松潘-甘孜地体中部晚三叠世安山质增生弧的确定及其意义

发布时间：2018-11-09 13:48

【摘要】：本文研究揭示,巴颜喀拉-松潘甘孜地体(简称松潘-甘孜地体)中部三叠系复理杂岩中的安山岩块是增生弧岩浆活动的产物,具有高度不均一均匀的岩石组构、地球化学与同位素组成。特别是这些安山岩显示了与松潘-甘孜三叠系海相浊积岩具有高度的Sr-Nd同位素亲缘性,沿亏损地幔和三叠系海相浊积岩混熔曲线分布,且主要分布于三叠系海相浊积岩端元区。这表明该增生弧安山质岩浆主要由增生楔中的海相浊积岩基质部分熔融形成,并受到了增生楔中大洋岩石圈残片等超镁铁/铁镁质组分的不同程度混染。安山岩时代(226.8±1.9Ma~213.7±0.9Ma)以及同时期广泛的S型花岗岩侵入活动(228±2Ma~204±7Ma)揭示增生弧形成于晚三叠世Norian期。前人工作表明,位于松潘-甘孜地体东北隅的诺尔盖-松潘盆地是一个周缘前陆盆地。因此,松潘-甘孜地体并非单一构造成因的地质体,至少由二叠纪-三叠纪演化的古特提斯大洋和中三叠世拉丁期-晚三叠世诺列期周缘前陆盆地两部分构成。前者是松潘-甘孜地体的主体部分,由松潘-甘孜古特提斯洋在三叠纪时期快速收缩形成的增生楔杂岩组成,其上发育增生弧,局部残存古特提斯大洋盆地及被构造移置的洋壳残片;后者为西秦岭弧(248~234Ma)与扬子地块碰撞的产物。
[Abstract]:In this paper, it is revealed that the andesite block in the Triassic complex in the central part of the Bayankara-Songpan Ganzi terrane is the product of accretive arc magma activity and has a highly heterogeneous rock fabric. Geochemistry and isotopic composition. In particular, these andesite show high Sr-Nd isotopic affinity with Songpan-Ganzi marine turbidite, and distribute along the mixed melting curve of depleted mantle and Triassic marine turbidite. And mainly distributed in the Triassic marine turbidite end member area. This indicates that the accretive arc anshan magma is mainly formed by partial melting of the marine turbidite matrix in the accretive wedge and is mixed with ultramafic / ferromagnesian components such as oceanic lithospheric debris in the accretive wedge to varying degrees. The andesite age (226.8 卤1.9Ma~213.7 卤0.9Ma) and the extensive S-type granite intrusion in the same period (228 卤2Ma~204 卤7Ma) revealed that the accretive arc was formed in the Norian period of the late Triassic. The previous work shows that the Norgey-Songpan basin located in the northeast corner of Songpan-Ganzi terrane is a peripheral Foreland basin. Therefore, the Songpan-Ganzi terrane is not a single tectonic geological body, and is composed at least of the PaleoTethys ocean, which evolved from Permian to Triassic, and the Foreland basin, from the Middle Triassic to the late Triassic. The former is the main part of the Songpan-Ganzi terrane, which is composed of the accretive wedge complex formed by the rapid contraction of the Songpan-Ganzi paleoTethys ocean during the Triassic period, on which the accretive arc is developed. Local remnant of the paleoTethys oceanic basin and the tectonic transposition of oceanic crust remains; The latter is the product of the collision between the West Qinling Arc (248~234Ma) and the Yangtze block.
【作者单位】：中国科学院大学地球科学学院;中国地质科学院地质研究所;中国地质调查局西安地质调查中心;
【基金】：国家自然科学基金项目(40472119、40872147) 中国地质调查局地质调查项目(12120113067500、DD20160201-07)联合资助
【分类号】：P542

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