Upper Permian rocks of South Island, New Zealand: Lithology, stratigraphy, structure, metamorphism and tectonics.
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Stratigraphy and lithology of Upper Permian and overlying Triassic rocks of the Key Summit-Nelson Regional Syncline are described. In general, these descriptions verify earlier stratigraphic observations by Wellman, Grindley, Waterhouse, and others. However, many new data are presented and several stratigraphic refinements and alterations are proposed.
It is proposed that the base of the Bryneira Group be extended downward to include a varied suite (ca 150 m thick) of conglomerates, red and green breccias, greenish volcanic sandstones, black siltstones, impure limestones, etc, which underlie the Howden limestone and overlie the highest volcanic rocks of the Humboldt Group. The name Upukerora Formation is proposed for these rocks. Lithologically similar rocks (e.g. upper part of the Glennie Formation) occur at the same stratigraphic horizon in the east limb of the Nelson Regional Syncline.
Following deposition of the Upukerora Formation, the area of the Key Summit-Nelson Regional Syncline -- a shallow-shelf at that time -- became the site of extensive carbonate sedimentation. The resulting rocks, the Howden and Wooded Peak limestones, consist very largely of comminuted (sand grade) prismatic shell fragments which were derived from the bivalve Atomodesma. Terrigenous debris, largely volcanogenic, comprises a relatively minor part of these rocks. The limestones are thin to absent in the southern part of the Key Summit Regional Syncline and in the northern part of the Nelson Regional Syncline. Thickness in the area between Key Summit and Mt. Barrington varies from 400-1000 m. Newly discovered Howden exposures are recorded from the west limb of the Key Summit Regional Syncline. These rocks resemble closely their east limb correlatives and also correlative strata in the Productus Creek Terrane. Similar Rocks also occur in the Arthurton Fold Belt and the Torlesse Terrane. It is suggested that a great sedimentary blanket (with a few holes) extended well beyond present syncline boundaries. Facies variations and possible shore-line positions are discussed.
Limestone sedimentation was succeeded by the deposition of terrigenous sands which now comprise the Annear and Tramway formations. These rocks comprise thin-bedded, calcareous and fossiliferous, sandstones and siltstones. Thickness of Annear-Tramway strata is generally similar to that of Howden-Wooded Peak strata. In addition, regional thickness variations tend to be in sympathy with variations in Howden-Wooded Peak thickness. The depositional environment remained similar to that of the Howden-Wooded Peak beds (a relatively shallow stable shelf), and Atomodesma continued to flourish. The terrigenous sand portion of Annear-Tramway rocks is distinctly more quartzose and less volcanogenic than other Bryneira-Maitai strata. Current-bedding at Mt. Barrington indicates sediment transport from west to east. Petrographically and stratigraphically similar rocks also occur in the Productus Creek and Torlesse terranes. It is suggested that the Annear and Tramway formations may comprise a portion of a relatively quartzofeldspathic sandstone blanket which originally spread across nearly the entire width of the New Zealand Geosyncline.
