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Geochronology, geochemistry, and tectonic implications of early Neoproterozoic granitic rocks from the eastern Beishan Orogenic Belt, southern Central Asian Orogenic Belt
Precambrian Research ( IF 3.8 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.precamres.2020.106016
Biren Wang , Xiaosong Yang , Shucai Li , Chao Teng , Xinjie Yang , Fuyong Huang , Xiaofei Zhang , Jun Cao , Yi Zhou , Huachuan Zhang , Jing Li

Abstract The distribution of Precambrian rocks and microcontinents is a key to understanding the architecture of the Beishan Orogenic Belt, southern Central Asian Orogenic Belt (CAOB). We present zircon U-Pb-Hf isotopic and whole-rock geochemical data for early Neoproterozoic granitic rocks from the eastern Shuangyingshan–Huaniushan Terrane in the Beishan Orogenic Belt. The zircon ages show that the granitic gneiss, the mylonitized granite, and the mylonitized monzonite formed at 895 Ma, 894 Ma, and 884 Ma, respectively. These ages confirm that the Shuangyingshan–Huaniushan Terrane is a microcontinental block and that Precambrian magmatic rocks are not restricted to the western Gubaoquan area. Both the gneiss and granite contain Al-rich muscovite, high SiO2 (69.59–78.10 wt%) contents, and show peraluminous features (molar Al2O3/(CaO + Na2O + K2O) values = 1.03–1.28), negative correlations of Th and Y with respect to Rb, typical features of S-type granites. The monzonite contains hornblende, and relatively low SiO2 (62.11–64.10 wt%), high CaO (5.33–5.41 wt%), Na2O (5.88–6.02 wt%), V and Cr contents, and low K2O/Na2O, Rb/Sr and Rb/Ba ratios, consistent with I-type granites. These studied granitic rocks are calc-alkaline to shoshonitic, and all exhibit similar LREE-enriched trace-element patterns, pronounced negative Eu anomalies, positive Rb, Th, U and K anomalies, negative Ba, Nb, Ta, Sr, P and Ti anomalies, evolved zircon eHf(t) values of −6.25 to + 1.09, and two-stage Hf model ages of 2.16–1.70 Ga. These characteristics suggest that they have mainly crustal sources, similar to coeval reported granitic rocks in the Beishan Orogenic Belt, and indicating an older crustal reworking event. The Precambrian basement of the Beishan Orogenic Belt shows evidence of Mesoproterozoic crustal growth and early Neoproterozoic crustal reworking, with zircon eHf(t) values plotting within the crustal evolution trend defined by 2.1–1.3 Ga crustal material, similar to the Yili, Central Tianshan and Northern Alxa blocks, and indicating an affinity with those blocks. Geochronological data from these blocks and terranes suggest that the southern CAOB contains an extensive assemblage of early Neoproterozoic magmatic rocks that are related to the assembly of Rodinia and can be trace over 2000 km as an east–west-trending belt.

中文翻译:

北山造山带东部、中亚造山带南部早新元古代花岗岩的年代学、地球化学和构造意义

摘要 前寒武纪岩石和微大陆的分布是了解北山造山带、中亚造山带南部(CAOB)结构的关键。我们提供了北山造山带双鹰山-花牛山地体东部早新元古代花岗岩的锆石U-Pb-Hf同位素和全岩地球化学数据。锆石年龄显示花岗片麻岩、糜棱花岗岩和糜棱二长岩分别形成于 895 Ma、894 Ma 和 884 Ma。这些年代证实了双鹰山-花牛山地块是一个微陆块,前寒武纪岩浆岩不仅限于古宝泉地区西部。片麻岩和花岗岩都含有富铝白云母,SiO2 (69.59–78.10 wt%) 含量高,并显示过铝质特征(摩尔 Al2O3/(CaO + Na2O + K2O) 值 = 1.03–1.28),Th 和 Y 与 Rb 的负相关,S 型花岗岩的典型特征。二长岩含有角闪石、相对较低的 SiO2 (62.11–64.10 wt%)、高 CaO (5.33–5.41 wt%)、Na2O (5.88–6.02 wt%)、V 和 Cr 含量,以及低 K2O/Na2O、Rb/Sr和 Rb/Ba 比值,与 I 型花岗岩一致。这些研究的花岗岩是钙碱性到钾长石质,都表现出类似的富含轻稀土的微量元素模式,显着的负 Eu 异常,正 Rb、Th、U 和 K 异常,负 Ba、Nb、Ta、Sr、P 和 Ti异常,演化的锆石 eHf(t) 值为 -6.25 至 + 1.09,两阶段 Hf 模型年龄为 2.16-1.70 Ga。这些特征表明它们主要具有地壳来源,与北山造山带同时期报道的花岗岩相似,表明发生了更古老的地壳改造事件。北山造山带前寒武纪基底显示出中元古代地壳生长和新元古代早期地壳改造的证据,锆石 eHf(t) 值绘制在由 2.1-1.3 Ga 地壳物质定义的地壳演化趋势内,类似于伊犁、中天山和北阿拉善区块,并表示与这些区块的亲和力。来自这些地块和地体的年代学数据表明,CAOB 南部包含大量新元古代早期岩浆岩组合,这些岩浆岩与 Rodinia 的组合有关,可以追溯到 2000 多公里,是一条东西走向的带。北山造山带前寒武纪基底显示出中元古代地壳生长和新元古代早期地壳改造的证据,锆石 eHf(t) 值绘制在由 2.1-1.3 Ga 地壳物质定义的地壳演化趋势内,类似于伊犁、中天山和北阿拉善区块,并表示与这些区块的亲和力。来自这些地块和地体的年代学数据表明,CAOB 南部包含大量新元古代早期岩浆岩组合,这些岩浆岩与 Rodinia 的组合有关,可以追溯到 2000 多公里,是一条东西走向的带。北山造山带前寒武纪基底显示出中元古代地壳生长和新元古代早期地壳改造的证据,锆石 eHf(t) 值绘制在由 2.1-1.3 Ga 地壳物质定义的地壳演化趋势内,类似于伊犁、中天山和北阿拉善区块,并表示与这些区块的亲和力。来自这些地块和地体的年代学数据表明,CAOB 南部包含大量新元古代早期岩浆岩组合,这些岩浆岩与 Rodinia 的组合有关,可以追溯到 2000 多公里,是一条东西走向的带。中天山和北阿拉善地块,并表明与这些地块的亲和力。来自这些地块和地体的年代学数据表明,CAOB 南部包含大量新元古代早期岩浆岩组合,这些岩浆岩与 Rodinia 的组合有关,可以追溯到 2000 多公里,是一条东西走向的带。中天山和北阿拉善地块,并表明与这些地块的亲和力。来自这些地块和地体的年代学数据表明,CAOB 南部包含大量新元古代早期岩浆岩组合,这些岩浆岩与 Rodinia 的组合有关,可以追溯到 2000 多公里,是一条东西走向的带。
更新日期:2021-01-01
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