroyed, and the rock is a fine-grained semi-opaque epidosite (e.g., 2301) the igneous origin of which may be inferred only by a comparison with less altered material. In one fragment (1945) phenocrysts of augite (now largely replaced by talc and chlorite) and of greatly altered plagioclase are imperfectly preserved. Vesicles infilled with coarse epidote and quartz (1493) or calcite (1945) are occasionally present.

(b) Andesites (1493, 2305, 2307). Andesitic rocks of several different types have been observed in the breccias. One of the least altered of these (2305) is a porphyritic type in which large tabular phenocrysts of medium andesine (sometimes 3 mm. in length) are enclosed in a groundmass of stout plagioclase prisms (0-1 mm. long) and scattered irregular grains of ilmenite. Small flakes of pale green chlorite and granules of epidote or clinozoisite have developed along the cleavage-planes of the phenocrysts and also occur interstitially among the feldspars of the groundmass. Good cubes of pyrite occur here and there, and, in one instance, are enclosed within one of the large feldspar phenocrysts. Occasional masses of chlorite quartz and iron ore, and rather irregular patches of almost pure chlorite perhaps represent infilled vesicles. The chlorite is a pale green distinctly pleochroic type with positive elongation and very low birefringence giving an anomolous violet-blue interference tint.

(c) Ceratophyres (1493, 2307). The presence of ceratophyres in the Te Anau breccias is of interest in view of the recent discovery of similar rocks in the Jureassic conglomerates of Nugget Point (J. B. Mackie) and Kawhia (J. A. Bartrum), as well as among the partially metamorphosed volcanic rocks of Bluff (H. Service). In 2307 large tabular phenocrysts of albite (about Ab93An7) are enclosed in a coarse trachytic base of albite laths which show combined Carlsbad and albite twinning. Small granules of opaque iron-ore are plentiful. Secondary minerals include rather coarse epidote and clinozoisite, granular sphene, acicular actinolite usually in sheaflike aggregates, a little chlorite and rarely calcite. The ceratophyre of 1493 is considerably more altered. The phenocrysts of albite, though sharply defined and still clearly showing the original sanidine habit and traces of Carlsbad twinning, are now largely replaced by a mixture of quartz, a fibrous zeolite and coarse yellow epidote. The groundmass consists of yellow epidote, sparsely scattered sheaves of actinolite needles, and a colourless indeterminate matrix (probably albite and quartz). Large prisms of smoky apatite are conspicuous, and drop-like granules of sphene are not uncommon.

(d) Plutonic rocks. In 1924 there are several fragments of what appear to be sheared diorites or gabbros, consisting of rather coarse xenomorphic pale green hornblende enclosed in greatly altered

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feldspar. Otherwise plutonic rocks are absent from the sections examined by the writer.

Non-igneous rocks represented by clastic fragments in the Te Anau breccias include micaceous and graphitic slates (1924, 2304, 2307), greywackes (1924, 2301, 2304, 2306), quartzites (1924, 2304, 2306) and calcareous mudstone (1945). The quartzites usually show the effects of marked cataclasis, and in addition to the main constituent may contain albite and interstitial calcite, secondary sericite and rare clastic grains of biotite and hornblende (1924). Though carefully searched for, no schists or other typical metamorphic rocks were noted with certainty; rare fragments of a rather coarse albite-chlorite rock, and of a zoisite-quartz rock (both in section 1924) may perhaps be of metamorphic origin however.

The chief minerals occurring as simple grains are plagioclase, quartz, augite and hornblende. Less frequent are iron-ore (e.g., 2301), colourless or smoky apatite (1924, 1945), yellow epidote (1945) and a yellow isotropic (?) glass (2301). By far the most plentiful of these is plagioclase which in most instances is completely saussuritised (rarely sericitised) or else partially replaced by coarse yellow epidote (e.g., 2301). Hornblende is especially plentiful in 1924, where different varieties respectively show deep blue-green (Z to c = 27°), deep brown, deep brownish-green and pale pinkish-brown absorption tints for the Z direction. Pale pink augite, usually partially replaced by talc and chlorite, is widely distributed. In 1945 the replacement clearly takes place in two stages, viz., augite → chlorite, and chlorite → talc (cf. Hess, 1933). Thus a grain of augite may be surrounded by a zone of chlorite which in turn is rimmed with talc; or chloritie pseudomorphs after pyroxene are often themselves replaced marginally and along cracks by secondary tale. The iron-ore grains appear usually to be intergrown magnetite and ilmenite. The latter mineral alters readily to translucent leucoxene, against which the opaque lamellae of black magnetite stand out in sharp relief. Finally the presence of rounded pseudo-morphous masses of green bowlingitic serpentine enclosing small granules of sphene are noted in a single section (1924).

The interstitial matrix between the mineral-grains and rock-fragments is composed mainly of yellow epidote or colourless clino-zoisite accompanied by chlorite and colourless indeterminate material which is probably albite and quartz. Granular sphene and iron-ore are commonly present, while sericite, talc and bowlingite were occasionally noted in minor amount.

Greywackes.

The greywackes are hard grey, greenish or occasionally red rocks, which differ from the breccias just described in that the grain-size is much smaller (usually 0.1 mm. to 0.5 mm.) and simple mineral grains are more plentiful than in the latter rocks. Though effects of metamorphism are never absent, the rocks here grouped as greywackes are distinguished from their more metamorphosed equivalents by lack of schistosity and persistence of clastic microstructure. The degree to which reconstitution has proceeded varies nevertheless even

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within the greywacke group, so that there is perfect transition to the more thoroughly altered rocks which will be described in a later section as semischists.

Though greatly subordinate to simple mineral-grains, heterogeneous rock-fragments are represented in most sections of grey-wackes examined. The commonest type is a dark carbonaceous slate, but volcanic rocks are not uncommon and in one section (1923) include examples of ceratophyres related to those described from the breccias.

