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1.
The Cauvery Shear Zone, Southern Granulite Terrain, India: A crustal-scale flower structure 总被引：2，自引：1，他引：2
The Cauvery Shear Zone (CSZ) is a crustal-scale shear system within the Southern Granulite Terrain along the southern margin of the Archaean Dharwar craton. Structural interpretation of satellite data and field observations reveal four major shear zones within the CSZ system. They show dextral shear kinematics synchronous with a major Neoproterozoic tectono-metamorphic event (D2) associated with intracrustal melting and migmatisation. The disposition, geometry and contemporaneity of shear fabrics of the CSZ system are modelled in terms of a crustal-scale flower structure akin to transpressional and collisional orogens. In the light of recent seismic evidence for a displaced Moho structure and a mid- to lower-crustal low velocity zone, the flower structure across the CSZ may extend to mantle depths. 相似文献
2.
Kei Sato M. Santosh Toshiaki Tsunogae T.R.K. Chetty Takafumi Hirata 《Journal of Asian Earth Sciences》2011,40(1):162-171
We report the petrological characteristics and preliminary zircon geochronology based on laser ablation ICP mass spectrometry of the various units in an accretionary belt within the Palghat-Cauvery Shear/Suture Zone in southern India, a trace of the Cambrian Gondwana suture. Zircons extracted from a plagiogranite in association with an ophiolite suite within this suture possess internal structure that suggests magmatic crystallization, and yield mid Neoproterozoic 206Pb/238U age of 817 ± 16 Ma (error: 1σ) constraining the approximate timing of birth of the Mozambique Ocean floor. Compiled age data on zircons separated from a quartzite and metamorphosed banded iron formation within the accretionary belt yields a younger intercept age of 759 ± 41 Ma (error: 1σ) which we relate to a mid Neoproteozoic magmatic arc. Detrital zircons extracted from the quartzite yield 207Pb/206Pb age peaks of about 1.9–2.6 Ga suggesting that they were sourced from multiple protolithis of Neoarchean and Paleoproterozoic. Metamorphic overgrowths on some zircon grains record ca. 500–550 Ma ages which are in good harmony with the known ages for the timing of high-grade metamorphism in this zone during the final stage of continent collision associated with the birth of the Gondwana supercontinent in the latest Neoproterozoic-Cambrian. The preliminary geochronological results documented in our study correlate with the subduction–accretion–collision history associated with the closure of the Mozambique Ocean and the final amalgamation of the Gondwana supercontinent. 相似文献
3.
The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates
of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been
classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association, stratigraphic position and geochemistry
of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite
and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging,
trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting
wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established.
Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits.
Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are
significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative
enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation.
Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high
salinity (17–23 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits
investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370–405 °C) with early
sulphide remobilisation in Tsumeb at 275 °C, whereas they are lower at Berg Aukas (up to 255 °C). Fluid inclusion leachate
analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and
chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction
with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African
orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached
the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred
in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type
deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation
of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct.
Received: 5 May 1999 / Accepted: 10 November 1999 相似文献
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5.
T. R. K. Chetty 《Journal of the Geological Society of India》2011,78(5):446-456
A tectonic map of Cuddapah Basin (CB) and its adjacent regions has been compiled using LANDSAT TM data and the available literature
on the prominent tectonic features which include Archaean greenstone belts, disposition of Proterozoic mobile belts along
with the associated mid-crustal shear zones, and the mafic dyke swarms. The field characteristics of the two major fault zones:
Gudur-Cuddapah and the Veldurti-Kalva-Gani fault system that cut across the CB have been re-examined and are re-interpreted
as typical of transfer faults, which are generated exclusively by extensional tectonics. The earlier concept that these fault
systems form a conjugate set of “Anderson type” causing the ‘Cuddapah salient’, needs to be reviewed. 相似文献
6.
