Show simple item record

dc.contributor.advisorKrishnan, Sajeev
dc.contributor.authorSamuel, Vinod Oommen
dc.date.accessioned2018-08-02T07:03:13Z
dc.date.accessioned2018-08-28T11:52:35Z
dc.date.available2018-08-02T07:03:13Z
dc.date.available2018-08-28T11:52:35Z
dc.date.issued2018-08-02
dc.date.submitted2015
dc.identifier.urihttps://etd.iisc.ac.in/handle/2005/4004
dc.identifier.abstracthttp://etd.iisc.ac.in/static/etd/abstracts/4802/G27171-Abs.pdfen_US
dc.description.abstractThe oldest dated rocks from the Acasta gneisses of the western Slave Province, Canada present an igneous age of ~4030 Ma. Following this the detrital zircons from the Jack Hills, Narryer Gneiss Terrane, Yilgarn Craton, Western Australia are identified as 4404 ±8 Ma. These discoveries suggest that crustal formation started as early as the Priscian Eon. Hitherto the Earth has gone through a series of interactions involving the atmosphere, hydrosphere, crust, mantle and core. However, only limited remnants of these early processes remain on the accessible crust due to extensive crustal reworking. The Southern Granulite Terrane (SGT) in the southern part of India represents the most extensive exposure of lower crustal granulite terranes in the world. This study mainly focuses on the characteristics of Archean (~2500 Ma) tectonics and nature of subsequent crustal growth, which led to the formation of Archean Nilgiri Block. Detailed fieldwork in this terrane and subsequent petrographic analysis revealed charnockites, hornblende-biotite gneiss, metagabbro/mafic granulite, websterite, amphibolite, Grt-Ky metasediment, metatuff and banded iron formation as the main rock types in this terrane. Field and petrographic results show a regional trend with garnet-orthopyroxene-biotite-quartz-plagioclase-K- feldspar bearing charnockites in the southern part which gets subsequently enriched in clinopyroxene that forms garnet-absent two pyroxene granulites consisting of orthopyroxene-clinopyroxene-quartz-plagioclase-K-feldspar towards the central part. Further north, metagabbro/mafic granulite is enriched in garnet-clinopyroxene-plagioclase assemblage. Websterite, amphibolite, metasediment, metatuff and banded iron formation are stacked and closely associated within this mafic belt in the north. The metagabbro represents peak P-T conditions of ~850°C and ~14kbar compared to the charnockites, which recorded a peak P-T of ~850°C and 9-10kbar. Petrographic results of oxide minerals show that the southern charnockitic part is abundant in rutile-ilmenite association represent reduced conditions compared to the oxidized magnetite-hematite-ilmenite associations in the mafic rocks. This oxidation trend is followed by pyrrhotite-chalcopyrite enriched southern charnockitic region that transforms to pyrite rich northern mafic belt. Ilmenite¬titanite association with no sulphides characterizes the hornblende-biotite gneiss in the entire Nilgiri Block. The geochemical variations of major, trace and rare earth elements show that the granulite-amphibolite grade felsic rocks evolved in an arc magmatic process leaving behind mafic magma, which later intruded into these rocks, in a subduction related arc magmatic process. The U-Pb LA-ICPMS and SHRIMP dating of charnockite, hornblende-biotite gneiss and met gabbros shows ca. 2550 Ma formation age and ca. 2450 Ma metamorphism in this terrane.en_US
dc.language.isoen_USen_US
dc.relation.ispartofseriesG27171en_US
dc.subjectContinental Crust - Southern Indiaen_US
dc.subjectCrustal Growth - Southern Indiaen_US
dc.subjectArchean Tectonics Nilgiris Blocken_US
dc.subjectGeology and Petrologyen_US
dc.subjectNilgiri Blocken_US
dc.subjectFelsic Granuliteen_US
dc.subjectCharnockiteen_US
dc.subjectMafic Granuliteen_US
dc.subjectMetagabbroen_US
dc.subjectArchean Crustal Blocksen_US
dc.subject.classificationEarth Sciencesen_US
dc.titleThe Crustal Evolution of Nilgiri Block, Southern India : A Study on Archean Tectonics and Crustal Growthen_US
dc.typeThesisen_US
dc.degree.namePhDen_US
dc.degree.levelDoctoralen_US
dc.degree.disciplineFaculty of Engineeringen_US


Files in this item

This item appears in the following Collection(s)

Show simple item record