The nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge 33–35N: A Sr-Nd-Hf isotopic perspective
The nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge 33–35N: A Sr-Nd-Hf isotopic perspective
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大西洋中脊 33°35°以下上地幔异质性的性质和起源：Sr-Nd-Hf 同位素视角
DOI：
10.1016/j.gca.2021.05.033
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发表时间：
2021
影响因子：
5
通讯作者：
Wang Xiaohong
中科院分区：
文献类型：
--
作者：
Guo Pengyuan;Niu Yaoling;Sun Pu;Zhang Junjie;Chen Shuo;Duan Meng;Gong Hongmei;Wang Xiaohong
我们提出了新的Sr-Nd-Hf同位素数据的洋中脊玄武岩从两个脊段（OH-1，OH-3）之间的海洋学家和海耶斯断裂带在大西洋中脊33-35°N限制的性质和起源的上地幔不均匀性下大西洋中脊。与主要和微量元素数据一起（Niu等人，2001），新的Sr-Nd-Hf同位素数据表明，这些熔岩的地幔来源包括三个组成部分，即，具有高放射成因Hf同位素组成（ADM）的亏损地幔，具有放射成因Sr和非放射成因Nd-Hf同位素组成的不相容元素富集组分（E-I型），以及具有放射成因Sr-Nd-Hf同位素组成的不相容元素亏损组分（即，E型II）。ADM和E-I型组分分别代表了在增厚的大洋岩石圈底部发育的古地幔熔融残留物和交代脉。独特的E-II型组件是最好的解释为最近的地幔熔融残留物的地球化学富集地幔，可能与亚速尔群岛地幔柱以北。综上所述，我们解释E-MORB为主的OH-1熔岩作为一个相对较高程度的熔融的地幔源的ADM基质和E-I型材料组成的，而N-MORB为主的OH-3熔岩作为一个较低程度的熔融的地幔源主要包括ADM和E-II型组件。这样的岩石学和地球化学的理解解释了地壳厚度的对比，脊形态和层析成像，地幔布格异常之间的两个脊段。
We present new Sr-Nd-Hf isotopic data on mid-ocean ridge basalts from two ridge segments (OH-1, OH-3) between the Oceanographer and Hayes fracture zones at the Mid-Atlantic Ridge 33–35°N to constrain the nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge. Together with the major and trace elements data (Niu et al., 2001), the new Sr-Nd-Hf isotopic data illustrate that the mantle sources of these lavas comprise three components, i.e., a depleted mantle with high radiogenic Hf isotopic compositions (ADM), an incompatible elemental enriched component with radiogenic Sr and un-radiogenic Nd-Hf isotopic compositions (E-type I), and an incompatible element depleted component with variably enriched Sr-Nd-Hf isotope compositions (i.e., E-type II). The ADM and E-type I components may be understood as representing ancient mantle melting residues and metasomatic veins developed at the base of the thickening oceanic lithosphere, respectively. The unique E-type II component is best explained as recent mantle melting residues of a geochemically enriched mantle, probably associated with the Azores mantle plume to the north. Taking together, we interpret the E-MORB dominated OH-1 lavas as resulting from a relatively higher degree melting of a mantle source composed of ADM matrix and E-type I material, whereas the N-MORB dominated OH-3 lavas resulting from lower degree melting of the mantle source primarily comprising ADM and E-type II components. Such a petrological and geochemical understanding explains the contrast in crustal thickness, ridge morphology and tomography, and mantle Bouguer anomalies between the two ridge segments.