The most plentiful mineral to occur as clastic grains is always plagioclase, while quartz is usually present in amounts varying between 5% and 15% of the total composition. Deep brown or green hornblende and pale pink augite are common, often in considerable amount. Rarer clastic minerals are green epidote, sphene, biotite, iron-ore, and in one instance (1950) colourless garnet. Typically the feldspar is greatly altered to semiopaque saussurite or aggregates of finely divided sericite, though traces of albite twinning usually persist sufficiently clearly to allow identification as plagioclase. The quartz grains are sometimes unstrained, but more often show undulose extinction, while in a few of the more strongly sheared specimens (e.g., 1998, 1927) they may even be partially or completely granulated. Replacement of hornblende by colourless tremolite is frequent. The tremolite builds up continuous borders surrounding residual grains of the parent mineral, and rather rarely itself suffers further replacement by nearly colourless, optically positive pennine (e.g., 1997, 1998). When augite is present it is usually unaltered (e.g., 2302) or else shows incipient replacement by chlorite and epidote (e.g., 1919). Rounded patches of tale and chlorite in some sections (e.g., 1950) may perhaps be pseudomorphous after pyroxene however.

In most of the greywackes a greyish semiopaque matrix of secondary minerals (epidote, chlorite, calcite, and sometimes actinolite or sphene) has commenced to develop interstitially, and intensifies the outlines of the individual grains even when the latter are completely replaced by alteration products. In the red greywackes of the Caples Valley (2303) the intergranular spaces are filled with cementing haematite and other iron-ore.

Petrography of the Partially Reconstituted Rocks.

Meta-andesite.

Partially altered massive igneous rocks are represented by a single specimen (2282) from the old track leading from Lake Howden to the Upper Hollyford. It is a green non-schistose rock macro-scopically resembling the partially reconstituted greywackes. Large tabular phenocrysts of oligoclase-andesine (Ab68 to Ab72) are plentiful; they enclose numerous granules and prisms of yellow epidote and are often penetrated marginally by needles of actinolite, but in contrast with the completely reconstituted groundmass of the rock, they still retain the appearance of being relatively unaltered. The most important constituents of the groundmass are pale green actinolite (in prisms ranging up to 1 mm. in length), yellow epidote and pale green chlorite, accompanied by minor quartz and accessory sphene. There is also a small quantity of interstitial colourless

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material which though indeterminate is probably mixed albite and quartz. A few vesicles now infilled with coarse yellow epidote were noted.

Semischists.

The semischists are an important though somewhat ill-defined group of partially reconstituted rocks intermediate between and showing gradual transition towards the greywackes and breccias on the one hand, and the true schists on the other. Their chief interest is that they afford clear evidence as to the nature of some of the metamorphic processes whereby the greywackes are transformed into schists.

The distinctive characters of the semischists may be summarised thus:—

  • (1) Macroscopically there is usually distint schistosity, but true foliation* is completely lacking.

  • (2) Microscopically the least altered specimens (e.g., 1926, 1988, 2060, 2061) retain a modified clastic structure, in which the outlines of the majority of the original grains, though distorted as a result of shearing, are still distinct. Even in the more strongly metamorphosed rocks (e.g., 1428, 1435, 2072, 2074) where reconstitution approaches completion, traces of clastic structure are still marked.

  • (3) Clastic grains of quartz, augite and hornblende in various stages of chemical and mechanical degradation are often relatively plentiful.

  • (4) The original feldspar grains typically are replaced by epidote-albite or sericite, which are clearly distinguishable as such in contrast with the opaque often irresolvable saussuritic aggregates characteristic of the greywackes.

  • (5) The residual clastic grains or pseudomorphs after these are enclosed in a matrix of crystalloblastic minerals, chief among which are epidote, albite, and chlorite. This usually imparts a green colour to the hand-specimen.

Granulation of quartz grains (e.g., 1428, 1922, 1933) and replacement of hornblende by colourless tremolite (e.g., 1428, 1454, 2072) take place in the semischists much as in the greywackes. Replacement of pyroxene by tremolite is particularly well shown in 2072, a greatly sheared rock in hand-specimens of which the component rock-fragments may be distorted and elongated to streaks 50 mm. x 2 mm. Here the pyroxene (pale brown faintly pleochroic augite) gives rise to elongated augen of fibrous or prismatic tremolite, enclosing large cores of residual augite. Commonly the latter have been greatly stretched and fractured, with crystallisation of fibrous tremolite along the resultant cracks. Small amounts of pennine, sphene and rarely interstitial quartz may be associated with the main alteration-product.

The crystalloblastic minerals of the enveloping matrix differ from those of the true schists only in their smaller grain-size and somewhat less perfect development. In addition to albite (never

[Footnote] * The term foliation is used throughout in the sense employed by Harker (1932, p. 203).

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more calcic than Ab96An4), epidote, chlorite and quartz, which are the principal minerals of this type, sericite, tremolite, calcite, stilpnomelane and sphene are common, while talc and zoisite were recorded in a few sections. Three rare accessories, viz., tourmaline (1429), scapolite (1929) and a doubtful mineral possibly a member of the custerite group (1929) merit fuller description as possible indicators of the passage of magmatic emanations during meta-morphism.

