The Chemical Petrology Characteristics And Tectonic Evolution Of Renacuo Volcanics Of Gaize, Tibet

As a product of magmatism in deep earth,volcanic rock can clearly reflect the m-agmatic activity and plate tectonic evolution. The Bangongcuo-Nujiang suture zonehas become the debated focus in native and foreign research due to its generation andevolution, especially the discovery of giant gold-bearing porphyry copper deposits, w-hich makes the research on the Mineralization of BN suture zone with remarkable ec-onomic benefits. And as source of ore-bearing materials, the Early Cretaceous magm-atic activity has great significances for analyzing metallogenic regularity.The research area is located in the southern qiangtang basin at north of Bangongcuo-Nujiang suture zone and south of Lungmu Co-Shuanghu suture zone. Based on thedetailed geological investigation of volcanic distribution, composition, volcanic appa-ratus in field and accurate geochronological, geochemical studies in laboratory, the m-ain achievements and recognition of this paperare are summarized as follows:It is considered that volcanic rock was mainly composed of basalts, andesites,dacites with interbedded acidic pyroclastic rocks. In the earlier stage, the volcanismwas manifested as the eruption of basaltic basic magma on a large scale,in contrast, atthe late stage, it mainly manifested as the eruption of acid rhyolite and pyroclasticrocks on a smaller scale.The isotope age of Renacuo volcanic rockranges from111.7to117.4Ma, suggesting an age of late Early Cretaceous.The volcanic rock belongs toa potassium-high potassium calc-alkali series, which is characterized by highlyenriched in LREE,LILE,and depleted in HFSE with a weak negative Eu anomaly.Allthe features of volcanic rock in research area show that the magmatism was probablyrelated to the mantle wedge partial melting,which affected by dehydration and breakoff of the subduction slab during collision between the Lhasa terrane and theQiangtang terrane induced by subduction and closure of Tethys ocean basin. Thenthere was a mixing course occurring on the mantle wedge partial melting with upper crust as well as a crystal fractionation which formed the Renacuo volcanic rock.Andthe completely closure time of Meso-Tethy should be in the late Early Cretaceous.