Evolution of Neoproterozoic Shillong Basin, Meghalaya, NE India: implications of supercontinent break-up and amalgamation

2021 ◽  
pp. 1-17
Author(s):  
Susobhan Neogi ◽  
Apoorve Bhardwaj ◽  
Amitava Kundu
Keyword(s):  
Structural Evolution ◽  
Low Grade ◽  
Peninsular India ◽  
Oblique Collision ◽  
Metasedimentary Rocks ◽  
Ne India ◽  
Fold Belts ◽  
Break Up ◽  
Tectonic Contact ◽  
Proterozoic Basement

Abstract Fragmentation and amalgamation of supercontinents play an important role in shaping our planet. The break-up of such a widely studied supercontinent, Rodinia, has been well documented from several parts of India, especially the northwestern and eastern sector. Interestingly, being located very close to the Proterozoic tectonic margin, northeastern India is expected to have had a significant role in Neoproterozoic geodynamics, but this aspect has still not been thoroughly studied. We therefore investigate a poorly studied NE–SW-trending Shillong Basin of Meghalaya from NE India, which preserves the stratigraphic record and structural evolution spanning the Neoproterozoic Era. The low-grade metasedimentary rocks of Shillong Basin unconformably overlie the high-grade Archean–Proterozoic basement and comprise a c. 4000-m-thick platform sedimentary rock succession. In this study, we divide this succession into three formations: lower Tarso, middle Ingsaw and upper Umlapher. A NW–SE-aligned compression event later caused the thrusting of these sedimentary rocks over the basement with a tectonic contact in the western margin, resulting in NE–SW-trending fold belts. The rift-controlled Shillong Basin shows a comparable Neoproterozoic evolution with the equivalent basins of peninsular India and eastern Gondwana. The recorded Neoproterozoic rift tectonics are likely associated with Rodinia’s break-up and continent dispersion, which finally ended with the oblique collision of India with Australia and the intrusion of Cambrian granitoids during the Pan-African Orogeny, contributing to the assembly of Gondwana. This contribution is the first to present a complete litho-structural evolution of the Shillong Basin in relation to regional and global geodynamic settings.

scholarly journals The thrust contact between the Canastra and Vazante groups in the Southern Brasília Belt: structural evolution, white mica crystallinity and implications for the Brasiliano orogeny

2016 ◽  
Vol 46 (4) ◽  
pp. 567-583 ◽  
Author(s):  
Manuela de Oliveira Carvalho ◽  
◽  
Claudio de Morisson Valeriano ◽  
Pamela Alejandra Aparicio González ◽  
Gustavo Diniz Oliveira ◽  
...  
Keyword(s):  
Structural Evolution ◽  
White Mica ◽  
Low Grade ◽  
Kink Bands ◽  
Metasedimentary Rocks ◽  
Kübler Index ◽  
Crenulation Cleavage ◽  
Thrust Sheets ◽  
Brasiliano Orogeny ◽  
Carbonaceous Phyllite

ABSTRACT: Two regional thrust-sheets of Neoproterozoic metasedimentary rocks occur in the Southern Brasília Belt, northwest Minas Gerais. The lower one comprises the Vazante Group, that is formed in the studied area, from base to top, by the Serra do Garrote (metapelites interlayered with carbonaceous phyllite), Serra do Poço Verde (beige to pink stromatolitic metadolomite with interlayered greenish slates), Morro do Calcário (gray stromatolitic metadolomite interlayered with gray slates) and Serra da Lapa (phyllite with dolarenitic lenses interlayered with slates) formations. The upper thrust sheet consists of the Canastra Group (Paracatu formation): laminated sericite phyllites and carbonaceous phyllites interlayered with quartzite. The Braziliano orogeny resulted in four phases of contractional deformation, associated with low-grade metamorphism. The first two (D1 and D2) are ductile, while the third and fourth ones (D3 and D4) are brittle-ductile. D1 developed a slaty S1 cleavage subparallel to the primary layering, with shallow to steep dips to NW. D2 developed a crenulation cleavage (S2) that dips moderately to NW and is associated with tight to isoclinal folds. D3 and D4 phases developed crenulations and open folds and kink bands. S3 dips steeply to NW, while S4 has moderate to steep dips to NE and SW. White mica crystallinity (Kübler index) measurements in metapelites indicate that both the Canastra and Vazante groups reached anchizone/epizone conditions, and metamorphic discontinuities along thrusts indicate that the peak of metamorphism is pre or syn-thrusting.

