Crystal uptake into aphyric arc melts: insights from two-pyroxene pseudo-decompression paths, plagioclase hygrometry, and measurement of hydrogen in olivines from mafic volcanics of southwest Japan.
Crystal uptake into aphyric arc melts: insights from two-pyroxene pseudo-decompression paths, plagioclase hygrometry, and measurement of hydrogen in olivines from mafic volcanics of southwest Japan.
复制标题
非非晶弧熔体中的晶体吸收：来自双辉石伪减压路径、斜长石湿度测量以及日本西南部镁铁质火山橄榄石中氢的测量的见解。
DOI：
10.1144/sp385.3
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Miyoshi M. Tamura Y. Hsieh H. and Yurimoto H.
中科院分区：
文献类型：
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作者：
Zellmer G. F.;Sakamoto N.;Iizuka Y.;Miyoshi M. Tamura Y. Hsieh H. and Yurimoto H.
通过对日本西南部基性岩的矿物学研究，推断出基性岩弧岩浆的P-T-X-H_2 O条件及其变化。来自几个火山的岩浆的双辉石热压测量法产生恒定的温度和可变的压力。熔体分离结晶模型表明，这种“伪减压路径”（PDPs）是文物，来自摄取辉石前晶形成在地壳水平范围内的等压冷却以前侵入的镁铁质熔体。结果表明，PDP可以用来限制氧逸度和侵入岩浆的初始水含量。这些限制和斜长石测湿表明，初始熔体H2O含量沿着西南日本弧系统地变化.用二次离子质谱法直接测定橄榄石中的氢，得到的橄榄石H2O含量始终很低，为11± 4ppm（1σ），沿弧变化很小（如果有的话）。MELTS模拟结果表明，钙长石和橄榄石的结晶主要发生在镁铁质熔体的上地壳分异过程中。综合数据表明，隐晶质熔体从地幔楔释放，采取了大部分，如果不是所有的晶体从以前侵入的深成岩在快速岩浆上升到表面。
Minerals of mafic rocks from the SW Japan arc have been studied to deduce P–T–X H2O conditions and their variations in mafic arc magmas. Two-pyroxene thermobarometry of magmas from several volcanoes yields constant temperatures and variable pressures. MELTS fractional crystallization modelling is employed to show that such ‘pseudo-decompression paths’(PDPs) are artefacts that derive from uptake of pyroxene antecrysts formed at a range of crustal levels by isobaric cooling of previously intruded mafic melts. It is shown that PDPs can be used to constrain oxygen fugacities and initial water contents of the intruded magmas. These constraints, and plagioclase hygrometry, indicate that initial melt H 2 O contents change systematically along the SW Japan arc. Direct determination of hydrogen in olivine by secondary ion mass spectrometry yields consistently low olivine H 2 O contents of 11±4 ppm (1σ), with little, if any, along-arc variations. MELTS modelling indicates that crystallization of calcic plagioclase and olivine dominantly occurs during upper crustal differentiation of mafic melts. The combined data indicate that aphyric melts are released from the mantle wedge, taking up most if not all crystals from previously intruded plutonic rocks during rapid magma ascent to the surface.