Study of Calc-Silicate Rocks of Hammer-Head Syncline from Southern Sandmata Complex, Northwestern India: Implications on Existence of an Archaean Protolith

Abstract

Existence of an Archaean protolith is suggested in present study from an ensemble of rocks named as Sandmata Complex from northwestern India which have a debatable stratigraphic status of Archaean vs. Proterozoic. Rocks of the Sandmata Complex are represented by a highly metamorphosed volcano-sedimentary complex with multiple cycles of deformation. The manifold tectono-thermal events have obscured the pristine character of the protoliths. In this work we present geochemical features of calc-silicate protolith that show consistent Archaean affinity in the Hammer-Head Syncline (HHS) from southern part of the Sandmata Complex. Notable geochemical characteristics of calc-silicate metasediments in the HHS include high Th/U, high Cr concentrations, high La/Th, moderate La/Yb, and weak positive Eu anomaly. Carbon and oxygen stable isotope compositions of these carbonate metasediments vary between -3.0 and -0.3‰ (δ 13 C carb ),-11.6 and -35.0 (δ 13 C org ) and -19.1 and -13.4‰, (δ 18 O) respectively. These geochemical observations are in conjunction with the recently published Neoarchaean ages from the HHS and the proximal Hooke syncline.