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Dynamics, EPMA Th‐U‐Total Pb Monazite Geochronology and Tectonic Implications of Deformational Fabric in the Lower‐Middle Crustal Rocks: A Case Study of Ambaji Granulite, NW India
Author(s) -
Tiwari Sudheer Kumar,
Biswal Tapas Kumar
Publication year - 2019
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2017tc004891
Subject(s) - granulite , geology , geochemistry , metamorphism , monazite , shear zone , geochronology , petrology , facies , zircon , tectonics , geomorphology , seismology , structural basin
Strain fabric and monazite microstructure were studied and dated by Electron Probe Microanalyser (EPMA) in situ Th‐U‐total Pb monazite geochronology in the Ambaji granulite, South Delhi terrane, NW India. The Ambaji granulite comprises pelitic, calcareous, and mafic granulites with several phases of granite intrusions, G 0‐3 . The granulites were deformed by three phases of folding, F 1–3 , during South De lhi orogeny and marked by a subhorizontal pervasive fabric, S 1 , axial planar to isoclinal‐recumbent F 1 folds that developed during granulite facies metamorphism. S 1 is overprinted by discrete sets of subvertical shear zones associated with a mylonitic fabric, S 2 , that were developed axial planar to NE‐SW striking upright F 2 folds and facilitated exhumation of granulite facies rocks to the upper crust. The shear zones show early history of high‐temperature thrust sense shear and late stage low‐temperature sinistral shear. The NW‐SE striking F 3 folds also affected the granulite facies rocks resulting in interference patterns and variations in regional structural trends. Brittle strike slip, and normal fault (S f fabric) that developed post F 3 , led the final exhumation of the granulite facies rocks to the surface. The S 1 monazites are Y‐depleted and recrystallized through dislocation creep, and the S 2 ‐S f monazites are Y‐enriched and recrystallized through dissolution‐precipitation creep. Different monazite population yielded distinct ages of circa 875‐857, 834‐778, and 764‐650 Ma for S 1 , S 2 , and S f strain, respectively, indicating that the South Delhi orogeny spanned 875‐650 Ma overlapping with the early phase of the Pan‐African orogeny or representing a transition between Grenvillian and Pan‐African orogeny.