Relatively large idioblastic prisms of tourmaline with strong pleochroism from deep blue to pale brown are unusually plentiful in 1429. Their occurrence is strictly limited to sharply defined oval masses of epidote (up to 30 mm. in diameter) which are composed essentially of dense yellow epidote and variable interstitial quartz. Tourmaline is usually though not invariably present in addition. In one large mass a semiopaque epidotic marginal zone devoid of tourmaline passes into a central translucent zone in which coarse tourmaline predominates over the associated finely granular epidote and quartz. These tourmaliniferous nodules might have originated either by local crystallisation of tourmaline under the influence of magmatic emanations during metamorphism, or by reconstitution of initially tourmaline-bearing rock-fragments. Against the former hypothesis are the limitation of tourmaline to nodules of epidosite, and its concentration in the central portion of the zoned nodule. On the other hand there are several difficulties against the alternative hypothesis of clastic origin, chief among which are the structure of the zoned mass and the complete absence of tourmaliniferous rock-fragments or even of definitely granitic rocks from the less altered greywackes and breccias of the Te Anau Series. The writer's previous record (Turner, 1933, p. 255) of a pebble of tourmaline-schist in this rock must therefore be placed as doubtful.

Seapolite occurs in a single specimen of semischist (1929) from the Livingstone Range, though also found in a few of the associated completely reconstituted schists. It occurs abundantly in slender idioblastic prisms 0.2 mm. in length with longitudinal cleavage and distant cross fracture, and is readily distinguished by its negative elongation, medium refractive index and birefringence, uniaxial character and negative optic sign.

In the same section there are small, irregular grains of a colourless mineral with medium refractive index, rather low birefringence and distinctive cleavage, frequently showing polysynthetic twinning remniscent of that of plagioclase. A section perpendicular to the acute bisectrix (Z) gives almost symmetrical extinction with reference to the twinning plane and principal cleavage, the extinction angles (Y to twinning plane) being 20° and 27° respectively in adjacent lamellae. The mineral is optically positive with a medium optic axial angle. Though the optical properties are striking, the writer has not been able to identify the mineral satisfactorily. The refractive index is distinctly higher than that of any plagioclase with the possible exception of anorthite, and the latter mineral is excluded by differences in optic sign and orientation, as well as by paragenetic association of the mineral in question with albite and other products of low-grade dynamic metamorphism. The refractive index is

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definitely too low for clinozoisite, zoisite or lawsonite, from all of which it also differs markedly in details of optic orientation. In many respects it closely resembles the rare contact minerals custerite and cuspidine, which, however, also differ as regards optic orientation and in having a much smaller extinction angle. It should nevertheless be noted that, though very closely related, cuspidine and custerite themselves show considerable differences in orientation of the bi-sectrices with reference to cleavage and twinning planes. It is therefore possible that the mineral in section 1929 may be related to the custerite group, especially in view of the fact that another halogen-bearing silicate (viz., scapolite) is abundantly distributed in the same rock.

Slates and Phyllites.

These are fine-grained perfectly fissile but non-foliated rocks, which though not nearly so widely developed as greywackes and allied rocks nevertheless constitute an important element in the Te Anau Series. Some of the least altered slates (e.g., 1942, 1947) retain, in part at least, a truly clastic structure, while the phyllites on the other hand appear to be completely reconstituted. The distinction here made between slates and phyllites is purely arbitrary, for the two make up a single petrographic unit. On this account, and since in many sections it is impossible to distinguish between clastic and crystalloblastic grains, the slates and phyllites have been grouped together among the partially reconstituted rocks.

Both microscopically and in hand-specimen the following rock-types may be distinguished: blue slates, grey slates, brown slates and blue phyllites.

In the typical blue slates (e.g., 1461, 1989) the chief constituents are colourless irresolvable quartz-albite, sericite, epidote (or clinozoisite), graphite or magnetite dust and pale green chlorite. Sparsely scattered granules of sphene, rather coarse grains of magnetite and sharply idioblastic prisms of pale tourmaline (e.g., 1461) are common, while apatite was recorded in a single instance (1461). A few of the sections (1445, 1942, 1947) differ from the normal blue slates in containing little or no recognisable sericite. Two specimens of blue slate from the lower part of the Greenstone Valley (1918, 1941) have suffered intense shearing accompanied by partial reconstitution, so that beneath the microscope lenses of slaty material are seen to alternate with streaks and lenses of recrystallised quartz-albite-epidote-sericite-calcite, while in hand-specimen the slaty cleavage has to some extent been obliterated and a streaky appearance imparted to the rock.

The grey slates include only two specimens (1450, 1460) which are distinguished in hand-specimen by their pale greyish colour. They differ from the blue slates in that carbon, iron-ore and sericite are rare, while pale chlorite is very plentiful. Actinolite and definite albite are both abundant in 1460.

A single specimen of pale brown slate (1946) having a most unusual mineral composition was obtained from the Caples Valley. The hand-specimen is rather poorly fissile and has the general appearance of an unaltered shale. In section at least 60% of the total

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composition is made up by stilpnomelane and tremolite, the remainder being sericite, quartz, epidote and a little sphene. The stilpnomelane* occurs in minute unoriented flakes (0.05 mm. long) distinguished by high birefringence and strong pleochroism from pale golden-yellow (X) to deep golden-brown (Z). The tremolite is in slightly larger prismatic crystals, also lacking orientation. Attention is drawn to the almost completely recrystallised state of this rock in view of its field association with the least altered representatives of the grey-wacke group.

The phyllites (e.g., 1462, 1954, 1994, 1995) are generally similar both in appearance and mineral composition to the blue slates, but differ in their coarser grain-size (averaging 0.02 mm. to 0.05 mm.), complete state of reconstitution and consequent glossy appearance in hand-specimen. Pale green sericite is usually though not always abundant, while tourmaline is present in almost every specimen. Unusual features are the occurrence of plentiful relatively coarse tremolite in 1462 and of brownish-green biotite (or possibly a stilpnomelane mineral) concentrated in ill-defined spots in 1954. In 1937 there are plentiful apparently clastic grains of opaque iron-ore (about 0.1 mm. in diameter), around which clear borders of granular or sometimes roughly radially fibrous quartz accompanied by a little sericite have crystallised (cf. Brammall, 1921, pl. vi, fig. 3). Strain-slip cleavage-planes have developed obliquely to the main schistosity in two specimens (2077, 2078); in the second of these, collected from an outcrop of phyllite immediately adjacent to a small sheared ultrabasic intrusion in the Routeburn Valley, there is a second set of finely spaced strain-slip cleavages, approximately perpendicular both to the first series and to the main schistosity. In one phyllite (1982) from Lake Harris, foliation is perfectly developed, indicating attainment of a distinctly higher grade of metamorphism than has been reached by other members of this group.

