Geochemical Characteristics And Geological Significance Of The Intrusive Rocks From Middle Triassic In The Lalinggaoli Area,Qinghai Province

The Lalingaoli area is located in the East Kunlun orogenic belt on the southwest margin of Qaidam basin and the north slope of Kunlun mountain.The area is characterized by frequent magmatic activity and extensive distribution of intrusive rocks.In recent years,the ore-prospecting work in East Kunlun area has made a great breakthrough.In this paper,the middle Triassic intrusive rocks concentrated in Lalinggaoli area have been selected as theresearch object,and the petrological,geochemical and chronological characteristics have been systematically analyzed.The relationship between tectonic evolution and mineralization in this area is discussed.The rocks assemblages of the middle Triassic intrusive rocks,which are mainly distributed in the Lalinggaoli area,Qinghai province,are medium-fine grained quartz diorite-tonalite-granodiorite-monzogranite-diorite-syenogranite etc.According to the analysis of petrol-geochemical elements in rocks,the contents of SiO₂ are from 55.78%to73.58%,Al₂O₃ are from 12.3%and 16.28%,K₂O are from 2.06%and 3.77%,Na₂O are from 1.94%and 3.62%,CaO are from 2.24%to 7.43%,MgO are from 0.41%to 7.08%,Fe₂O₃ are from 0.37%to 2.53%,K₂O/Na₂O are from 0.66 and 1.51,CaO/K₂O are from0.83 and 3.61,AR are from 1.49 to 2.33,σare from 1.6 to1.92.The middle Triassic intrusive rocks in the study area belong to a series of granite with high potassium calcium carbonate.FeO,Fe₂O₃,MgO,MnO,TiO₂ exhibit a negative correlation with SiO₂,whereas AR,DI and K₂O exhibit a positive correlation with SiO₂.P₂O₅ increasing trend showed a negative correlation with the SiO₂,It indicates that the middle Triassic intrusive rocks in the study area,which are mainly composed of quartz diorite-tonalite-granodiorite-monzogranite belong to I-type granites.The characteristics of rare earth elements show that∑REE is 110.69×10^-6197.8×10^-6,LREE/HREE is 6.512¹7.595,the value of（La/Yb）_N is from 6.575 to 24.879.It shows that the light rare earth elements are enriched in the Triassic intrusive rocks in the study area.In trace elements Rb,Th,K and Hf are relatively enriched,while Ba,Nb,Sr,P and Ti are relatively deficient.The LA-ICP-MS zircon U-Pb dating results show that the Middle Triassic granodiorite dating data distributed in the Lalinggaoli area are 235.5±1.9 Ma and 234.9±1.3 Ma.When projecting the related diagrams of tectonic environment discrimination,the selected rock samples mostly fall in the pre-collision granite and volcanic arc granite area,forming the active continental plate margin volcanic arc before plate collision,belonging to the origin of subduction granite and crust-mantle mixed source,which further proves the existence of East Kunlun magmatic arc.A series of metallogenic facts,represented by the Kaerqueka copper polymetallic deposit,have been found to be closely related to the Middle Triassic subduction granite.