Magma to mud to magma

Abstract

Early Permian (Cisuralian) S-type monzogranites of the Bundarra Supersuite, New England Orogen (NEO), eastern Australia, have chemical and isotopic compositions indicative of their being derived from young, weathered, volcanogenic sedimentary source rocks. High δ 18O zrn values of zircon precipitated from the melt phase of the magma (ca. 11.5%) confirm that the previously measured high granite whole-rock values (δ 18O WR) are a primary magmatic feature. Abundant inherited detrital zircon cores with a range of dates (360-300Ma) and distinctly lower δ 18O zrn values (ca. 5-10%) were derived from mostly young (Carboniferous) volcanogenic source rocks that became less primitive and more isotopically diverse with time. The age difference between the youngest inherited zircon population and the earliest zircon growth during magma genesis is about 15Ma. An arc-related volcanogenic sedimentary pile built up over about 50Ma was weathered, buried, and partially melted, producing voluminous peraluminous magmas within no more than ca. 15Ma of the youngest source sediment being deposited. The time interval between the initiation of melting and post-emplacement magma crystallization was about 5Ma. The S-type Bundarra Supersuite in the NEO is a rare case in which the entire geologic cycle has been captured by zircon. Recognizing this is uniquely possible because of the relatively simple populations of inherited and newly-grown zircon, and their distinctive oxygen isotopic compositions. Show more