东准噶尔卡拉麦里SSZ型蛇绿岩地球化学及其构造意义
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新疆青河、奇台县红柳沟—苏吉泉一带1∶5万区域地质矿产调查资助项目(QD200508)


Geochemical characteristics and tectonic significanceof Kalamaili SSZ ophiolite from Eastern Junggar
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    摘要:

    卡拉麦里蛇绿岩带受控于卡拉麦里深大断裂,主要由超镁铁质岩体、镁铁质岩脉和火山熔岩组成。超镁铁质岩体主要由地幔方辉橄榄岩组成,并有纯橄岩和铬铁矿矿石产出。超镁铁质岩石具有低SiO2、高MgO、LREE富集的“V”字形和LREE略富集型稀土元素分布模式,具有SSZ(supra subduction zone)型的地幔橄榄岩特征。玄武岩、堆晶辉长岩以及辉长闪长岩岩脉具有低Al2O3、TiO2、K2O + Na2O含量,且K2O<Na2O,具相对高的MgO和极低的P2O5含量,具低Ti/V比值(10~20)、低的稀土元素丰度和LREE弱亏损型稀土元素配分模式,显示与洋内板块俯冲作用有关的SSZ型蛇绿岩地球化学特征。碱性玄武岩则具有洋岛玄武岩特征,具有高Al2O3、TiO2(2.50%~3.43%,平均3.16%)、K2O+Na2O(7.36%~9.40%)、P2O5(0.509%~1.579%,平均0.80%)和Ti/V(>50),相对低MgO(1.84%~2.81%,平均2.60%)的特征,富集不相容元素并具高的稀土元素总量和轻稀土元素明显富集的稀土元素配分模式,显示洋岛玄武岩特征,代表了洋盆早期洋内热点作用。卡拉麦里蛇绿岩带反映了哈萨克斯坦准噶尔联合陆块与西伯利亚板块的古洋盆经历了洋内热点作用和大洋板块洋内俯冲消减的演化过程。

    Abstract:

    The Kalamaili ophiolite belt controlled by regional deepfracture zone consists of ultramafic rock bodies,mafic dikes and volcanics. The ultramafic rocks are composed of mantle harzburgites with dunite pods and chromitite ores and characterized by low SiO2, high MgO, LREEenriched Vshaped and LREEslightly enriched patterns. They represent a typical mantle section of the suprasubduction zone (SSZ) setting. The lowTi basalts and their crystallized accumulative dikes comprising gabbro and gabbrodiorite display a lowTi affinity of the island arc tholeiite (IAT) ophiolitic series from the SSZ setting, having, as most distinctive chemical features, low Al2O3, TiO2,K2O+Na2O and K2O<50), low MgO (1.84%~2.81%, 2.60% on average), enrichment of incompatible elements and high abundance of REE with LREEenriched REE patterns. They probably are remnants of ocean island,representing the ocean hotspot at the early development stage of the ocean, and might have constituted the hotspot that resulted in the initial extension environment in this region. It can be concluded that the Kalamaili ophiolite belt represents the Devonian oceanic lithosphere relics of the ocean basin that separated the KazkhstanJunggar united continental block from Siberian plate, suggesting that the ocean basin experienced the process from the early intraocean hotspot to the late intraocean plate subduction.

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杨梅珍,吴宏恩,杨高学,2009,东准噶尔卡拉麦里SSZ型蛇绿岩地球化学及其构造意义[J].岩石矿物学杂志,28(3):251~263.

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