大别造山带白垩纪花岗岩对太古宙基底的再造:来自U-Pb年代学、Sr-Nd-Hf同位素的证据
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1.中国地质调查局武汉地质调查中心,湖北武汉;2.中国地质调查局武汉地质调查中心;3.云南大学地球科学学院

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中国地质调查局项目(编号:DD20190050, DD20221634)与中国地质调查局花岗岩成岩成矿地质研究中心开放基金(课题号:PMGR202002)资助


Reconstruction of Archaean basement in the Dabie orogen: constraints from geochronology and Sr-Nd-Hf isotope of the Early Cretaceous Daqishan granite
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1.Wuhan Center of Geological Survey, China Geological Survey;2.School of Earth Sciences, Yunnan University

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    摘要:

    本文对大别山南部大崎山花岗岩进行了系统的野外调查、岩石学、地球化学、锆石U-Pb和Sr-Nd-Hf同位素研究。锆石U-Pb结果显示大崎山花岗岩侵位于早白垩世,其年龄为124~120 Ma。样品具有较高的SiO2(69.3%~75.2%)、Al2O3(13.4%~15.3%)和全碱(7.94%~8.71%)含量,较低的MgO(0.23%~0.84%)、TiO2(0.16%~0.49%)与TFeO(1.05%~2.66%)含量,A/CNK=1.01~1.03,显示弱过铝质特征。岩石富集大离子亲石元素(如Rb、K、Pb)、轻稀土元素以及Th、U等,亏损高场强元素(如Nb、Ta、Ti)、重稀土元素以及Sr和Ba,具有明显Eu负异常(δEu = 0.34~0.52),属于高钾钙碱性的I型花岗岩,这些地球化学特征表明研究区花岗岩经历了以斜长石、钾长石和磷灰石为主的分离结晶作用。它们的锆石εHf(t)值为–32.9~–15.2,对应tDM2为3258~2140 Ma,而全岩εNd(t)为–22.5~–15.8,对应tDM2=2754~2209 Ma,指示其岩浆源区主要为古老地壳物质。样品中含有大量的~2.65 Ga继承锆石,锆石εHf(t)为–7.3~3.6,显示与贾庙地区2.65~2.63 Ga片麻状花岗岩有良好的亲缘性。大崎山地区花岗岩可能源自北大别太古宙基底的再造,其源区还存在年轻地壳物质的参与,可能形成于古太平洋板块的俯冲板片在130 Ma后快速后撤的伸展背景。

    Abstract:

    We present detailed geochronological, geochemical and Sr-Nd-Hf isotopic data for the late Mesozoic granitic rocks in the Daqishan region of the Dabie orogen. LA-ICP-MS U-Pb dating indicates that the Daqishan granites formed in the Early Cretaceous with an age of 124~120 Ma. These granites have high SiO2 (69.3%~75.2%),Al2O3 (13.4%~15.3%), and a total alkali of Na2O+K2O(7.94%~8.71%) with A/CNK=1.01~1.03, low MgO(0.23%~0.84%), TiO2(0.16%~0.49%) and TFeO(1.05%~2.66%). In addition , these granites are distinctively enriched in LILE and LREE,depleted in HSFE, HREE, with obvious negative Eu anomaly(δEu = 0.34~0.51), belonging to calc-alkaline I-type granite. The parental magmas were likely experienced fractional crystallization of plagioclase, K-feldspar and apatite. The Cretaceous zircons have negative εHf(t) values and εNd(t),ranging from -32.9 to -15.2 and -22.5 to -15.8,with corresponding tDM2 of 3258 Ma to 2140 Ma and 2754 Ma to 2209 Ma, indicating a significant ancient materials involved in the Cretaceous magmatism. Because of approximate U-Pb age and Hf isotopic composition, it is speculated that the inherit zircons of ~2.65 Ga in Daqishan granites have a certain genetic relationship with the granites of 2.65~2.63 Ga in Jiamiao area. The Daqishan granites may have been generated from the partial melting of Archean crust in the Dabie orogen, and were dominated by the extensional regime in the middle-late Mesozoic relating to the westward subduction of the Pacific plate.

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  • 收稿日期:2022-05-07
  • 最后修改日期:2022-08-03
  • 录用日期:2022-09-13
  • 在线发布日期: 2022-12-15
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