S. Whitley, R. Halama, R. Gertisser, T. Hansteen, M. Frische, Torsten Vennemann
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Oxygen isotope data of mineral separates and calculated δ18O melt values are in line with extensive closed-system fractional crystallisation at magmatic temperatures, without a requirement for extensive assimilation of the subvolcanic continental basement. The xenolith minerals compositionally overlap with phenocrysts from the volcanic rocks, but they also contain evidence for the presence of highly evolved melt compositions in the form of melt inclusions with extremely silica-rich compositions (up to 82 wt.% SiO2) and high enrichments of incompatible trace elements coupled with increasing negative Eu anomalies in clinopyroxenes. Since these characteristics correlate systematically with differentiation indices and rock type, they are interpreted to reflect melt evolution via fractional crystallisation as the dominant differentiation process with no significant role of reactive porous flow. These observations highlight that trapped melt fractions can influence mineral compositional variations in the plutonic xenoliths, and in turn the mineral compositions demonstrate a melt compositional variability not preserved in the volcanic rock record.","PeriodicalId":33053,"journal":{"name":"Volcanica","volume":"8 1","pages":""},"PeriodicalIF":2.5000,"publicationDate":"2024-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"A record of magmatic differentiation in plutonic xenoliths from Santorini (Greece)\",\"authors\":\"S. Whitley, R. Halama, R. Gertisser, T. Hansteen, M. Frische, Torsten Vennemann\",\"doi\":\"10.30909/vol.07.02.421446\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Plutonic xenoliths from volcanic arcs provide unique insights into transcrustal magmatic systems in subduction zone settings. 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引用次数: 0
摘要
火山弧的柱状异长岩为了解俯冲带环境中的跨地壳岩浆系统提供了独特的视角。在希腊爱琴海中部火山弧的圣托里尼火山,在过去约 360 ka 年内喷发的一系列熔岩和火成岩中都发现了柱状异长岩。它们在矿物学上各不相同,从透辉石到橄榄辉长岩、辉长岩、榴辉岩和闪长岩。根据矿物和熔融包裹体成分进行的热压计算表明,在浅地壳至中地壳深度(P < 400 兆帕)的一系列温度(1100 至 750 °C)范围内发生了平衡,但没有证据表明在较低地壳深度发生了结晶。矿物分离的氧同位素数据和计算出的δ18O熔体值与岩浆温度下广泛的封闭系统分块结晶相吻合,而不需要亚火山大陆基底的广泛同化。异岩石矿物在成分上与火山岩的表晶重叠,但它们也含有证据表明存在高度演化的熔体成分,其形式为熔体包裹体,具有极其丰富的二氧化硅成分(二氧化硅含量高达 82 wt.%)和高富集度的不相容微量元素,以及在闪长岩中不断增加的负 Eu 异常。由于这些特征与分异指数和岩石类型有系统的相关性,因此可以解释为它们反映了熔体通过部分结晶的演化过程,这是主要的分异过程,而反应性多孔流的作用并不显著。这些观察结果突出表明,被截留的熔体分馏可以影响柱状异长岩中矿物成分的变化,反过来,矿物成分也展示了火山岩记录中没有保留的熔体成分变化。
A record of magmatic differentiation in plutonic xenoliths from Santorini (Greece)
Plutonic xenoliths from volcanic arcs provide unique insights into transcrustal magmatic systems in subduction zone settings. At Santorini volcano in the Central Aegean Volcanic Arc (Greece), plutonic xenoliths occur throughout a sequence of lavas and pyroclastic rocks erupted within the last ~360 ka. They are mineralogically variable, ranging from troctolites to olivine gabbros, gabbros, gabbronorites, and diorites. Thermobarometric calculations based on mineral and melt inclusion compositions indicate equilibration over a range of temperatures (1100 to 750 °C) at shallow to mid-crustal depths (P <400 MPa), but there is no evidence for crystallisation at lower crustal depths. Oxygen isotope data of mineral separates and calculated δ18O melt values are in line with extensive closed-system fractional crystallisation at magmatic temperatures, without a requirement for extensive assimilation of the subvolcanic continental basement. The xenolith minerals compositionally overlap with phenocrysts from the volcanic rocks, but they also contain evidence for the presence of highly evolved melt compositions in the form of melt inclusions with extremely silica-rich compositions (up to 82 wt.% SiO2) and high enrichments of incompatible trace elements coupled with increasing negative Eu anomalies in clinopyroxenes. Since these characteristics correlate systematically with differentiation indices and rock type, they are interpreted to reflect melt evolution via fractional crystallisation as the dominant differentiation process with no significant role of reactive porous flow. These observations highlight that trapped melt fractions can influence mineral compositional variations in the plutonic xenoliths, and in turn the mineral compositions demonstrate a melt compositional variability not preserved in the volcanic rock record.