40Ar/39Ar whole-rock phyllite ages from late Precambrian rocks of the Avalon composite terrane, New Brunswick: evidence of Silurian–Devonian thermal rejuvenation

1994 ◽  
Vol 31 (5) ◽  
pp. 818-824 ◽  
Author(s):  
R. David Dallmeyer ◽  
R. Damian Nance
Keyword(s):  
New Brunswick ◽  
Low Grade ◽  
Fine Grained ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
Minimum Age ◽  
Tectonic Contact ◽  
Age Constraints ◽  
Gas Fractions ◽  
Thermal Overprint

Several variably deformed and metamorphosed, late Precambrian volcanic–sedimentary successions have been recognized within the Avalon composite terrane exposed in the Caledonian Highlands of southern New Brunswick. Whole-rock samples of metasedimentary phyllite and phyllitic metatuff from the oldest (ca. 600–635 Ma) Avalonian succession display similar, internally discordant 40Ar/39Ar age and apparent K/Ca spectra. Intermediate-temperature gas fractions were experimentally evolved solely from very fine grained, cleavage-aligned white micas. These yield apparent ages between ca. 430 and 410 Ma, and are interpreted to closely date a static Late Silurian – Early Devonian thermal rejuvenation.Evidence for a Silurian – Devonian thermal event has not been previously documented in Avalonian rocks of the Caledonian Highlands (Caledonia assemblage). However, a thermal overprint of similar age (ca. 400 Ma) is recorded by metamorphic muscovite in high-grade gneisses and platformal metasedimentary rocks (Brookville assemblage), which are in tectonic contact with the low-grade Caledonia assemblage. These potentially correlative thermal overprints may provide minimum age constraints on the juxtaposition of these contrasting tectono-stratigraphic assemblages, which are likely to have been palinspastically separate tectonic elements during the earliest Paleozoic.

scholarly journals Paleomagnetic data support Early Permian age for the Abor Volcanics in the lower Siang Valley, NE India: Significance for Gondwana-related break-up models

2012 ◽  
Vol 50 ◽  
pp. 105-115 ◽  
Author(s):  
Jason R. Ali ◽  
Jonathan C. Aitchison ◽  
Sam Y.S. Chik ◽  
Alan T. Baxter ◽  
Scott E. Bryan
Keyword(s):  
Paleomagnetic Data ◽  
Early Permian ◽  
Data Support ◽  
Ne India ◽  
Break Up

Spatial variation in provenance signal: identifying complex sand sourcing within a Carboniferous basin using multiproxy provenance analysis.

2021 ◽  
pp. jgs2021-045
Author(s):  
B. Anders ◽  
S. Tyrrell ◽  
D. Chew ◽  
C. Mark ◽  
G. O'Sullivan ◽  
...  
Keyword(s):  
Spatial Variation ◽  
Drainage System ◽  
Provenance Analysis ◽  
Rock Composition ◽  
Content Type ◽  
Metasedimentary Rocks ◽  
Sedimentary System ◽  
Supplementary Material ◽  
Sandstone Formation ◽  
Proterozoic Basement

Multiple factors (e.g. source rock composition, climate, nature/scale of sedimentary system) influence the volume and composition of sediment delivered to basins. Fluctuations in these parameters produce cryptic source signals which can vary within the same sedimentary system. Bespoke multi-proxy provenance approaches, targeted at minerals of variable stability, allow for an assessment of natural biasing (recycling) and intra-basinal spatial variations.Provenance of fluvial/deltaic sandstones (Mullaghmore Sandstone Formation) in the NW Carboniferous Basin, Ireland, has been constrained using zircon and apatite U-Pb geochronology, trace elements in apatite and Pb-in-K-feldspar analysis. Zircon U-Pb grain populations are consistent with feldspar data, suggesting Proterozoic basement highs offshore Ireland and Scotland were the main contributor with minor supply from Archean-Palaeoproterozoic rocks of Greenland/NW Scotland and Caledonian-aged rocks. However, apatite data shows a much larger proportion of Caledonian-aged grains of metamorphic origin, suggesting significant sediment was recycled from Neopropterozoic metasedimentary rocks. The spatial variation in provenance indicates that, at onset of clastic input, sediment was being routed to the basin through a complex drainage system, comprising of several discrete hinterland catchments, rather than supply from a single, large interconnected sedimentary system. Such complexities can only be identified with the careful application of a bespoke multi-proxy provenance approach.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5536691

40Ar/ 39Ar laser dating of Zongwulong ductile shear zone in northeastern Tibetan Plateau ：Constrains on the closure time of the northmost Paleo-Tethys ocean

