摘要
胶北地块变质基底的蛇纹岩、蛇纹岩化尖晶石方辉橄榄岩、尖晶石橄榄斜方辉石岩、角闪石岩自形成以后,经历了早期的高角闪岩相和晚期绿片岩相的变质作用,因而记录了三个阶段的矿物组合：早期的Opx1＋Ol1＋Spl1;中期的Opx2＋Ol2＋Spl2＋Amp2和晚期的Amp3＋Srp3＋Mag3＋Cal组合。超镁铁岩中普遍存在的角闪石,具有粒状变晶结构特征,形成于角闪岩相和绿片岩相的变质作用过程。蛇纹石没有受到应力作用的迹象,显示其形成于晚期非挤压环境的交代变质作用过程。尖晶石橄榄岩中斜方辉石的矿物化学以及尖晶石橄榄岩的高Mg O含量都表现出克拉通橄榄岩的性质。角闪石岩的稀土元素配分图解的（La/Sm）N的比值1.11-1.41,（La/Yb）N的比值0.91-1.61,超镁铁岩多元素图解显示无高场强元素异常,都表明胶北地块变质基底的超镁铁岩形成的构造背景或是裂谷环境。尖晶石矿物的Mg#0.72-0.79、Cr#0.06-0.12表明交代变质成因。方辉橄榄岩橄榄石的Fo值88.42-90.50、超镁铁质岩石全岩主元素的分散性、较大的∑REE含量变化以及Si/Al-（Mg＋Fe）/Al和Mg/Ti-Fe/Ti主元素的比值图解所表现出的超镁铁岩与角闪石岩具有成因联系等,都表明胶北变质基底的超镁铁岩可能是具有堆晶成因的一套幔源岩浆系列。高MgO含量（16%-42%）表现出前寒武纪变质基底的橄榄岩地幔性质;高水含量反映出漫长地质历史时期变质作用过程。
The ultramafic rocks,including serpentinite,serpentinized spinel-orthopyroxene peridotite,spinel olivine pyroxenite and spinel-bearing amphibolite, were collected from the metamorphic basement of Jiaobei terrene. They record three-stage mineral assemblages： Opx1＋ Ol1＋ Spl1,Opx2＋ Ol2＋ Spl2＋ Amp2 and Amp3＋ Srp3＋ Mag3＋ Cal,and experienced high amphibolite facies and greenschist facies metamorphism. Amphibole porphyroblasts pervasively occur in each type rock,formed during high amphibolite and green-schist facies metamorphism. No deformation was observed in the serpentinite,indicating that serpentinization occurred in the late stage by metasomatism. Chemical compositions of the orthopyroxenites and high Mg O spinel peridotites are of characteristics of cratonic peridotite. REE rations of（ La / Sm）N1. 11 ~ 1. 41,（ La / Yb）N0. 91 ~ 1. 61 in amphibolite,and no HSFE anomaly in multielement pattern in the ultramafic rocks indicate that the ultramafic rocks are probably formed in a continental rift environment. Spinel compositions in the spinel peridotities have Mg#0. 72 ~ 0. 79,Cr#0. 06 ~ 0. 12 showing the metasomatic origin. Fo 88. 42 ~ 90. 50 in harzburgite,dispersive distribution of major elements of ultramafic rocks,big variation of ∑REE,the genetic relationships of diagrams of ultrmafic rocks and amphibolites from Si / Al-（ Mg ＋ Fe） / Al and Mg / Ti-Fe / Ti are all indicative of that the ultramafic rocks from the metamorphic basement of the Jiaobei terrane are probably a cumulate origin of a set of mantle-derived magma. High Mg O content（ 16%~ 42%） in ultramafic rocks exhibit a characteristics of the mantle from Precambrian basement,and high water contents of ultramafic rocks reflect the complicated metamorphic processes from long-term geological evolution.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第6期1549-1563,共15页
Acta Petrologica Sinica
基金
国家基础研究发展计划(973项目)(2012CB416606)
国家自然科学基金项目(41272072)联合资助
关键词
变质基底
超镁铁岩
矿物
岩石地球化学
胶北地块
Metamorphic basement
Ultramafic rocks
Mineralogy
Petrological geochemistry
Jiabei terrene
