西北地质Issue(3)：14-25,12.
青海热水地区晚三叠世火山岩地球化学特征及构造环境
Geochemistry and Tectonic Setting of Late Triassic Volcanic Rocks in Reshui Area,Qinghai
摘要
Abstract
Reshui area is located in the binding site of Qinling,Qilianshan and Kunlunshan orogenic belt, and the late Triassic volcanic rock developed in the area is part of Elashan formation.As a set of volcano rocks with high K content,low Ti content and metaluminous calc-alkaline characteristics,the late Triassic rock are mainly consisted of dacite and dacitic pyroclastic rock,followed by neutral andesitic volcano rock and acidic rhyolitic volcano rock.The content of SiO2 is between 59.62% and 76.46%,the content of ALK ranges from 6.59% to 8.04%,the content of ANK is from 1.14 to 1.80,and the value of Rittmann coefficient varies between 1.72 and 2.41,the degree of rock mineral fractionation crystallization is high,but the degree of consolidation is common.The total of REE is between 126.76 × 10-6 and 240.07 × 10-6 ,the average value of LREE/HREE is 10.19,indicating that the rock belongs to the LREE enrichment type.Besides,the enrichment degree of LREE is higher than HREE,theδEu value mostly falls between 0.37 and 0.56 and the loss is more obvious.The REE patterns are right dipping slow smooth curves.LILE such as Rb,Ba,U,K,and Th are enriched,and HFSE such as Nb,Ta, Ti,P are depleted.Primitive mantle trace element spider diagram show a significant W type high on the left and low on the right,with obvious characteristics of arc volcanic rocks.Mg # is almost within a range of 16 to 36,the value of 206Pb/204Pb is from 18.181 to 18.218,while the value of 207Pb/204Pb is between 15.570 and 15.588,then the value of 208Pb/204Pb is among 38.368 to 38.529.All these values indicate that the magma derived from the lower crust.The volcanic rocks are related to Type A subduction,and according to Hf/3-Th-Nb/1 6 and other tectonic environment discrimination diagrams, the rocks are found formed in an epicontinental arc environment.关键词
地球化学特征/构造环境/鄂拉山组/热水地区/陆缘弧Key words
geochemistry/tectonic setting/Elashan formation/reshui area/epicontinental arc分类
天文与地球科学引用本文复制引用
李运冬,刘小玉..青海热水地区晚三叠世火山岩地球化学特征及构造环境[J].西北地质,2014,(3):14-25,12.基金项目
青海省国土资源厅地质勘查基金项目“青海省都兰县热水地区J47E023009、J47E024009两幅1∶5万区域地质矿产调查”(2009-04) （2009-04）
