Abstract
We present comprehensive petrological, major-trace element, in situ zircon U-Pb dating and Sr-Nd-Pb isotopic data for Muchen granitoid (western Zhejiang Province, Southeast China), to constrain the petrogenesis of alkaline A-type granites and the geodynamic setting of Southeast China in the Early Cretaceous. The Early Cretaceous Muchen quartz monzonite yielded zircon U-Pb crystallization ages of 111.3 ± 0.7 Ma and is metaluminous to weakly peraluminous with SiO2 contents ranging from 59 to 69 wt.%, and can be classified as alkaline A-type granitoid. The quartz monzonites have low (87Sr/86Sr)i values (0.7052 to 0.7061) and high εNd(t) values (−2.6 to −2.0), similar to nearby coeval mafic rocks that have been proposed to be derived from the enriched lithospheric mantle. The high Nb/Ta ratios (16.7 to 30.1, average 21.8) and low Nb/U ratios (as low as 3.5) indicate the involvement of slab-derived melt and fluids in this mantle. These geochemical properties of the Muchen quartz monzonites indicated that they might be from a phlogopite-bearing and rutile-rich subduction-modified subcontinental lithospheric mantle, and underwent strong fractional crystallization of olivine + orthopyroxene + plagioclase during magma ascent. The low Mg# values of these alkaline rocks (<30 mostly) may indicate a low-pressure source in a back-arc setting. The early Cretaceous alkaline granitoids in Southeast China are related to the continental back-arc setting caused by deep angle subduction of the paleo-Pacific plate.
Highlights
Widespread Mesozoic igneous rocks in Southeast China [1,2], were mainly emplaced in the Jurassic and Cretaceous periods [3,4]
A-type granites or alkaline intrusions generally develop during continental extension in post-orogenic or intraplate settings [14,15,16,17], and can be used to investigate lithospheric sources and magma evolution of these rocks, and geodynamic processes
Previous studies show that A-type granites in SE China are generally high-silica (SiO2 > 70 wt.%) rocks [9,13,33,34,35,36], making it difficult to determine whether mantle materials have been involved in their formation
Summary
Widespread Mesozoic igneous rocks in Southeast China [1,2], were mainly emplaced in the Jurassic and Cretaceous periods [3,4]. Minerals 2020, 10, 80 of tholeiitic rock derived from underplated mafic magma in the crust [20,21], re-melting metaluminous and peraluminous tonalite or granodiorite [22,23], fractional crystallization from mafic magmas with or without crustal assimilation [24,25,26,27], and magma mixing between mantle-derived and crust-derived magma [28,29,30,31,32]. Understanding the features of low-SiO2 alkaline rocks can provide important insights into the petrogenesis of the A-type granitoids
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