2021 ◽  
Author(s):  
Wanli Gao ◽  
Zongxiu Wang
Keyword(s):  
Shear Deformation ◽  
Shear Zone ◽  
Ductile Deformation ◽  
Low Grade ◽  
Ductile Shear Zone ◽  
The South ◽  
Oblique Collision ◽  
Ductile Shear ◽  
Tethys Ocean ◽  
Tectonic Belt

<p><strong><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.67d6c7216eff55356050161/sdaolpUECMynit/12UGE&app=m&a=0&c=5572aca4b392eef83f52919e1be673e9&ct=x&pn=gepj.elif&d=1" alt="">Abstract</strong>：The Zongwulong tectonic belt (ZTB) is located between the northern Qaidam tectonic belt and the south Qilian orogenic belt and contains Late Paleozoic and Early- Middle Triassic strata. Structural features and geochronology of Zongwulong ductile shear zone have key implications for the tectonic property of the ZTB. This study integrated field structure, microscopic structure and <sup>40</sup>Ar/<sup>39</sup>Ar laser probe analysis. The shear zone strikes ~NEE-SWW and dips at a high angle, with a NWW-SEE trending and WE stretching lineation, indicating the shear zone as a thrust- slip shear ductile shear. The asymmetric folds, rotating porphyroclast,structural lens and crenulation cleavage can be seen in the field. Mica fish, S − C fabrics, σ type quartz porphyroclastic and quartz wire drawing structure can also be observed under microscope, indicating that the strike- slip- related ductile deformation and mylonitization occurred under low- grade greenschist facies conditions at temperatures of <em>300° C − 400° C</em>.  The highly deformed<br>mylonite schist yielded <sup>40</sup>Ar/<sup>39</sup>Ar ages <em>(245.8±1.7)Ma </em>and <em>(238.5±2.6)</em>Ma for muscovite and biotite, respectively, indicating that the shear deformation occurred during the Early- Mid Triassic. Combined with comprehensive analysis of regional geology and petrology, the authors hold that the age of ductile shear deformation represents the time of Triassic orogeny in the ZTB. The oroginic activity was probably related to the oblique collision between the South Qilian block and the Oulongbuluke block after the closure of the northermost Paleo-Tethys ocean.</p>

Late Carboniferous Schlingen in the Gotthard nappe (Central Alps) and their relation to the Variscan evolution

2021 ◽  
Author(s):  
Mario Buehler ◽  
Roger Zurbriggen ◽  
Alfons Berger ◽  
Marco Herwegh ◽  
Daniela Rubatto
Keyword(s):  
Shear Zone ◽  
Country Rock ◽  
Structural Evolution ◽  
Point Of View ◽  
Swiss Alps ◽  
Low Grade ◽  
Central Alps ◽  
Structural Investigations ◽  
Alpine Belt ◽  
Main Cluster

<p>Many pre‐Mesozoic basements of the Alpine belt contain kilometre‐scaled folds with steeply inclined axial planes and fold axes. Those structures are referred to as Schlingen folds. They deform polymetamorphic gneisses, often Late‐Ordovician metagranitoids and are cross‐cut themselves by Permian intrusions. However, the structural evolution of such Schlingen is still not completely understood and their geodynamic significance for the Variscan evolution is not clear. To close this gap, this study investigates in detail a well-preserved Schlingen structure in the Gotthard nappe (Central Swiss Alps). This Schlingen fold evolved by a combination of shearing and folding under amphibolite facies conditions. Detailed digital field mapping coupled with petrological and structural investigations reveal local synkinematic migmatisation in the fold hinges parallel to axial planes. U‐Pb dating of zircons separated from associated leucosomes reveal cores that record a detrital country rock age of 450 ± 3 Ma, and rims with a range of dates from 270 to 330 Ma. The main cluster defines an age of 316 ± 4 Ma. We ascribe this Late‐Carboniferous age to peak metamorphic conditions of the late‐Variscan Schlingen phase.</p><p>The pre-Schlingen structures are subdivided into three older deformation events, which are connected to the Cenerian and post-Cenerian deformations. In addition, until now unknown, post Schlingen-, but pre-Alpine transpressional deformation have been detected and described. This superimposed deformation produced locally a low-grade foliation and minor undulation of the Schlingen structures.</p><p>The detail data of the investigated fold structures are linked with already described Schlingen folds in the wider Alpine realm, which all are concentrated in the most southern parts of the Variscides. From a geodynamic point of view and based on the new tectono-metamorphic constraints, we propose Schlingen formation preceded and concurred the crustal-scale transpressional tectonics of the East Variscan Shear Zone. This scenario separates, at least in a structural sense, the Southern Variscides from more northern parts (also Gondwana derived) inside Pangea, where Schlingen folds are absent.</p>

scholarly journals Structural pattern and emplacement mechanisms of the Krížna cover nappe (Central Western Carpathians)

