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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 &#177; 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>_i</i> values (0.7052 to 0.7061) and high &#949;_Nd(<i>t</i>) values (&#8722;2.6 to &#8722;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 (&lt;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.