A suite of massive, green, unfossiliferous, volcanogenic sandstones are widespread within both limbs of the regional syncline, and they are commonly quite thick -- 150-1200 m. They are especially well-developed in the vicinity of the Key Summit Ridge, and it is proposed that a new formation, the Key Summit Sandstone, be recognized (previous maps have included both Key Summit and Annear strata within the Howden and Tapara formations). The correlative formation in the Nelson Regional Syncline is the Little Ben Sandstone. Key Summit - Little Ben sediments consist almost entirely of first cycle basaltic and andesitic debris which appears to have been deposited quite rapidly (probably from turbidity currents) in an elongated basin or trench. Formation of this basin appears to have coincided with cessation of deposition of quartzo-feldspathic sediment of the Annear and Tramway formations, and also with the virtual disappearance of Atomodesma from Bryneira-Maitai seas. The axis of the basin of deposition appears to have coincided approximately with the present regional syncline axis. Petrographically and stratigraphically similar rocks of the basal Hawtel Formation occur in the Productus Creek Terrane, however these sands were probably deposited upon a shallow, stable shelf which lay to the west of the Key Summit-Little Ben basin. The coarsely volcanogenic sedimentation of the Key Summit-Little Ben formations ended rather abruptly. Overlying rocks, the Tapara and Greville formations, consist of unfossiliferous, grey, interlaminated sands and muds. Bedding laminae tend to be continuous and undisturbed, and coarser laminae commonly show size grading. Thickness is approximately 1000-1500 m. Fine grain-size of most Tapara-Greville rocks renders evaluation of provenance rather difficult, however, the coarser portion of these rocks contains both volcanic and plutonic debris. Tuffs are present, but uncommon. The tops of the Tapara and Greville formation is defined by an abrupt lithologic change to reddish sediment. These overlying "red beds", approximately 500 m thick, comprise the Winton and Waiua formations. Apart from the presence of hematite, Winton-Waiua rocks bear a very close lithologic and mineralogic resemblance to Tapara-Greville strata. No evidence is recognized for volcanism contemporaneous with Winton-Waiua sedimentation. Textural relations suggest that hematite in these rocks formed during weathering (prior to sedimentation) and also during diagenesis. Sedimentary rocks which may be correlated with Tapara-Greville and Winton - Waiua Strata are not recognized beyond the Key Summit- Nelson Regional Syncline-Arthurton Fold Belt. These sediments probably accumulated in a deep marine trench which was essentially coincident with the Key Summit-Nelson Regional Syncline.
The youngest Bryneira-Maitai strata comprise the Countess and Stephens formations. Both units consist predominantly of unfossiliferous green volcanogenic sandstones and associated finer grained rocks; thickness ranges up to 1800 m. Basal Stephens strata, herein named the Gordons Member, are characterized by an abundance of tuffs, conglomerates and limestones. Similar beds, but without limestone also occur at the base of the Countess Formation. Stratigraphic contrasts between Countess and Stephens rocks are described and it is shown that these contrasts may be explained in terms of local geologic structure. Tuffs, limestones and conglomerates of the upper Productus Creek Group (upper Hawtel-Wairaki formations) may be correlated tentatively with Gordons Member.
The Countess Formation is overlain unconformably by about 1500 m of conglomerates, tuffs, volcanogenic sandstones and argillites of the Snowdon Formation (new name). These rocks contain Triassic fossils (Etalian Stage). Similar strata appear to overlie the Stephens Formation. A period of latest Permian or early Triassic crustal unrest in inferred.
Aspects of regional geology, local stratigraphy and petrography are discussed for all areas known to contain Upper Permian strata. Geology of the Key Summit-Nelson Regional Syncline and parallel adjoining terranes is discussed in detail: ten area maps, each accompanied by a text, are presented. The regional syncline is shown to be nearly isoclinal and to possess remarkable continuity. The eastern synclinal limb is overturned in most areas, and the east-limb contact between Bryneira-Maitai rocks and Lower Permian (Humboldt-Lee River) rocks is characterized by an unconformity. In contrast, the western synclinal limb is consistently "right-way-up", and the contact between Bryneira-Maitai rocks and Lower Permian (Alabaster-Brook Street) rocks is consistently faulted (Hollyford-Waimea Fault). Certain intra-Bryneira-Maitai faults (e,.g. Upukerora and Whangamoa) are shown to be extremely continuous structures.
Other areas containing Upper Permian strata are also discussed; these include Productus Creek, Mataura Island, South Canterbury and Parapara Peak.
The regional reports also include metamorphic data. Mineral assemblages are tabulated and mineral distribution illustrated with regard to stratigraphic and regional distribution. Positions of mineralogic isograds are reported.
Volcanogenic debris in Upper Permian rocks has been very extensively reconstituted under lower grade metamorphic conditions. Mineralogic and petrographic data pertaining to a variety of a authigenic minerals are presented. Some relict detrital minerals are also described. Rock-forming zeolite minerals are restricted to the lowest grade metamorphic rocks studied. In general, data pertaining to these minerals conform with observations of previous workers. It should be noted, however, that some burial metamorphic analcime concentrates possess unusually low silica contents, and also that authigenic analcime, heulandite and laumontite have been recorded from Tertiary rocks from the Hollyford-Waimea Graben and from the Te Anau and Nelson basins.
