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首页> 外文期刊>Contributions to Mineralogy and Petrology >The importance of fractional crystallization and magma mixing in controlling chemical differentiation at Suphan stratovolcano, eastern Anatolia, Turkey
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The importance of fractional crystallization and magma mixing in controlling chemical differentiation at Suphan stratovolcano, eastern Anatolia, Turkey

机译：土耳其安那托利亚东部素攀层火山的分级结晶和岩浆混合对控制化学分化的重要性

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摘要

Suphan is a 4,050 m high Pleistocene-age stratovolcano in eastern Anatolia, Turkey, with eruptive products consisting of transitional calc-alkaline to mildly alkaline basalts through trachyandesites and trachytes to rhyolites. We investigate the relative contributions of fractional crystallization and magma mixing to compositional diversity at Suphan using a combination of petrology, geothermometry, and melt inclusion analysis. Although major element chemistry shows near-continuous variation from basalt to rhyolite, mineral chemistry and textures indicate that magma mixing played an important role. Intermediate magmas show a wide range of pyroxene, olivine, and plagioclase compositions that are intermediate between those of basalts and rhyolites. Mineral thermometry of the same rocks yields a range of temperatures bracketed by rhyolite (～750°C) and basalt (～1,100°C). The linear chemical trends shown for most major and trace elements are attributed to mixing processes, rather than to liquid lines of descent from a basaltic parent. In contrast, glassy melt inclusions, hosted by a wide range of phenocryst types, display curved trends for most major elements, suggestive of fractional crystallization. Comparison ofthese trends to experimental data from basalts and trachyandesites of similar composition to those at Suphan indicates that melt inclusions approximate true liquid lines of descent from a common hydrous parent at pressures of ～500 MPa. Thus, the erupted magmas are cogenetic, but were generated at depths below the shallow, pre-eruptive magma storage region. We infer that chemical differentiation of a mantle-derived basalt occurred in the mid- to lower crust beneath Suphan. A variety of more and less evolved melts with >55 wt% SiO_2 then ascended to shallow level where they interacted. The presence of glomerocrysts in many lavas suggests that cogenetic plutonic rocks were implicated in the interaction process. Blending of diverse, but cogenetic, minerals, and melts served to obscure the true liquid lines of descent in bulk rocks. The fact that chemical variation in melt inclusions preserves deep-seated chemical differentiation indicates that inclusions were trapped in phenocrysts prior to shallow-level blending. Groundmass glasses evolved after mixing and display trends that are distinct from those of melt inclusions.
机译：Suphan是位于土耳其安那托利亚东部的一个4,050 m高的更新世时代的平流层火山，喷发产物包括钙钙盐过渡到轻质碱性玄武岩，经钙锰铁矿和钙钛矿到流纹岩。我们结合岩石学，地热测定法和熔体夹杂物分析方法，研究了素攀的部分结晶和岩浆混合对成分多样性的相对贡献。尽管主要元素化学成分从玄武岩到流纹岩几乎连续变化，但矿物化学成分和质地表明岩浆混合起着重要作用。中间岩浆表现出范围广泛的辉石，橄榄石和斜长石组成，介于玄武岩和流纹岩之间。相同岩石的矿物测温法得出的温度范围由流纹岩（〜750°C）和玄武岩（〜1100°C）包围。对于大多数主要元素和痕量元素显示的线性化学趋势归因于混合过程，而不是来自玄武岩母体的液体下降线。相比之下，玻璃状熔体夹杂物（由广泛的表晶类型组成）显示出大多数主要元素的弯曲趋势，暗示了部分结晶。将这些趋势与组成与素攀相似的玄武岩和菱锰铁矿的实验数据进行比较表明，熔体夹杂物在〜500 MPa的压力下近似于一个普通含水母体的真实下降液体线。因此，喷出的岩浆是共生的，但产生于浅层，喷发前的岩浆储存区以下的深度。我们推断，地幔衍生的玄武岩的化学分化发生在素攀下方的中下地壳。各种> 55 wt％SiO_2的或多或少析出的熔体随后在相互作用的地方上升到较浅的水平。在许多熔岩中均存在肾小球隐隐现象，这表明共生的深成岩与相互作用过程有关。多种多样但共生的矿物和熔体的混合作用掩盖了散装岩石中真实的下降液体线。熔融夹杂物中的化学变化保留了深层次的化学差异这一事实表明，在浅层混合之前，夹杂物被困在了隐晶中。混合后，地物玻璃演化并显示出与熔融夹杂物截然不同的趋势。

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