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位于北祁连山俯冲杂岩带南面的东草河蛇绿岩是一个构造移置岩块(大小为3km×6km).其下部岩石组合为多期次侵入的岩床状堆晶纯橄岩-橄长岩-斜(钙)长岩-斜(钙)长质辉长岩-辉长岩系列,其中可见不谐合的纯橄岩-橄长岩侵入体.往上过渡到均质的辉长岩-苏长质辉长岩系列,顶部则有辉绿岩质岩墙与玄武岩质熔岩.矿物结晶顺序为橄榄石±铬尖晶石→斜长石→单斜辉石→斜方辉石→钛铁氧化物矿物.堆晶岩中的铬尖晶石成分(Mg#:42-66,Cr#:41-57)类似于现今的洋壳特征.堆晶岩石与均质岩石系列中的斜长石与单斜辉石成分变化,反映了岩浆结晶分异的过程且与现今的洋壳成分特征相似.辉绿-玄武质熔岩的全岩地球化学成分与N-MORB类似.东草河蛇绿岩组成岩石群的REE与微量元素蛛网图分布特征显示它们是N-MORB岩浆分异的结果.利用SHRIMP锆石U-Pb定年法,获得苏长质辉长岩的锆石206Pb/238U加权平均年龄为(497±7)Ma,代表东草河蛇绿岩的构造侵位年龄.由岩石建造、矿物化学、全岩地球化学与定年学的研究结果,可以确认东草河蛇绿岩是一个古祁连洋洋壳残片,为古祁连洋向北俯冲的一个重要标志.
The Dongcaohe ophiolite, located on the south of the North Qilian subduction complex, is a tectonic displacement block (3km × 6km in size). The lower part of the rock assemblage is a multi-stage intrusion bedrock dunite - Rock-ramp (calcium) feldspar-ramp (calcium) gabbro-gabbros series, in which disharmonic dacite-pała intrusions can be seen and uplifted to a homogeneous gabbro - Peridotrophic gabbro series, with diabase dykes and basaltic lavas on top, with mineral crystallized in the order of olivine ± chrome spinel → plagioclase → clinopyroxene → orthopyroxene → titanium Iron oxide minerals. The chromium spinel composition (Mg #: 42-66, Cr #: 41-57) in the hematite rocks is similar to today’s oceanic crust characteristics. The ramp length in the series of hematite and homogeneous rocks Rock and clinopyroxene composition, reflecting the process of magmatic crystallization differentiation and similar to the characteristics of today’s oceanic crust.Gram-basaltic lava has the same geochemical composition as N-MORB, REE and trace element cobweb distribution characteristics of rock-forming rocks show that they are the result of N-MORB magmatic differentiation.Using SHRIMP zircon U-Pb dating method, the zircon 2 The weighted average age of 06Pb / 238U is (497 ± 7) Ma, representing the tectonic emplacement age of the Dongcahe ophiolite. It can be confirmed from the results of rock construction, mineral chemistry, whole rock geochemistry and dating data that the Dongcaohe The ophiolite is an ancient Qilian oceanic crust, an important symbol of the northward subduction of the ancient Qilian Ocean.