Non-zeolitic Ca-Al-silicate minerals are, petrologically, the most important minerals recorded; they include lawsonite, prehnite, pumpellyite and epidote. Lawsonite, a mineral indicative of relatively high pressures during metamorphism, is especially widespread in Bryneira-Maitai rocks. It occurs in apparent stability with prehnite, pumpellyite and epidote, but not with zeolites. Bryneira-Maitai epidote tends to be iron-rich, and some data suggest that it is of the "high index" variety.
Calcite is the prevalent polymorph of CaCO3 in all rocks studied. A few occurrences of aragonite are recorded from the vicinity of ultramafic bodies.
Authigenic amphiboles are uncommon. They include tremolite-actinolite, which does not co-exist with lawsonite, and a blue amphibole (probably of the riebeckite-magnesioriebeckite series) which co-exists with lawsonite in at least two occurrences. Metamorphic hornblende occurs in certain Lower Permian mafic volcanic and intrusive rocks. Hornblende also occurs widely, but not abundantly, as a detrital mineral.
Clinopyroxene minerals, augite and salite, occur as detrital grains in numerous rocks. Neither jadeite nor any other authigenic pyroxene has been recognized in the Upper Permian rocks studied. Metamorphic diopside occurs in some Lower Permian rocks.
Authigenic phyllosilicate minerals include chlorite, sericite, celadonite, stilpnomelane, biotite and montmorillonoid clays. Chlorite is virtually ubiquitous; the optically negative variety is found in rocks of all metamorphic grades, whereas optically positive chlorite is absent from lowest grade rocks but becomes increasingly abundant in rocks of slightly higher metamorphic grade. Sericite, probably phengitic, is also widespread. Celadonite is restricted to the lower grade rocks studied. Several previously unrecorded celadonite-bearing mineral assemblages are listed. Stilpnomelane is restricted to rocks in which reconstitution is well advanced. It co-exists with epidote and with amphiboles, but is very rare or absent in zeolite-, prehnite-, and lawsonite-bearing rocks. Biotite occurs in metamorphosed Upper Permian sediments from Parapara Peak, and in addition it occurs as a detrital mineral in many other rocks. Montmorillonoid clays are restricted to zeolite facies rocks.
Microcrystalline Sphene is abundant and widespread. Quartz and albite occur in nearly every mineralogically reconstituted rock. Some rocks contain detrital Ca-plagioclaae and orthoclase which have escaped reconstitution.
Oxide and sulfide minerals include authigenic hematite and pyrite, which are both abundant but do not co-exist, minor chalcopyrite and pyrrhotite, and detrital magnetite and chromite.
Dispersed carbonaceous material has been concentrated from numerous metamorphic rocks and analysed by X-ray and electron diffraction methods. A classification to describe sub-graphitic material is proposed, and progressive graphitization is discussed. Carbonaceous material in zeolite facies rocks is nearly amorphous; well-crystallized graphite is first recognized in amphibolite facies rocks.
Minor occurrences of tourmaline, apatite, garnet, rutile and allanite are also reported.
On the basis of these observations, nine metamorphic zones are defined and mapped. They are correlated with recognized mineral facies -- zeolite, prehnite-pumpellyite, lawsonite-albite-chlorite, pumpellyite-actinolite, greenschist, and blueschist. Several subfacies are tentatively recognized.
Phase rule considerations and textural relationships are taken to indicate widespread approach to equilibrium, however in many cases the extent of an equilibrium assemblage may be restricted to a microscopic volume or rock. In addition, compositional zoning in certain minerals (e.g. pumpellyite and epidote) implies small-scale disequilibrium.
The behaviour and classification of chemical components is discussed. Some evidence suggests that H2O and/or CO2 may not have possessed perfect mobility during metamorphism. A minimum of four and a maximum of seven components (Al2O3 , CaO, FeO, MgO, Fe2O3 , H2), CO2) are considered to be determining components (Korzhinskii terminology).
Numerous three- and four-component determining systems are explored chemographically. Comparison of these diagrams provides some clues regarding mineralogic reactions which may define zone boundaries. However, successful identification of metamorphic reactions by this method requires prior correct recognition of the determining chemical components.
