Back-arc basins
Back-arc basins
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DOI：
10.1007/978-1-4615-3540-9_10
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
A. Saunders;J. Tarney
中科院分区：
文献类型：
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作者：
A. Saunders;J. Tarney
正如这本书所说明的，大洋玄武岩的成分是多种多样的。这种多样性不仅来自于次火山岩浆房的低压分馏，而且还来自于伴随地幔熔融的固-液分馏。同位素和化学研究还揭示了大洋下地幔成分的总体不均匀性（第15章），反映了过去2.5 Ga甚至更长时间内的主要分化和再循环（如洋壳俯冲）。为了充分理解并评估所有这些因素，有必要研究许多构造环境中的玄武岩成因。对破坏性板块边界岩浆活动的研究提供了有关地壳再循环规模的重要信息，这可能会影响我们对地壳和地幔演化的理解。本章讨论一种特殊类型的大洋玄武岩，即在破坏性板块边界的伸展盆地中喷发的玄武岩。这些盆地通常被称为弧后盆地，通常被镁铁质洋壳包围，并通过类似于主要洋盆中发生的伸展和岩浆过程形成。一般而言，俯冲带上方岩石圈的伸展和分离使地幔橄榄岩上涌和俯冲。在其他条件相同的情况下，大多数硅酸盐在较低的压力下具有较低的熔点。因此，地幔可以上升到足够高的水平，达到熔点，尽管没有额外的热能输入。这将导致玄武岩（或类玄武岩）熔体的形成，与大洋中脊玄武岩（MORB）的形成方式大致相同。
As illustrated in this book, oceanic basalts are compositionally diverse. This diversity arises not only from low pressure fractionation in sub-volcanic magma chambers, but also during the solid-liquid fractionation that accompanies melting of the mantle. Isotopic and chemical studies also reveal gross heterogeneity in the composition of the sub-oceanic mantle (Chapter 15) reflecting major differentiation and recycling (eg subduction of oceanic crust) throughout the past 2.5 Ga, or even longer. To fully understand, and thus evaluate, all of these factors, it is necessary to study basalt genesis in many tectonic settings. The study of magmatism at destructive plate boundaries provides important information about the scale of crustal recycling, which may in time influence our understanding of the evolution of the crust and mantle.This chapter deals with a special type of oceanic basalt, namely that erupted within extensional basins at destructive plate boundaries. These basins, commonly termed back-arc basins, are often floored by mafic oceanic crust, and are formed by extensional and magmatic processes akin to those occurring in the major ocean basins. In general terms, extension and separation of the lithosphere above a subduction zone allows mantle peridotite to upwell and decompress. Other things being equal, most silicates have lower melting points at lower pressures. Thus, mantle may ascend to a sufficiently high level that its melting point is reached, despite there being no extra input of thermal energy. This will lead to the formation of basaltic (or basalt-like) melts, in much the same way that is envisaged for the formation of mid-ocean ridge basalts (MORB).