Academic literature on the topic 'Schists New Caledonia'

AbstractThe basement under the Late Cretaceous unconformity in New Caledonia consists of three amalgamated terranes. They are all oceanic, arc-related and developed offshore from the eastern Gondwana active margin during periods of marginal basin development. Téremba Terrane is composed of deep sea Permian to Mesozoic arc-derived volcanic rocks and greywackes. The Koh–Central Terrane includes at its base an ophiolite with island arc tholeiites and boninites (Koh Ophiolite) of Late Carboniferous to Early Permian age overlain by a thick sequence of greywacke (Central Range Volcaniclastic Rocks) of Permian to Late Jurassic age. The Téremba Terrane and the Koh–Central Terrane may be part of the same forearc basin, with the rocks from the Koh–Central Terrane deposited in a deeper environment. The Boghen Terrane is a metamorphic complex composed of schists, broken formations and mafic–ultramafic mélange, derived from mixed terrigenous and volcanic sources. The overall fine grain size and laminar bedding suggest deep sea and more distal deposition than the other terranes. The maximum depositional ages from detrital zircons suggest deposition during the Early Jurassic to Early Cretaceous. The terrane is interpreted as a metamorphosed subduction complex that includes blueschist and greenschist facies metamorphic rocks exhumed through the Koh–Central Terrane. At a regional scale, the nature of these three pre-Late Cretaceous terranes confirms the existing palaeogeographical reconstructions, which locate New Caledonia outboard the ocean–continent subduction that surrounded Gondwana during the Paleozoic and Early Mesozoic. A detailed analysis of these terranes and their relationship with East Australian terranes of the same age shows that a marginal basin system probably existed between mainland Gondwana and proto-New Caledonia and closed before the Late Cretaceous. A tentative detailed reconstruction of this margin during the Carboniferous–Early Cretaceous period is proposed.

Geochronological studies in northern Wedel Jarlsberg Land, southwestern Svalbard (Norway), showed that the Tonian (c. 950 Ma) igneous rocks were subjected to metamorphism during the Torellian (c. 640 Ma) and early Caledonian (470–460 Ma) events. Predominant augen gneisses, derived from a Tonian protolith, are intercalated in that area, with schists comprising two distinct metamorphic mineral assemblages. The M1 (Torellian) assemblage containing garnet-I + quartz + plagioclase-I + biotite-I + muscovite-I was formed under amphibolite-facies conditions at c. 550–600 °C and 5–8 kbar (1 kbar = 100 MPa). The M2 (Caledonian) assemblage comprising garnet-II + quartz + plagioclase-II + biotite-II + muscovite-II + zoisite + chlorite crystallized at c. 500–550 °C and 9–12 kbar, corresponding to epidote–amphibolite facies conditions. The M2 mineral assemblage constitutes the pervasive Caledonian fabric of the schists that was subsequently reactivated in a left-lateral strike-slip shear regime. The subsequent c. 70° clockwise rotation of the original structure to its present position was caused by a large-scale passive rotation during the Paleogene Eurekan orogeny. The new pressure–temperature estimates suggest that metamorphic basement in the study area was consolidated during the Torellian middle-grade event and then overprinted by Caledonian moderate- to high-pressure subduction-related metamorphism. A following sinistral shear zone assembled the present structure of basement units. Our results pose a question about the possible extent of Torellian precursor to the Caledonian basement across the High Arctic and the scale of its subsequent involvement in early Caledonian subduction. In conjunction with previous studies, the results suggest a possible correlation between southwestern Spitsbergen and the Pearya Terrane in Ellesmere Island.

Pycnandra Benth. is a member of the pantropical family Sapotaceae (Chrysophylloideae) and the Niemeyera complex, a group that is found in Australia and New Caledonia. Generic limits in the complex have been problematic and Pycnandra is here given a circumscription to include the entire clade that is restricted to New Caledonia. Several lineages are therefore relegated to the subgeneric level that will subsequently be revised. In a first step, we revise P. subgenus Pycnandra with 12 recognised species, of which seven (P. atrofusca, P. cylindricarpa, P. glaberrima, P. linearifolia, P. longipetiolata, P. paucinervia and P. viridiflora) are described as new. Subgenus Pycnandra is endemic to Grande Terre, the main island of New Caledonia. The members grow in a wide range of habitats from dry maquis vegetation to moist humid forest, from sea level to the higher massif, and on ultramafic soils to schist and greywacke. Diagnostic characters for Pycnandra include absence of staminodes, a single-seeded fruit, plano-convex cotyledons and lack of endosperm. A glabrous ovary is a useful character distinguishing P. subgenus Pycnandra from the congeners, although there are two exceptions. P. viridiflora is included in the subgenus even though it has a pubescent ovary and Ochrothallus wagapensis is excluded despite a glabrous ovary. Because of past and present mining and logging activities in New Caledonia, conservation assessments are urgently needed. Preliminary IUCN Red List assessments are here provided for all members of the subgenus Pycnandra. Three species (P. longipetiolata, P. paniensis and P. paucinervia) are proposed the IUCN status Endangered and another (P. viridiflora) is proposed to be Critically Endangered.

