摘要
摘要：洞错蛇绿岩出露于改则县洞错北约20km处，去申拉以南，地表形态为楔状体，大致沿日土一改则一丁青断裂带分布；侵位于侏罗系木嘎岗13群中，并被下白垩统朗山组不整合覆盖。蛇绿岩剖面各岩石单元发育齐全：主要由地幔橄榄岩（方辉橄榄岩、二辉橄榄岩）、堆晶岩、辉绿岩墙和壳层熔岩组成。对洞错蛇绿岩地幔橄榄岩和均质辉长岩中尖晶石和辉石化学成分测定和构造环境判别分析显示：洞错地区尖晶石二辉橄榄岩（XDC28）投点于深海橄榄岩区域，指示尖晶石二辉橄榄岩经历了少于10％的熔体提取，而方辉橄榄岩分别经历了13％-30％的亏损，代表了亏损程度较弱的地幔橄榄岩残留（〈30％），明显不同于岛弧环境地幔橄榄岩强烈亏损的特征。辉石化学成分研究确认了尖晶石二辉橄榄岩属于深海橄榄岩。斜方辉石和单斜辉石具有不同的形态和化学成分，反映了不同的结晶温度（分别为900～1000℃，〈500～600℃）。前者为岩石的形成温度，而后者则为冷却变质或重结晶过程中达到再平衡时的温度。
The Dong Tso ophiolite,with a wedge exposure shapeis,is located at 20 km north of Dong Tso,Gertse county. The ophiolite emplaced in the Jurassic strata of the Mugagangri Group,and was overlain unconformably by the Cretaceous strata of the Langshan Group. The Dong Tso ophiolite consists of all common units,such as the mantle peridotite of lherzolite and harzburgite,cumulate rocks,diabase dyke,and basaltic lavas. The spinel and pyroxene in the mantle peridotite and massive gabbro of the Dong Tso ophiolite were analyzed using EMPA and EDS methods. The spinel from the Dong Tso spinel lherzolite plots in the region of abyssal peridotite on the tectonic discrimination diagrams. Chemical compositions of the spinels show that the spinel iherzolite experienced < 10% melt extraction while the harzburgites experienced about 13% to 30% melt extraction,which are much lower than that of the typical mantle peridotite of island arc affinity. The mineral composition of the gabbro is similar to those of the typical mafic intrusions. Combined with the reported data,we conclude that the Dong Tso ophiolite was developed mainly in a normal oceanic ridge and experienced gradual melt extraction. The geothermomal calculation results show that the orthopyroxene and clinopyroxene crystallized at 900 ～ 1000 ℃ and < 500 ～ 600 ℃,respectively. The former should be the formation temperature of the host rock,while the latter may represent the equilibrium temperature of the metamorphism or re-crystallization.
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2013年第2期308-319,共12页
Geotectonica et Metallogenia
基金
国家自然科学基金项目(批准号:40534019和41102139)资助
关键词
洞错蛇绿岩
矿物学特征
尖晶石
橄榄石
辉石
Dong Tso ophiolite
mineralogical characteristic
spinel
olivine
pyroxene
