Fine-scale isotopic variation in Mariana Trough basalts: evidence for heterogeneity and a recycled component in backarc basin mantle
Fine-scale isotopic variation in Mariana Trough basalts: evidence for heterogeneity and a recycled component in backarc basin mantle
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DOI：
10.1016/0012-821x(90)90188-4
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发表时间：
1990-10
影响因子：
5.3
通讯作者：
A. Volpe;J. Macdougall;G. W. Lugmair;J. Hawkins;P. Lonsdale
中科院分区：
文献类型：
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作者：
A. Volpe;J. Macdougall;G. W. Lugmair;J. Hawkins;P. Lonsdale
在17°40′N和18°30°N之间的马里亚纳海槽中，通过对轴向脊进行疏浚，用阿尔文和精细尺度取样，发现了同位素组成介于N型MORB和马里亚纳岛弧玄武岩之间的玄武岩。玄武岩成分受局部构造-形态控制;在Pagan变换和17°56′N洋脊偏移所界定的较深洋脊段发现了MORB类玄武岩，而从较浅洋脊向北的玄武岩是典型的马里亚纳海槽玄武岩（MTB），其成分介于两种端元岩石类型之间。弧后扩张中心的一个短段（100 km）内发现的具有如此多样同位素特征的玄武岩，限制了马里亚纳海槽地幔源区变异的化学特征和分布。Srsingle bondNdsingle bondPb同位素变异表明MTB源在单个熔融批次的尺度上是不均匀的。与MORB源区相似，MTB源区的主要成分为亏损橄榄岩。富集的成分，最明显的弧状玄武岩和密切混合在MTB，具有类似的马里亚纳弧玄武岩中观察到的同位素特征。同位素数据表明，马里亚纳轴脊玄武岩的源的变化可以解释混合弧状和MORB状地幔。我们推测，在弧后源区存在古老的大洋岩石圈碎片。这种岩石圈成分可能反映了早于弧后盆地裂谷作用的俯冲海底或弧前火山弧地幔的残余。
Fine-scale sampling withalvinand by dredging of the axial ridge in the Mariana Trough between 17°40′N and 18°30°N recovered basalts with isotopic compositions that span the range between N-type MORB and Mariana island arc basalts. There is a local tectonic-morphological control on basalt compositions; MORB-like basalts are found on the deeper ridge segment bounded by the Pagan transform and the ridge offset at 17°56′N, while basalts from the shallower ridge to the north are typical Mariana Trough basalts (MTB) having compositions intermediate between the two endmember rock types. Arc-like basalts were recovered from one site on the axial ridge.The discovery of basalts with such diverse isotopic characteristics from a short (100 km) section of this backarc spreading center constrains the chemical characteristics and distribution of mantle source variability in the Mariana Trough. Srsingle bondNdsingle bondPb isotopic variability suggests that the MTB source is heterogeneous on the scale of individual melt batches. The principal component in the MTB mantle source region is depleted peridotite similar to the source of MORB. The enriched component, most evident in the arc-like basalts and intimately mixed in MTB, has isotopic characteristics similar to those observed in the Mariana arc basalts. The isotopic data suggest that source variability for Mariana axial ridge basalts can be explained by mixed arc-like and MORB-like mantle. We hypothesize that there are fragments of old oceanic lithosphere in the backarc source region. This lithospheric component may reflect remnants of subducted seafloor or forearc-volcanic arc mantle that predate rifting in the backarc basin.