Evolution of silicic magmas in the Kos-Nisyros volcanic center, Greece: a petrological cycle associated with caldera collapse
Evolution of silicic magmas in the Kos-Nisyros volcanic center, Greece: a petrological cycle associated with caldera collapse
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希腊科斯-尼西罗斯火山中心硅质岩浆的演化：与火山口塌陷相关的岩石循环
DOI：
10.1007/s00410-011-0663-y
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发表时间：
2011
影响因子：
3.5
通讯作者：
C. Schnyder
中科院分区：
文献类型：
--
作者：
O. Bachmann;C. Deering;J. S. Ruprecht;C. Huber;A. Skopelitis;C. Schnyder
在爱琴海东部的科斯-尼西罗斯火山中心，在过去的~3 Ma中发生了多次岩浆（英安岩和流纹岩）喷发。在此期间，岩浆从喷发温度较低（≤750-800°C; Kefalos和科斯英安岩和流纹岩）的富含角闪石黑云母的单元转变为较热的含辉石的单元（>800-850°C; Nisyros流纹岩），并过渡回较冷的岩浆（Yali流纹岩）。新的全岩成分，矿物化学和锆石Hf同位素表明，这三种类型的岩浆遵循相同的分化趋势：它们都是由晶体分馏和小地壳同化（AFC）的父母与中间组合物的特点是高Sr/Y和低Nb含量，下面的潮湿，高氧逸度的液体线下降典型的俯冲带。由于科斯-凯法洛斯型岩浆和尼西罗斯型岩浆之间的转换是在该地区主要破火山口坍塌后立即发生的，（161 ka科斯高原凝灰岩; KPT），我们认为KPT期间岩浆房的有效排空抽出了大部分可喷发的、充满挥发分的岩浆，并由于快速卸载、减压，和同时结晶。随后，该系统重新建立了一个浅的镁铁质生产带，从中地壳到下地壳重新充电。在破火山口坍塌（尼西罗斯单位）之后，从这些母体演化而来的第一次火山喷发比破火山口形成事件更热（高达100°C），并且从具有不同矿物比例（更多斜长石和更少角闪石）的储层中喷发。我们解释这样的变化，反映了稍微干燥的条件下，在岩浆柱后，由于减压事件的破火山口坍塌。随着时间的推移，上地壳中间泥逐渐过渡到冷湿状态，在凯法洛斯-科斯阶段占主导地位。最近爆发的高SiO2流纹岩的Yali岛，这是低温和含水相（透长石，石英，黑云母），表明另一个大的，潜在的爆炸岩浆房目前正在建设下的科斯-Nisyros火山中心。
Multiple eruptions of silicic magma (dacite and rhyolites) occurred over the last ~3 My in the Kos-Nisyros volcanic center (eastern Aegean sea). During this period, magmas have changed from hornblende-biotite-rich units with low eruption temperatures (≤750–800°C; Kefalos and Kos dacites and rhyolites) to hotter, pyroxene-bearing units (>800–850°C; Nisyros rhyodacites) and are transitioning back to cooler magmas (Yali rhyolites). New whole-rock compositions, mineral chemistry, and zircon Hf isotopes show that these three types of silicic magmas followed the same differentiation trend: they all evolved by crystal fractionation and minor crustal assimilation (AFC) from parents with intermediate compositions characterized by high Sr/Y and low Nb content, following a wet, high oxygen fugacity liquid line of descent typical of subduction zones. As the transition between the Kos-Kefalos and Nisyros-type magmas occurred immediately and abruptly after the major caldera collapse in the area (the 161 ka Kos Plateau Tuff; KPT), we suggest that the efficient emptying of the magma chamber during the KPT drew out most of the eruptible, volatile-charged magma and partly solidified the unerupted mush zone in the upper crust due to rapid unloading, decompression, and coincident crystallization. Subsequently, the system reestablished a shallow silicic production zone from more mafic parents, recharged from the mid to lower crust. The first silicic eruptions evolving from these parents after the caldera collapse (Nisyros units) were hotter (up to >100°C) than the caldera-forming event and erupted from reservoirs characterized by different mineral proportions (more plagioclase and less amphibole). We interpret such a change as a reflection of slightly drier conditions in the magmatic column after the caldera collapse due to the decompression event. With time, the upper crustal intermediate mush progressively transitioned into the cold-wet state that prevailed during the Kefalos-Kos stage. The recent eruptions of the high-SiO2 rhyolite on Yali Island, which are low temperature and hydrous phases (sanidine, quartz, biotite), suggest that another large, potentially explosive magma chamber is presently building under the Kos-Nisyros volcanic center.