New constraints on the Cretaceous geodynamics of paleo-Pacific plate subduction: Insights from the Xiaojiang–Beizhang granitoids, Zhejiang Province, southeast China

The relationship between the evolution of Cretaceous magmatism along the southeastern margin of Eurasia and subduction of the paleo-Pacific plate remains controversial. Here we investigate the petrogenesis of the Xiaojiang–Beizhang ferroan and magnesian granitoids, melanocratic microgranular enclaves (MME) that are found within the granitoids, and an associated mafic dyke exposed in southeast China to provide new constraints on the geodynamics of paleo-Pacific plate subduction. Zircon U–Pb ages indicate that the ferroan and magnesian granitoids were emplaced in the Cretaceous (ca. 120 and 110 Ma, respectively), and that the MME and mafic dyke are coeval with their host granitoids. Geochemical characteristics imply that the granitoids were produced by partial melting of crustal rocks and mixed with mantle-derived magmas. The MME are derivatives of the mafic magmas that intruded the silicic magmas. Two phases of mafic magmatism are evident. Stage 1 mafic rocks (the ca. 120 Ma MME) were derived mainly from the subcontinental lithospheric mantle (SCLM) with some contribution from asthenospheric mantle. The parental mafic magmas for Stage 2 (the ca. 110 Ma MME and mafic dykes) were derived from interaction and metasomatism of the SCLM and asthenosphere with slab-derived fluids. Iron enrichment or depletion in the granitoids was controlled mainly by oxygen fugacity and pressure. Our new data, combined with previously published data from Cretaceous igneous rocks in southeastern China, reveal major geochemical changes at 136 and 118 Ma, respectively. The 132–119 Ma igneous rocks record the minimal addition of slab-derived components to their source, and provide strong evidence for an abrupt change in the direction of motion of the paleo-Pacific plate from southwest to northwest at ca. 125–122 Ma

Petrogenesis and tectonic setting of Mesozoic granitic rocks in Eastern South China

Triassic, Jurassic and Early Cretaceous granitoids in eastern South China were systematically sampled and their ages, geochemical compositions and zircon Hf isotopes were analysed. Six stages of Mesozoic granitoids, with different ages, textures and geochemical characteristics are identified. The granitoids were generated during an Andean-type orogenic cycle along the eastern margin of China in the Mesozoic and the properties of the granitoids were determined by their sources and temperature-pressure-water-redox conditions during melting and fractionation

A Mesozoic Andean-Type Orogenic Cycle in Southeastern China as Recorded by Granitoid Evolution

Petrology, magnetic susceptibilities, zircon U-Pb ages, zircon Hf isotopes and whole-rock geochemical data are used to constrain the evolution of Mesozoic high-potassium granitic rocks that record an Andean-type orogenic cycle in the southeastern China segment of the Western Pacific. Decreasing melting pressures of the granitic magmas from the Late Triassic to the Early Cretaceous, as reflected by decreasing Sm/Yb ratios, point to a general trend of crustal attenuation with time in western Zhejiang Province. Five distinct stages of granitic magmatism are identified: (1) 230 to 215 Ma: high-temperature, high-pressure dehydration melting in a reduced and thickened crust caused by flat-slab subduction of the paleo-Pacific Plate; (2) 170 to 150 Ma: low-temperature, high-pressure water-fluxed melting in an oxidized and thickened crust caused by the foundering of the paleo-Pacific Plate; (3) 140 to 130 Ma: low-temperature, low-pressure dehydration melting of the continental crust caused by extension of the lithosphere; (4) 130 to 125 Ma: high-temperature, low-pressure dehydration melting of the refractory materials in the continental crust caused by further extension of the lithosphere and possibly basaltic underplating; and (5) 115 to 100 Ma: emplacement of fractionation products of hydrous basalts from the enriched continental lithospheric mantle

Late Jurassic–Early Cretaceous irregular rollback of the paleo-Pacific plate in the Gan-Hang Volcanic Belt

This dataset includes the data for a paper that is submitted to JGR-Solid Earth, including the Zircon U-Pb age dating results, major and trace element compositions, Sr and Nd isotopic compositions, zircon Hf isotopic compositions of the volcanic rocks in the Moshishan Group of the Dazhou volcanic basin

Crust–mantle interaction triggered by oblique subduction of the Pacific plate: geochronological, geochemical, and Hf isotopic evidence from the Early Cretaceous volcanic rocks of Zhejiang Province, southeast China

<div><p>Large-scale volcanism in the late Mesozoic was a prominent geological event in southeast China. The late Mesozoic volcanic sequences, named the Moshishan Group, are exposed in Zhejiang Province and are predominantly felsic in composition with subordinate mafic magma and rare andesites. To understand the late Mesozoic tectonic evolution of southeast China, we present zircon U–Pb dating, major and trace element analyses, and Hf isotopic compositions from felsic volcanic rocks of the Moshishan Group. Zircon U–Pb dating shows that the Moshishan Group formed between 145 and 129 Ma. The ε_Hf(<i>t</i>) of the analysed zircons ranges from −16.58 to +6.89, and the <i>T</i>_DM2 age ranges from 753 to 2238 Ma with a major peak at ca. 1870 Ma. Hf isotopic compositions of zircons in Early Cretaceous volcanic rocks are more radiogenic than that of the metamorphic basement rocks, indicating a juvenile component in these magmas. Major element concentrations show that the volcanic rocks mainly belong to the high-K calc-alkaline series. Both zircon saturation temperatures and the ε_Hf(<i>t</i>) values of zircons gradually increased with the evolution of the magma. Trace element data indicates that neither magmatic differentiation of mantle-derived magma nor mixing of magmas from different sources were the predominant magmagenetic processes. Earlier studies suggest that contemporaneous underplating contributed to the heat source that induced crustal melting and to the material origin that inconsistently mixed with the local crustal melts. Magmatic underplating is likely to have occurred because of the southwestward subduction of the Pacific plate with episodic slab rollback. The data obtained in this study suggest that the crust–mantle interaction under the influence of slab rollback played a progressive role in the formation of Early Cretaceous felsic volcanic rocks in southeast China.</p></div