Magmatic evolution of the Campi Flegrei and Procida volcanic fields, Italy, based on interpretation of data from well-constrained melt inclusions
Magmatic evolution of the Campi Flegrei and Procida volcanic fields, Italy, based on interpretation of data from well-constrained melt inclusions
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意大利 Campi Flegrei 和 Procida 火山田的岩浆演化，基于对约束良好的熔体包裹体数据的解释
DOI：
10.1016/j.earscirev.2018.06.003
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发表时间：
2018
影响因子：
12.1
通讯作者：
Manning, Craig E.
中科院分区：
文献类型：
--
作者：
Esposito, Rosario;Badescu, Kimberly;Steele-MacInnis, Matthew;Cannatelli, Claudia;De Vivo, Benedetto;Lima, Annamaria;Bodnar, Robert J.;Manning, Craig E.
熔融包裹体研究的主要目标之一是在微观尺度上约束岩浆储层中发生的喷发前物理和化学过程。最近，几项研究集中在火山系统的岩浆分异上，根据管道系统中不同时间和位置捕获的MI数据，得出了详细的解释。理想情况下，应该按照熔融包裹体组合（MIA）协议收集和测试MI数据，该协议包括研究和分析同时捕获的MI组，因此，在相同的化学和物理条件下。然而，在许多情况下，在幼年火山斑晶中罕见的MIA妨碍了这种方法，导致MI作为爆发前条件记录者的有效性的不确定性。在这项研究中，我们重点研究了意大利南部Campi Flegrei （CF）和Procida岛（IP）火山系统的MI，包括本研究数据和文献数据。该数据库中包含的MI分布在水晶石、斜辉石、斜长石、黑云母和橄榄石中，因此，它们代表了在整个分化过程的不同阶段被捕获的熔体。我们开发了一种协议，从与单个岩浆系统相关的数据集中选择最可靠的MI。作为第一步，我们将MI数据与同一岩浆系统的大块岩石数据进行比较。这种比较表明，大多数MI显示的主要元素组成落在或接近大块岩石的范围内——这些MI被认为是“正常的”。一些MI显示异常成分，不代表与斑晶主体平衡的熔体，因此被排除在数据集之外。在第二步中，我们仅从先前确定的“正常”MI中选择无气泡MI来解释挥发性演化。在第三步中，我们比较了“正常”无气泡MI的组成与流纹岩- melt模拟预测的组成，假设了各种初始条件。玄武质-粗面玄武质MI与流纹岩- melt预测数据对比表明，其中一组MI记录了挥发饱和岩浆在≥200 MPa（≥7.5 km）至30 MPa（~1 km）范围内以多压分晶分异的地球化学演化过程。另一组MI记录了喷发前由原始玄武质岩浆与先前存在的原始粗玄武质岩浆混合而形成的岩浆室的补给。CF以下~7.5 km处粗玄武质岩浆的广泛等压结晶可能产生粗玄武质-phonolitic岩浆，例如与那不勒斯黄凝灰岩（NYT）相关的岩浆，其特征是含水量相对较高。这些挥发物饱和的粗砂质-声母岩岩浆在上升到地表的过程中可能引发高强度的喷发。
One of the main goals of studying melt inclusions (MI) is to constrain the pre-eruptive physical and chemical processes that have occurred in a magma reservoir at the micro-scale. Recently, several studies that focused on magmatic differentiation of volcanic systems produced detailed interpretations based on data from MI trapped at different times and locations in the plumbing system. Ideally, MI data should be collected and tested following the melt inclusion assemblage (MIA) protocol that consists of studying and analyzing groups of MI that were trapped at the same time, and, thus, at the same chemical and physical conditions. However, the rarity of MIA in juvenile volcanic phenocrysts precludes this methodology in many cases, leading to uncertainty concerning the validity of the MI as recorders of pre-eruptive conditions.In this study, we focused on MI from the Campi Flegrei (CF) and the Island of Procida (IP) volcanic systems in southern Italy, including data from this study and data from the literature. The database included MI hosted in sanidine, clinopyroxene, plagioclase, biotite and olivine, and, thus, represents melts trapped at various stages in the overall differentiation process. We developed a protocol to select the most reliable MI from a dataset associated with a single magmatic system. As a first step we compare MI data with bulk rock data for the same magmatic system. This comparison reveals that most MI show major element compositions that fall within or close to the range for bulk rocks – these MI are considered to be “normal”. Some MI show anomalous compositions and are not representative of the melt in equilibrium with the phenocryst host and were excluded from the data set. In the second step we selected only bubble-free MI from the previously identified “normal” MI to interpret the volatile evolution. In the third step we compare compositions of the “normal” bubble-free MI to compositions predicted by rhyolite-MELTS simulations, assuming a variety of initial conditions.Comparison of data obtained from basaltic-trachybasaltic MI with rhyolite-MELTS predictions indicates that one group of MI records the geochemical evolution of a volatile-saturated magma differentiating by polybaric fractional crystallization from ≥200 MPa (≥7.5 km) to 30 MPa (~1 km). Another group of MI records recharge of the magma chamber by a primitive basaltic magma that mixes with the preexisting primitive trachybasaltic magma before eruption. Extensive isobaric crystallization of the trachybasaltic magmas at ~7.5 km beneath CF may have generated trachytic-phonolitic magmas, such as those associated with the Neapolitan Yellow Tuff (NYT) that is characterized by a relatively high H2O content. These volatile-saturated trachytic-phonolitic magmas likely trigger high-magnitude eruptions during their ascent to the surface.
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