CAJ | 학술논문

对鄂西黄陵背斜南部宜昌太平溪、邓村一带崆岭岩群中的元古宙庙湾岩组强烈变形变质超镁铁-镁铁质岩的研究表明.镟铁质岩主要为似层状细粒斜长角闪岩.变辉长岩岩体、岩脉及辉绿岩岩脉.超锾铁质岩则主要为蛇纹石化纯橄榄岩、方辉橄榄岩,呈构造岩片、岩块分布于斜长角闪岩之中.细粒斜长角闪岩TiO_2=1.14%～1.48%,稀土元素配分型式为略亏损一平坦型,无明显的Eu异常,(La/Yb)_N=0.87～1.12,La/Nb、Ce/Zr、Zr/Nb、zr/Y、Ti/Y平均值分别为1.04、0.15、18.78、2.53、290.51,Nb/Th平均为9.88,显示为大洋中脊构造环境形成的N-MORB型拉斑玄武岩;变辉长岩具典型的堆晶结构特征.稀土元素配分型式为平坦型,具明显的Eu正异常;蛇纹石化纯橄榄岩的稀土元素配分型式具中稀土元素略亏损的U形特征.显示为LREE略富集的地幔岩.上述特征表明,黄陵背斜南部崆岭岩群中的元古宙庙湾岩组实际上是一套混杂堆积的古大洋蛇绿岩残片.元古宙庙湾蛇绿岩的发现为华南扬子克拉通存在中元古代洋盆和哥伦比亚超大陆聚合、裂解构造事件提供了重要的证据.
대악서황릉배사남부의창태평계、산촌일대공령암군중적원고주묘만암조강렬변형변질초미철-미철질암적연구표명.선철질암주요위사층상세립사장각섬암.변휘장암암체、암맥급휘록암암맥.초환철질암칙주요위사문석화순감람암、방휘감람암,정구조암편、암괴분포우사장각섬암지중.세립사장각섬암TiO_2=1.14%～1.48%,희토원소배분형식위략우손일평탄형,무명현적Eu이상,(La/Yb)_N=0.87～1.12,La/Nb、Ce/Zr、Zr/Nb、zr/Y、Ti/Y평균치분별위1.04、0.15、18.78、2.53、290.51,Nb/Th평균위9.88,현시위대양중척구조배경형성적N-MORB형랍반현무암;변휘장암구전형적퇴정결구특정.희토원소배분형식위평탄형,구명현적Eu정이상;사문석화순감람암적희토원소배분형식구중희토원소략우손적U형특정.현시위LREE략부집적지만암.상술특정표명,황릉배사남부공령암군중적원고주묘만암조실제상시일투혼잡퇴적적고대양사록암잔편.원고주묘만사록암적발현위화남양자극랍통존재중원고대양분화가륜비아초대륙취합、렬해구조사건제공료중요적증거.
Studies of strongly deformed and metamorphosed mafic-ultramafic rocks from the Proterozoic Miaowan Formation in the high-grade metamorphic Kongling Group in the southern Huangling anticline show that the nafic rocks are composed of layered fine-grained amphibolites,metagabbro rockbodies and dykes and diabase dykes,while the ultramafic rocks are mainly composed of serpentinized dunite and harzburgite,cropping out as tectonite slices and blocks within amphibolites.The geochemical features of the fine-grained layered amphibolite rocks including:TiO_2=1.14%-1.48%,slighdy depleted-flat type REE curve with no obvious Eu anomaly,(La/Yb)_N=0.87-1.12,average La/Nb,Ce/Zr,Zr/Nb,Zr/Y,Ti/Y are respectively 1.04,0.15,18.78,2.53,290.51,and the average of Nb/Th is 9.88.These features show that these amphibolites are N-MORB type tholeiites typical of those formed in mid-ocean ridge tectonic settings.The metagabbro have typical cumulate texture,fiat REE dismbution and obvious positive Eu anomaly:The REE characteristics of serpentinized dunite show a U-shape of slight loss of middle REE,representing cumulates meta- somatized by LREE slightly enriched mantle.All these features indicate that the mafic-ultramafic rocks from the Proterozoic Miaowan Formation within Kongling Group in the southern part of Huangling anticline,are a structurally dismembered ophiolite resting above Miaowan ophiolite supplies important evidence for the existence of an Mesoproterozoic oceanic basin,as well as tectonic events of Columbia supercontinent aggregation and break-up.