Crystalline Limestones and Calc-phyllites.

Calcareous rocks are not plentiful in the Te Anau Series and were observed only in the vicinity of Lake Howden and the Living-stone Range.

A typical massive grey limestone (2308) from near the north end of Lake Howden consists principally of calcite which has completely recrystallised as a mosaic of xenoblastic grains (0.05 mm.) often showing lamellar twinning. This encloses plentiful shattered grains (0.2 mm.) of albite (Ab95An5), penetrated along cracks and cleavage-planes by veinlets of calcite continuous with that of the enclosing matrix. Opaque iron-ore is not uncommon, while quartz is rare. From the lack of associated definitely clastic material or of metamorphic minerals other than calcite, the albite appears to be an authigenic constituent of the original limestone (cf. Spencer, 1925).

A single specimen (1931) of fissile blue arenaceous limestone or calc-phyllite was collected near the highest point on the Howden-Eglinton Valley track. About 90% of the rock is recrystallised

[Footnote] * cf. F. J. Turner and C. O. Hutton, Stilpnomelane and Related Minerals as Constituents of Schists from Western Otago, New Zealand, Geol. Mag., vol. lxxii, pp. 1–8, 1935.

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calcite and quartz in equal quantity, the average grain-size being 0.05 mm. The remaining minerals are opaque iron-ore (or graphite), epidote, sericite, albite, chlorite, sphene, zoisite and rare golden tourmaline.

Petrography of Completely Reconstituted Rocks.

General Features.

With advancing metamorphism, the semischists and related rocks described above pass imperceptibly into true schists in which complete reconstitution and establishment of chemical equilibrium is attained or closely approached. Though relict minerals are thus absent from the ideal schists, this criterion is not universal, for in several of the green schists relict fragments of partially altered augite and rarely of hornblende still persist.

Still more characteristic of the schists of this group are complete elimination of the original structure of the parent rock, and incipient development of foliation under the operation of metamorphic diffusion. Outlines of the clastic feldspar grains can no longer be distinguished, while there is little or no trace of the augen of granulated quartz which are so characteristic of the more strongly metamorphosed of the semischists. The foliae themselves are often contorted and ruptured and typically are rather poorly developed. This absence of regular coarse foliation such as marks the typical schists of Central Otago indicates that the grade of metamorphism in the western Wakatipu area was never as high as that reached further east in the region between Queenstown and Lake Wanaka. Again, the grain-size, though on the average noticeably coarser than in the semischists, is distinctly less than in schists of the Central Otago type.

A number of distinct petrographic types are represented, but by far the most extensively developed of these are green schists characterised by one of the assemblages chlorite-epidote-albite or actinolite-epidote-albite, and derived from greywackes, breccias or perhaps rarely from basic lavas. Sericitic schists of semi-pelitic composition and ferruginous haematite-sericite-schists also occur rather frequently. The remaining types—quartz-albite-schists, calc-schists and stilpnomelane-schist—have a very limited distribution.

Chlorite-epidote-albite-schists (e.g., 1434, 1976, 1984).

The most extensively developed of the green schists are dark green thinly-foliated rocks composed essentially of chlorite, epidote, and albite in varying proportions, and having an average grain-size of roughly 0.02 mm. to 0.05 mm. The chlorite is a poorly bi-refringent optically positive variety with distinct pleochroism from pale yellow (Z) to rather deep green (X), and gives brownish-yellow anomolous interference tints. Yellow highly ferriferous epidote is often the most important mineral present, and tends in many rocks to be concentrated in finely granular epidotic foliae which on account of their brittleness are liable to shattering and disruption on becoming contorted (e.g., 1984, 1986). The exact composition of the albite cannot usually be determined since the size of the grains is very

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small and they are for the most part untwinned. The refractive index is uniformly less than that of Canada balsam however, and the optic sign is positive.

Small amounts of quartz and granular sphene are present in almost every section, while calcite (1449, 1458), sericite (1436, 1981), actinolitic amphibole (1459, 1984) and haematite (1437) may, in rare cases, be relatively plentiful, marking transitions to other groups of schists. Blue tourmaline was recorded in two sections (1434, 1436) in the latter of which it is an important accessory. In 1433 there are occasional relict grains of pink augite partially replaced by chlorite, epidote and minor sphene, while in 1437 some of the foliae contain relict fragments of partially altered basic lava in which augite in all stages of replacement by amphibole may still be distinguished.

The amphibole of 1437 is an unusual type, the properties of which must be recorded in detail. It occurs as isolated acicular prisms or marginal fringes replacing augite grains in the incompletely reconstituted relicts referred to above, and also as the main constituent of secondary veinlets which cut irregularly across the foliation-planes and appear to have formed subsequently to the main phase of the metamorphism. The pleochroism is very striking and follows the scheme:—

  • X = pale yellow,

  • Y = deep blue with a greenish tinge,

  • Z = deep blue with a lavender tinge,

  • Y > Z > X.

