Pre-eruptive PTX fluid-conditions of the Afyon Volcanic Complex (Western Anatolia, Turkey): Studies of natural rocks and phase equilibria experiments
Pre-eruptive PTX fluid-conditions of the Afyon Volcanic Complex (Western Anatolia, Turkey): Studies of natural rocks and phase equilibria experiments
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阿菲永火山群（土耳其西部安纳托利亚）喷发前的 PTX 流体条件：天然岩石和相平衡实验的研究
DOI：
10.1016/j.lithos.2021.106297
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发表时间：
2021
期刊：
影响因子：
3.5
通讯作者：
Spallanzani R.
中科院分区：
文献类型：
--
作者：
Dogan-Kulahci G.D;Cichy S.B;Temel A;Spallanzani R.
本研究试图了解喷发前的岩浆储存和结晶条件的中中新世年龄，硅饱和粗面岩的阿菲永火山杂岩（AVC）在西安纳托利亚，土耳其。根据高K_2O、K_2O/Na_2O比值和Mg ~（2+）可分为中钾质（IPG）和超钾质（UPG）两类。在这里，我们比较计算的压力（P）-温度（T）的条件下，从天然样品的地热压力计算的结果，高压，高温相平衡实验。IPG样品富含二氧化硅（57-64重量% SiO2），而UPG样品显示中等SiO2含量为56-58重量%。UPG具有高K2 O含量（约9wt%）、K2 O/Na 2 O比率（约10wt%）和Mg#值（75-77）。IPG斑晶由斜长石+黑云母+角闪石+单斜辉石±斜方辉石±透长石±金云母和氧化物组成，UPG矿物组合由角闪石+金云母+单斜辉石+橄榄石+透长石和氧化物组成。IPG和UPG富集大离子亲石元素（LILE），均具有Nb、Sr、Zr和Ti元素的负异常。此外，IPG显示Pb的正异常。IPG和UPG都表现出轻稀土元素（LREE）的富集，而IPG表现出更显着的Eu负异常相比，UPG。斜长石分馏作用可能在岩浆生成中起作用。在IPG样品中，Ni和Cr值分别在（3.3-18.8 ppm）和（2.6-27.8 ppm）之间;而UPG样品具有（119.1-120.7 ppm）Ni和（212.1-219.9 ppm）Cr。IPG和UPG的Dy/Yb比值均大于2，可能表明源中存在石榴石。天然IPG单斜辉石-熔体对的地质温压计算意味着更高的PT条件（Dogan-Kulahci等人，2015年），而在这项研究中，高压/高温（HP/HT）相平衡实验在2-4 kbar，6-9 km和c. 900 °C。新的斜长石熔体计算证实了较低的平均岩浆储存温度，这是接近实验结果，但仍然略有升高。因此，天然岩石和实验数据的微量元素结果可能意味着一个深石榴子石岩浆源混合较浅的岩浆（IPG）是喂养火山喷发。
This study is trying to understand the pre-eruptive magma storage and crystallization conditions of the Middle Miocene aged, silica-saturated trachytic rocks of the Afyon Volcanic Complex (AVC) in Western Anatolia, Turkey. Those rocks can be divided by their high K2O, K2O/Na2O ratio and Mg# into two groups, namely the intermediate-potassic (IPG) and the ultrapotassic (UPG). Here we are comparing calculated pressure (P) - temperature (T) conditions derived from geothermobarometric calculations of natural samples with results of high-pressure, high-temperature phase equilibria experiments. IPG samples are richer in silica (57–64 wt% SiO2), whereas UPG samples show intermediate SiO2contents of 56–58 wt%. UPG are having high K2O contents (˃9 wt%), K2O/Na2O ratios (˃10 wt%) and Mg# values (75–77). IPG phenocrysts comprise plagioclase + biotite + amphibole + clinopyroxene ± orthopyroxene ± sanidine ± phlogopite and oxides, while UPG mineralogical assemblage consists of amphibole + phlogopite + clinopyroxene + olivine + sanidine and oxides. IPG and UPG are enriched in Large-Ion Lithophile Elements (LILE), and both have negative anomalies in Nb, Sr, Zr and Ti elements. Additionally, IPG shows positive anomalies in Pb. Both IPG and UPG display enrichment in Light Rare Earth Elements (LREE), while IPG shows a more significant negative anomaly in Eu when compared to UPG. Plagioclase fractionation may play a role in magma generation. In IPG samples Ni and Cr values range between (3.3–18.8 ppm) and (2.6–27.8 ppm), respectively; whereas UPG samples have (119.1–120.7 ppm) Ni and (212.1–219.9 ppm) Cr. Dy/Yb ratios of IPG and UPG are higher than 2 and may indicate that garnet was present in the source. Geothermobarometric calculations for natural IPG clinopyroxene-melt pairs imply higher PT conditions (Dogan-Kulahci et al., 2015), while in this study high-pressure/high-temperature (HP/HT) phase equilibria experiments recreated the natural mineral assemblage at 2–4 kbar, 6–9 km and c. 900 °C. New plagioclase-melt calculations have confirmed lower mean magma storage temperatures, which are closer to the experimental results but still slightly elevated. Thus, trace element results of the natural rocks and experimental data may imply that a deep garnet-bearing magma source mixed with shallower magmas (IPG) was feeding the volcanic eruption.
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