Successful application of the phase rule also relies on correct recognition of determining components. Bearing in mind this reservation, the writer concludes that phase rule considerations are generally compatible with attainment of equilibrium under di- or multi-variant conditions. Some assemblages suggest possible univariant or invariant conditions, or alternatively disequilibrium.
Metamorphic temperatures and pressures constitute the primary controls over distribution of Ca-Al-silicate minerals. The stability fields of most of these minerals overlap. For example, prehnite-pumpellyite assemblage rocks occur interbedded with lawsonite-pumpellyite assemblage rocks in several areas. Possible secondary controls of mineral distribution include chemical composition of the host rock and varying chemical potential of volatile components. These secondary controls are discussed in some detail.
The p - t conditions of metamorphism are investigated and a tentative p - t-facies diagram is presented. The formation of lawsonite-albite-chlorite facies mineral assemblages requires an abnormally low thermal gradient, probably less than 15°C/km.
The data presented -- stratigraphic, lithologic, structural, and metamorphic -- may be synthesized in a geotectonic history. Upper Permian rocks of South Island, New Zealand accumulated in a rapidly evolving and tectonically complex geosyncline. Numerous paleotectonic (i.e. pre- Rangitata Orogeny) structural elements and geologic terranes can be recognized within this geosynclinal framework: these ancient structures exerted a profound control over geosynclinal sedimentation and also over subsequent tectogenesis. They are recognizable today in such features as the Median Tectonic Line, Hollyford-Waimea Fault, Southland-Kawhia Regional Syncline (i.e. synclinorium), and the Key Summit-Nelson Regional Syncline. Some other major structural features, e.g. Alpine Fault, Livingstone Fault, are not recognized within the paleotectonic framework.
Two sedimentary facies belts -- Hokonui and Alpine -- of Permian to Jurassic age, divide the geosyncline into two longitudinal provinces. The facies belts are separated from each other by the Dun Mountain Ultramafic Belt, and it is suggested that this belt may consist partly of sub-geosynclinal basement. Two parallel regional synclines -- Key Summit-Nelson and Southland-Kawhia -- lie within the Hokonui belt. It is emphasized that these structures differ from each other tectonically and chronologically and are nowhere co-linear. Although presently orogenic fold belts, they inherited their structural position and synclinal form from the geosynclinal framework in which they originated. The regional synclines are bordered in part by major faults -- Hollyford-Waimea, Gunn-Eighty Eight -- which are shown to coincide with structural breaks in the geosynclinal basement and also with stratigraphic discontinuities.
A model for paleotectonic evolution of the New Zealand Geosyncline is proposed and briefly discussed.
Abundant unstable terrigenous and pyroclastic debris as well as deep sedimentary burial rendered Permian rocks mineralogically unstable. Thus zeolite and prehnite-pumpellyite facies burial metamorphism proceeded between Permian and late Jurassic or Cretaceous times. In contrast, structural evidence and K-Ar dates suggest that the formation of lawsonite occurred only during early Cretaceous -- Rangitata -- time.
Several important attributes of Upper Permian rocks can be related to width of the Hokonui Facies Belt. These include -- sedimentary facies and stratigraphic thickness, degree of textural reconstitution, mineralogic grade of metamorphism, depth of post-Rangitata erosion, and possibly K-Ar age of slates. Thus highest grade Bryneira-Maitai metasediments lie in the narrow, tightly appressed medial portion of the elongate Key Summit-Nelson Regional Syncline, a position where width of the Hokonui Facies Belt is minimal. Metamorphic grade decreases with increase in Width of the Hokonui Belt.
It is proposed that the New Zealand Geosyncline was driven westward into the continental Western Province during Rangitata orogenesis. The Key Summit-Nelson Regional Syncline became uncoupled from the western part of the Hokonui belt and was rapidly dragged deep into the crust, perhaps with the descending limb of a convection cell.
Dextral strike-slip movement along the Alpine Fault commenced following the climax of Rangitata orogenesis. Movement probably occurred in spasms, and is still active today. Data presented herein may be regarded as consistent with the hypothesis that the Key Summit and Nelson regional synclines originated as one continuous structure. Displacement along the Alpine Fault severed this structure and separated the two portions by 480 km.
