Geochemical Genesis And Tectonic Properties Of Diabase In Funing Area,Southeast Yunnan,China

Funing area is located in the combination zone of South China plate and Indo-Chinese plate tectonic units,and the basic rock mass dominated by diabase is widely exposed.There are still great disputes about its structural properties,formation age and evolution mechanism.In this paper,a detailed baddeleyite(zircon)U-Pb chronology,major and trace rare earth elements analysis and Hf isotopic characteristics of titanium gabbro diabases outcropped in Naping areas of Funing are carried out.The diagenetic age,petrogenesis,magma source properties and tectonic background of titanium gabbro diabase and diabase in the study area are studied.The LA-ICP-MS baddeleyite U-Pb dating results show that the diagenetic age of the Naping titanium gabbro diabase is 255.6±5.0Ma(MSWD=3.0),formed in the Late Permian-Early Triassic,which is basically consistent with the main eruption time of Emeishan large igneous province,revealing that it should be the product of basaltic magma homogenization in Emeishan.Whole rock geochemical analysis shows that Naping titanium gabbro diabases belong to calc alkaline and high potassium calc alkaline series rocks.In addition,Naping titanium gabbro diabase has high contents of Mg O,Fe₂O₃^T,Ti O₂ and rare earth elements(?REE=110?184×10^-6),and has the characteristics of right-leaning rare earth element distribution pattern with relatively enriched light rare earth elements and relatively depleted heavy rare earth elements,shows weak to moderate Eu positive anomaly.At the same time,it is enriched in large ion lithophile elements and relatively depleted in high field strength elements such as Ta,Nb,Zr and Hf,showing the characteristics of oceanic island basalt(OIB).The negative?_Hf(t)values of Naping titanium gabbro diabase titanium gabbro diabase are relatively wide,in which the?_Hf(t)values of Naping titanium gabbro diabase titanium gabbro diabase are-11.9?-4.8 and-18.3?-2.0,respectively,which are similar to the zircon Hf isotopes of the basic intrusive rocks in Funing and adjacent areas of southeast Yunnan,indicating that the magma originated from the enriched mantle source area and was affected by crustal contamination.Through comprehensive research and comparison,it is considered that the characteristics of Naping titanium gabbro diabase and Emeishan high-titanium basalt are highly consistent,and they are part of Emeishan high-titanium basalt.It is inferred that the Funing area in southeast Yunnan may have experienced multiple magmatic intrusions at least during the Late Permian-Middle Triassic,which provides new geological data for the study of tectonic-magmatic evolution in the whole area.