粤西云开岩群中"变质超镁铁质岩"的原岩识别OA

[Objective]The meta-supracrustal rocks of the Yunkai Group in the Yunkai area host various types of"meta-mafic-ultramafic rocks."Identifying their protoliths is of great significance for deepening the understanding of Precambrian sedimentation and multiphase episodic orogenic processes in the Yunkai region.[Methods]This study conducts petrological and mineralogical investigations of the"meta-ultramafic rocks"from Luoxia,Luoding,using zircon chronology and electron probe microanalysis.[Results]Minera-logical analysis reveals a type of"meta-ultramafic rock"within the Yunkai Group that is mainly composed of Ca-Fe-Al-rich garnet,Ca-rich diopside and hedenbergite,and epidote,similar to calc-silicate skarn mineral assemblages.Whole-rock geochemistry of the Luoxia samples shows significantly high CaO(17.8-20.8 wt.%),MnO(1.28-2.45 wt.%),and low total alkali contents(<1 wt.%).Geochemical evidence suggests that this type of"meta-ultramafic rock"was formed by hydrothermal metasomatism of magnesian calcareous carbonate rocks.Zircon U-Pb dating indicates that the protolith was deposited later than 630-519 Ma.[Conclusion]Combined with existing data,it is concluded that the protolith of some"meta-ultramafic rocks"in the Yunkai Group is carbonate rock,which may represent part of the Ediacaran to Early Cambrian littoral facies fine-grained clastic-carbonate sedimentary sequence in the Yunkai area.