2012 ◽  
Vol 63 (1) ◽  
pp. 13-32 ◽  
Author(s):  
Roberta Prokešová ◽  
Dušan Plašienka ◽  
Rastislav Milovský
Keyword(s):  
Driving Forces ◽  
Structural Evolution ◽  
Evolutionary Model ◽  
Structural Data ◽  
Western Carpathians ◽  
Low Grade ◽  
Structural Pattern ◽  
Thrust Tectonics ◽  
Central Western Carpathians ◽  
Nappe Emplacement

Structural pattern and emplacement mechanisms of the Krížna cover nappe (Central Western Carpathians)The Central Western Carpathians are characterized by both the thick- and thin-skinned thrust tectonics that originated during the Cretaceous. The Krížna Unit (Fatric Superunit) with a thickness of only a few km is the most widespread cover nappe system that completely overthrusts the Tatric basement/cover superunit over an area of about 12 thousands square km. In searching for a reliable model of its origin and emplacement, we have collected structural data throughout the nappe body from its hinterland backstop (Veporic Superunit) to its frontal parts. Fluid inclusion (FI) data from carbonate cataclastic rocks occurring at the nappe sole provided useful information about the p-T conditions during the nappe transport. The crucial phenomena considered for formulation of our evolutionary model are: (1) the nappe was derived from a broad rifted basinal area bounded by elevated domains; (2) the nappe body is composed of alternating, rheologically very variable sedimentary rock complexes, hence creating a mechanically stratified multilayer; (3) presence of soft strata serving as décollement horizons; (4) stress and strain gradients increasing towards the backstop; (5) progressive internal deformation at very low-grade conditions partitioned into several deformation stages reflecting varying external constraints for the nappe movement; (6) a very weak nappe sole formed by cataclasites indicating fluid-assisted nappe transport during all stages; (7) injection of hot overpressured fluids from external sources (deformed basement units) facilitating frontal ramp overthrusting under supralithostatic conditions. It was found that no simple mechanical model can be applied, but that all known principal emplacement mechanisms and driving forces temporarily participated in progressive structural evolution of the nappe. The rear compression operated during the early stages, when the sedimentary succession was detached, shortened and transported over the frontal ramp. Subsequently, gravity spreading and gliding governed the final nappe emplacement over the unconstrained basinal foreland.

scholarly journals A preserved early Ediacaran magmatic arc at the northernmost portion of the Transversal Zone central subprovince of the Borborema Province, Northeastern South America

2016 ◽  
Vol 46 (4) ◽  
pp. 491-508 ◽  
Author(s):  
Benjamim Bley de Brito Neves ◽  
◽  
Edilton José dos Santos ◽  
Reinhardt Adolfo Fuck ◽  
Lauro César Montefalco Lira Santos ◽  
...  
Keyword(s):  
Granitic Rocks ◽  
Lower Plate ◽  
Low Grade ◽  
Northeast Brazil ◽  
The South ◽  
Magmatic Arc ◽  
Continental Plate ◽  
Borborema Province ◽  
Northern Portion ◽  
Fold Belts

ABSTRACT: Magmatic arcs are an essential part of crust-forming events in planet Earth evolution. The aim of this work was to describe an early Ediacaran magmatic arc (ca. 635-580 Ma) exposed in the northernmost portion of the Transversal Zone, central subprovince of Borborema Province, northeast Brazil. Our research took advantage of several syntheses by different authors, including theses and dissertations, carried out on magmatic rocks of the study area for the last 30 years. The ca. 750 km long and up to 140 km wide arc, trending ENE-WSW, is preserved to the south of the Patos Lineament, between 35º15' and 42º30'W and 7º15' and 8ºS. About 90 different stocks and batholiths of I-type granitic rocks were mapped along this orogenic zone, preferentially intruding low-grade schists of the Cryogenian-Ediacaran Piancó-Alto Brígida (SPAB) belt. Three igneous supersuites are recognized: a) epidote-bearing granodiorites and tonalites ("Conceição" type); b) high-K calc-alkaline granites ("Itaporanga" type); c) biotite granodiorites of trondhjemite affinity ("Serrita" type). A fourth group of peralkalic and shoshonitic rocks occurs to the south of the previous ones, reflecting special tectonic conditions. NNE-SSW trending Paleoproterozoic fold belts, surrounding Archean nuclei, characterize the continental part of the northern lower plate. The oceanic fraction of this lower plate was recycled by subduction and scarce remnants of which may be seen either within the enclosing low-grade schists or as xenoliths within the arc intrusions. The upper continental plate presents WSW-ENE structural trends and is composed of Neoproterozoic fold belts and Paleoproterozoic reworked basement inliers. Available data bear clear evidence of an Ediacaran magmatic arc built at the northern portion of the Transversal Zone in the Borborema Province, northeast Brazil.

