连点成线:熔岩穹丘透视与火成岩爆发有关的岩浆活动

IF 3.5 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
L Smithies Sarah, M Gravley Darren, A R Gualda Guilherme
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引用次数: 0

摘要

与流纹岩火山口相关的穹顶喷发为了解超大型(10 km3)流纹岩岩浆系统是如何随着时间的推移而形成的提供了重要的视角。我们重点研究了在350-240 ka火成岩爆发之前、期间和紧随其后的陶波火山带中部的流纹岩火山口。我们确定了约 650 至 150 ka 之间的 103 次穹隆喷发,并整理了来自这些穹隆的 239 份文献全岩成分。对于每种成分,我们都使用流纹岩-MELTS测地仪模拟了从岩浆泥浆中提取岩浆的压力以及岩浆泥浆的矿物组合。我们使用锆石饱和地热仪计算了萃取温度。我们的研究表明,岩浆从典型的含石英岩浆泥浆中提取的深度(~50 - 425 MPa,~2 - 16 km)和温度(~750 - ~850 °C)范围很广。在整个 TVZ 中心区,有两种主要的萃取压力模式:1)150 - 175 MPa;2)250 - 325 MPa,这与 1)脆性-韧性转变深度(~6 千米)和略低于其他 TVZ 岩浆典型的爆发前储存深度(100 - 150 MPa,~4 - 6 千米)相一致;以及 2)以前的地球物理研究在 ~8 千米以下成像的部分熔融区域相一致。在某些地区,地壳结构、岩浆提取深度和岩浆成分之间存在明显的相关性。在Whakamaru破火山口,破火山口坍塌后在破火山口内部喷发的圆顶是在约810 °C的温度下从约225至约350兆帕斯卡的压力下提取的,其成分与形成破火山口的喷发成分不同。这些穹隆沿着正断层排列,表明断裂为岩浆从补给恢复活力的深层熔岩中提取创造了通道。沿Whakamaru火山口构造边缘喷发的穹隆具有与形成火山口的喷发相似的非常进化的、含角闪石的成分,以及在~770 °C、~100 - ~200 MPa的较浅、较冷的萃取,这表明为这些穹隆提供营养的岩浆是沿火山口边界断层移动的形成火山口的较古老岩浆系统的残余。在整个爆发期和整个TVZ中部地区,岩浆萃取的两个结构层次(约6千米和9-12千米)持续存在,这表明有必要进一步研究控制蘑菇云发展深度的因素。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Connecting the dots: the lava domes’ perspective of magmatism related to an ignimbrite flare-up
Dome eruptions associated with rhyolitic calderas offer an important insight into how extremely large (>>10 km3), rhyolitic magma systems are constructed through time. We focus on rhyolitic calderas in the central Taupō Volcanic Zone leading to, during, and immediately following the 350 – 240 ka ignimbrite flare-up. We identified 103 dome eruptions that are dated between ca. 650 and 150 ka and collated 239 literature whole-rock compositions from these domes. For each composition, we modelled the pressure of magma extraction from the magma mush and the mineral assemblage of the mush using the rhyolite-MELTS geobarometer. We calculated extraction temperatures using zircon saturation geothermometry. We show that magmas are extracted from typically quartz-bearing magma mush at a wide range of depths (~50 – 425 MPa, ~2 – 16 km) and temperatures (~750 – ~850 °C). Throughout the central TVZ, there are two dominant extraction pressure modes at 1) 150 – 175 MPa and 2) 250 – 325 MPa, consistent with 1) the depth of the brittle-ductile transition (~6 km) and just below typical pre-eruptive storage depths of other TVZ magmas (100 – 150 MPa, ~4 – 6 km); and 2) partial melt regions imaged below ~8 km by previous geophysical studies. In some regions, there is a clear correlation between crustal structures, the depth of magma extraction, and the composition of the magmas. In the Whakamaru caldera, the domes erupted inside the caldera following caldera collapse are extracted from ~225 to ~350 MPa at ~810 °C and have orthopyroxene-bearing compositions dissimilar to the caldera-forming eruption. These domes are aligned along normal faults, suggesting that rifting creates pathways for magma extraction from a deeper mush rejuvenated by recharge. The domes erupted along the structural margins of the Whakamaru caldera have very evolved, hornblende-bearing compositions, similar to the caldera-forming eruption and shallow, colder extraction from ~100 – ~200 MPa at ~770 °C, suggesting the mush feeding these domes is a remnant of the older caldera-forming magma system mobilised along the caldera-bounding faults. Two structural levels of magma extraction at ~6 km and 9 – 12 km are persistent throughout the flare-up period and across the central TVZ region, demonstrating the need for further investigation into the factors controlling the depth of mush development.
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来源期刊
Journal of Petrology
Journal of Petrology 地学-地球化学与地球物理
CiteScore
6.90
自引率
12.80%
发文量
117
审稿时长
12 months
期刊介绍: The Journal of Petrology provides an international forum for the publication of high quality research in the broad field of igneous and metamorphic petrology and petrogenesis. Papers published cover a vast range of topics in areas such as major element, trace element and isotope geochemistry and geochronology applied to petrogenesis; experimental petrology; processes of magma generation, differentiation and emplacement; quantitative studies of rock-forming minerals and their paragenesis; regional studies of igneous and meta morphic rocks which contribute to the solution of fundamental petrological problems; theoretical modelling of petrogenetic processes.
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