Zircon U-Pb and Hf isotopes of volcanic rocks from the Batamayineishan Formation in the eastern Junggar Basin
Zircon U-Pb and Hf isotopes of volcanic rocks from the Batamayineishan Formation in the eastern Junggar Basin
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DOI：
10.1007/s11434-010-4151-y
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发表时间：
2010-10
影响因子：
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通讯作者：
Yuping Su;Jianping Zheng;W. Griffin;Huayun Tang;S. O’Reilly;Xiang Lin
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文献类型：
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作者：
Yuping Su;Jianping Zheng;W. Griffin;Huayun Tang;S. O’Reilly;Xiang Lin
通过对巴塔玛依内山组玄武岩锆石U-Pb年龄、微量元素和Hf同位素的研究，获得了玄武岩锆石的内部构造特征。玄武岩取自准噶尔盆地陆梁隆起东部的参参1井。锆石微量元素数据表明，所有样品均为岩浆岩，稀土元素配分模式相似，均为Ce正异常（δCe=5.06 ~ 134），Eu负异常（δEu=0.06 ~ 0.55），并富集重稀土元素。在25个颗粒中，一致年龄分为3组：300.4± 1.3Ma（n=11）、339.2± 2.7Ma（n=3）和392.0± 1.7Ma（n=8）。其余3个颗粒的206 Pb/238 U年龄分别为510±7、488±6和453±6 Ma。最年轻的和谐年龄（即，300.4±1.3 Ma），这与巴塔玛依内山组上部的取样位置一致。另一方面，奥陶纪和早泥盆世等年龄与盆地周围岛弧火山岩（富集Pb）或蛇绿岩的年龄一致。早、中古生代锆石的正Hf（t）值（+3.6 ~+10.5）可能表明，火山岩所穿越的基底时代可能是古生代，由残留洋壳和岛弧杂岩形成。晚古生代（~ 300.4Ma）锆石的δ Hf（t）值（+4.2 ~+17.1）表明玄武岩岩浆来源于软流圈地幔或亏损岩石圈地幔的部分熔融。这些岩浆受到早-中古生代物质的轻微混染。晚石炭世玄武岩代表了后碰撞构造背景下上地壳幔源岩浆的直接喷发。因此，我们认为大陆地壳的大规模垂直生长发生在晚石炭世之前。
An internal structural study was conducted to investigate U-Pb age, trace elements and Hf isotopes of basaltic zircons from the Batamayineishan Formation. The basalt was obtained from drill well San-Can 1 on the eastern Luliang uplift within the Junggar Basin. Trace element data of zircons show that all samples are magmatic, with similar REE patterns, including positive Ce (δCe=5.06–134), but negative Eu (δEu=0.06⦒0.55) anomalies and enrichment in heavy rare earth elements. Among 25 grains, the concordant ages were subdivided into three groups; ages of 300.4±1.3 Ma (n=11), 339.2±2.7 Ma (n=3) and 392.0±1.7 Ma (n=8). Three remaining grains were nearly concordant, with206Pb/238U ages of 510±7, 488±6 and 453±6 Ma, respectively. The youngest concordant age (i.e., 300.4±1.3 Ma) could be interpreted as the formation age of the studied basaltic rock; this is consistent with the sampling position at the upper part of the Batamayineishan Formation. On the other hand, ages such as Ordovician and early Devonian are consistent with the ages of island-arc volcanic rocks (enrichment in Pb) or ophiolites around the basin. Moreover, the positiveɛHf(t) values of the early and middle Paleozoic zircons (+3.6–+10.5) may suggest that the basement traversed by the studied volcanic rocks may be Paleozoic in age, formed from the residual oceanic crust and island-arc complex. TheɛHf(t) values (+4.2–+17.1) of the late Paleozoic (∼300.4 Ma) zircons suggest that the basaltic magmas were derived from partial melting of the asthenospheric mantle or depleted lithospheric mantle. These magmas were slightly contaminated by the existence of early-middle Paleozoic materials. The late Carboniferous basalts represent direct eruption of mantle-derived magmas at the upper crustal level during a post-collisional tectonic setting. We therefore consider that extensive vertical growth of the continental crust to have occurred before the late Carboniferous.