Tracing exhumation of the Dabie Shan ultrahigh-pressure metamorphic complex using the sedimentary record in the Hefei Basin, China
Tracing exhumation of the Dabie Shan ultrahigh-pressure metamorphic complex using the sedimentary record in the Hefei Basin, China
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DOI：
10.1130/b26524.1
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发表时间：
2010
影响因子：
4.9
通讯作者：
Shaofeng Liu;Guowei Zhang;B. Ritts;Huiping Zhang;M. Gao;C. Qian
中科院分区：
文献类型：
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作者：
Shaofeng Liu;Guowei Zhang;B. Ritts;Huiping Zhang;M. Gao;C. Qian
合肥盆地侏罗系为辫状河、冲积-扇沉积体系，具有总体上向上粗化的层序特征。多重物源分析表明，合肥盆地沉积源区由多种岩石组成，包括轴向大别山变质杂岩的超高压、高压变质岩和扬子基底岩、陆镇关杂岩花岗岩、中低变质岩和北淮阳褶皱冲断带的阳山群砂岩。盆地西部的中侏罗世剖面具有较高的END值(176 Ma)，变化范围为−13.8~−11.3；盆地中部的剖面具有较高的147Sm/144ND比值，为0.1168~0.1266，较低的END值(176 Ma)，为−15.0~−14.5。盆地东部某剖面沉积物的END值最低(176 Ma)，−为2 2.0~−14.6，TDm最高，为1.8~2.4Ga，147Sm/144Nd值较低，为0.0937~0.1067。合肥盆地沉积物碎屑组分和Nd同位素组成的物源分析表明，大别山造山带的折返深度自西向东递增，超高压变质岩和高压变质岩的剥离年龄由早侏罗世向西变化。晚三叠世和侏罗纪的折返速率从∼平均1.4 mm/a向东增加到∼2.5 mm/a。盆地中的沉积物记录了造山带中的幕式逆冲事件和周期性的剥离。
Jurassic rocks in the Hefei Basin were deposited by braided-fluvial and alluvial-fan systems, characterized by a general coarsening-upward sequence. Multiproxy provenance analyses demonstrate that the sediment source areas for the Hefei Basin are composed of a variety of rocks, including ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic rocks and Yangtze basement rocks of the axial Dabie Shan metamorphic complex, the Luzhenguan complex granite, low- and medium-grade metamorphic rocks, and the Yangshan Group sandstone in the North Huaiyang fold and thrust belt. A Middle Jurassic section in the western part of the basin is characterized by relatively high e Nd values (at 176 Ma), ranging from −13.8 to −11.3, whereas a section in the middle part of the basin has higher 147 Sm/ 144 Nd ratios, from 0.1168 to 0.1266 and somewhat lower e Nd values (at 176 Ma), from −15.0 to −14.5. Sediments in a section in the eastern part of the basin have the lowest e Nd values (at 176 Ma), ranging from −22.0 to −14.6, the highest T DM values, from 1.8 to 2.4 Ga, and low 147 Sm/ 144 Nd ratios, from 0.0937 to 0.1067. Provenance analyses of detrital compositions and Nd isotopic compositions of the sediments in the Hefei Basin clearly demonstrate that the depth of exhumation in the Dabie Shan orogen increases from the west to the east; the unroofing ages of the UHP and HP metamorphic rocks change from Early Jurassic to Late Jurassic westward. The exhumation rate during the Late Triassic and Jurassic is inferred to have increased eastward from ∼1.4 mm/a to ∼2.5 mm/a on average. The sediments in the basin record the episodic thrusting events and periodic unroofing in the orogen.