Detrital zircon ages of Proterozoic meta-sedimentary rocks and Paleozoic sedimentary cover of the northern Yili Block: Implications for the tectonics of microcontinents in the Central Asian Orogenic Belt
Detrital zircon ages of Proterozoic meta-sedimentary rocks and Paleozoic sedimentary cover of the northern Yili Block: Implications for the tectonics of microcontinents in the Central Asian Orogenic Belt
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DOI：
10.1016/j.precamres.2014.07.018
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发表时间：
2014-10
影响因子：
3.8
通讯作者：
Hongsheng Liu;Bo Wang;L. Shu;B. Jahn;Yoshiyuki Lizuka
中科院分区：
文献类型：
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作者：
Hongsheng Liu;Bo Wang;L. Shu;B. Jahn;Yoshiyuki Lizuka
中亚造山带是世界上最大的增生造山带之一。它主要由岛弧、增生楔和微大陆混合而成。揭示前寒武纪大陆块体的起源，对于认识中国大陆的构造格局和地球动力学演化具有重要意义。为了更好地了解北天山伊力地块北部前寒武纪变质沉积岩和晚古生代未变形砂岩的区域构造演化，本文对其进行了碎屑锆石U-Pb年龄测定。来自温泉变质杂岩（WMC）的两个云母片岩样品显示出相似的锆石年龄分布模式，峰值分别为~ 0.43 Ga、~ 0.54 Ga、~ 0.65 ~ 0.68 Ga、~ 0.74 ~ 0.79 Ga、~ 0.89 ~ 0.92 Ga、~ 1.3 ~ 1.55 Ga和~ 1.69 ~ 1.70 Ga。在单个样品中也分别识别出了~ 1.1和~ 2.2 Ga的小年龄峰。中元古代长城系一千层岩的碎屑锆石年龄主要在855 ~ ~ 1500 Ma之间，在~ 906 Ma有单峰。根据锆石年代学资料和相应的CL图像分析，云母片岩和千层岩的原岩沉积时间应分别晚于645 Ma和850 Ma，并在志留纪中晚期经历了中、低度变质作用。变质沉积物的年龄模式与附近的花岗质和高变质岩的年龄模式吻合较好，表明碎屑锆石颗粒主要来源于局部变质/结晶基底。在云母片岩中发现了年龄较大的锆石（~ 1.0 ~ 2.2 Ga），而在千层岩中却没有这样的锆石群，这说明：(1)云母片岩和千层岩的原岩来源不同，沉积时间不同；(2)伊利地块北部可能存在中元古代至古元古代的岩石。三个未变形的砂岩样品在~ 368-376 Ma之间产生一致的单一年龄峰，仅含有少量元古代碎屑锆石颗粒。峰值年龄与邻近的中国北天山晚古生代弧岩浆岩年龄一致。因此，砂岩可能沉积于泥盆世晚期至石炭世早期的弧前或弧间盆地，其周围元古代基底未暴露或完全隔离。通过对其与周边克拉通和微陆块锆石年龄格局的对比，得出：(1)北部伊利地块具有与中国中天山和吉尔吉斯北天山相似的元古代基底；(2)这些微陆块与塔里木克拉通同源，但与西伯利亚克拉通有所区别。
The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens in the world. It was formed mainly by amalgamation of island arcs, accretionary wedges and microcontinents. Revealing the origins of the Precambrian continental blocks is essential for the understanding of the tectonic framework and geodynamic evolution of the CAOB. In this paper we present detrital zircon U–Pb ages of Precambrian meta-sedimentary rocks and late Paleozoic undeformed sandstone from the northern Yili Block, Chinese North Tianshan, in order to better understand the regional tectonic evolution. Two mica-schist samples from the Wenquan Metamorphic Complex (WMC) show similar zircon age distribution patterns with peaks at ∼0.43 Ga, ∼0.54 Ga, ∼0.65–0.68 Ga, ∼0.74–0.79 Ga, ∼0.89–0.92 Ga, ∼1.3–1.55 Ga and ∼1.69–1.70 Ga, respectively. Minor age peaks of ∼1.1 and ∼2.2 Ga are also separately recognized in individual samples. A phyllite from the Mesoproterozoic Changcheng System yielded detrital zircon ages mainly ranging from 855 to ∼1500 Ma with a single peak at ∼906 Ma. According to the analysis of age data and corresponding CL images of the dated zircon grains, protoliths of the mica-schists and phyllite should have deposited later than 645 Ma and 850 Ma, respectively, and were subjected to medium- to low-grade metamorphism during mid-late Silurian time. The good agreement between the age patterns of the meta-sediments and those of the nearby granitic and high-grade metamorphic rocks of the WMC indicates that the detrital zircon grains were mainly derived from the local metamorphic/crystalline basement. Occurrence of much older zircons (∼1.0–2.2 Ga) in the mica-schists and absence of such zircon populations in the phyllite suggest that (1) the protoliths of the mica-schists and phyllite had distinct sources and were deposited at different time, and (2) Mesoproterozoic to Paleoproterozoic rocks probably existed in the northern Yili Block. Three undeformed sandstone samples yielded consistent single age peak at ∼368–376 Ma and contain only a few Proterozoic detrital zircon grains. The peak age is in agreement with ages of neighboring late Paleozoic arc magmatic rocks in the Chinese North Tianshan. Thus, the sandstone was probably deposited during latest Devonian to earliest Carboniferous time in a forearc or interarc basin, around which Proterozoic basement was not exposed or completely isolated. A comparison between the zircon age patterns of the northern Yili Block and the surrounding cratons and microcontinents leads us to conclude that (1) the northern Yili Block had a Proterozoic basement similar to that of the Chinese Central Tianshan and Kyrgyz North Tianshan, and (2) these microcontinental blocks share the same origin as the Tarim Craton, but are distinguished from the Siberian Craton.