The optic axial plane is transverse to 010 and the crystals are positively or negatively elongated due to the fact that the axial plane is more nearly horizontal than vertical (Z = b; Y to c = 28°). The birefringence is weak, though not extremely so, with (β—α) distinct and (γ—β) nearly zero. There is very strong dispersion of the bisectrices. The mineral obviously belongs to one of the glaucophane, riebeckite or arfvedsonite series, in all of which varieties having transverse optic axial planes are well known. The arfvedsonites may be ruled out, however, since in these the optic axial plane approaches the vertical position and the elongation is thus always negative. Among possible varieties of the glaucophane and riebeckite series the present mineral agrees best with crossite, from which it differs distinctly in having paler absorption tints and higher extinction angle. The former of these differences might well be due to admixture of the tremolite molecule. Indeed, application of the principles laid down by Murgoci (1906, 1922) as to correlation of optical properties with chemical composition in the sodic amphiboles leads to conclusons in perfect agreement with the view that the present mineral is a member of Kunitz's (1930) riebeckite-glaucophane series close to crossite, but containing in addition a certain amount of tremolite or actinolite. This is further supported by the presence in the section under consideration of paler varieties of amphibole obviously transitional to actinolite.

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Actinolite-epidote-albite-schists.

Green schists in which actinolite is sufficiently plentiful to rank as an essential mineral (20% to 50% of the total composition) are not uncommon in the western Wakatipu region (e.g., 1975, 1980, 1983, 1985). In structure and in macroscopic appearance they resemble the green schists of the previous section, from which they differ, however, in mineralogical composition. Actinolite, albite and epidote are the most important constituent minerals, but these are always accompanied by smaller amounts of chlorite and accessory sphene. Sericite (1985) is rarely present in small quantities, but calcite which is frequently a minor constituent of the non-actinolitic schists, is here completely absent. In some of the sections there may be small amounts of quartz, but this mineral was not determined with certainty. Undestroyed fragments of pink augite in process of replacement by actinolite occur sparsely in some sections (e.g., 1975).

The actinolite is usually pale green in colour and occurs as needles and acicular prisms (up to 1 mm. long) which tend to be especially large and well developed in the albitic foliae. Blue amphibole allied to the crossite of 1447 sometimes occurs as cores to the larger actinolite prisms (e.g., 1985), but is never plentiful. It may be noted here that there is no indication in these rocks that the amphibole is breaking down or suffering replacement by other minerals such as chlorite. On the contrary, the crystals of actinolite are always more perfectly developed than those of associated minerals, and appear to have grown in chemical equilibrium with the mineral assemblage of which they form a part. This applies also to those of the chlorite-albite-epidote-schists which contain accessory actinolite.

Chlorite, epidote and albite have the same properties as in the schists of the previous group. Sphene is usually more abundant, and in some sections (e.g., 1985) is pseudomorphous after ilmenite. Iron-ores (magnetite and haematite) are rare and are never idioblastic.

Sericite-schists.

The sericite-schists are represented by two specimens (1970, 1972), while a third (2312) is transitional to the chlorite-epidote-albite-schists. They are finely foliated, silky, pale green schists with distinct linear schistosity due to minute corrugation of the foliae which are alternately quartzose and micaceous. The grain-size is small (about 0-02 mm. to 0-05 mm.). The principal mineral is pale green uniaxial sericite, but quartz and a pale optically negative chlorite are also abundant, while minute grains of epidote are rather plentiful. Accessory minerals include xenoblastic sphene and rare magnetite and tourmaline (1970). From their mineralogical composition these sericite-schists appear to be truly pelitic.

Ferruginous Schists.

These are highly fissile fine-grained schists with a distinctive pink or purplish colour and silky appearance (e.g., 1971, 1973, 1977). The grain-size, though never coarse, varies between wide limits even within a single section: e.g., in 1971 it is usually less than 0-05 mm., but in some foliae averages 0-25 mm. Sericite and haematite are

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always among the principal minerals of these schists, and are accompanied by albite, epidote and chlorite, any of which may be present in sufficient abundance to rank as an essential constituent. Quartz, though usually present in small quantities, is never plentiful, while magnetite (e.g., 1987) and calcite (1979a) occasionally enter into the composition.

The sericite is always a pale green uniaxial type. The chlorite is uniaxial, optically positive and distinctly pleochroic from pale yellow (Z) to deep green (X), but appears to have a higher birefringence than does that of the green schists. Minute blood-red scales of haematite are always plentiful. Bending of mica and chlorite laminae (e.g., 1971), granulation and production of secondary twinning in the larger albites (e.g., 1971) and contortion and disruption of the micaceous and epidotic foliae respectively, are common microscopic indications of secondary cataclasis.

Quartz-albite-schists.

Quartzo-feldspathic schists are rare in the region under consideration, being represented by two specimens only (1430, 1446). They are well-foliated, fine-grained, pale greenish grey rocks consisting mainly of quartz and albite which together make up about 75% of the total composition. The remaining minerals are chlorite, sericite and accessory calcite, epidote and beryl.

The composition of the albite in 1430 was determined as about Ab94An6. The chlorite is a pale green nearly isotropic type with positive elongation, and shows Prussian blue interference tints between crossed nicols. It is thus quite distinct from the chlorite of the other schists described in this paper, but is identical with that of the quartzo-feldspathic schists of Central Otago and South Westland (c.f. Turner, 1933, p. 185; 1934, p. 165). The mineral identified as beryl is especially plentiful in 1430, where it occurs as very pale green non-pleochroic prisms 0-05 mm. long, with medium refractive index, low birefringence (estimated as about 0-01), straight extinction and negative elongation. This latter property is especially distinctive. The mineral has not been recorded in any other schist from the area under discussion.

Calc-schists.

A single specimen of calc-schist from the Routeburn Valley (2065) is a grey non-foliated fissile rock composed mainly of calcite, albite and quartz. Calcite makes up 50% of the total composition and occurs as relatively large, irregular, often polysynthetically twinned grains (0-4 mm.) which are locally so abundant as to form a continuous mass enclosing grains of albite and quartz. Small flakes of pale chlorite are plentifully scattered throughout the section, while stilpnomelane, sphene, epidote and weathered iron-ore occurs as accessories. The rock appears from its composition to have been originally an arenaceous limestone.

