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赣东北地区早前寒武纪超基性熔岩—层状侵入岩的初步研究 预览 被引量:4

PRELIMINARY STUDY ON EARLY PRECAMBRIAN ULTRAMAFIC LAVA—AYERED INTRUSIONS IN NORTHEASTERN JIANGXI
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摘要 赣东北地区早前寒武纪超基性熔岩-层状侵入岩是扬子克拉通绿岩带的残块。科马提岩为橄榄质;稀土特征表明以Ⅱa型科马提岩为主,可能有Ⅲ型科马提岩。(La/Sm)N值〉2说明其源区已被富轻稀土的液体或岩浆流体交代过。扬子克拉通的花岗-绿岩带地体的地球化学特征着晚太古代时它与南非克拉通有更密切的联系。 The early Precambrian ultramafic lava - layered intrusions, distributed in northeastern Jiangxi, are composed of dunite, peridotite, enstenite-bearing peridotite, olivine-bearing pyroxenolite, pyroxenolite, sefstromite-bearing ultramafic rock and ultramafic komati-ite. The series is characterized with high magnesium, poor alkali, low calcium and aluminium, as well as inhomogeneous titanium. The contents of Cr, Ni and Co increase to the maximum during the MgO being 33 %-36% , then decrease with increasing of the MgO. The komatiites of the Ⅱ a-type (LREE enriched sub-type in the HREE depleted type) seems to be dominate, and the komatiite of Ⅲ-type (the HREE enriched type) might be existent. The average MgO content is 34. 66% , a little higher than that in South Africa and Southeastern Brazil. Because of alteration, the CaO content is lower. The Content of Cr, Ni, Co and Zr in the komatiite are similar with ultramafic komatiites all over the world, while Ti and Y relatively lower , so that the ratios of Ti/Zr and Y/Zr lower. The ultramafic lava - layered intrusions should be relics of Late Archean greenstone belt. The 2741. 40 Ma of Nd iso-topic model age comprehends that there develops the Late Archean geological record in northeastern Jiangxi. The granite-greenstone belt terrains in the region and Sichuan, being a part of the Yangtze Craton, have unique geochemical features, such as low-Al type TTG suite, ** a-type komatiite, etc. , which are similar with that of the Swaziland Gneiss and ko'matiite in the Onverwacht Group in the South Africa respectively. Possibly, the Yangtze Craton had a relatively closer relation with the South African Craton during early Precambrian, even was once a part of the latter.
作者 吴根耀 符鹤琴 WU Genyao FU Heqin 1) (Laboratory of Lithosphere Tectonic Evolution, Institute of Geology, Academia Sinica, Beijing 100029) 2) (Jiangxi Institute of Geoscience, Jiangxi 330201)
出处 《大地构造与成矿学》 EI CAS CSCD 1995年第4期 354-362,共9页 Geotectonica et Metallogenia
关键词 早前寒武纪 熔岩 层状侵入岩 超基性 komatiite of Ⅱ a-type, Late Archean greenstone belt, northeastern Jiangxi
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