摘要
熬油沟蛇绿岩位于甘肃省肃南县祁青乡。其地质-地球化学特征表明;蚀变作用形成的蛇纹岩,原岩为方辉橄榄岩,所有的岩石类型均以相对富集轻稀土(LREE)和大离子亲石元素(LILE)为特征,并且玄武质熔岩显示出幔柱型大洋中脊玄武岩(P-MORB)的地球化学特征,说明岩浆来源于与洋岛玄武岩(OIB)源相似的富集地幔。玄武质岩石的MgO、Cr、Ni含量以及Mg值较低,说明它们不是原始岩浆,而是经过了橄榄石、Cr-尖晶石和斜长石等矿物分离结晶作用以后形成的岩浆。其构造环境可能为小洋盆初始扩张时的扩张脊。
The Aoyougou ophiolite is situated in the Qiqing township, Sunan County, Gansu Province. It consists of serpentinite, accumulative rocks, diabase dikes, basaltic rocks (including pillow lavas and block lavas) and red-banded siliceous rocks. The ophiolite has been cut into several microthons by thrusts. The mineralogical and petrochemical characteristics show that the primary rock of serpentinite is harzburgite perior to serpentinization. The SiO2 contents of diabase and lavas range from 45. 60% to 52. 83% , and TiO2 contents from 1. 42% to 3. 22% , resembling those of MORE and ocean island basalts. The diagrams of SiO2 vs. Nb/Y and SFeO vs.ΞFeO/MgO indicate that all basaltic rocks belong to tholeiite series. All rock types in the ophiolite, including harzburgite, are characterized by relatively enrichment in LREE and LILE. The geochemical characteristics of basaltic lavas in the ophiolite resemble P-MORB, which implies that they originated from the enrichment mantle simliar to OIB. Low MgO, Cr and Ni contents and Mg value of basaltic rocks suggests that they not be the primary magamas melted directly from mantle sources, but the evolved magmas after fractional crystallization of olivine, Cr-spinel in magma chamber, so its primary magma might be infered to be the picritic magma which was richer in Mg and Cr than the basalts in the Aoyougou ophiolite. Its tectonic environment may be the spreading ridge of a small oceanic basin at the start.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1998年第1期42-51,共10页
Acta Geologica Sinica
基金
国家计划委员会国地司科技找矿攻关项目
关键词
蛇绿岩
地球化学
岩石成因
螯油沟
甘肃
ophiolite
geochemistry
petrogenesis
Aoyougou
Gansu Province
