西藏察隅地区中侏罗世马里组——兼论“春节桥组”的时代
Middle Jurassic Mali Formation of the Zayü area, Tibet—with a discussion of the age of the Chunjieqiao Formation
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摘要: 西藏察隅地区的中侏罗统马里组 ,原划为下泥盆统春节桥组。通过岩石地层层序、岩石组合、沉积地球化学、重矿物特征、与下伏地层的接触关系等调查 ,以及巴通期双壳类化石组合的新发现 ,认为均与同一构造带洛隆地区的中侏罗统马里组相同。因此 ,下泥盆统春节桥组应该废弃。马里组是怒江洋盆在晚三叠世—早侏罗世闭合时 ,澜沧江弧与三缅村弧发生强烈碰撞造山 ,在三缅村弧后拉张的前陆盆地或山间盆地中沉积的一套中侏罗世红色磨拉石建造。Abstract: The Middle Jurassic Mali Formation in the Zayü area, Tibet, was originally assigned to the Lower Devonian Chunjieqiao Formation. Correlation of the lithostratigraphic sequences, rock associations, sedimentary geochemical characteristics and heavy minerals, studies of contact relationships with the underlying strata and discovery of the Bathonian bivalve assemblage indicate that this formation is equivalent to the Middle Jurassic Mali Formation in the Lhorong area in the same tectonic belt. Therefore the name of the Lower Devonian Chunjieqiao Formation should be discarded. The Mali Formation is a Middle Jurassic red molasse formation deposited in the Sanmiancun back arc extensional foreland basin or intermontane basin during the closing of the Nujiang oceanic basin in the Late Triassic Early Jurassic and strong collisional orogeny in the Lancangjiang arc and Sanmiancun arc.
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