Pycnandra is a genus of Sapotaceae (Chrysophylloideae), restricted to New Caledonia, and includes ~60 species. The genus is a member of the monophyletic Niemeyera complex of Australia and New Caledonia and it is characterised by the lack of staminodes and a fruit containing a single seed, plano-convex cotyledons and absence of endosperm. In New Caledonia, several segregate genera have been recognised, but weak cladistic support for these groups and homoplasious morphology renders a narrow generic concept untenable. Instead, a broad generic circumscription of Pycnandra with an infrageneric classification recognising the subgenera Achradotypus, Leptostylis, Pycnandra, Sebertia and Trouettia results in a stable nomenclature. Here we revise Pycnandra subg. Achradotypus that includes 14 species, of which five (P. belepensis, P. blaffartii, P. bracteolata, P. glabella, and P. ouaiemensis) are described as new. Members of subg. Achradotypus are distinguished from other subgenera on the basis of a character combination of two stamens opposite each corolla lobe (except P. litseiflora), glabrous leaves (except P. belepensis and P. decandra), a distinctive reticulate tertiary leaf venation (except P. comptonii), and sepal-like bracts that often are borne along the pedicel. All species are restricted to Grande Terre except for P. decandra, whose distribution also extends to nearby Art Island (Belep Islands), and P. belepensis, which is endemic to that same island. The members grow in a wide range of vegetation types from dry maquis to humid forest, from sea level to the highest mountain massif, and on ultramafic soils to schist and greywacke (not limestone). Because of past and present threats such as mining, logging and fire, preliminary IUCN Red List assessments are provided for all species. Five taxa (P. chartacea, P. decandra subsp. decandra, P. glabella, P. litseiflora, and P. neocaledonica) are proposed the IUCN status Endangered, and P. belepensis and P. ouaiemensis are proposed to be Critically Endangered. We suggest that some locations where these species occur should be given protection in the form of nature reserves.

The Lilljeborgfjellet Conglomerate Formation composes the lower part of the alluvial Siktefjellet Group of northwestern Spitsbergen's Old Red Sandstone succession. Siktefjellet strata are of late Silurian or early Devonian age, but lack precise age-diagnostic fossils. They are unconformably overlain by conglomerates and sandstones of the Red Bay Group, which contain a well established fish fauna of Lochkovian age. The Lilljeborgfjellet Conglomerate rests with a major unconformity on high-grade (with eclogites) schists and gneisses, with associated corona gabbros and granitic gneisses. Previous isotope-age studies have shown that these igneous rocks yield U/Pb ages of c. 950 Ma, and that the eclogite facies metamorphism may be of Caledonian or late Neoproterozoic age. The high P/high T rocks are intercalated with and overlain by schists affected only by Caledonian amphibolite facies metamorphism, recorded by 40Ar/39Ar and Rb/Sr cooling ages of 400–430 Ma.In the Lochkovian Red Bay Group of the Raudfjorden Graben, two horizons of tuffites occur, interbedded with sandstones. New studies of eight zircons from these volcanic rocks have provided single-zircon lead-evaporation ages of c. 950 and c. 1350 Ma; one yielded 440 Ma. All these zircons are probably derived from the underlying basement rocks, the ages being significantly older than the Devonian host strata (c. 410 Ma).The clasts in the Lilljeborgfjellet Conglomerate are generally angular to subrounded and derived locally from the underlying high-grade metamorphic complex. A subordinate (usually less than 1%, but up to about 10%) component of the clasts is a quartz porphyry that is not known in the exposed bedrock anywhere in northwestern Spitsbergen. The quartz porphyries are better rounded than the other clasts; however, the maximum diameter reaches 1.5 metres, indicating that transport distances are unlikely to have exceeded a few kilometres. Three quartz porphyry boulders have been dated by the single-zircon lead-evaporation method and shown to be of Palaeoproterozoic age, yielding ages of 1735±4, 1736±5 and 1739±5 Ma that have not previously been detected in the northwestern part of Svalbard's Caledonides.The quartz porphyry clasts show no evidence of the widespread high-grade tectonothermal activity of Mesoproterozoic and early Palaeozoic age that influenced northwestern Spitsbergen. It is therefore concluded that the most probable source of these clasts lies to the east in the unexposed basement beneath the Old Red Sandstones of the Andrèeland–Dicksonland Graben. The Lilljeborgfjellet quartz porphyry clasts are closely similar in age to the granitic rocks of Ny Friesland. Whereas the latter were subject to Caledonian high amphibolite facies metamorphism, the quartz porphyry clasts have only been affected by a low greenschist facies overprint. Nevertheless, the similarity in age suggests an affinity to Ny Friesland and it is proposed here that the Breibogen–Bockfjorden Fault defines the most important boundary between Svalbard's Caledonian terranes.