Victoria's Proterozoic basement controls the distribution of its southern margin petroleum basins

2009 ◽  
Vol 49 (2) ◽  
pp. 581
Author(s):  
David Taylor ◽  
David Moore
Keyword(s):  
Central Victoria ◽  
Southern Margin ◽  
Break Up ◽  
Proterozoic Basement ◽  
Thinned Continental Crust ◽  
Clean Break ◽  
Western Victoria ◽  
Gippsland Basin ◽  
Ocean Boundary ◽  
East West

There are three petroleum basins of differing character off the Victorian coast: the Otway, Bass and Gippsland basins. These formed during continental rifting between Australia, Antarctica and New Zealand, associated with the break up of Gondwana Marked variation in the development of these basins appears to have been largely controlled by the distribution of Proterozoic basement—the Selwyn Block—under central Victoria. Lying deep under central Victoria, this block surfaces towards the coast and continues southward as the Proterozoic crust of western Tasmania. The boundaries of this block are coincident with the boundaries separating the three basins. The Otway Basin in western Victoria represents a clean break between Australia and Antarctica. The Otway Basin has thick fill upon thinned continental crust with an outboard break to a continent-ocean boundary. The overall geometry here is a classic lower plate margin. This clean continental break-up failed to propagate eastward across the Proterozoic Selwyn Block. Instead, localised continental stretching resulted in some grabens and the overlying steers head sag of the Bass Basin. True continental separation was transferred southward to the margin of the Tasmania/Selwyn Block. The Gippsland Basin lies east of the Selwyn Block. Its development reflects initial southern margin rifting, but this was overtaken by orthogonal-oriented Tasman rifting. This left the Gippsland Basin with a complex interplay of north-south and east-west structures controlling the platforms, terraces and deeps.

Inversion of magnetic and frequency-domain electromagnetic data for investigating lithologies associated with gold mineralization in the Canadian Malartic area, Québec, Canada

2020 ◽  
pp. 1-20
Author(s):  
Mehrdad Darijani ◽  
Colin G. Farquharson
Keyword(s):  
Frequency Domain ◽  
Gold Mineralization ◽  
Volcanic Rocks ◽  
Tetrahedral Mesh ◽  
Iron Formation ◽  
Magnetic Data ◽  
Low Grade ◽  
Metasedimentary Rocks ◽  
Magnetic Inversion ◽  
Northern Edge

Canadian Malartic is an Archean low-grade bulk tonnage native gold deposit. The deposit is mostly located in altered clastic metasedimentary rocks, mafic–ultramafic dykes, and monzodioritic porphyry intrusions. Airborne magnetic and frequency-domain electromagnetic (EM) data were inverted to reconstruct the geological units associated with the mineralization, especially the intrusive masses. The 3-D inversion of magnetic data, which used a tetrahedral mesh to a depth of 2.4 km, shows that mafic volcanic rocks and iron formation rocks extend to depth in the area, more so than diabase dykes. The magnetic inversion also shows that the diorite and monzodiorite rocks of the Lac Fournière A pluton are dipping toward the south on its northern edge at the contact with the metasedimentary rocks. The 1-D inversion of the frequency-domain EM data, for both electrical conductivity and magnetic susceptibility, is able to reconstruct geological structures to a depth of approximately 100 m, providing more details and information about these features. The intrusive masses such as diabase dykes, diorite and monzodiorite rocks, and mafic volcanic rocks are reconstructed as electrically conductive structures in the inversion results. The metasedimentary rocks are resistive, and the overburden is conductive in most of the area. The geophysical data and inversion results suggest the presence of some features (such as diabase dykes and monzodiorite rocks) that are not yet present on some parts of the geology map. A comparison of the EM-derived susceptibility and the magnetic-derived susceptibility over the iron formations can reveal the effect of remanent magnetization.

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