It is proposed that the base of the Bryneira Group be extended downward to include a varied suite (ca 150 m thick) of conglomerates, red and green breccias, greenish volcanic sandstones, black siltstones, impure limestones, etc, which underlie the Howden limestone and overlie the highest volcanic rocks of the Humboldt Group. The name Upukerora Formation is proposed for these rocks. Lithologically similar rocks (e.g. upper part of the Glennie Formation) occur at the same stratigraphic horizon in the east limb of the Nelson Regional Syncline.
Following deposition of the Upukerora Formation, the area of the Key Summit-Nelson Regional Syncline -- a shallow-shelf at that time -- became the site of extensive carbonate sedimentation. The resulting rocks, the Howden and Wooded Peak limestones, consist very largely of comminuted (sand grade) prismatic shell fragments which were derived from the bivalve Atomodesma. Terrigenous debris, largely volcanogenic, comprises a relatively minor part of these rocks. The limestones are thin to absent in the southern part of the Key Summit Regional Syncline and in the northern part of the Nelson Regional Syncline. Thickness in the area between Key Summit and Mt. Barrington varies from 400-1000 m. Newly discovered Howden exposures are recorded from the west limb of the Key Summit Regional Syncline. These rocks resemble closely their east limb correlatives and also correlative strata in the Productus Creek Terrane. Similar Rocks also occur in the Arthurton Fold Belt and the Torlesse Terrane. It is suggested that a great sedimentary blanket (with a few holes) extended well beyond present syncline boundaries. Facies variations and possible shore-line positions are discussed.
Limestone sedimentation was succeeded by the deposition of terrigenous sands which now comprise the Annear and Tramway formations. These rocks comprise thin-bedded, calcareous and fossiliferous, sandstones and siltstones. Thickness of Annear-Tramway strata is generally similar to that of Howden-Wooded Peak strata. In addition, regional thickness variations tend to be in sympathy with variations in Howden-Wooded Peak thickness. The depositional environment remained similar to that of the Howden-Wooded Peak beds (a relatively shallow stable shelf), and Atomodesma continued to flourish. The terrigenous sand portion of Annear-Tramway rocks is distinctly more quartzose and less volcanogenic than other Bryneira-Maitai strata. Current-bedding at Mt. Barrington indicates sediment transport from west to east. Petrographically and stratigraphically similar rocks also occur in the Productus Creek and Torlesse terranes. It is suggested that the Annear and Tramway formations may comprise a portion of a relatively quartzofeldspathic sandstone blanket which originally spread across nearly the entire width of the New Zealand Geosyncline.
A suite of massive, green, unfossiliferous, volcanogenic sandstones are widespread within both limbs of the regional syncline, and they are commonly quite thick -- 150-1200 m. They are especially well-developed in the vicinity of the Key Summit Ridge, and it is proposed that a new formation, the Key Summit Sandstone, be recognized (previous maps have included both Key Summit and Annear strata within the Howden and Tapara formations). The correlative formation in the Nelson Regional Syncline is the Little Ben Sandstone. Key Summit - Little Ben sediments consist almost entirely of first cycle basaltic and andesitic debris which appears to have been deposited quite rapidly (probably from turbidity currents) in an elongated basin or trench. Formation of this basin appears to have coincided with cessation of deposition of quartzo-feldspathic sediment of the Annear and Tramway formations, and also with the virtual disappearance of Atomodesma from Bryneira-Maitai seas. The axis of the basin of deposition appears to have coincided approximately with the present regional syncline axis. Petrographically and stratigraphically similar rocks of the basal Hawtel Formation occur in the Productus Creek Terrane, however these sands were probably deposited upon a shallow, stable shelf which lay to the west of the Key Summit-Little Ben basin. The coarsely volcanogenic sedimentation of the Key Summit-Little Ben formations ended rather abruptly. Overlying rocks, the Tapara and Greville formations, consist of unfossiliferous, grey, interlaminated sands and muds. Bedding laminae tend to be continuous and undisturbed, and coarser laminae commonly show size grading. Thickness is approximately 1000-1500 m. Fine grain-size of most Tapara-Greville rocks renders evaluation of provenance rather difficult, however, the coarser portion of these rocks contains both volcanic and plutonic debris. Tuffs are present, but uncommon. The tops of the Tapara and Greville formation is defined by an abrupt lithologic change to reddish sediment. These overlying "red beds", approximately 500 m thick, comprise the Winton and Waiua formations. Apart from the presence of hematite, Winton-Waiua rocks bear a very close lithologic and mineralogic resemblance to Tapara-Greville strata. No evidence is recognized for volcanism contemporaneous with Winton-Waiua sedimentation. Textural relations suggest that hematite in these rocks formed during weathering (prior to sedimentation) and also during diagenesis. Sedimentary rocks which may be correlated with Tapara-Greville and Winton - Waiua Strata are not recognized beyond the Key Summit- Nelson Regional Syncline-Arthurton Fold Belt. These sediments probably accumulated in a deep marine trench which was essentially coincident with the Key Summit-Nelson Regional Syncline.
