A Comparative Study Of Granite Gravels And Granitoids Of The Baoding Formation In Ciping,Huili County

The Ciping area of Huili County,Sichuan Province is located 40 km southeast of Panzhihua City,Sichuan Province.It belongs to the Chuxiong Mesozoic foreland basin on the western margin of the Yangtze block,or is located in the inner belt of the Emeishan large igneous rock province.The near-south-trending fault zone controls the distribution of strata and magmatic rocks.There are frequent magmatic activities in the region.For example,there are magmatic rocks formed after Neoproterozoic,Permian and Mesozoic magmatic activities.They are widely distributed in the region.,Especially the magmatic activity of the basalt-granite series related to the Permian Emeishan mantle plume has an important influence on the regional tectonic evolution.The Upper Triassic Baoding Formation in the study area is widely distributed,and its bottom conglomerate is not well studied.Whether the granite gravel originates from the lower Fuziping granite body has been a long-term geological issue.Through the actual measurement of the Baoding Formation section,the granite gravel of the Baoding Formation conglomerate and the Ciping granite body are comparatively studied petrology,zircon U-Pb chronology,whole-rock geochemistry and other characteristics,and the rock types of the two granites,The characteristics of magma source area and its genesis.The main knowledge gained is as follows:?1?The lithology of the Upper Triassic Baoding Formation is a combination of conglomerate,feldspar quartz sandstone,lithic sandstone,argillaceous siltstone and silty mudstone.The conglomerate is located at the bottom of the Baoding Formation.It is divided into upper and lower sections;the lithology as a whole is positive-grained,and the lithology of the granite gravel in the bottom of the Baoding Formation is Wenxiang granite.?2?The granite found in the Ciping granite body is a medium-coarse-grained granite.The lithology includes monzonitic granite and biotite syenite.The formation age is Middle Triassic,and its zircon U-Pb age is 244.8±1.5 Ma..?3?The granite gravel of Baoding formation conglomerate was formed in the Late Permian with zircon U-Pb age of 252.6±1.7 Ma.The Wenxiang granite gravels in Baoding formation conglomerate do not come from Ciping granite body,and Baoding formation and underlying Ciping granite body are sedimentary unconformity contact relationship.?4?Ciping granite has a low iron content and a high K₂O content.It is a type of high potassium rock and belongs to aluminum supersaturated rock?A/CNK=1.06?1.10?.The rock mass is rich in light rare earth elements and has a moderately negative Eu anomaly??Eu=0.16?0.22?.The trace elements of the rock mass show significant losses of Ba,Sr,P,Ti,and Nb.?5?The granite gravel in the Baoding Formation conglomerate is significantly depleted in iron group elements.The K₂O content is high,and it is a potassium rock type;it belongs to the potassium alkaline rock series,with slightly supersaturated aluminum?A/CNK=1.01?1.06?.The granite gravel is enriched with light rare earth elements,which has a strong negative Eu anomaly??Eu=0.05?0.08?.In terms of trace elements,Ba,Sr,P,Ti,Nb,Zr are obviously depleted,Ba,Sr,P,Ti The degree of loss is more significant than that of Ciping granite.?6?The geochemical characteristics of rocks show that the Ciping granite body belongs to A2 type granite,and the granite gravel of Baoding formation conglomerate belongs to A1 type granite.The tectonic environment formed by both of them is extensional environment.?7?The authors suggest that the Late Permian Wenxiang granite gravels in the conglomerate of Baoding formation of the upper Triassic are the products of magmatic activities of the Emeishan mantle plume in the Permian.They belong to the late stage of gabbro syenite granite magmatic activity series in Panxi area.The Ciping granite body is the product of Indosinian magmatic activity and formed by the melting of the crust The late products of EMeishan mantle plume magmatism inherited material,and its magma source area may be indirectly affected by Emeishan mantle plume magmatism.