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首页> 外文期刊>Contributions to Mineralogy and Petrology >Origin of rhyolite and rhyodacite lavas and associated mafic inclusions of Cape Akrotiri, Santorini: the role of wet basalt in generating calcalkaline silicic magmas
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Origin of rhyolite and rhyodacite lavas and associated mafic inclusions of Cape Akrotiri, Santorini: the role of wet basalt in generating calcalkaline silicic magmas

机译：圣托里尼阿克罗蒂里角流纹岩和流纹岩熔岩以及相关的镁铁质包裹体的起源：湿玄武岩在生成钙碱性硅质岩浆中的作用

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摘要

Amphibole-bearing mafic inclusions (low to medium-K high-alumina basalt to basaltic andesite) comprise 4.1 vol% of calc-alkaline rhyolite and rhyodacite lavas on Akrotiri Peninsula, Santorini, Greece. Physical features indicate a magmatic origin for the inclusions, involving mingling with the host silicic magma and quenching. Water contents of the mafic magmas are estimated to have been above 4% at water pressures of 1.8 kbars or more at temperatures of approximately 950-1,000 ℃. Three evolutionary stages are inferred in their petrogenesis. In the first stage infiltration of slab fluids promotes partial melting in the mantle to generate primitive wet basaltic magmas enriched in LREE, LILE, Th and U in comparison to N-type MORB. In the second stage storage and crystal differentiation of primitive magmas occurred in the lithospheric mantle or deep crust, involving olivine, spinel and clinopyroxene followed by amphibole and plagioclase. In the third stage differentiated mafic magma intrudes into porphyritic silicic magma at shallower crustal levels (estimated at 7-10 km). Mingling and quenching of the mafic magmas within the silicic host causes chemical or physical interactions between the inclusions and the host prior to and during eruption. The silicic lavas have geochemical affinities with the mafic inclusions, but are relatively depleted in MREE, HREE and Y and enriched in Rb relative to Ba and K. These observations are consistent with involvement of amphibole in magma genesis due either to crystal differentiation from wet basalt or to partial melting of mafic rocks with residual amphibole. Crystallization of wet basalt in the deep crust is preferred on the basis of physical considerations.
机译：含闪石的镁铁质包裹体（低至中等K的高铝玄武岩至玄武质安山岩）占希腊圣托里尼Akrotiri半岛的钙碱性流纹岩和流纹岩熔岩的4.1％（体积）。物理特征表明夹杂物的岩浆成因，包括与基质硅质岩浆混合并淬灭。在约950-1,000℃的温度下，当水压为1.8 kbars或更高时，铁镁质岩浆的含水量估计已超过4％。在其成岩作用中推断出三个进化阶段。在第一阶段，与N型MORB相比，平板流体的渗透促进了地幔的部分熔融，从而产生了富含LREE，LILE，Th和U的原始湿玄武岩浆。在第二阶段，原始岩浆的储集和晶体分化发生在岩石圈地幔或深地壳中，涉及橄榄石，尖晶石和斜辉石，然后是闪石和斜长石。在第三阶段，分化的铁镁质岩浆侵入到地壳浅层的斑状硅质岩浆（估计为7-10 km）。硅质基质中镁铁质岩浆的混合和淬灭会在喷发之前和爆发期间引起夹杂物和基质之间的化学或物理相互作用。硅质熔岩与镁铁质包裹体具有地球化学亲和力，但相对于Ba和K而言，MREE，HREE和Y相对贫乏，且Rb富集。这些观察结果与闪石参与岩浆成因相符，这归因于湿玄武岩的晶体分化或使镁铁质岩石与残留的角闪石部分融化。基于物理考虑，优选地壳中湿玄武岩的结晶。

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