The youngest Bryneira-Maitai strata comprise the Countess and Stephens formations. Both units consist predominantly of unfossiliferous green volcanogenic sandstones and associated finer grained rocks; thickness ranges up to 1800 m. Basal Stephens strata, herein named the Gordons Member, are characterized by an abundance of tuffs, conglomerates and limestones. Similar beds, but without limestone also occur at the base of the Countess Formation. Stratigraphic contrasts between Countess and Stephens rocks are described and it is shown that these contrasts may be explained in terms of local geologic structure. Tuffs, limestones and conglomerates of the upper Productus Creek Group (upper Hawtel-Wairaki formations) may be correlated tentatively with Gordons Member.
The Countess Formation is overlain unconformably by about 1500 m of conglomerates, tuffs, volcanogenic sandstones and argillites of the Snowdon Formation (new name). These rocks contain Triassic fossils (Etalian Stage). Similar strata appear to overlie the Stephens Formation. A period of latest Permian or early Triassic crustal unrest in inferred.
Aspects of regional geology, local stratigraphy and petrography are discussed for all areas known to contain Upper Permian strata. Geology of the Key Summit-Nelson Regional Syncline and parallel adjoining terranes is discussed in detail: ten area maps, each accompanied by a text, are presented. The regional syncline is shown to be nearly isoclinal and to possess remarkable continuity. The eastern synclinal limb is overturned in most areas, and the east-limb contact between Bryneira-Maitai rocks and Lower Permian (Humboldt-Lee River) rocks is characterized by an unconformity. In contrast, the western synclinal limb is consistently "right-way-up", and the contact between Bryneira-Maitai rocks and Lower Permian (Alabaster-Brook Street) rocks is consistently faulted (Hollyford-Waimea Fault). Certain intra-Bryneira-Maitai faults (e,.g. Upukerora and Whangamoa) are shown to be extremely continuous structures.
Other areas containing Upper Permian strata are also discussed; these include Productus Creek, Mataura Island, South Canterbury and Parapara Peak.
The regional reports also include metamorphic data. Mineral assemblages are tabulated and mineral distribution illustrated with regard to stratigraphic and regional distribution. Positions of mineralogic isograds are reported.
Volcanogenic debris in Upper Permian rocks has been very extensively reconstituted under lower grade metamorphic conditions. Mineralogic and petrographic data pertaining to a variety of a authigenic minerals are presented. Some relict detrital minerals are also described. Rock-forming zeolite minerals are restricted to the lowest grade metamorphic rocks studied. In general, data pertaining to these minerals conform with observations of previous workers. It should be noted, however, that some burial metamorphic analcime concentrates possess unusually low silica contents, and also that authigenic analcime, heulandite and laumontite have been recorded from Tertiary rocks from the Hollyford-Waimea Graben and from the Te Anau and Nelson basins.
Non-zeolitic Ca-Al-silicate minerals are, petrologically, the most important minerals recorded; they include lawsonite, prehnite, pumpellyite and epidote. Lawsonite, a mineral indicative of relatively high pressures during metamorphism, is especially widespread in Bryneira-Maitai rocks. It occurs in apparent stability with prehnite, pumpellyite and epidote, but not with zeolites. Bryneira-Maitai epidote tends to be iron-rich, and some data suggest that it is of the "high index" variety.
