U-Pb ages and trace elements of detrital zircons from Early Cretaceous sedimentary rocks in the Jiaolai Basin, north margin of the Sulu UHP terrane: Provenances and tectonic implications
U-Pb ages and trace elements of detrital zircons from Early Cretaceous sedimentary rocks in the Jiaolai Basin, north margin of the Sulu UHP terrane: Provenances and tectonic implications
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DOI：
10.1016/j.lithos.2012.08.002
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发表时间：
2012-12
期刊：
影响因子：
3.5
通讯作者：
S. Xie;Y. Wu;Zeming Zhang;Ya-Fei Qin;Xiaochi Liu;Hao Wang;Zhen Qin;Qian Liu;Saihong Yang
中科院分区：
文献类型：
--
作者：
S. Xie;Y. Wu;Zeming Zhang;Ya-Fei Qin;Xiaochi Liu;Hao Wang;Zhen Qin;Qian Liu;Saihong Yang
大别-苏鲁造山带是世界上最大的超高压造山带。为了限制大别山带的构造去顶，对大别山带周边沉积盆地的碎屑矿物进行了大量的研究。另一方面，对与苏禄带有关的盆地中的碎屑岩的研究仍然很少。胶莱盆地是一个与苏鲁造山带相邻的中生代沉积盆地。对采自胶莱盆地北方和南部边缘早白垩世莱阳群的两个砂岩样品进行了锆石U-Pb定年和微量元素分析。锆石U-Pb年龄主要集中在约1000 ~ 10000 μ m。2500-2400、2000-1700、850-700和330- 130 Ma，在约2000 - 1700年有一个小峰。1100 Ma和几个太古代。大多数锆石的结构特征反映了岩浆起源，而一些晚古元古代和三叠纪锆石显示均匀的CL图像和低Th/U比值，表明变质成因。新元古代的年龄与苏禄海变质岩的原岩年龄一致，这意味着苏禄海可能是该组分的主要来源。然而，大多数新元古代锆石是自形到半自形或角形的，并且没有被过度生长所包围，这意味着，低变质新元古代变质火成岩发生沿着的北方边缘的苏禄考或变质沉积物覆盖在苏禄考的高压-超高压岩石可能提供源材料，这些碎屑锆石。古元古代晚期和早期的年龄峰值与胶北陆块的热事件相一致，略晚于扬子陆块。这表明胶北玄武岩是古元古代-太古宙碎屑锆石组分的潜在源区。在所研究的样品中只发现了两个早古生代锆石颗粒，表明早古生代弧没有延伸到苏鲁地区。根据苏鲁造山带附近不同岩石类型的分布，早白垩世碎屑锆石可能来源于苏鲁造山带的白垩纪侵入岩。包括6个变质颗粒和2个变质增生边在内的8个碎屑锆石给出了三叠纪的年龄，这些年龄可能来自苏鲁地区的高压-超高压岩石。变质增生环的变质年龄为246± 3 Ma，可能记录了苏禄海俯冲变质作用的时间。其中一个变质颗粒的年龄为212± 2 Ma，反映了一次退变质事件。根据稀土元素配分模式，其余6个三叠系分析可分为两组。其中4个岩石的加权平均年龄为230± 6 Ma，重稀土元素配分模式接近平坦，Eu有轻微的负或正异常。最后两个颗粒富集重稀土元素，结合它们的年龄和稀土配分模式，认为它们可能来自其他不同的超高压岩石。在莱阳群中发现了三叠纪变质锆石，表明苏鲁超高压岩石在早白垩世之前就出露地表。
The Dabie–Sulu orogen in east-central China is the largest UHP belt in the world. Many studies have dealt with detrital minerals from sedimentary basins surrounding the Dabie belt in order to constrain the tectonic unroofing of this terrane. On the other hand, still few are the works focused on detritals from the basins associated with the Sulu belt. The Jiaolai basin, adjacent to the Sulu belt, is made of Mesozoic sedimentary rocks. Two sandstone samples collected from the Early Cretaceous Laiyang Group in the northern and southern margins of the Jiaolai basin were selected for zircon U–Pb dating and trace element analysis. The zircons show main U–Pb age clusters at ca. 2500–2400, 2000–1700, 850–700, and 330–130Ma, with a minor peak at ca. 1100Ma and a few Archean ages. Most zircons show texture features reflecting a magmatic origin, whereas several late Paleoproterozoic and Triassic zircons show homogeneous CL images and low Th/U ratios, indicating a metamorphic origin. The Neoproterozoic ages are consistent with the protolith ages of the metamorphic rocks in the Sulu terrane, implying that the Sulu tarrane may be a major source for this component. Whereas most Neoproterozoic zircons are euhedral to subhedral or angular in shape and are not surrounded by overgrowths, this implies that low-grade metamorphic Neoproterozoic metaigneous rocks ocurring along the northern margin of the Sulu terrane or metasediments overlying the HP–UHP rocks in the Sulu terrane might provide source materials to these detrital zircons. The late and early Paleoproterozoic age peaks are consistent with the thermal events occurred in the Jiaobei terrane, slightly younger than those in the Yangtze Block. These suggest that the Jiaobei terrane was a potential source for the Paleoproterozoic to Archean detrital zircon components. Only two early Paleozoic zircon grains were found in the studied samples, indicating the early Paleozoic arc did not extend into the Sulu terrane. According to the distribution of different kinds of rock adjacent to the Sulu terrane, the Early Cretaceous detrital zircons may be potentially derived from Cretaceous plutons from the Sulu belt. Eight detrital zircons including six metamorphic grians and two metamorphic overgrowth rims yield the Triassic ages, which might be derived from HP–UHP rocks from the Sulu terrane. A metamorphic overgrowth rim yields a metamorphic age of 246±3Ma, probably recording the timing of the prograde metamorphism of the Sulu terrane. One metamorphic grain yields an age of 212±2Ma, which is interpreted to record a retrograde metamorphic event. Based on the REE patterns, the remaining six Triassic analyses can be subdivided into two groups. Four of them record a weighted mean age of 230±6Ma and show nearly flat HREE patterns and slight negative or positive Eu anomalies. The last two grains are enriched HREE; considering their ages and the REE patterns, it is suggested that they may originate from other diverse UHP rocks. The Triassic metamorphic zircons were detected in the Laiyang Group, indicating that the Sulu UHP rocks were exposed to the surface before the Early Cretaceous.