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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Geochemical and petrological constraints on rear-arc magma genesis processes in Ecuador: The Puyo cones and Mera lavas volcanic formations
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Geochemical and petrological constraints on rear-arc magma genesis processes in Ecuador: The Puyo cones and Mera lavas volcanic formations

机译：厄瓜多尔弧后岩浆成因过程的地球化学和岩石学约束：Puyo锥体和Mera熔岩火山形成

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The Puyo scoria cones and the Mera lava flows, two newly recognized volcanic formations dated between Late Pliocene to Middle Pleistocene, extend the limits of the Ecuadorian rear-arc volcanic province some 100 km to the south. The Puyo scoria cones have erupted K-rich absarokites containing olivine, diopside and phlogopite, whereas the Mera lava flows display a basic andesite composition, with olivine and minor augite phenocrysts. In addition to high contents in L1LE, LREE and HFSE, the Puyo absarokites exhibit many characteristics of primitive melts, namely high Cr (590-310 ppm) and Ni (330-154 ppm) contents, high Mg# (64-70) and they contain forsteritic olivine (Fo_(82-89))- The composition of the most primary Puyo absarokite was used in petrogenetic models, in order to constrain the genesis of these high-K magmas. Major and trace elements models, as well as isotopic data, indicate that the source of Puyo magmas is a hydrated phlogopite-and garnet-bearing lherzolite. Phlogopite crystallization in the mantle wedge is triggered by the metasomatism by 3-5% of a SiO_(2~-), H_2O-rich liquid generated by slab melting. Partial melting of the subducted oceanic crust beneath Ecuador is allowed by the subduction of the young and warm Carnegie Ridge, which modifies the thermal regime of the Benioff zone. A low degree (1-4%) of partial melting of the metasomatized mantle wedge, leaving a variable garnet (4-7%) ±phlogopite (0-4%) lherzolitic residual assemblage, leads to the compositions of the entire Puyo absarokite series and is consistent with previous petrogenetic models developed for the Ecuadorian volcanic arc. Indeed, the homogeneity of isotopic data across the arc suggests a similar source for the whole Ecuadorian magmas.
机译：Puyo火山岩锥和Mera熔岩流是两个新近认可的火山岩层，形成于上新世晚期至中更新世之间，将厄瓜多尔后弧火山省的范围向南延伸了约100公里。 Puyo火山灰岩喷发了富含钾的辉石岩，其中含有橄榄石，透辉石和金云母，而Mera熔岩流显示出基本的安山岩成分，并带有橄榄石和次要的辉石隐晶。除了在L1LE，LREE和HFSE中含量高之外，普约（Puyo）赤铁矿还具有许多原始熔体的特征，即高Cr（590-310 ppm）和Ni（330-154 ppm）含量，高Mg＃（64-70）和它们包含镁橄榄石（Fo_（82-89））-在成岩模型中使用了最主要的Puyo滑石的成分，以限制这些高K岩浆的成因。主要和微量元素模型以及同位素数据表明，Puyo岩浆的来源是含水化金云母和石榴石的锂铁矿。板坯融化产生的SiO_（2〜-），富含H_2O的SiO_（2〜-），富含H_2O的液体通过交代作用触发了地幔楔中的金云母结晶。新生而温暖的卡内基岭的俯冲作用使得厄瓜多尔下方俯冲的洋壳部分融化，这改变了贝尼奥夫地区的热力状态。交化后的地幔楔的部分熔融程度低（1-4％），留下了可变的石榴石（4-7％）±金云母（0-4％）的沸石残留组合物，导致整个Puyo钠铅矿系列的成分并与先前为厄瓜多尔火山弧开发的成岩模型一致。确实，整个弧线同位素数据的同质性​​表明整个厄瓜多尔岩浆的来源相似。

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