首页|Dynamics of Early Neoproterozoic accretion, west-central India: I. Geochronology and Geochemistry
Dynamics of Early Neoproterozoic accretion, west-central India: I. Geochronology and Geochemistry
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The Godhra-Chhota Udepur (GC) sector (west-central India) is the zone of convergence between two crustal-scale accretion zones, i.e. the N/NNE-striking Aravalli Delhi Fold Belt (ADFB) against the E-striking Central Indian Tectonic Zone (CITZ). In this study, we demonstrate the two orogens welded during the Early Neoproterozoic. In the GC sector, recumbently folded basement gneisses, shallow-dipping granitoid mylonites and a suite of allochthonous supracrustal rocks experienced top-to-the south thrusting and nappe formation (D2 deformation). The shallow-dipping crustal domain was modified by the superposition of a network of WNW/W-striking transpressional shear zones and related folds (D3 deformation). The D2-D3 deformations occurred due to oblique crustal convergence marked by the emplacement of pre-D2, post-D2 and syn-D3 granitoids. The post-D2, syn-D3 granite-granodiorites are weakly peraluminous, calc-alkalic, having ferroan to magnesian affinity, and characterised by LREE-enriched moderately fractionated REE patterns with variable negative Eu anomalies. Trace element geochemistry and whole rock Sr-Nd systematics suggest the granitoids were derived from dominantly meta-greywacke precursors. In South-GC, U-Pb zircons in the basement gneisses yield upper intercept/Concordia dates at 1.65-1.60 Ga for high-grade metamorphism. The lower intercept/Concordia dates in the gneisses coincide with the 0.95-0.93 Ga emplacement age of post-D2/syn-D3 granitoids throughout GC. However, the pre-D2 granitoids in South-GC are older, —1.03 Ga. By contrast, pre-D2 granitoids in North-GC yield Late Neoarchean (2.5 Ga) Concordia/upper intercept emplacement ages, identical to the emplacement age of the Archean granites in the ADFB; the lower intercept/Concordia age is 0.95-0.93 Ga. The 2.5 Ga granites did not experience the 1.65-1.60 Ga high-grade metamorphism, but both the lidiodemic units shared the 0.95-0.93 Ga D2-D3 deformation-metamorphism and the emplacement of post-D2 and syn-D3 0.95-0.93 Ga granitoids. The juxtaposition of the —2.5 Ga granitoids and the 1.65-1.60 Ga gneisses is attributed to the 1.03-0.93 Ga ADFB-CITZ oblique accretion that involved contemporaneous emplacement of syn-collisional S-type granitoids..
Aravalli-Delhi Fold BeltCentral Indian Tectonic ZoneArchean granites and Paleoproterozoic gneissesEarly Neoproterozoic accretionsyn-collisional granitoids
Anwesa Banerjee、Nathan Cogne、Nicole Sequeira
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Departent of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, India
Univ Rennes, CNRS, Geosciences Rennes, UMR 6118, 35000 Reraxes, France
School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleigao Plateau, Goa 403206, India
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