Zircon U–Pb and trace element data from rocks of the Huai’an Complex: New insights into the late Paleoproterozoic collision between the Eastern and Western Blocks of the North China Craton
Zircon U–Pb and trace element data from rocks of the Huai’an Complex: New insights into the late Paleoproterozoic collision between the Eastern and Western Blocks of the North China Craton
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DOI：
10.1016/j.precamres.2010.01.007
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发表时间：
2010-04
影响因子：
3.8
通讯作者：
Jing Wang;Y. Wu;Shan Gao;M. Peng;Xiaochi Liu;Laishi Zhao;Lian Zhou;Z. Hu;H. Gong;
中科院分区：
文献类型：
--
作者：
Jing Wang;Y. Wu;Shan Gao;M. Peng;Xiaochi Liu;Laishi Zhao;Lian Zhou;Z. Hu;H. Gong;
横贯华北造山带（TNCO）被解释为一个陆-陆碰撞带，离散的太古宙东西陆块沿此沿着拼合形成华北陆块的基底。其形成的时间尚未得到精确的限制。选取华北地台北方段淮安杂岩中的5个高级变质岩和1个伟晶岩脉共6个样品进行了锆石U-Pb定年和微量元素分析。英云闪长岩-奥长花岗岩-花岗闪长岩（TTG）片麻岩和高压（HP）镁铁质麻粒岩样品中含有岩浆锆石核，其原岩形成年龄分别为2503±17和1964± 38 Ma。两套变质沉积岩中岩浆成因的碎屑锆石U-Pb年龄为2683±22 ~ 1964± 13 Ma，具有一致或中等不一致的特征，表明它们主要来源于TNCO，部分可能来源于华北太古代陆壳岩石。TTG片麻岩和两种变质沉积岩中的变质锆石表现出低重稀土含量、平坦的重稀土配分模式和负Eu异常，表明它们与石榴子石和长石形成于麻粒岩相环境。HP基性麻粒岩中的变质锆石和TTG片麻岩中的浅色体样品也具有亏损的HREE含量，平坦的HREE模式，但只有弱的负Eu异常，这也可能指示麻粒岩相条件下形成的，而弱Eu异常可能是由于全岩成分。所有这些变质锆石的形成温度为702-749°C，接近该地区高压麻粒岩的峰值变质温度。他们有相同的年龄。1845 Ma是淮安杂岩高压麻粒岩相变质作用的最佳估计年龄。这些结果证实了前人提出的华北地块东西部在沿着TNCO上发生晚古元古代碰撞的模式。另一方面，部分变质锆石呈平面或多边形分带，高Th、U含量和高Th/U比值，高稀土含量和陡的重稀土配分模式，表明它们是在部分熔融过程中结晶的，石榴子石大量分解。它们的加权平均年龄为1819± 13 Ma，我们认为这是退变质作用的时间。结合前人的研究结果，认为该地区高级变质岩中的变质锆石有3个年龄峰值，分别为1876±6，1849±2，1814± 4 Ma。这些可能表明一个长期的事件或至少三个“高峰”的变质作用。切割镁铁质麻粒岩柱面理的伟晶岩脉的年龄为1806± 15 Ma，标志着淮安地区东西陆块碰撞的结束。
The Trans-North China Orogen (TNCO) is interpreted as a continent–continent collisional belt along which the discrete Archean Eastern and Western Blocks amalgamated to form the basement of the North China Craton. The timing of its formation has not been precisely constrained yet. Six samples, including five high-grade metamorphic rocks and a pegmatite dike, from the Huai’an Complex in the northern segment of the TNCO were selected for zircon U–Pb dating and trace element analysis. A tonalite-trondhjemite-granodiorite (TTG) gneiss sample and a high-pressure (HP) mafic granulite sample contain magmatic zircon cores, yielding protolith formation ages of 2503±17 and 1964±38Ma, respectively. Detrital zircons of magmatic origin in two metasedimentary rocks show concordant or moderately discordant U–Pb ages of 2683±22 to 1964±13Ma, indicating that they were mainly derived from the TNCO with some possibly derived from the Archean continental rocks of the North China Craton. Metamorphic zircons in the TTG gneiss and two metasedimentary rocks exhibit low HREE contents, flat HREE patterns and negative Eu anomalies, implying their formation coeval with garnet and feldspar under grannulite-facies conditions. Metamorphic zircons in an HP mafic granulite and a sample of leucosome from a TTG gneiss also have depleted HREE contents, flat HREE patterns, but only weak negative Eu anomalies, which may also indicate formation under granulite-facies conditions, whereas the weak Eu anomalies may be due to the whole-rock composition. All these metamorphic zircons have formation temperatures of 702–749°C, approaching the peak metamorphic temperatures of HP granulite rocks in this area. They have identical ages of ca. 1845Ma within analytical errors, which is the best estimate age for HP granulite-facies metamorphism of the Huai’an Complex. These results confirm previous models proposing late Paleoproterozoic collision between the Eastern and Western Blocks of the North China Craton along the TNCO. On the other hand, some metamorphic zircons in the leucosome sample show planar or polygonal zoning, high Th, U contents and high Th/U ratios, high REE contents and steep HREE patterns, indicating that they crystallized during partial melting with abundant garnet decomposition. They yielded a weighted mean age of 1819±13Ma, which we interpret to register the time of retrograde metamorphism. Combined with previously published data, there are three age peaks at 1876±6, 1849±2, and 1814±4Ma for metamorphic zircons from high-grade metamorphic rocks in the TNCO. These may indicate either a protracted event or at least three ‘peaks’ of metamorphism. A pegmatite dike cutting the foliation of a mafic granulite boudin was dated at 1806±15Ma, which signifies termination of collision between the Eastern and Western Blocks in the Huai’an area.