|
|
|
|
|
|
|
|
MPN-06 Extreme metamorphism during the amalgamation of Gondwana: Tectonics, rates and models
|
|
|
|
U-Pb isotopic age constraints on event timing in the Southern Granulite Terrane, India
|
|
|
|
Chris Clark, Curtin University of Technology (Australia)
Alan Collins, The University of Adelaide (Australia)
Pete Kinny, Curtin University of Technology (Australia)
Ian Fitzsimons, Curtin University of Technology (Australia)
Richard Taylor, The University of Edinburgh (United Kingdom)
|
|
|
|
The Southern Granulite Terrane (SGT) in India lies to the south of the Archaean Dharwar craton and consists of Palaeoproterozoic orthogneisses, metasedimentary rocks, and charnockites. The SGT can be divided into a number of terranes based on protolith and thermal/deformational events. The Salem Block that lies immediately south of the Dharwar Craton and continue as far south as the Palghat-Cauvery shear system (PCSS). The PCSS is a >100 km wide, crust-cutting, system of anastomosing shear zones that cuts migmatitic mafic gneisses, and contains high-pressure granulites. The Madurai and Trivandrum Blocks lie south of the PCSS and are separated from each other by the Achankovil shear zone, an enigmatic structure with a pronounced magnetic and seismic anomaly. Both the Madurai and Trivandrum Blocks were extensively deformed and metamorphosed to granulite-facies during the Neoproterozoic.
The Salem Block charnockites give a magmatic age of ∼2.54 Ga and are cross cut by undeformed leucogranites with overgrowth ages of ∼2.48 Ga. No evidence for Ediacaran-Cambrian overgrowths were observed in this area. PCSS rocks have an inherited Archaean/Palaeoproterozoic zircon component. Rims on inherited cores and newly formed metamorphic grains yield an age of ∼0.53 Ga older than those analysed in monazites at ∼0.52 Ga. The Madurai Block metasediments also contain an Archaean detrital zircon component. The U-Pb age spectra of detrital zircons in these metasedimentary gneisses indicate that their protoliths were deposited after ∼1700 Ma. U-Pb zircon and monazite data yield distinct age populations possibly related to thermal pulses within the Ediacaran-Cambrian orogenic event.
The rocks in the Achankovil shear zone have anomalously juvenile isotopic compositions and model ages relative to the bounding Madurai and Trivandrum Blocks. Detrital zircons from metasedimentary gneisses along the southern margin of the Achankovil shear zone yielded Neoproterozoic maximum depositional ages. Metamorphic U-Pb zircon and monazite data yield ages between 0.55 and 0.52 Ga. The protoliths to many of the metasedimentary gneisses in the Trivandrum Block were sourced from Palaeoproterozoic and Neo-Archaean rocks and were deposited some time after c. 1900 Ma. The gneisses were subsequently metamorphosed during the Ediacaran-Cambrian with monazite and zircon growth recording events at 0.56, 0.54 and 0.52 Ga.
|
|
|
|
|
|
|
|
|