Calcite is the prevalent polymorph of CaCO3 in all rocks studied. A few occurrences of aragonite are recorded from the vicinity of ultramafic bodies.
Authigenic amphiboles are uncommon. They include tremolite-actinolite, which does not co-exist with lawsonite, and a blue amphibole (probably of the riebeckite-magnesioriebeckite series) which co-exists with lawsonite in at least two occurrences. Metamorphic hornblende occurs in certain Lower Permian mafic volcanic and intrusive rocks. Hornblende also occurs widely, but not abundantly, as a detrital mineral.
Clinopyroxene minerals, augite and salite, occur as detrital grains in numerous rocks. Neither jadeite nor any other authigenic pyroxene has been recognized in the Upper Permian rocks studied. Metamorphic diopside occurs in some Lower Permian rocks.
Authigenic phyllosilicate minerals include chlorite, sericite, celadonite, stilpnomelane, biotite and montmorillonoid clays. Chlorite is virtually ubiquitous; the optically negative variety is found in rocks of all metamorphic grades, whereas optically positive chlorite is absent from lowest grade rocks but becomes increasingly abundant in rocks of slightly higher metamorphic grade. Sericite, probably phengitic, is also widespread. Celadonite is restricted to the lower grade rocks studied. Several previously unrecorded celadonite-bearing mineral assemblages are listed. Stilpnomelane is restricted to rocks in which reconstitution is well advanced. It co-exists with epidote and with amphiboles, but is very rare or absent in zeolite-, prehnite-, and lawsonite-bearing rocks. Biotite occurs in metamorphosed Upper Permian sediments from Parapara Peak, and in addition it occurs as a detrital mineral in many other rocks. Montmorillonoid clays are restricted to zeolite facies rocks.
Microcrystalline Sphene is abundant and widespread. Quartz and albite occur in nearly every mineralogically reconstituted rock. Some rocks contain detrital Ca-plagioclaae and orthoclase which have escaped reconstitution.
Oxide and sulfide minerals include authigenic hematite and pyrite, which are both abundant but do not co-exist, minor chalcopyrite and pyrrhotite, and detrital magnetite and chromite.
Dispersed carbonaceous material has been concentrated from numerous metamorphic rocks and analysed by X-ray and electron diffraction methods. A classification to describe sub-graphitic material is proposed, and progressive graphitization is discussed. Carbonaceous material in zeolite facies rocks is nearly amorphous; well-crystallized graphite is first recognized in amphibolite facies rocks.
Minor occurrences of tourmaline, apatite, garnet, rutile and allanite are also reported.
On the basis of these observations, nine metamorphic zones are defined and mapped. They are correlated with recognized mineral facies -- zeolite, prehnite-pumpellyite, lawsonite-albite-chlorite, pumpellyite-actinolite, greenschist, and blueschist. Several subfacies are tentatively recognized.
Phase rule considerations and textural relationships are taken to indicate widespread approach to equilibrium, however in many cases the extent of an equilibrium assemblage may be restricted to a microscopic volume or rock. In addition, compositional zoning in certain minerals (e.g. pumpellyite and epidote) implies small-scale disequilibrium.
The behaviour and classification of chemical components is discussed. Some evidence suggests that H2O and/or CO2 may not have possessed perfect mobility during metamorphism. A minimum of four and a maximum of seven components (Al2O3 , CaO, FeO, MgO, Fe2O3 , H2), CO2) are considered to be determining components (Korzhinskii terminology).
Numerous three- and four-component determining systems are explored chemographically. Comparison of these diagrams provides some clues regarding mineralogic reactions which may define zone boundaries. However, successful identification of metamorphic reactions by this method requires prior correct recognition of the determining chemical components.
Successful application of the phase rule also relies on correct recognition of determining components. Bearing in mind this reservation, the writer concludes that phase rule considerations are generally compatible with attainment of equilibrium under di- or multi-variant conditions. Some assemblages suggest possible univariant or invariant conditions, or alternatively disequilibrium.
