Abstract

Author:
Alip Roya, Sadhana M. Chatterjee, Upama Duttac, Ayan Kumar Sarkara, Anirban Mannaa

Doi: 10.26480/gsrj.02.2024.48.54

This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

The South Delhi Fold Belt (SDFB) constitutes a linear NE-SW trending belt of Proterozoic age in the northwestern part of India. The western margin of the SDFB is demarcated by intense deformation known as the Phulad Shear Zone (810 Ma). Quartzo-feldspathic rocks associated with calc-silicate in the Phulad area of SDFB, Rajasthan, are characterized by compositional banding parallel to regional foliation that developed synchronously with the reverse shearing of PSZ. The rocks preserve a series of reaction textures that postdate the regional foliation. The bulk composition of the rocks is represented by quartz + plagioclase, along with domains rich in garnet, amphibole, epidote, K-feldspar and calcite. The zoning pattern in porphyroblastic garnet implies that during initial metamorphic conditions, garnet with high Mn, Fe, Mg and low Ca was stable and gradually converted to low Mn, Fe, Mg and very high Ca bearing composition. A thinly developed garnet layer, i.e. corona near plagioclase, calcite, and quartz, represents the rim of porphyroblastic garnet, as evident from the compositional equivalence. The rim/coronal garnet is replaced by the formation of amphibole, followed by the stabilization of epidote-quartz symplectite mantling both coronal garnet and amphibole. NCFMASH pressure-temperature pseudosection reveals that the stabilization of rim/coronal garnet, followed by amphibole and then by epidote-quartz symplectite, experienced cooling in the retrograde arm of a clockwise P-T path with an insignificant amount of decompression. Interpretation of reaction textures in P-T pseudosection indicates a prominent cooling history of the ~810 Ma shearing event of PSZ.