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

Hui-Min Su,Xiang-Ke Wu,Dong-Yang Zhang,Jia-Bin Shao,Xi-Qiang Huang,Shao-Yong Jiang

doi:10.1038/s41598-021-91045-1

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.

Highlights

IntroductionIn the Qin-Hang belt (QHB), occurrence of Early-Middle Jurassic mafic intrusive and volcanic rocks are reported only in the Nanling Range and eastern QHB, such as the Daoxian and Ningyuan basalts from southern Hunan (150–154 Ma and 170–174 Ma)[3], and Antang basalts from central Jiangxi (168 Ma)[4], up to now, no Late Mesozoic mafic rocks have been reported in the western QHB which locates further interior in the South China Block (SCB)
Cretaceous mafic rocks are first reported in the northern Guangxi region from the western Qin-Hang belt in the interior South China Block
We report our recent investigations that identified several Late Mesozoic mafic intrusions from the Baotan area of the northern Guangxi region which located along the western Qin-Hang belt (QHB) in the Yangtze Block (YB) side just next to the western interior Cathaysia Block (CB) (Fig. 1b,c)

Summary

Introduction

In the Qin-Hang belt (QHB), occurrence of Early-Middle Jurassic mafic intrusive and volcanic rocks are reported only in the Nanling Range and eastern QHB, such as the Daoxian and Ningyuan basalts from southern Hunan (150–154 Ma and 170–174 Ma)[3], and Antang basalts from central Jiangxi (168 Ma)[4], up to now, no Late Mesozoic mafic rocks have been reported in the western QHB which locates further interior in the SCB It is still highly debatable whether or not the paleo-Pacific plate subduction can reach up to the interior SCB as far as the YB, and if so, what is the role of the paleo-suture zone of Neoproterozoic that amalgamates the two blocks of YB and CB. Different from the widespread Neoproterozoic mafic rocks that have been subjected to variable degrees of alteration and/or mineralization in this r egion[10,11], the mafic rock samples collected in this study are relatively fresh and suffered only very slightly alteration

Methods

Results

Conclusion