扬子北缘后河杂岩花岗岩类及其对古元古代造山作用的响应
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P588.12+1

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国家自然科学基金项目(42172214);西北大学大陆动力学国家重点实验室科技部项目


Granitoids from Houhe Complex in northern margin of the Yangtze Block and their response to Paleoproterozoic orogeny
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    摘要:

    后河杂岩作为扬子北缘早前寒武纪基底岩石的重要组成部分,其岩石成因和构造背景尚不清楚,进而制约了对扬子北缘乃至整个扬子地块在古元古代时期的地质演化过程的理解。本文选取碑坝地区后河杂岩中的奥长花岗岩和二长花岗岩为研究对象,开展全岩主量、微量元素和Sm-Nd同位素、锆石U-Pb年代学及Lu-Hf同位素综合研究。U-Pb测年结果表明奥长花岗岩和二长花岗岩均形成于古元古代晚期,二者的结晶年龄分别为2 101±10 Ma和2 072±15 Ma。全岩主量、微量元素分析结果显示,奥长花岗岩具有高硅、富钠、低钾、贫镁的特征,属于准铝质-弱过铝质钙碱性I型花岗质岩石系列,且显示岛弧花岗岩的特征;锆石εHf(t)值为-0.8~+4.6,全岩εNd(t)值为+0.1~+1.1,两阶段Hf模式年龄(tDM2)为3 005~ 2 469 Ma。与奥长花岗岩相比,二长花岗岩具有相对较低的硅含量,但是相对富镁、铝和钾,属于弱过铝质的高钾钙碱性I型花岗岩。其稀土元素总量较高,轻、重稀土元素之间分异明显,伴随弱负Eu异常,并富集Rb、Ba、Th等大离子亲石元素,相对亏损Nb、Ta、Ti等高场强元素,亦具有岛弧花岗岩的特征。此外,该岩石具有较高的Mg#值以及Cr和Ni含量,锆石εHf(t)值为-2.9~+2.4,全岩εNd(t)值为+0.1~+0.9,两阶段Hf模式年龄(tDM2)为2 939~ 2 604 Ma。根据上述特征,推测奥长花岗岩主要是由新太古代玄武质大陆下地壳部分熔融形成的,其形成过程中经历了一定程度的分离结晶作用,而二长花岗岩是幔源岩浆底侵并导致新太古代古老大陆地壳部分熔融形成的,其中有岩石圈地幔物质的添加。结合扬子北缘已报道的古元古代晚期(2.1~2.0 Ga)镁铁质-长英质岩浆活动的时空分布和岩石成因,推测扬子北缘碑坝地区后河杂岩中2 101~2 072 Ma的花岗质岩石形成于活动陆缘弧环境,是扬子北缘对全球古元古代哥伦比亚超大陆聚合过程的响应。

    Abstract:

    The Houhe Complex is an important part of the early Precambrian basement rocks in northern margin of the Yangtze Block. However, its genesis and tectonic setting are still unclear, which restricted our understanding on the geological evolution of northern margin of the Yangtze Block and even the entire Yangtze Block during the Paleoproterozoic period. In this study, analyses of whole-rock major and trace elements, Sm-Nd isotopes, zircon U-Pb geochronology and in-situ Lu-Hf isotopes are performed on trondhjemite and monzogranite from the Houhe Complex in Beiba area, northern margin of the Yangtze Block. The U-Pb dating results show that the crystallization ages of trondhjemite and monzogranite are 2 101±10 Ma and 2 072±15 Ma, respectively. The trondhjemite samples exhibit the characteristics of high silicon and sodium, low potassium and magnesium. Most samples belong to metaluminous to weakly peraluminous and calc-alkaline I-type granitic rock series and exhibit characteristics of island arc granite. Their zircon εHf(t) values range from -0.8 to + 4.6, with whole-rock εNd(t) values ranging from +0.1 to +1.1 and two-stage Hf model ages (tDM2) ranging from 3 005 Ma to 2 469 Ma. In contrast, the monzogranite rocks show low silicon, but high magnesium, aluminum and potassium, belonging to weakly peraluminous and high-K calc-alkaline I-type granite. Their total rare earth element concentrations are relatively high. The differentiation between light and heavy rare earth elements is obvious, accompanied by weak negative Eu anomalies. The monzogranite rocks are also enriched in large ion lithophile elements (Rb, Ba and Th), and depleted in high field strength elements (Nb, Ta and Ti). They have high Mg# values, and Cr and Ni contents, with zircon εHf(t) values of - 2.9~+ 2.4, and whole-rock εNd(t) values of +0.1~+0.9 and two-stage Hf model ages (tDM2) of 2 939~2 604 Ma. All these data indicate that the trondhjemite was mainly produced by partial melting of Neoarchean basaltic rocks in the lower crust, with a certain degree of fractional crystallization. The monzogranite was generated by partial melting of ancient Neoarchean continental crust caused by underplating of mantle-derived magma, with addition of lithospheric mantle material. Considering the temporal and spatial distribution, and petrogenesis of the late Paleoproterozoic (2.1~2.0 Ga) mafic-felsic magmatic rocks reported in northern margin of the Yangtze block, it is supposed that the Paleoproterozoic (2 101~2 072 Ma) granitoid rocks from the Houhe Complex in Beiba area, northern margin of the Yangtze block, were formed under an active continental margin arc setting, related to convergent process of global Paleoproterozoic Columbia supercontinent.

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引用本文

李霄琦,赵燕,张瑞英,等, 2025. 扬子北缘后河杂岩花岗岩类及其对古元古代造山作用的响应[J]. 岩石矿物学杂志, 44(1):24~50.
LI Xiao-qi, ZHAO Yan, ZHANG Rui-ying, et al, 2025. Granitoids from Houhe Complex in northern margin of the Yangtze Block and their response to Paleoproterozoic orogeny[J]. Acta Petrologica et Mineralogica, 44(1): 24~50.

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  • 收稿日期:2024-04-24
  • 最后修改日期:2024-08-08
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  • 在线发布日期: 2025-01-15
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