Metamorphic temperatures and pressures constitute the primary controls over distribution of Ca-Al-silicate minerals. The stability fields of most of these minerals overlap. For example, prehnite-pumpellyite assemblage rocks occur interbedded with lawsonite-pumpellyite assemblage rocks in several areas. Possible secondary controls of mineral distribution include chemical composition of the host rock and varying chemical potential of volatile components. These secondary controls are discussed in some detail.
The p - t conditions of metamorphism are investigated and a tentative p - t-facies diagram is presented. The formation of lawsonite-albite-chlorite facies mineral assemblages requires an abnormally low thermal gradient, probably less than 15°C/km.
The data presented -- stratigraphic, lithologic, structural, and metamorphic -- may be synthesized in a geotectonic history. Upper Permian rocks of South Island, New Zealand accumulated in a rapidly evolving and tectonically complex geosyncline. Numerous paleotectonic (i.e. pre- Rangitata Orogeny) structural elements and geologic terranes can be recognized within this geosynclinal framework: these ancient structures exerted a profound control over geosynclinal sedimentation and also over subsequent tectogenesis. They are recognizable today in such features as the Median Tectonic Line, Hollyford-Waimea Fault, Southland-Kawhia Regional Syncline (i.e. synclinorium), and the Key Summit-Nelson Regional Syncline. Some other major structural features, e.g. Alpine Fault, Livingstone Fault, are not recognized within the paleotectonic framework.
Two sedimentary facies belts -- Hokonui and Alpine -- of Permian to Jurassic age, divide the geosyncline into two longitudinal provinces. The facies belts are separated from each other by the Dun Mountain Ultramafic Belt, and it is suggested that this belt may consist partly of sub-geosynclinal basement. Two parallel regional synclines -- Key Summit-Nelson and Southland-Kawhia -- lie within the Hokonui belt. It is emphasized that these structures differ from each other tectonically and chronologically and are nowhere co-linear. Although presently orogenic fold belts, they inherited their structural position and synclinal form from the geosynclinal framework in which they originated. The regional synclines are bordered in part by major faults -- Hollyford-Waimea, Gunn-Eighty Eight -- which are shown to coincide with structural breaks in the geosynclinal basement and also with stratigraphic discontinuities.
A model for paleotectonic evolution of the New Zealand Geosyncline is proposed and briefly discussed.
Abundant unstable terrigenous and pyroclastic debris as well as deep sedimentary burial rendered Permian rocks mineralogically unstable. Thus zeolite and prehnite-pumpellyite facies burial metamorphism proceeded between Permian and late Jurassic or Cretaceous times. In contrast, structural evidence and K-Ar dates suggest that the formation of lawsonite occurred only during early Cretaceous -- Rangitata -- time.
Several important attributes of Upper Permian rocks can be related to width of the Hokonui Facies Belt. These include -- sedimentary facies and stratigraphic thickness, degree of textural reconstitution, mineralogic grade of metamorphism, depth of post-Rangitata erosion, and possibly K-Ar age of slates. Thus highest grade Bryneira-Maitai metasediments lie in the narrow, tightly appressed medial portion of the elongate Key Summit-Nelson Regional Syncline, a position where width of the Hokonui Facies Belt is minimal. Metamorphic grade decreases with increase in Width of the Hokonui Belt.
It is proposed that the New Zealand Geosyncline was driven westward into the continental Western Province during Rangitata orogenesis. The Key Summit-Nelson Regional Syncline became uncoupled from the western part of the Hokonui belt and was rapidly dragged deep into the crust, perhaps with the descending limb of a convection cell.
Dextral strike-slip movement along the Alpine Fault commenced following the climax of Rangitata orogenesis. Movement probably occurred in spasms, and is still active today. Data presented herein may be regarded as consistent with the hypothesis that the Key Summit and Nelson regional synclines originated as one continuous structure. Displacement along the Alpine Fault severed this structure and separated the two portions by 480 km.
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xxv, 2 vols 1: 316 Pages, 2: 317-624 Pages; 30cm Maps and plate folded in seperated book.
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1969Landis
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Citation
Landis, C.A., “Upper Permian rocks of South Island, New Zealand: Lithology, stratigraphy, structure, metamorphism and tectonics.,” Otago Geology Theses, accessed March 23, 2025, https://theses.otagogeology.org.nz/items/show/35.