New zircon U–Pb and Hf–Nd isotopic constraints on the timing of magmatism, sedimentation and metamorphism in the northern Prince Charles Mountains, East Antarctica

Abstract

The northern Prince Charles Mountains (PCM) in East Antarctica represent the largest continuously exposed section of the Rayner Complex and may provide important insights into the tectonic evolution of the Rayner orogen. We present new U–Pb and Hf isotopic data for zircons from felsic orthogneisses, mafic granulites, paragneisses and charnockites and additional Nd isotopic data for the former two rock types from the Beaver Lake area in the northern PCM. Zircons from the felsic orthogneisses document protolith ages of ca. 1170–1070Ma, with Hf and Nd model ages of 1.99–1.74Ga, suggesting the generation of the felsic magmas by partial melting of crustal rocks that were extracted from the mantle during the Paleoproterozoic. Detrital zircons from one paragneiss sample yield a major age population at ca. 1480–1140Ma and three subordinate populations at ca. 2130–1850, 1780–1620 and 1010–860Ma, whereas those from another paragneiss sample produce a major age population at ca. 1180–830Ma and a subordinate age population at ca. 1370–1230Ma. Discounting the effects of zircon recrystallization during post-depositional metamorphism, we infer that the sedimentary precursors to the aforementioned paragneiss samples were deposited after ca. 1200 and 1020Ma, respectively, in intra- or back-arc basins of the Rayner continental arc. Charnockites were either emplaced at ca. 980Ma or episodically at ca. 1050 and ca. 950Ma, with Hf model ages of 1.97–1.90Ga. They were derived from partial melting of a Paleoproterozoic source region similar to the surrounding felsic orthogneisses at deeper levels. Zircon overgrowth domains from all of the studied rock types indicate that high-grade metamorphism took place at ca. 945–915Ma. Only one paragneiss sample from the Else Platform preserves evidence of Cambrian metamorphic reworking. Based on published data from the Rayner Complex and the Eastern Ghats Belt of India, we speculate that long-lived convergent processes between the Indian craton and East Antarctica lasted from ca. 1500 to 900Ma. Therefore, the Rayner Complex may represent the exposed orogenic root of a large Meso-Neoproterozoic accretionary orogen.