首页> 外文期刊>Geological Society of America Bulletin >Detrital zircon provenance from three turbidite depocenters of the Middle-Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment production
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Detrital zircon provenance from three turbidite depocenters of the Middle-Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment production

机译:中国中部上三叠统松潘-甘孜矿床的三个浊浊沉积中心的碎屑锆石物源:碰撞构造,侵蚀性掘尸和沉积物产生的记录

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To test the idea that the voluminous upper Middle to Upper Triassic turbidite strata in the Songpan-Ganzi complex of central China archive a detrital record of Dabie ultrahigh-pressure (UHP) terrane unroofing, we report 2080 single detrital U-Pb zircon ages by sensitive high-resolution ion microprobe-reverse geometry (SHRBVIP-RG) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis from 29 eastern Songpan-Ganzi complex sandstone samples. Low (<0.07) Th/U zircons, consistent with crystallization under UHP conditions, are rare in eastern Songpan-Ganzi complex zircon, and U-Pb ages of low Th/U zircons are incompatible with a Dabie terrane source. An unweighted pair group method with arithmetic mean nearest-neighbor analysis of Kolmogorov-Smirnov two-sample test results reveals that the eastern Songpan-Ganzi complex is not a single contiguous turbidite system but is instead composed of three subsidiary depocenters, each associated with distinct sediment sources. The northeastern depocenter contains zircon ages characterized by Paleozoic and bimodally distributed Precambrian zircon populations, which, together with south- to southeast-directed pa-leocurrent data, indicate derivation from the retro-side of the Qinling-Dabie (Q-D) collisional orogen wedge. In the central depocenter, the dominantly Paleozoic detrital zircon signature and south- to southwest-oriented paleocurrent indicators reflect a profusion of Paleozoic zircon grains. These data are inter- preted to reflect an influx of material derived from erosion of Paleozoic supra-UHP rocks of the Dabie terrane in the eastern Qinling-Dabie orogen, which we speculate may have been enhanced by development of a mon-soonal climate. This suggests that erosional unroofing played a significant role in the initial phase of UHP exhumation and likely influenced the petrotectonic and structural evolution of the Qinling-Dabie orogen, as evidenced by compressed Triassic isotherms/ grads reported in the Huwan shear zone that bounds the Dabie terrane to the north. The central depocenter deposits reflect a later influx of bimodally distributed Precambrian zircon, signifying either a decrease in the influx of Paleozoic zircon grains due to stalled UHP exhumation and/or dilution of the same influx of Paleozoic zircons by spilling of Precambrian zircon from the northeastern depocenter into the central depocenter basin, perhaps due to infilling and bypass of sediment from the northern depocenter or due to initial collapse and constriction of the eastern Songpan-Ganzi complex basin. The southeastern depocenter of the eastern Songpan-Ganzi complex bears significant Paleozoic, Neoproterozoic, and Paleoproterozoic zircon populations derived from the South China block and Yidun arc complex, likely recording nascent uplift of the Longmenshan deformation belt due to impingement of the Yidun arc complex upon the western margin of the South China block.
机译:为了验证中国中部松潘-甘孜构造体中大量的上三叠纪至上三叠纪浊质地层记录了大别超高压(UHP)地层顶化的碎屑记录,我们报告了2080个单碎屑U-Pb锆石年龄松潘-甘孜州东部29个复杂砂岩样品的高分辨率离子微探针反向几何学(SHRBVIP-RG)和激光烧蚀-电感耦合等离子体质谱(LA-ICP-MS)分析。低(<0.07)Th / U锆石与超高压条件下的结晶一致,在松潘-甘孜州东部复杂的锆石中很少见,低Th / U锆石的U-Pb年龄与大别山地源不相容。用Kolmogorov-Smirnov两个样本测试结果进行算术平均最近邻分析的非加权成对组方法表明,松潘-甘孜东部构造体不是单个连续的浊积体系统,而是由三个辅助沉积中心组成,每个沉积中心都与不同的沉积物有关资料来源。东北沉积中心包含以古生代和双峰分布的前寒武纪锆石种群为特征的锆石年龄,再加上从南向东南定向的古洋流数据,表明其起源于秦岭-大别(Q-D)碰撞造山带楔的后侧。在中央震中,主要是古生代碎屑锆石特征和从南向西南方向的古流指示符,反映了古生代锆石的大量分布。这些数据被解释为反映了东秦岭-大别造山带大别地层的古生界超-UHP岩石侵蚀所产生的物质涌入,我们推测这可能由于季风气候的发展而得到增强。这表明,侵蚀性屋面在UHP掘出的初期起着重要作用,并且可能影响了秦岭-大别造山带的岩石构造和结构演化,如湖湾剪切带中以大别地层为界的三叠系等温线/梯度压缩所证明的那样。去北边。中央沉积中心沉积物反映了后来出现的双峰分布的前寒武纪锆石的涌入,这表明由于UHP掘出停止而导致的古生代锆石的流入减少和/或由于从东北沉积中心溢出的前寒武纪锆石而稀释了相同的古生代锆石的涌入。进入中央沉积中心盆地,可能是由于北部沉积中心的沉积物充填和绕过,或者是由于松潘-甘孜东部盆地的初始塌陷和收缩。松潘—甘孜构造体的东南沉积中心有大量的华南地块和一墩弧复合体衍生的古生代,新元古代和古元古代锆石种群,可能是由于一墩弧复合体撞击到龙门山变形带的新生隆起。华南街区的西缘。

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