Stilpnomelane-schist.

Under this heading is included a single specimen of brownish-grey rock (1974) which from its poorly developed schistosity and lack of foliation might equally well be grouped with the semischists.

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In section the original clastic structure has been almost eliminated, for the quartz and feldspar grains have been sheared and stretched to long flat lenses and streaks of recrystallised material. The original feldspars have been replaced by streaks of finely granular albite crowded with prisms of colourless clinozoisite, while lenses of granulated quartz are abundantly distributed through the section. Stilpnomelane with the usual pleochroism from deep brown (Z) to pale golden-yellow (X) is an important constituent of the rock, Accessories include yellow epidote, sphene, chlorite, sericite and dusty iron-ore.

Zones of Progressive Metamorphism.

The transformation of parts of the Te Anau Series to schists and phyllites is a result of low-grade dynamothermal or regional metamorphism (c.f. Turner, 1933, pp. 251–253; 1934, pp. 169, 170). Any attempt to establish zones of progressive metamorphism must be based upon changes which accompany the transition from greywacke through semischist to green schist, for rocks of this composition greatly predominate over all others in the western Wakatipu region.

The whole of the area mapped lies well within the Zone of Chlorite as defined for quartzo-feldspathic rocks or for pelites. Further, the mineral assemblages which make up the crystalloblastic fraction of all the rocks concerned are constant no matter what may be the degree of reconstitution attained. In other words, greywackes, semischists and green schists represent different stages in the establishment of the same chemical equilibria. On this account it is impossible to draw isograds based upon index-minerals within the Zone of Chlorite.

It is suggested, however, that since the degree to which reconstitution has proceeded in rocks of a particular type must depend upon the intensity of metamorphism experienced, this factor may well be used as a basis for zonal subdivision in cases such as that under discussion. The Zone of Chlorite as developed in the western Wakatipu region is thus divided into three subzones, viz.: Chl.1 or zone of slightly altered greywackes; Chl. 2 or zone of semischists; Chl. 3 or zone of fine-grained rather poorly foliated green schists. In other districts such as much of Western and Central Otago where the schists are coarse in grain and thoroughly foliated, a fourth subzone Chl.4 might be recognised. There is imperceptible gradation from one zone to another, and the exact positions of the limiting isograds are necessarily arbitrary. Nevertheless application of the principle is not difficult in practice and serves to bring out variations in metamorphic grade which could not otherwise be represented on the map, and whose recognition will undoubtedly prove important in interpreting the history of the low-grade rocks which are so extensively developed throughout Otago. In the present region restriction of the rock-types specified above to three distinct subzones is strikingly consistent, though not without exceptions.

In Subzone Chl.1 the greywackes and breccias retain their original clastic structure, but already show the effects of incipient mechanical and chemical reconstitution as described in a previous

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section of this paper. In pelitic and other fine-grained sediments there has been considerable chemical reaction accompanied by the development under directed pressure of distinct slaty cleavage, so that slates of various types are typical of this subzone. Calcareous rocks are not recorded.

In Subzone Chl. 2 the greywackes and breccias have been converted to semischists in which chemical readjustment is relatively far advanced and clastic structure partially obliterated as schistosity develops for the first time. Originally fine-grained sediments are now represented by slates and fine-grained non-foliated phyllites, in the latter of which chemical equilibrium is already reached. Calcareous rocks have been converted to crystalline limestones and calcphyllites. The single specimen of meta-andesite belongs to this zone.

In the rocks of Subzone Chl. 3 complete chemical reconstitution is characteristic of initially fine and coarse rocks alike, except that relicts of femic minerals tend to persist here and there in some of the schists. Where the rocks are derivatives of greywackes and breccias a rather poorly developed foliation is characteristic, but perfect foliation is characteristic of the phyllites of this zone and usually distinguishes them from the non-foliated pelitic phyllites of Subzone Chl.2. Among the green schists (derived originally from greywackes and breccias) there is a marked tendency for either of two distinct mineral assemblages to develop. These are—

chlorite-epidote-albite (+ minor sphene and quartz), and actinolite-epidote-albite-chlorite (+ minor sphene and quartz).

Calcite is frequently a member of the first of these assemblages, but never enters into the second. Other characteristic assemblages are as follows, minor constituents being recorded in brackets:—

  • sericite-chlorite-quartz (-albite),

  • haematite-sericite-albite (-quartz-epidote-chlorite),

  • quartz-albite (-chlorite-sericite),

  • calcite-albite-quartz (-epidote-sphene),

  • quartz-albite-stilpnomelane-epidote.

The schists recently described from the Forbes Range and Rees Valley some distance north-east of the present area (Turner, 1934) belong mainly to the Chl.3 subzone, but show a south-west transition towards Chl.2 and grade north-east into rocks which more properly belong to Chl.4

The Significance of Actinolite.

The significance of actinolite and similar amphiboles low in alumina as constituents of green schists is not fully understood. It has for some time been considered by many writers that actinolitic green schists are formed at a distinctly higher metamorphic grade than are chlorite-albite-epidote-schists, but this hypothesis is open to some doubt. Eskola (1925, pp. 77, 78) discusses the possible conditions under which these two mineral assemblages may be developed, and concludes that the evidence afforded by the Karelian green schists of Eastern Fennoscandia on the whole supports the possibility that “actinolitic hornblendes” remain stable at the lowest grades

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of metamorphism, provided CO2 and water are absent or nearly so. This view was more recently put forward by the writer (Turner, 1933a, pp. 534, 537) as the result of observations made upon New Zealand green schists, and has since been somewhat elaborated in a second paper.* The opposite view, that actinolitic amphibole of low-grade green schists is metastable or in a state of forced equilibrium, and that the only true equilibria at low grade are chlorite-epidote-albite and chlorite-albite, has recently been affirmed by Wiseman (1934, pp. 374, 411) and supported by Professor Tilley (Wiseman, 1934, p. 416).

