Radiogenic isotopes in enriched mid-ocean ridge basalts from Explorer Ridge, northeast Pacific Ocean
Radiogenic isotopes in enriched mid-ocean ridge basalts from Explorer Ridge, northeast Pacific Ocean
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东北太平洋探险家海脊富集的洋中脊玄武岩中的放射性同位素
DOI：
10.1016/j.gca.2017.06.032
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发表时间：
2017
影响因子：
5
通讯作者：
S. Scott
中科院分区：
文献类型：
--
作者：
B. Cousens;D. Weis;M. Constantin;S. Scott
与岩浆供应变化有关的地形极端梯度在南探索者海岭（SER）上观察到，该海岭是胡安德富卡海岭系统北方的一部分。我们报告了24个玄武岩全岩和玻璃样品的放射性同位素（Pb，Sr，Nd，Hf）和地球化学数据，这些样品是从SER的长度和Explorer Deep（SER北部的裂谷）中采集的。SER的熔岩形成南北地球化学梯度，在北方轴向高点以E-MORB为主，并从T-MORB到N-MORB向洋脊的南部最深处变化。MORB沿着洋脊不相容元素比值与同位素比值之间的线性关系与洋脊下岩浆的混合一致，从而产生从E-到N-MORB的地理梯度。E-MORB具有高Sr和Pb，低Nd和Hf同位素比值，典型的富集地幔，包括FOZO或HIMU同位素组分。胡安·德富卡海岭北方的西谷和奋进段也包括这种同位素成分，但在SER玄武岩中FOZO或HIMU成分的比例更为极端。FOZO或HIMU组分可能是含石榴子石的橄榄岩，或嵌入橄榄岩中的石榴子石辉石岩。石榴辉石岩的闪烁更好地解释了极浅的SER轴向高、高Nb/La和La/Sm以及“富集”的同位素组成。
Extreme gradients in topography related to variations in magma supply are observed on the Southern Explorer Ridge (SER), part of the northern Juan de Fuca ridge system. We report radiogenic isotope (Pb, Sr, Nd, Hf) and geochemical data for twenty-four basalt whole-rock and glass samples collected from the length of the SER and from Explorer Deep, a rift to the north of the SER. Lavas from the SER form a north-south geochemical gradient, dominated by E-MORB at the northern axial high, and range from T-MORB to N-MORB towards the southern deepest part of the ridge. Linear relationships between incompatible element ratios and isotopic ratios in MORB along the ridge are consistent with mixing of magmas beneath the ridge to generate the geographic gradient from E- to N-MORB. The E-MORB have high Sr and Pb, and low Nd and Hf isotopic ratios, typical of enriched mantle that includes a FOZO or HIMU isotopic component. The West Valley and Endeavour segments of the northern Juan de Fuca ridge also include this isotopic component, but the proportion of the FOZO or HIMU component is more extreme in the SER basalts. The FOZO or HIMU component may be garnet-bearing peridotite, or a garnet pyroxenite embedded in peridotite. Recycled garnet pyroxenite better explains the very shallow SER axial high, high Nb/La and La/Sm, and the “enriched” isotopic compositions.