Geochemistry of the Neoproterozoic Metasedimentary Gamble Brook Formation, Avalon Terrane, Nova Scotia: Evidence for a Rifted‐Arc Environment along the West Gondwanan Margin of Rodinia

Abstract

Abstract The Neoproterozoic Gamble Brook Formation in the Avalon Terrane of Nova Scotia consists of quartzitic, pelitic, and psammitic metasedimentary rocks. The formation is generally interpreted to have been deposited in an Atlantic‐type passive margin setting along the Amazonian margin of Rodinia before the main ca. 650–550‐Ma phase of Avalonian subduction‐related magmatism. The geochemical and Sm‐Nd isotopic signature of these metasedimentary rocks, however, shows that although the quartzites are predominantly derived from ancient cratonic basement, the pelites and psammites were derived from moderately fractionated mafic to intermediate proto‐Avalonian crust. The two contrasting sources for the Gamble Brook rocks are incompatible with a passive margin setting and are instead interpreted to reflect deposition along a basin margin within a rifted‐arc environment. Taken as a whole, the Amazonian margin of Gondwana preserves evidence of episodic subduction in a western Pacific‐like setting between 1000 a...