Detrital Zircon U-Pb Geochronology of the Xilin Group: Constraints for the Early Paleozoic Tectonic Evolution of the Songliao Massif,Acta Geologica Sinica-English Edition

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Detrital Zircon U-Pb Geochronology of the Xilin Group: Constraints for the Early Paleozoic Tectonic Evolution of the Songliao Massif
Acta Geologica Sinica-English Edition ( IF 3.5 ) Pub Date : 2021-03-24 , DOI: 10.1111/1755-6724.14684
Tianjiao SANG ₁ , Fuping PEI ₁ , Wenliang XU ₁ , Zhiwei WANG ₂ , Ji JIAO ₁ , Jingyang WEI ₁ , Yipeng WANG ₁

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The Xilin Group, composed of the Chenming, Laodaomiaogou, Qianshan and Wuxingzhen formations, is one of the Early Paleozoic terranes in the eastern Songliao Massif, mainly consisting of thick layers of fine clastic and carbonate rocks. This study presents LA-ICP-MS zircon U-Pb geochronological data for the Laodaomiaogou and Qianshan formations, further constraining their provenance and the Early Paleozoic tectonic evolution of the Songliao Massif on the eastern Central Asian Orogenic Belt. Most zircons from the Laodaomiaogou and Qianshan formations show magmatic oscillatory zoning and high Th/U ratios (0.26–2.41). Zircon U-Pb dating results indicate that the detrital zircons from the silty mudstone of the Laodaomiaogou Formation yield peak ages of 634 Ma, 775 Ma, 820 Ma, 880 Ma and 927 Ma, as well as multi-episodic Archean to Paleoproterozoic and Mesoproterozoic ages (1405–643 Ma), implying its deposition time is younger than ∼634 Ma. Furthermore, the occurrence of Early Cambrian fossils indicates that the Laodaomiaogou Formation was deposited during the late stage of the Early Cambrian (∼514 Ma). The zircons from the K-bentonite of the Qianshan Formation show four peak ages of 444 Ma, 471 Ma, 489 Ma and 518 Ma and the youngest age peak of 444 ± 4 Ma (n = 6) indicates that the Qianshan Formation was deposited during the Late Ordovician. In addition, the peak ages of the detrital zircons in the silty mudstone of the Qianshan Formation are 472 Ma and 498 Ma, as well as two other concordant points with ²⁰⁷Pb/²⁰⁶Pb apparent ages of 1824 Ma and 1985 Ma. The dating results in this study, together with published data, indicate the absence of Pan-African magmatic events in the Songliao Massif prior to the initial deposition of the Xilin Group, in contrast to those distributed widely in the Jiamusi Massif. Taken together, we conclude that the depositional provenance of the Laodaomiaogou and Qianshan formations was derived from the Songliao Massif. Furthermore, the characteristics of the detrital zircon age composition and rock associations indicate that the Laodaomiaogou Formation formed in a passive continental margin environment, in contrast to the Qianshan Formation, which formed in an active continental margin environment. The above results also imply that the Songliao and Jiamusi massifs might not have collided before the Late Ordovician.

中文翻译：

锡林群碎屑锆石U-Pb年代学：松辽地块早古生代构造演化的制约因素

锡林群由晨鸣组、老道庙沟组、潜山组和五行镇组组成，是松辽地块东部早古生代地体之一，主要由厚层细碎屑岩和碳酸盐岩组成。本研究提供了老道庙沟组和前山组的LA-ICP-MS锆石U-Pb年代学数据，进一步确定了它们的物源以及中亚造山带东部松辽地块的早古生代构造演化。老道庙沟组和千山组的锆石大多呈现岩浆振荡分带和高Th/U比（0.26-2.41）。锆石U-Pb定年结果表明，老道庙沟组粉砂质泥岩碎屑锆石的产峰年龄分别为634 Ma、775 Ma、820 Ma、880 Ma和927 Ma，以及多幕式太古宙至古元古代和中元古代（1405-643 Ma），表明其沉积时间小于~634 Ma。此外，早寒武世化石的出现表明老道庙沟组沉积于早寒武世晚期（～514 Ma）。千山组 K 膨润土锆石呈现 444 Ma、471 Ma、489 Ma 和 518 Ma 四个峰值年龄，最小年龄峰值为 444 ± 4 Ma (n = 6) 表明千山组沉积于晚奥陶世。此外，前山组粉砂质泥岩碎屑锆石的峰值年龄分别为472 Ma和498 Ma，另外还有2个与²⁰⁷ Pb/ ^{206一致的点。}1824 Ma 和 1985 Ma 的 Pb 表观年龄。本研究的测年结果和已发表的数据表明，在锡林群初始沉积之前，松辽地块中不存在泛非岩浆事件，而佳木斯地块中广泛分布的岩浆事件形成鲜明对比。综合来看，老道庙沟组和千山组的沉积物源来源于松辽地块。此外，碎屑锆石年龄组成和岩石组合特征表明，老道庙沟组形成于被动大陆边缘环境，而前山组形成于活跃大陆边缘环境。上述结果也暗示松辽地块和佳木斯地块在晚奥陶世之前可能没有发生碰撞。

更新日期：2021-03-24

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