T.R.K.Chetty Y.J.BhaskarRao 《《幕》》2004,27(4):295-296
Considering its central position in East Gondwana reconstructions, the Indian subcontinent figures prominently in the studies, which were envisaged under the recently conceptualized international project—““LEGENDS““ (Lithospheric Evolution of Gondwana East from interdisciplinary Deep Surveys), a major initiative by international scientific community to study continents of the southern hemisphere. The CC-8 subcommittee of the International Lithospheric Programme (ILP) has also accepted the LEGENDS initiative. 相似文献
7.
Arshath Ramkilowan Naven Chetty Meena Lysko Derek Griffith 《Journal of the Indian Society of Remote Sensing》2013,41(3):531-538
Higher water temperatures and nutrient loads, along with forecasted climate changes are expected to result in an increase in the frequency and intensity of eutrophication-linked algal blooms (Bernard, 2010, unpublished). The destructive impact such phenomena have on marine and freshwater systems threaten aquaculture, agriculture and tourism industries on a global scale (Bernard, 2010, unpublished). An innovative research project, Safe Waters Earth Observation Systems (SWEOS) proposes the use of space-based remote sensing techniques, coupled with in-situ radiometric technology to offer a powerful and potentially cost effective method of addressing algal bloom related hazards. The work presented in this paper focuses on the decision making processes involved in the development of autonomous bio-optical sensors whose purpose includes, but is not limited to; water constituent monitoring, satellite calibration validation and ocean colour satellite product matchups. Several criteria including cost, optical throughput, linearity and spectral sensitivity were examined in an attempt to choose the detector best suited for its intended application. The CMOS based module tested in the laboratory experiments that was found to have produced the best performance-cost ratio was chosen for integration into the in-water radiometric device built and tested at the Council for Scientific and Industrial Research (CSIR) (Ramkilowan et al. 2012, unpublished). Mass production of this prototype technology will commence, pending data quality comparable to that of an already calibrated, in-water radiometer; to be tested at field trials in Elands Bay (32°17′45.82″S; 18°14′44.45″E), Loskop Dam (25°27′15.25″S; 29°17′28.21″E) and Saldanha Bay (33° 3′11.38″S; 17°59′54.29″E). 相似文献
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Regional mapping of a section across the Eastern Ghats Mobile Belt (EGMB) north of the Godavari graben in Eastern Peninsular India by using Landsat Thematic Mapper data enables recognition of a number of shear zones, lineaments, and structural domes and basins. A conspicuous megashear occurs at the western boundary of the granulite facies rocks of the EGMB adjacent to the Archean granite-greenstone craton. The confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature. The strike extensions of this shear belt extend through to the Elchuru alkaline complex, Prakasam District, Andhra Pradesh, and the syenite plutons of Koraput district, Orissa. The contrasting lithologies, metamorphism and structural history on either side of the shear zone suggests that it might be a Precambrian suture zone. The mesoscopic structural features in the EGMB include prominent foliation with moderate to steep dips, folds, faults/shears, S-C fabrics, pinch and swell structures and other linear fabric elements. These observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence. The major rock units in this part of EGMB comprise garnetiferous sillimanite gneisses, quartzites and calc-granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks. The contact of the two rock units is generally sheared and often migmatised. The structural fabric suggests two major tectonic events: an essentially horizontal tectonic regime resulting in thrust systems and associated structures, subsequently followed by strike-slip tectonics characterized by high shear strains. Features such as westward-verging thrusts, large-scale recumbent folds, major shear zones, structural domes and basins, indications of tectonic crustal shortening, extensive calc-alkali magmatism and widespread migmatization in the region are attributed to collisional processes during Proterozoic times. The spatial disposition of the EGMB and its linkage with the distribution of similar rock units during the late Precambrian time in a global tectonic scenario are discussed. 相似文献
10.
T. R. K. Chetty D. P. Mohanty T. Yellappa 《Journal of the Geological Society of India》2012,79(2):151-154
A new map of structural architecture has been compiled involving modern mapping techniques at the cratonmobile belt interface
in the Western Ghats around the Coorg granulite massif revealing the occurrence of important shear zones. The shear zones
are linked to the Moyar-Bhavani Shear Zone in Southern India. The nature, geometry and kinematics of the shear zones in the
granulitic crust and the cratonic part are distinctly different. 相似文献