Paleoproterozoic arc magmatism in the North China Craton: No Siderian global plate tectonic shutdown

Abstract

Arc magmatism in convergent plate margins has been a major contributor to continental growth. Following arc–arc and arc–continent collisions in the Archean leading to the amalgamation of micro-blocks, the North China Craton (NCC) witnessed major pulses of continental arc magmatism during the Paleoproterozoic. In this study, we present geochemistry, zircon U–Pb geochronology and Lu–Hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major Paleoproterozoic suture zones in the NCC — the Inner Mongolia Suture Zone (IMSZ) and the Trans-North China Orogen (TNCO). Our zircon U–Pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207Pb/206Pb weighted mean ages of 2410±41Ma for metagranite, 2480±12Ma, 2125±18Ma, 1946±8Ma, 1900±15Ma and 1879±12Ma from metagabbros, 2446±11Ma from charnockite, and 1904±6Ma and 1901±9Ma from metatuffs. The 207Pb/206Pb upper intercept age of zircons in the khondalite shows 2102±76Ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros. The khondalites also carry a group of concordant metamorphic zircons with 207Pb/206Pb mean age of 1881±20Ma. Metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890±14Ma and 1852±19Ma respectively. The age data suggest prolonged arc magmatism in a convergent margin setting during ca. 2.48 to 1.9Ga, followed by metamorphism at ca. 1.89–1.85Ga associated with the final collision. Lu–Hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive εHf values (−1.9 to 6.8; mean 1.8). The εHf and TDMC data suggest that the magmas were mostly derived from Neoarchean and Paleoproterozoic juvenile components. The salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction-derived arc components with minor input from continental crust. The results presented in this study, together with those from previous investigations in different domains of the IMSZ and TNCO suggest major Paleoproterozoic arc magmatic events in the NCC lasting for nearly 600millionyears associated with the final assembly of the crustal blocks into a coherent craton. Construction of the final cratonic architecture of the NCC thus witnessed not only the arc–continent amalgamations at 2.7–2.5Ga, but also major crust building events in the Paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin, followed by intense deformation and metamorphism during the final collision at 1.85–1.80Ga. The prominent Paleoproterozoic magmatic records in the NCC do not support the proposal of global plate tectonic shutdown in the Siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the Paleoproterozoic.