Modern-style plate tectonics manifested by the late Neoarchean TTG-sanukitoid suite from the Datong-Huai'an Complex, Trans-North China Orogen

Abstract

When modern-style plate tectonics started and operated on a specific old craton has been a key point involving the early Earth's evolution. In order to address this issue on the evolution of the Neoarchean North China Craton (NCC), we investigated a representative successive magmatic rock suite of tonalite-trondhjemite-granodiorite (TTG) and sanukitoid in the Datong-Huai'an Complex. Geochemically, TTG gneisses in the Datong-Huai'an Complex can be divided into high-pressure (HP) and low-pressure (LP) TTG rocks. The HP TTGs emplaced at ∼2538–2497 Ma and 2441 Ma, respectively. Geochemical data shows that they are characterized by steep rare earth element (REE) patterns, obvious negative Nb, Ta, Ti anomalies and positive δEu anomalies, high Sr/Y, Nb/Ta and (La/Yb)N ratios, and positive ɛHf (t) (+2.1 to +9.1) and δ18O values (avg. 5.5‰ to 6.0‰). Their protolith is interpreted as the consequence of partial melting of a subducted oceanic slab with garnet and minor rutile as residual phases. In contrast, the LP TTGs emplaced at ∼2518 Ma. They display flat REE patterns, slightly negative Nb, Ta, Ti anomalies and negative δEu anomalies, low Sr/Y, Nb/Ta and (La/Yb)N ratios, positive ɛHf (t) (+3.4 to +5.9) and high δ18O values (avg. 5.9‰ to 6.1‰). They were most likely generated by partial melting of the mafic lower crust with residual plagioclase and amphibolite in the source region. The sanukitoid rocks emplaced at 2517–2485 Ma and show high MgO, Cr and Ni concentrations but relatively low (La/Yb)N values, positive ɛHf (t) values (+1.5 to +5.4), and higher δ18O values (avg. 6.8‰ to 7.5‰), suggesting that they were originated from partial melting of the mantle peridotite that was previously modified by slab-derived or sediment-derived melts. Combined with previous petrological, geochronological and geochemical data, we propose that the Datong-Huai'an Complex recorded the prolonged magmatism through ca. 2.56 Ga to 2.44 Ga, which was characterized by the high-angle subduction of oceanic lithosphere, leading to the opening of a mantle wedge, slab rollback and back-arc extension. All these lines of evidence manifested that a modern-style plate tectonics regime started along the western margin of the NCC Eastern Block during the late Neoarchean, though the interior Eastern Block was still dominated by the mantle plume-induced crustal growth and vertical tectonism.