The breakup of continents generates dyke swarms, basins, and hyperextension assemblages. Once incorporated in new orogens the latter can provide crucial information on origins and tectonic processes. The Nålfjell Complex in the Caledonian Skillefjord Nappe of northern Norway has many of the characteristics of an hyperextension assemblage, notably the presence of solitary serpentinite bodies exposed by exhumation of serpentinized mantle, and now embedded in schists, amphibolites, mylonites, marbles, and felsic gneisses The Skillefjord Nappe is a lithologically diverse, imbricated and discontinuous allochthton. It comprises felsic gneisses and dykes dated by zircon U-Pb to ca. 3100, 2940, 2830, 2510 and 1800-1750 Ma. These rocks yield titanite ages of 2810-2700, 1750, 1660-1590 Ma and 420-430. Metagabbro intruded at 1995 Ma. The ages and evolution of the Skillefjord Nappe are very distinct from those of the structurally higher Svaertholt Terrane (>1030 Ma sediments deformed and intruded by granite at 980-950 Ma), and the Sørøy Terrane (characterized by a multistage 900 to 500 Ma evolution). The assembly of these disparate elements was completed at 420 Ma. The timing of hyperextension is uncertain. The serpentinites have a primitive Pb isotopic composition indicating old depleted mantle lithosphere. Extensional processes from the Palaeoproterozoic to Ediacaran are considered.Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/cc/caledonian-wilson-cycle

Svalbard's Northwestern Basement Province is traditionally divided into the Albert I Land and the Biscayarhalvøya terranes. New U–Pb age data on zircon and monazite and structural and geochemical data provide first evidence of early Paleozoic deposits south of the Biscayarhalvøya Terrane indicating the possible existence of a third terrane: the Germaniahalvøya Terrane. This area is represented by a Cambro-Ordovician succession of mica schist and marble (Lernerøyane Group) and its higher-grade metamorphic equivalent (Liefdefjorden Migmatite Complex), which were affected by the Taconian phase (migmatization at c. 469 Ma) and the Scandian phase (c. 422–415 Ma) of the Caledonian Orogeny. During the Scandian phase, the ductile Lerner Deformation Zone was formed. New isotopic data from the eclogite-bearing Richarddalen Complex of the Biscayarhalvøya Terrane imply the formation as an Ordovician–Silurian collision-related mélange dominantly composed of c. 730 to 600 Ma Timanian island-arc-derived detritus and igneous rocks, partly eclogite-facies metamorphosed at c. 656 Ma, and Tonian meta-igneous rocks. After amphibolite-facies metamorphism of the mélange matrix at c. 423 Ma, the Richarddalen Complex and the Stenian–Tonian Biscayarfonna Group were juxtaposed and mylonitized by the dextral Biscayarhalvøya Deformation Zone.Supplementary material: The complete geochemical and U-Pb isotope geochemical dataset as well as additional figures are available at https://doi.org/10.6084/m9.figshare.c.5778735

ABSTRACT Forty-three new U-Pb zircon ages from metasedimentary and igneous rock units throughout the Cobequid Highlands of northern mainland Nova Scotia, Canada, provide new insights into the Neoproterozoic evolution of this long-enigmatic part of Avalonia in the northern Appalachian orogen. Contrasts in ages and rock types resulted in the identification of fault-bounded Neoproterozoic assemblages of units forming the Bass River, Jeffers, and Mount Ephraim blocks. In the Bass River block, quartzite, metawacke, and minor calc-silicate rocks and marble (Gamble Brook Formation) with a maximum depositional age of 945 ± 12 Ma are associated with subaqueous mafic volcanic rocks, siltstone, and ironstone (Folly River Formation) and intruded by 615–600 Ma calc-alkalic subduction-related dioritic to granitic rocks of the Bass River plutonic suite. The contrasting Jeffers block forms most of the Cobequid Highlands and consists mainly of intermediate to felsic volcanic, epiclastic, and minor plutonic rocks. The western and eastern areas of that block yielded ages mainly ca. 607–592 Ma for both volcanic and plutonic rocks, whereas the central area has ages of ca. 630–625 Ma from both volcanic and plutonic rocks and inheritance in overlying Devonian conglomerate. The Mount Ephraim block forms the eastern part of the highlands and includes possible ca. 800 Ma quartzofeldspathic, semipelitic and pelitic gneiss and schist of the Mount Thom Formation, ca. 752 Ma volcanic arc rocks of the Dalhousie Mountain Formation and related 752–730 Ma gabbroic/dioritic to granitic plutons of the Mount Ephraim plutonic suite and Six Mile Brook pluton, as well as ca. 631 Ma granitoid rocks of the Gunshot Brook pluton. The pre–750 Ma high-grade regional metamorphism and deformation and 752–730 Ma subduction-related magmatism recorded in the Mount Ephraim block were previously unrecognized in Avalonia. Evidence from zircon inheritance and Sm-Nd isotopic data in igneous units suggests linkages among these now-separate areas, and comparison with other parts of Avalonia in the northern Appalachian orogen suggests similarity to southeastern New England.