Changes in stable isotope ratios of metapelites and marbles during regional metamorphism, Mount Lofty Ranges, South Australia: implications for crustal scale fluid flow

Abstract

The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470-515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (∼350-400°C) to migmatite grade (∼700°C) over 50-55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, δ18O values of "normal" metapelites decrease from 14-16‰ to as low as 9.0‰, while δ18O values of calcite in "normal" marbles decrease from 22-24‰ to as low as 13.2‰ These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears n..