Characteristics and tectonic setting of the shoshonite rock association
Characteristics and tectonic setting of the shoshonite rock association
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DOI：
10.1016/0024-4937(80)90067-5
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发表时间：
1980-01
期刊：
影响因子：
3.5
通讯作者：
G. Morrison
中科院分区：
文献类型：
--
作者：
G. Morrison
对钾玄岩主要产状的回顾表明，有一组接近硅饱和、富钾且铁富集程度低，不能明确地归类为钙碱性或碱性玄武岩组合的一部分。这一组在这里被称为钾玄岩岩石组合。橄榄玄岩岩石组合的特征是：紫苏辉石-橄榄石规范玄武岩，低铁富集，高Na 2 O + K2 O，高含量的轻离子亲石元素，高但可变的Al 2 O3，高Fe 2 O3/FeO和低TiO 2。矿物学特征包括：基质中斜长石和透长石共存，斜长石斑晶上有钾长石镶边，斜长石An 50 − 85 Ab 40 − 15 Or 10 − 0和低TiO 2含量，单斜辉石中缺乏铁富集。大陆边缘的钾玄岩比高钾钙碱性岩或钙碱性岩套更年轻，地层更高，离海沟更远，但岩套之间存在完整的递变。在一些岛弧中也有类似的分带现象。在其他岛弧有没有空间分带的套房，但连续更多的富钾熔岩以上不断陡峭的俯冲带产生。陡化导致俯冲带的“失败”或翻转以及弧内的隆起和块断。钾玄岩最常与这一阶段的岛弧发育有关。
A review of the major occurrences of shoshonitic rocks suggests there is a group that is near-silica saturated, K-rich and has low iron enrichment that cannot be unambigously classified as part of calc-alkaline or alkali-basalt associations. This group is here referred to as the shoshonite rock association. The shoshonite rock association is characterised by: hypersthene-olivine normative basalts, low iron enrichment, high Na2O + K2O, high content of light ion lithophile elements, high but variable Al2O3, high Fe2O3/FeO and low TiO2. Mineralogical characteristics include: coexisting plagioclase and sanidine in the groundmass, K-feldspar rims on plagioclase phenocrysts, plagioclase An50−85Ab40−15Or10−0and low TiO2content and lack of iron enrichment in clinopyroxene. Shoshonitic rocks on continental margins are younger, stratigraphically higher and more distant from the oceanic trench than the high-K calc-alkaline or calc-alkaline suites, but there is a complete gradation between the suites. A similar zonation occurs in some island arcs. In other island arcs there is no spatial zonation of the suites but successively more K-rich lavas are produced above an ever steepening subduction zone. Steepening leads to ‘failure’ or flipping of the subduction zone and uplift and block faulting within the arc. Shoshonitic rocks are most commonly associated with this phase of island are development.