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引用本文:朱清波,靳国栋,赵希林,张传林,舒徐洁,洪文涛. 赣北晚中生代岭上超镁铁岩的岩石成因:年代学与地球化学制约[J]. 中国地质, 2020, 47(4): 1092-1108.
ZHU Qingbo,JIN Guodong,ZHAO Xilin,ZHANG Chuanlin,SHU Xujie,HONG Wentao. Petrogenesis of the late Mesozoic Lingshang ultramafic intrusion in northern Jiangxi Province:Chronologic and geochemical constraints[J]. Geology in China, 2020, 47(4): 1092-1108(in Chinese with English abstract).
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赣北晚中生代岭上超镁铁岩的岩石成因:年代学与地球化学制约
朱清波1, 靳国栋1, 赵希林1, 张传林2, 舒徐洁1, 洪文涛1,3
1.中国地质调查局南京地质调查中心, 江苏 南京 210016;2.河海大学, 江苏 南京 210098;3.南京大学, 江苏 南京 210023
摘要:
华南内陆在晚中生代发生了广泛的岩石圈伸展减薄事件,赣北新余地区的岭上超镁铁岩体形成于(120.8±1.4)Ma的早白垩世晚期,其作为钦杭结合带东段早白垩世幔源岩浆活动的记录,是研究华南中部晚中生代地幔属性及地球深部动力学过程的良好对象。在系统分析岭上超镁铁质岩的LA-MC-ICP-MS锆石U-Pb年代学、Lu-Hf同位素和元素地球化学特征的基础上,探讨了该超镁铁质岩的源区特征及其所反映的大地构造背景。数据表明,岭上超镁铁岩在形成过程中未遭受明显的地壳混染,其MgO含量集中且与TiO2、Al2O3、Ni、Th等元素之间不存在明显的线性关系,反映该岩体未发生显著的结晶分异作用。但Mg#的变化范围和La-Sm分异程度反映堆晶作用和部分熔融可能对岩浆演化有所影响。稀土和微量元素(如Nb、Ta、Zr、Hf等)特征类似于板内玄武岩(OIB),低SiO2、高Ti、高Fe/Mn比值和Ni等特征均显示与软流圈地幔关系密切。但锆石εHft)(6.83~11.41)未达到亏损地幔的程度、Nb/Ta比值接近于岩石圈地幔值,且在相关元素图解中具尖晶石橄榄岩地幔源区低程度部分熔融的特征。反映岭上超镁铁岩可能是晚中生代陆内伸展背景下,上涌的软流圈物质与富集岩石圈地幔相互作用并发生部分熔融,深部超镁铁质岩浆沿构造薄弱带快速侵位的产物。
关键词:  超镁铁岩  晚中生代  岩石圈伸展减薄  OIB  地质调查工程  江西
DOI:10.12029/gc20200413
分类号:P597+.3;P595
基金项目:中国地质调查局项目“武夷山松溪—庆元地区区域地质调查”(DD20190045)资助。
Petrogenesis of the late Mesozoic Lingshang ultramafic intrusion in northern Jiangxi Province:Chronologic and geochemical constraints
ZHU Qingbo1, JIN Guodong1, ZHAO Xilin1, ZHANG Chuanlin2, SHU Xujie1, HONG Wentao1,3
1.China Geological Survey Nanjing Geological Survey Center, Nanjing 210016, Jiangsu, China;2.Hohai University, Nanjing 210016, Jiangsu, China;3.Nanjing University, Nanjing 210023, Jiangsu, China
Abstract:
Extensive lithospheric extensional thinning events occurred during the late Mesozoic in the interior of South China block. As a record of the early Cretaceous ((120.8±1.4)Ma) mantle-derived magmatic activities in the eastern part of the Qingzhou-Hangzhou juncture belt, the Lingshang ultramafic intrusion in Xinyu of northern Jiangxi is a good object for studying the mantle attribute and geodynamic process of the late Mesozoic in central South China. Based on a systematic analysis of the geochronology from La-MC-ICP-MS zircon U-Pb, Lu -hf isotopes and element geochemistry of the Lingshang ultramafic rocks, the authors investigated the intrusion, the source area characteristics of the ultramafic intrusion and the tectonic background reflected by them. Lingshang ultramafic intrusion suffered no significant crustal contamination. The content of MgO is concentrated with no obvious linear relationship with TiO2, Al2O3, Ni, Th, and some other components, implying no significant crystallization differentiation. However, the range of Mg# and La-Sm differentiation indicates that heap crystallization and partial melting might have exerted an effect on magmatic evolution. The characteristics of rare earth and trace elements (Nb, Ta, Zr, Hf, etc.) are similar to those of intraplate basalt (OIB), and the characteristics of low SiO2, high Ti, high Fe/Mn ratio and Ni are all closely related to asthenosphere mantle. However, the εHf(t) of zircons (6.83-11.41) are less than the value of the depleted mantle, and Nb/Ta ratios are close to the ratio of lithospheric mantle, suggesting low degree partial melting of spinel peridotite mantle source region in the relevant element diagram. All of these data suggest that the Lingshang ultramafic intrusion may be the result of the interaction between asthenosphere mantle and lithospheric mantle under the background of late Mesozoic intracontinental extension. The upwelling asthenosphere material led to the low-degree partial melting of the preexisting spinel peridotite mantle source area, and the deep ultramafic magma was emplaced rapidly along the tectonic weak zone to form the Lingshang ultramafic intrusion.
Key words:  ultramafic rocks  Late Mesozoic  lithospheric extensional thinning  OIB  geological survey engineering  Jiangxi Province