New identification and significance of Early Cretaceous mafic rocks in the interior South China Block

Abstract

Early Cretaceous mafic rocks are first reported in the northern Guangxi region from the western Qin-Hang belt in the interior South China Block. A systematic investigation of zircon U–Pb dating, whole-rock geochemistry, Sm–Nd isotopes and zircon Hf–O isotopes for these mafic rocks reveals their petrogenesis and the mantle composition as well as a new window to reconstruct lithospheric evolution in interior South China Block during Late Mesozoic. Zircon U–Pb dating yielded ages of 131 ± 2 Ma to 136 ± 2 Ma for diabase and gabbro from Baotan area, indicating the first data for Early Cretaceous mafic magmatism in the western Qing-Hang belt. These mafic rocks show calc-alkaline compositions, arc-like trace element distribution patterns, low zircon εHf(t) of − 9.45 to − 6.17 and high δ18O values of + 5.72 to + 8.09‰, as well as low whole-rock εNd(t) values of − 14.27 to − 9.53. These data suggest that the studied mafic rocks are derived from an ancient lithospheric mantle source that was metasomatized during Neoproterozoic subduction. Thus, the occurrence of these mafic rocks indicates a reactivation of Neoproterozoic subducted materials during an extension setting at Late Mesozoic in the western Qin-Hang belt, an old suture zone that amalgamates the Yangtze and Cathaysia blocks.

Caledonian Tin Mineralization in the Jiuwandashan Area, Northern Guangxi, South China

“…After folding of the Neoproterozoic Sibao Group, magma was intruded along faults, which formed mafic-ultramafic intrusions and the Motianling, Yuanbaoshan, and other large granitic plutons in the Jiuwandashan area [33]. Previous studies have shown that Neoproterozoic subduction materials were reactivated and formed a series of mafic igneous rocks during late Mesozoic extension [42]. No other magmatism has been identified in or near the study area.…”