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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Silicic volcanism and back-arc extension related to migration of the Late Cainozoic Australian-Pacific plate boundary
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Silicic volcanism and back-arc extension related to migration of the Late Cainozoic Australian-Pacific plate boundary

机译：与晚新生代的澳大利亚-太平洋板块边界的迁移有关的硅质火山作用和弧后扩展

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The initial phases of large-scale silicic and bimodal volcanism within an active Miocene arc (Coromandel Volcanic Zone, CVZ) are preserved on several small islands in northern New Zealand. Major- and trace-element compositions classify the rocks as high-K, calc-alkaline, silicic lavas which have some of the low-ion lithophile element and high-field-strength element characteristics of convergent margin lavas. The silicic lavas (～12 Ma) are spatially associated with a relatively primitive basalt of similar age (12.06 +- 0.25 Ma), which is a sub-alkaline tholeiite with an anomalously high TiO_2 content and as such it is not a typical arc basalt. Isotopically, the samples indicate the presence of oceanic sediment in their petrogenesis. An explanation for the geochemical and isotopic compositions of the northern CVZ rocks involves migration of the Australian-Pacific convergent margin orientation from a north-south direction (Northland Volcanic Arc), through a northeast-southwest direction (CVZ), and finally subparallel to the orientation of the presently active Taupo Volcanic Zone. The silicic eruptives thereby preserve a trail of volcanic edifices within a back-arc basin. The edifice-trail exhibits a general northwest to southeast younging trend and lies perpendicular to the axis of the contemporaneous Coromandel Volcanic Arc. Late-Cainozoic migration of the convergent margin and subduction system is proposed as the mechanism for extension across the back-arc region of the CVZ, producing large-scale back-arc silicic volcanism, and minor associated basalts, perpendicular to the orientation of the main arc.
机译：活跃的中新世弧（Coromandel火山区，CVZ）内的大规模硅质和双峰火山的初始阶段保存在新西兰北部的几个小岛上。主要元素和微量元素组成将岩石分类为高钾，钙碱性，硅质熔岩，它们具有会聚边缘熔岩的一些低离子亲石元素和高场强元素特征。硅质熔岩（〜12 Ma）在空间上与相近年龄（12.06 +-0.25 Ma）的较原始玄武岩有关，后者是具有异常高的TiO_2含量的亚碱性辉绿岩，因此它不是典型的弧形玄武岩。同位素表明，岩石形成过程中存在海洋沉积物。对北部CVZ岩石的地球化学和同位素组成的解释涉及澳大利亚-太平洋会聚边缘取向从北-南方向（Northland Volcanic Arc）到东北-西南方向（CVZ）的迁移，最后与目前活跃的陶波火山带的方向。因此，硅质喷发物保留了弧后盆地内的一堆火山构造。大厦尾迹显示出西北向东南的总体年轻化趋势，并且垂直于同期的科罗曼德火山弧的轴线。提出了收敛边缘和俯冲系统的晚新生代运移，作为在CVZ背弧区域扩展，形成大规模背弧硅质火山岩和次要相关玄武岩的机制，垂直于主要盆地的方向弧。

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