Mid-Neoproterozoic amphibolite facies metamorphism at the northern margin of the Yangtze craton
Mid-Neoproterozoic amphibolite facies metamorphism at the northern margin of the Yangtze craton
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扬子克拉通北缘中新元古代角闪岩相变质作用
DOI：
10.1016/j.precamres.2017.10.010
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发表时间：
2017-10
期刊：
影响因子：
--
通讯作者：
陈龙耀
中科院分区：
文献类型：
--
作者：
胡娟;l刘晓春;曲玮;陈龙耀
新元古代扬子克拉通大陆边缘的构造背景长期以来一直存在争议。斗岭杂岩是扬子克拉通北部的一小段结晶基底；其研究可能为了解该地区的构造演化提供有用的见解。在本文中，我们报告了都灵杂岩中发生的中级区域变质作用。岩相结构和矿物成分表明，都灵杂岩的角闪岩相岩石经历了从十字石-蓝晶石级到硅线石级的渐进变质演化。传统的地温气压测量将前变质阶段的 P-T 条件定义为 490–560°C 和 6–7.5kbar，而高峰变质阶段的 P–T 条件为 630–720°C 和 8–11kbar。峰后演化的特点是减压和热弛豫。来自石榴子角闪岩和变泥岩的变质锆石以及来自非同步变形伟晶岩荚的岩浆锆石产生的 U-Pb 年龄在 820±5Ma 和 779±3Ma 之间，其中两个种群的年龄约为 1000±5Ma。 820–815Ma 和约。分别为 790–780Ma。来自变泥岩的黑云母还给出了两个 40Ar/39Ar 平台年龄，分别为 814±4Ma 和 790±5Ma。据推测，变质作用高峰发生在大约。 820–815Ma，随后的冷却发生在大约。 790–780Ma。考虑到斗岭杂岩独特的前寒武纪地壳历史，以及伴随顺时针P-T路径的中级角闪岩相变质作用，我们认为这些观测结果为新元古代中期小斗岭地块与扬子克拉通北缘的碰撞提供了证据。这次碰撞之后，沿着扬子克拉通北部可能立即形成了新增生的安第斯型活动大陆边缘。
The tectonic setting of the continental margin of the Yangtze craton during the Neoproterozoic has long been a subject of debate. The Douling Complex is a small segment of crystalline basement in the northern Yangtze craton; the study of which may provide useful insights into the tectonic evolution of this area. In this paper we report medium-grade regional metamorphism that occur in the Douling Complex. Petrographical textures and mineral compositions suggest that amphibolite facies rocks from the Douling Complex underwent a progressive metamorphic evolution from staurolite–kyanite grade to sillimanite grade. Conventional geothermobarometry definesP–Tconditions to be 490–560 °C and 6–7.5 kbar for prograde metamorphic stage and 630–720 °C and 8–11 kbar for peak metamorphic stage. The post-peak evolution is characterized by decompression and thermal relaxation. Metamorphic zircons from garnet amphibolites and metapelites and magmatic zircons from asyn-deformed pegmatite pod yield U–Pb ages between 820 ± 5 Ma and 779 ± 3 Ma, with two populations at ca. 820–815 Ma and ca. 790–780 Ma, respectively. Biotites from metapelites also give two40Ar/39Ar plateau ages of 814 ± 4 Ma and 790 ± 5 Ma. It is inferred that peak metamorphism occurred at ca. 820–815 Ma and subsequent cooling took place at ca. 790–780 Ma. Considering the distinct Precambrian crustal history of the Douling Complex, together with medium-grade amphibolite facies metamorphism accompanied by a clockwiseP–Tpath, we propose that these observations provide evidence for the collision of the small Douling block with the northern margin of the Yangtze craton during the Mid-Neoproterozoic. Immediately after this collision, a newly accreted Andean-type active continental margin may have formed along the northern Yangtze craton.
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