Early Cretaceous subduction of Paleo-Pacific Ocean in the coastal region of SE China: Petrological and geochemical constraints from the mafic intrusions
Early Cretaceous subduction of Paleo-Pacific Ocean in the coastal region of SE China: Petrological and geochemical constraints from the mafic intrusions
复制标题
DOI：
10.1016/j.lithos.2019.03.010
复制
发表时间：
2019-06
期刊：
影响因子：
3.5
通讯作者：
Bo Zhang;F. Guo;Xiaobing Zhang;Yangming Wu;Guoqing Wang;Liang Zhao
中科院分区：
文献类型：
--
作者：
Bo Zhang;F. Guo;Xiaobing Zhang;Yangming Wu;Guoqing Wang;Liang Zhao
中国东南部中生代构造岩浆活动一直被认为与古太平洋俯冲作用有关。然而，缺乏强有力的岩石学和地球化学证据，从俯冲有关的镁铁质火成岩重建俯冲带的架构。本文综合了中国东南沿海早白垩世三个镁铁质侵入体（平潭、戴千山和泉州）的岩石学、矿物化学、锆石U-Pb年龄、斜长石和全岩Sr、Pb同位素组成、微量元素和Sr-Nd-Pb-Hf同位素数据，旨在了解它们与古太平洋俯冲作用的成因联系。镁铁质岩石主要由钙质角闪石和富钙斜长石组成，并显示出不同程度的晶体堆积。岩石学观察和质量平衡计算表明，其母岩浆为含水钙碱性岩浆，具有典型的弧型微量元素特征。这些岩石还具有“类地壳”同位素特征，即，中度放射成因Sr、非放射成因Nd和高度放射成因Pb成分。在现场斜长石Sr和Pb同位素比值和几乎相同的同位素组成之间的斜长石和散装岩石在每个入侵的狭窄的变化表明，在岩浆演化过程中的地壳同化的一个小角色。相反，这种“壳状”同位素特征主要是由于通过俯冲沉积物的输入源富集。进一步的元素同位素模拟结果表明，母岩浆可能是由熔融的亏损地幔源通过俯冲沉积物衍生的熔体交代。因此，早白垩世镁铁质侵入体的产生可以解释为一个相对较热的大洋板片俯冲，在此期间，来自俯冲沉积物的熔体作为一个主要的代理人，以丰富地幔楔。我们的研究结果提供了强有力的岩石学和地球化学约束下的早白垩世俯冲的古太平洋之下的中国东南部，并建议，增加俯冲沉积物来源的熔体可能是一个重要的机制，地幔富集在相对较热的俯冲带。
The Mesozoic tectono-magmatism in SE China has widely been considered to relate to subduction of the Paleo-Pacific Ocean. However, there lacks robust petrologic and geochemical evidence from subduction-related mafic igneous rocks to reconstruct the architecture of the subduction zone. This paper presents a comprehensive geochemical dataset (petrography, mineral chemistry, zircon U-Pb age, in-situ Sr and Pb isotope compositions of plagioclase and whole-rock major, trace element and Sr-Nd-Pb-Hf isotope data) of three early Cretaceous (Pingtan, Daiqianshan and Quanzhou) mafic intrusions from the coastal region in SE China, with aims to understand their petrogenetic link with subduction of the Paleo-Pacific Ocean. The mafic rocks comprise predominantly calcic hornblende and Ca-rich plagioclase and show varying degrees of crystal accumulation. Petrological observations and mass balance calculation indicate their parental magmas are hydrous and calc-alkaline with typical arc-type trace element features. These rocks are also characterized by “crust-like” isotopic signatures, i.e., moderately radiogenic Sr, unradiogenic Nd and highly radiogenic Pb compositions. The narrow variations of in-situ plagioclase Sr and Pb isotope ratios and the nearly identical isotope compositions between the plagioclase and bulk rock in each intrusion indicate a minor role of crustal assimilation during magmatic evolution. Instead, such “crust-like” isotopic signatures were largely resulted from source enrichment through an input of subducted sediment. Further element-isotopic modeling results suggest that the parental magmas were likely produced by melting of a depleted mantle source metasomatized via the subducted sediment-derived melt. Generation of the early Cretaceous mafic intrusions can thus be explained by subduction of a relatively hot oceanic slab, during which melt derived from the subducted sediment acted as a predominant agent to enrich the mantle wedge. Our results provide powerful petrological and geochemical constraints on the early Cretaceous subduction of the Paleo-Pacific Ocean beneath the SE China and suggest that addition of subducted sediment-derived melt may be an important mechanism for mantle enrichment in relatively hot subduction zones.