西北地质
西北地質
서북지질
NORTHWESTERN GEOLOGY
2014年
3期
14-25
,共12页
地球化学特征%构造环境%鄂拉山组%热水地区%陆缘弧
地毬化學特徵%構造環境%鄂拉山組%熱水地區%陸緣弧
지구화학특정%구조배경%악랍산조%열수지구%륙연호
geochemistry%tectonic setting%Elashan formation%reshui area%epicontinental arc
青海热水地区位于秦祁昆三大造山带的结合部位,该区发育晚三叠世鄂拉山组火山岩。岩石类型以英安岩及英安质火山碎屑岩为主,其次为中性的安山质火山岩和酸性的流纹质火山岩,为一套高 K、低 Ti、准铝质的钙碱性系列火山岩。SiO2含量为59.62%~76.46%,总碱含量 ALK 为6.59%~8.04%,ANK 在1.14~1.80,里特曼系数σ在1.72~2.41,岩石矿物结晶分离程度高,但固结程度一般。稀土总量 REE在126.76×10-6~240.07×10-6,LREE/HREE均值为10.19,属轻稀土富集型,且轻稀土富集程度高于重稀土富集程度,δEu 值多在0.37~0.56亏损较为明显,稀土元素标准化配分曲线均呈右倾较缓的平滑曲线。大离子半径亲石元素 Rb、Ba、U、K、Th较为富集,高场强元素 Nb、Ta、Ti、P等较为亏损,原始地幔标准化配分曲线呈明显左高右低的“W”型,具有明显的弧火山岩特点。Mg#大部分在16~36,206 Pb/204 Pb=18.181~18.218,207 Pb/204 Pb=15.570~15.588,208 Pb/204 Pb=38.368~38.529,显示岩浆来源于下地壳。该区火山岩与 A型俯冲构造活动有关,利用 Hf/3-Th-Nb/16等构造环境判别图解分析,其形成于陆缘弧环境。
青海熱水地區位于秦祁昆三大造山帶的結閤部位,該區髮育晚三疊世鄂拉山組火山巖。巖石類型以英安巖及英安質火山碎屑巖為主,其次為中性的安山質火山巖和痠性的流紋質火山巖,為一套高 K、低 Ti、準鋁質的鈣堿性繫列火山巖。SiO2含量為59.62%~76.46%,總堿含量 ALK 為6.59%~8.04%,ANK 在1.14~1.80,裏特曼繫數σ在1.72~2.41,巖石礦物結晶分離程度高,但固結程度一般。稀土總量 REE在126.76×10-6~240.07×10-6,LREE/HREE均值為10.19,屬輕稀土富集型,且輕稀土富集程度高于重稀土富集程度,δEu 值多在0.37~0.56虧損較為明顯,稀土元素標準化配分麯線均呈右傾較緩的平滑麯線。大離子半徑親石元素 Rb、Ba、U、K、Th較為富集,高場彊元素 Nb、Ta、Ti、P等較為虧損,原始地幔標準化配分麯線呈明顯左高右低的“W”型,具有明顯的弧火山巖特點。Mg#大部分在16~36,206 Pb/204 Pb=18.181~18.218,207 Pb/204 Pb=15.570~15.588,208 Pb/204 Pb=38.368~38.529,顯示巖漿來源于下地殼。該區火山巖與 A型俯遲構造活動有關,利用 Hf/3-Th-Nb/16等構造環境判彆圖解分析,其形成于陸緣弧環境。
청해열수지구위우진기곤삼대조산대적결합부위,해구발육만삼첩세악랍산조화산암。암석류형이영안암급영안질화산쇄설암위주,기차위중성적안산질화산암화산성적류문질화산암,위일투고 K、저 Ti、준려질적개감성계렬화산암。SiO2함량위59.62%~76.46%,총감함량 ALK 위6.59%~8.04%,ANK 재1.14~1.80,리특만계수σ재1.72~2.41,암석광물결정분리정도고,단고결정도일반。희토총량 REE재126.76×10-6~240.07×10-6,LREE/HREE균치위10.19,속경희토부집형,차경희토부집정도고우중희토부집정도,δEu 치다재0.37~0.56우손교위명현,희토원소표준화배분곡선균정우경교완적평활곡선。대리자반경친석원소 Rb、Ba、U、K、Th교위부집,고장강원소 Nb、Ta、Ti、P등교위우손,원시지만표준화배분곡선정명현좌고우저적“W”형,구유명현적호화산암특점。Mg#대부분재16~36,206 Pb/204 Pb=18.181~18.218,207 Pb/204 Pb=15.570~15.588,208 Pb/204 Pb=38.368~38.529,현시암장래원우하지각。해구화산암여 A형부충구조활동유관,이용 Hf/3-Th-Nb/16등구조배경판별도해분석,기형성우륙연호배경。
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.
