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首页> 外文期刊>Contributions to Mineralogy and Petrology >Acigöl rhyolite field, central Anatolia (part II): geochemical and isotopic (Sr–Nd–Pb, δ18O) constraints on volcanism involving two high-silica rhyolite suites
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Acigöl rhyolite field, central Anatolia (part II): geochemical and isotopic (Sr–Nd–Pb, δ18O) constraints on volcanism involving two high-silica rhyolite suites

机译：安纳托利亚中部阿西格尔流纹岩场（第二部分）：地球化学和同位素（Sr–Nd–Pb，δ 18 O）对火山活动的约束，涉及两个高硅质流纹岩套件

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摘要

The Acigöl rhyolite field erupted the most recent high-silica rhyolites within the Cappadocian Volcanic Province of central Anatolia, Turkey. It comprises two sequences of domes and pyroclastic rocks with eruption ages of ~150–200 ka (eastern group) and ~20–25 ka (western group). Compositionally, the eastern rhyolite group lavas are less evolved (SiO2 = 74–76 wt%), whereas the western group has higher silica abundance (SiO2 = ~77 wt%) with extremely depleted feldspar-compatible trace elements. Within each group, compositional variability is small and 143Nd/144Nd (0.51257–0.51265) and Pb isotope compositions (206Pb/204Pb = 18.87–18.88, 207Pb/204Pb = 15.65–15.67 and 208Pb/204Pb = 38.94–38.98) are homogeneous. The western group rhyolites have δ18O(zircon) overlapping mantle values (5.7 ± 0.2‰), whereas eastern group rhyolites are enriched in δ18O by ~0.5‰, consistent with a tendency to lower εNd values. By contrast, western group rhyolites have markedly more radiogenic 87Sr/86Sr ratios (0.7065–0.7091) compared to those of the eastern group (0.7059–0.7065). The presence of angular granitic xenoliths and a correlation between hydration (based on loss on ignition data) and 87Sr/86Sr in the western lavas, however, indicates that Sr was added during the eruption or post-eruption alteration. Isotope constraints preclude the possibility that the rhyolite magmas formed by partial melting of any known regional crystalline basement rocks. Basalts and andesites erupted in the periphery of the Acigöl field are characterised by 87Sr/86Sr ratios between 0.7040 and 0.7053, 143Nd/144Nd = 0.51259–0.51300, 206Pb/204Pb = 18.85–18.87, 207Pb/204Pb = 15.646–15.655, 208Pb/204Pb = 38.90–38.97. The isotopic and trace element data favour an origin of the rhyolites by mixing of basaltic/andesitic magmas with minor amounts of crustal melts and followed by extensive fractional crystallization.
机译：Acigöl流纹岩场喷发了土耳其中部安纳托利亚中部卡帕多西亚火山省内最新的高硅质流纹岩。它包括圆顶和火山碎屑岩的两个序列，喷发年龄为〜150–200 ka（东部组）和〜20–25 ka（西部组）。从成分上讲，东部流纹岩组熔岩的演化较少（SiO 2 = 74–76 wt％），而西部组的二氧化硅丰度较高（SiO 2 =〜77 wt％） ％）与长石兼容的痕量元素耗尽。在每个组中，组成变异性很小， 143 Nd / 144 Nd（0.51257–0.51265）和Pb同位素组成（ 206 Pb / 204 Pb = 18.87–18.88， 207 Pb / 204 Pb = 15.65–15.67和 208 Pb / 204 Pb = 38.94–38.98）是同质的。西部流纹岩的δ 18 O（锆石）地幔重叠值（5.7±0.2‰），而东部流纹岩的δ 18 O富集约0.5‰，与降低εNd值的趋势一致。相比之下，与东部组（0.7059-0.7065）相比，西部组流纹岩的放射源 87 Sr / 86 Sr比率（0.7065-0.7091）明显更多。西部熔岩中存在角状花岗岩异岩和水化（基于点火数据的损失）与 87 Sr / 86 Sr之间的相关性表明，Sr是在喷发或喷发后更改期间添加。同位素约束排除了流纹岩岩浆通过任何已知的区域性结晶基底岩石部分熔融而形成的可能性。 Acigöl场外围喷出的玄武岩和安山岩的特征是 87 Sr / 86 Sr比值介于0.7040和0.7053之间， 143 Nd / < sup> 144 Nd = 0.51259–0.51300， 206 Pb / 204 Pb = 18.85–18.87， 207 Pb / 204 Pb = 15.646–15.655， 208 Pb / 204 Pb = 38.90–38.97。同位素和微量元素数据通过将玄武岩/安山岩岩浆与少量地壳熔体混合，然后进行广泛的分步结晶，有利于流纹岩的起源。

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