The evidence afforded on this subject by the Te Anau Series may be summarised thus:—

  • (1) One or other of two distinct mineral assemblages tends to crystallise in rocks of the green schist type, viz.:—

  • chlorite-epidote-albite-sphene, and

    actinolite-epidote-albite-chlorite-sphene.

    In the second of these assemblages chlorite is of minor importance. Actinolite may occur in the chlorite-epidote-albite-schists, but only in small amount, in accordance with the principle that the ideal mineral assemblages characteristic of different metamorphic facies are seldom completely attained (c.f. Eskola, 1925, p. 73).

  • (2) The frequent presence of calcite—sometimes in abundance—in the non-actinolitic schists is significant when contrasted with its universal absence in the actinolitic types. Where accessory actinolite occurs in a schist, association of calcite and actinolite has occasionally been observed however.

  • (3) Direct replacement of pyroxene or hornblende by tremolite such as may be observed in many greywackes and semischists might conceivably be interpreted as approach toward equilibrium through an intermediate disequilibrium stage according to Ostwald's law (cf. Wiseman, 1934, p. 374). But to the writer this explanation does not appear to be readily applicable to the case of continued growth, from minute nuclei, of relatively large idioblasts of actinolite in completely reconstituted schists, and especially in highly albitic foliae where they represent crystallisation of material which has migrated short distances by the process of metamorphic diffusion.

  • (4) Nowhere in the district west of Lake Wakatipu does the grade of metamorphism approach the maximum possible for the Zone of Chlorite. On this account and since actinolite has commenced to crystallise in some rocks which have suffered only very slight metamorphism variation in grade cannot be invoked as an explanation of the alternative development of actinolitic and non-actinolitic assemblages.

The above facts appear to be most satisfactorily interpreted on the assumption that under the same range of conditions of temperature and directed pressure crystallisation has followed any one of

[Footnote] * F. J. Turner, Contribution to the Interpretation of Mineral Facies in Metamorphic Rocks, Am. Jour. Sci., vol. xxix, pp. 409–421, 1935.

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three alternative courses governed by the amount of water and CO2 locally available during reconstitution:—

  • (a) When abundant water has been available lime has been removed from the system and the metasilicates have been replaced by chlorite and epidote, giving rise to the assemblage chlorite-epidote-albite.

  • (b) When CO2 has been present in addition to water, the excess lime set free in the breaking down of pyroxene and hornblende has crystallised as calcite, and in this way the calcite-bearing chlorite-epidote-albite-schists have originated.

  • (c) When sufficient water or CO2 to effect the above changes has been lacking, i.e., where recrystallisation has taken place in a closed system, the original pyroxene and amphibole have given risen to actinolite accompanied by appropriate amounts of chlorite and epidote. The corresponding assemblage is actinolite-epidote-albite-chlorite.

Relation to Schists of Central Otago.

The rocks of the Te Anau Series pass eastward into semischists and poorly foliated schists which are developed along the western sides of the Dart Valley and Lake Wakatipu. Along the eastern shores of the lake and throughout the Forbes and Richardson Ranges further north, rather more strongly metamorphosed schists of the Central Otago type come in, and in these also the grade of meta-morphism definitely rises in a north-easterly direction towards the Upper Shotover and Matukituki Valleys. This field transition from the Te Anau Series to the Central Otago Schists (Maniototo Series or Wanaka Series) is supported by tectonic and petrographic similarities between the two series. [Compare Marshall's (1918) demonstration of transition from greywackes now known to be Permian to the schists of Central Otago in the Tuapeka district.]

The writer's belief (Turner, 1933, pp. 251–253) that the schists of Otago and South Westland are products of dynamothermal metamorphism caused by folding, and modified, more especially in the deep zones, by the effects of uprising granitic batholiths need not be elaborated here. But attention may be drawn once more to the fact that there is a considerable body of evidence to show that the Te Anau Series is itself invaded by apophyses from the granite intrusions. The frequent occurrence of crystalloblastic tourmaline in the Te Anau rocks, as in the Maniototo schists further north-east, is a further indication that the granite intrusives post-date the Te Anau Series. It must be admitted that much of the tourmaline observed in slates belonging to this latter series may owe its existence to the presence of boron in the parent mudstones, much as recently demonstrated by Goldschmidt and Peters in the case of European pelites. But this explanation can scarcely apply to the tourmaline which sometimes occurs in abundance in green schists and semischists derived from greywackes and breccias in which definite granitic fragments are as yet unrecorded. Magmatic origin is further supported by occasional association with minerals such as scapolite and beryl.

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On these assumptions, the date of metamorphism of the Otago and Westland schists—previously placed provisionally as Palaeozoic (post-Ordovician)—must be either late Permian or post-Palaeozoic. The writer has already shown that there is strong reason to believe that the main metamorphism and plutonic invasion occurred prior to the commencement of the Triassic-Jurassic period of sedimentation, the initiation of which cannot be placed later than the close of mid-Triassic times. It is probable therefore that the metamorphism took place at the close of the Permian or during the first half of the Triassic period. This accords with Hutton's frequently-asserted view that the Maitai and Triassic rocks are separated by strong unconformity, resulting from profound orogenic movements accompanied by plutonic intrusion.

Acknowledgements.

The writer wishes to acknowledge his indebtedness to the Royal Society of New Zealand for a grant from the Hutton Fund to defray part of his field expenses; to the Council of the University of Otago for further financial assistance in a similar respect; to Messrs W. E. La Roche, J. B. Mackie and H. Service, who rendered valuable help in the field; and to Professor W. N. Benson for his stimulating advice and discussion during the progress of the laboratory investigations.

Locality-list of Specimens Cited.

  • 1428–1430 1433–1437 Boulders, Momus Cr., Routeburn.

