Geochemistry and Sr‐Nd isotopes of the Late Mesozoic lamprophyres in the Chaohu area, eastern China: Petrogenesis and tectonic implications
Geochemistry and Sr‐Nd isotopes of the Late Mesozoic lamprophyres in the Chaohu area, eastern China: Petrogenesis and tectonic implications
复制标题
中国东部巢湖地区晚中生代煌斑岩地球化学和Sr-Nd同位素：岩石成因及构造意义
作者：
Mo Chen;Longming Li;Tianxiang Kan;Hang Liu;Xilin Zhao;Jiahao Li;Xu Han
下扬子区巢湖地区广泛分布着晚中生代的层状化石。这些幔源岩对认识中国东部晚中生代地幔源区特征和构造环境具有重要意义。巢湖地区的石首鱼可分为两类。I型层状陶瓷具有低SiO2（43.8-44.5重量%）和TiO 2（1.06- 1.14wt%），高MgO（13.5- 17.5wt.%）相容元素含量高，富集LREE和LILE，亏损HFSE。它们具有高的初始87 Sr/86 Sr（0.70767-0.70904）和负的εNd（t）（−4.8-−4.4）。II型层状陶瓷的特征在于低含量的SiO2（43.0-45.4重量%），高TiO 2（1.74- 2.55wt.%），MgO（9.17-15.4重量%），兼容的元素。它们也富含LREE和LILE，但缺乏HFSE。它们显示出富集的Sr-Nd同位素组成，初始87 Sr/86 Sr值（0.70773-0.70886）和εNd（t）值（−8.6-−7.8）。与II型层状矿物相比，I型层状矿物显示出更高的Mg#和MgO含量，但TiO 2显著更低。此外，I型层状岩体具有相对相似的初始87 Sr/86 Sr比值，但εNd（t）值高于II型层状岩体。I型和II型纹层的地球化学特征的差异可能是由含角闪石的石榴二辉橄榄岩地幔的不同程度的部分熔融造成的。岩石圈地幔被晚白垩世期间古太平洋板块俯冲回退引起的流体交代。
Late Mesozoic lamprophyres are widespread in the Chaohu area of the Lower Yangtze region, eastern China. These mantle‐derived rocks are of great significance for understanding the characteristics of mantle source and tectonic environment of eastern China during the Late Mesozoic. The lamprophyres from the Chaohu area can be divided into two types. The type‐I lamprophyres have low SiO2(43.8–44.5 wt.%) and TiO2(1.06–1.14 wt.%), high MgO (13.5–17.5 wt.%) and high contents of compatible elements, and are enriched in LREE and LILE but depleted in HFSE. They have high initial87Sr/86Sr (0.70767–0.70904) and negative εNd (t) (−4.8 to −4.4). The type‐II lamprophyres are characterized by low contents of SiO2(43.0–45.4 wt.%), high TiO2(1.74–2.55 wt.%), MgO (9.17–15.4 wt.%), and compatible elements. They are also enriched in LREE and LILE but depleted in HFSE. They show enriched Sr‐Nd isotopic compositions with initial87Sr/86Sr values (0.70773–0.70886) and εNd (t) values (−8.6 to −7.8). The type‐I lamprophyres show higher Mg#and MgO contents but significant lower TiO2than the type‐II lamprophyres. In addition, the type‐I lamprophyres have relatively similar initial87Sr/86Sr ratios but higher εNd(t) values than the type‐II lamprophyres. The difference of geochemical characteristics between the type‐I and type‐II lamprophyres may be caused by different degrees of partial melting of an amphibole‐bearing garnet lherzolite mantle. The lithospheric mantle was metasomatised by the fluids caused by the rollback of the Paleo‐Pacific plate subduction during the Late Cretaceous.