Abstract The geochemical signatures of subducting crust have been identified in various types of mafic igneous rocks at convergent plate boundaries, where island arc basalts (IAB) and continental arc andesite are accepted as the typical products of subduction zone magmatism. These crustal signatures are commonly represented not only by enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to normal mid-ocean ridge basalts (MORB), but also by enrichment in radiogenic Sr isotopes but depletion in radiogenic Nd isotopes relative to the primitive mantle. Such enriched signatures also occur in oceanic island basalts (OIB) and their continental counterparts, but their origin has been controversial in igneous petrology. The present review focuses on the origin of enriched signatures in mafic igneous rocks above subduction zones. Although these mafic rocks are distributed in both interplate and intraplate areas, they are generally categorized into two series according to their trace element distribution patterns in the primitive mantle-normalized diagram. One is IAB-like series, showing enrichment in LILE, Pb and LREE but depletion in HFSE such as Nb and Ta relative to heavy rare earth elements (HREE). The other is OIB-like series, exhibiting enrichment in LILE and LREE, enrichment or non-depletion in high field strength elements (HFSE) but depletion in Pb relative to HREE. In either series, these mafic igneous rocks show enhanced enrichment of LILE and LREE with increasing their incompatibility relative to normal MORB, indicating the presence of crustal materials in these mafic igneous rocks. Inspection of the mass balance in major and trace elements between source and product indicates that subducting crustal rocks were not directly incorporated into the mantle sources of both series. Instead, they underwent metamorphic dehydration and partial melting at different depths to produce liquid phases, which dominate the budget of fluid- to melt-mobile elements and their pertinent radiogenic isotopes in the mantle sources. As a consequence, the composition of liquid phases is a key to the geochemical composition of both series. Therefore, the crustal materials are transferred by the liquid phases via metasomatic reactions into the mantle sources at the slab-mantle interface in subduction channels. As such, the difference in the geochemical transfer from the subducting crust into the mantle can account for the difference in the composition between the interplate IAB-like and intraplate OIB-like series. This provides a holistic model for the origin of both IAB- and OIB-like series mafic igneous rocks above subduction zones.

中文翻译：

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俯冲带上方基性岩浆作用的化学地球动力学

摘要 在会聚板块边界的各种基性火成岩中已经识别出俯冲地壳的地球化学特征，其中岛弧玄武岩（IAB）和大陆弧安山岩被认为是俯冲带岩浆作用的典型产物。这些地壳特征通常不仅表现为大离子亲石元素 (LILE) 和轻稀土元素 (LREE) 相对于正常洋中脊玄武岩 (MORB) 的富集，而且还表现为放射性 Sr 同位素的富集但放射性同位素的耗尽相对于原始地幔的 Nd 同位素。这种丰富的特征也出现在大洋岛玄武岩 (OIB) 及其大陆玄武岩中，但它们的起源在火成岩岩石学中一直存在争议。本综述的重点是俯冲带上方镁铁质火成岩中富集特征的起源。这些基性岩虽然分布在板间区和板内区，但在原始地幔-归一化图中，根据其微量元素分布规律，一般可分为两大系列。一个是类IAB系列，相对于重稀土元素（HREE），LILE、Pb和LREE富集，而HFSE（如Nb和Ta）则缺乏。另一个是OIB-like系列，表现出LILE和LREE富集，高场强元素（HFSE）富集或非贫化，但Pb相对于HREE贫化。在任一系列中，这些镁铁质火成岩显示出 LILE 和 LREE 的富集增强，并且它们相对于正常 MORB 的不相容性增加，表明这些镁铁质火成岩中存在地壳物质。对源和产物之间主量元素和微量元素质量平衡的检查表明，俯冲地壳岩石没有直接纳入两个系列的地幔源。相反，它们在不同深度经历了变质脱水和部分熔融以产生液相，这些液相在地幔源中支配着流体到熔体移动元素及其相关放射性同位素的预算。因此，液相的组成是两个系列地球化学组成的关键。因此，地壳物质通过交代反应被液相转移到俯冲通道板片-地幔界面的地幔源中。因此，从俯冲地壳到地幔的地球化学转移的差异可以解释板间IAB类和板内OIB类系列之间的成分差异。这为俯冲带上方的 IAB 和 OIB 类系列基性火成岩的起源提供了一个整体模型。