  • 1445, 300 yards above foot-bridge, Routeburn.

  • 1446, 1 ml. from junction with Dart, Routeburn.

  • 1449, 1450, Mouth of Routeburn Valley.

  • 1454, Top of main waterfall, Upper Routeburn.

  • 1458, 1459, Lake Harris Basin.

  • 1460–1462, Middle Portion of Routeburn Valley.

  • 1493, Eglinton Valley road, 31 mls. above Te Anau.

  • 1918, 1919, Lower part of Greenstone Valley.

  • 1922, Upper part of Greenstone Valley.

  • 1923, Lower part of Greenstone Valley.

  • 1924–1926, Middle and upper parts of Greenstone Valley.

  • 1927, 1 ¼ mls. from Howden, Eglinton track.

  • 1929, 1931, North end of Livingstone Range.

  • 1933, 1937, East shore of Lake Fergus, Upper Eglinton.

  • 1941, ¼ ml. below mouth of Caples R., Greenstone.

  • 1942, 1945–1947, 1950 Caples Valley.

  • 1954, West shore of Lake Wakatipu, 2 ½ mls. north of Greenstone River.

  • 1970, 1971, ¼ ml. from Howden, Routeburn track.

  • 1972, ½ ml. from Howden, Routeburn track.

  • 1973, 2 ½ mls. from Howden, Routeburn track.

  • 1974, 2 ¾ mls. from Howden, Routeburn track.

  • 1975, Bluffs N. of Lake McKenzie, Routeburn track.

  • 1976–1987, Bluffs S. side of Lake Harris.

Picture icon

Geological Map of the district North-west of Lake Wakatipu, showing progressive metamorphism of the Te Anau Series.

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  • 1988, 1989, S.–W. slopes of Mt. Somnus, Routeburn.

  • 1994, 1995, Routeburn Gorge.

  • 1997, 1998, Boulders, Momus Cr., Routeburn.

  • 2061, 2062, Boulders, Momus Cr., Routeburn.

  • 2072, 2074, Southern tributary to Routeburn, 2 mls. above junction of Routeburn with Dart River.

  • 2077, Boulder, Momus Cr., Routeburn.

  • 2078, 300 yds. above foot-bridge, Routeburn.

  • 2282, 1 ml. from Howden, Upper Hollyford track.

  • 2302, 2304, Caples Valley.

  • 2305–2307, Eglinton Valley Road, 31 mls. above Te Anau.

  • 2308, ¼ ml. W. of Lake Howden.

  • 2312, ¾ ml. from Howden, Lower Hollyford track.

List of Literature Cited.

  • Brammall, A., 1921. Reconstitution Processes in Shales, Slates and Phyllites, Min. Mag., vol. xix, pp. 211–224.

  • Cox, S. H., 1878. Report on the Geology of the Te Anau District, Rept. Geol. Expl. Geol. Surv. N.Z., 1877–8, pp. 110–118.

  • — 1879. The Wakatipu and Greenstone District, Rept. Geol. Expl. Geol. Surv. N.Z., 1878–79, pp. 53–55.

  • Eskola, P., 1925. The Mineral Development of Basic Rocks in the Karelian Formations, Fennia, 45, No. 19, pp. 1–93.

  • Harker, A., 1932. Metamorphism, Methuen and Co., London.

  • Hector, J., 1865. On the Geology of Otago, New Zealand, Q.J.G.S., vol. 21, pp. 124–128.

  • — 1881. Progress Report, Rept. Geol. Expl. Geol. Surv. N.Z., 1879–80, pp. xxvii-xxx.

  • — 1892. Progress Report, Rept. Geol. Expl. Geol. Surv. N.Z., 1890–91, pp. xli-xlix.

  • Hess, H. H., 1933. Hydrothermal Metamorphism of an Ultrabasic Intrusive at Schuyler, Virginia, Am. Jour. Soi., vol. 24, pp. 377–408.

  • Kunitz, W., 1930. Die Isomorphieverhältnisse in der Hornblende Gruppe, Neues Jahrb. Min,. Beil. Bd. lx, pp. 171–250.

  • McKay, A., 1881. District West and North of Lake Wakatipu, Rept. Geol. Expl. Geol. Surv. N.Z., 1879–80, pp. 118–149.

  • Marshall, P., 1918. The Geology of the Tuapeka District, Bull. Geol. Surv. N.Z., No. 19.

  • Murgoci, G. M., 1906. Contribution to the Classification of the Amphiboles, Bull. Dept. Geol. Univ. California, vol. 4, No. 15, pp. 359–386.

  • — 1922. Sur les propriétés des amphiboles bleues, Compt. Rend. Acad. Sci. Paris, vol. 175; pp. 372–374.

  • Park, J., 1887. On the District between the Dart and Big Bay, Rept. Geol. Expl. Geol. Surv. N.Z., 1886–87, pp. 121–137.

  • — 1921. Geology and Mineral Resources of Western Southland, Bull. Geol. Surv. N.Z., No. 23.

  • Spencer, E., 1925. Albite and other Authigenic Minerals in Limestone from Bengal, Min. Mag., vol. xx, pp. 365–381.

  • Turner, F. J., 1933. The Metamorphic and Intrusive Rocks of Southern Westland, Trans. N.Z. Inst., vol. 63, pts. 2 and 3, pp. 178–284.

  • — 1933a. The Genesis of Oligoclase in Certain Schists, Geol. Mag., vol. lxx, pp. 529–541.

  • — 1934. Schists from the Forbes Range and Adjacent Country, Western Otago, Trans. Roy. Soc. N.Z., vol. 64, pp. 161–174.

  • Wiseman, J. D. H., 1934. The Central and South-west Highland Epidiorites; a Study in Progressive Metamorphism, Q.J.G.S., vol. xl, pp. 354–417.