2024年2月23日出版的《地球化学学报》杂志发表了印度尼西亚加札马达大学Suhendro, Indranova团队的一项研究成果。研究揭示了印度尼西亚爪哇岛中部的Sumbing山玄武安山岩—英安岩组合的岩石学、地球化学和晶体粒度分布规律，和研究人员对岩浆储层动力学和岩石成因的认识。

研究人员称，Sumbing山地层排列为LF1，PDC1，LF2，LF3，LF4，LF5，LF6，LF7，LD1，LD2；研究进一步将这些岩石划分为两类。在最老的(LF1)样品中观察到的I型样品MgO含量较低，Ba/Nb、Th/Yb和Sr含量较高。其余样品(PDC1-LD2)为II型，其特征是高MgO和低Ba/Nb, Th/Yb和Sr值。I型来源于富AOC(蚀变洋壳)的熔体，其熔融经历了显著的地壳同化作用，而II型来源于富地幔熔体，其熔融同化作用不明显。

II型岩浆(PDC1-LF3)的早期阶段被认为是一个封闭的体系，由玄武岩安山岩演化为安山岩(55.0-60.2 wt% SiO₂)，斑晶逐渐增大(0.30-0.48 [数学处理误差]，晶体尺寸分布(CSD)斜率逐渐减小(从-3.9到-2.9)。石英和斑晶含量波动的证据(分别在55.9-59.7wt%和0.25-0.41[数学处理误差])，结合弯曲和陡峭(从-5.0到-3.3) CSD曲线，反映了中期(LF4-LF6)岩浆系统开放(即岩浆混合)与封闭岩浆系统之间的交替条件。最后，在最终阶段(LF7-LD2)再次进入封闭体系，岩浆达到英安质成分(最高达68.9%wt%的SiO₂)，斑晶含量丰富(0.38-0.45[数学处理误差])，CSD坡度平缓(从-4.1到-1.2)

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据了解，研究通过对1个火山碎屑密度流(PDC1)矿床、7个熔岩流(LF1-7)和2个山顶熔岩穹丘(LD1， 2)等10个岩石样品的研究，以了解Sumbing山的岩石成因和岩浆动态变化。

附：英文原文

Title: Petrology, geochemistry, and crystal size distribution of the basaltic andesite–dacite association at Mt. Sumbing, Central Java, Indonesia: Insights to magma reservoir dynamics and petrogenesis

Author: Suhendro, Indranova, Yuliawan, Endra, Zen, Revina Fitri, Rahmawati, Zulfa Yogi, Priyana, Pandu Eka, Diwijaya, Sonna, Suhartono, Muhammad Alsamtu Tita Sabila Pratama, Jonathan, Andre, El Zamzamy Latief, Gammanda Adhny

Issue&Volume: 2024-02-23

Abstract: Ten rock samples consisting of one pyroclastic density current (PDC1) deposit, seven lava flows (LF1–7), and two summit lava domes (LD1, 2) were studied to understand the petrogenesis and magma dynamics at Mt. Sumbing. The stratigraphy is arranged as LF1, PDC1, LF2, LF3, LF4, LF5, LF6, LF7, LD1, and LD2; furthermore, these rocks were divided into two types. Type I, observed in the oldest (LF1) sample, has poor MgO and high Ba/Nb, Th/Yb and Sr. The remaining samples (PDC1–LD2) represent type II, characterized by high MgO and low Ba/Nb, Th/Yb and Sr values. We suggest that type I is derived from AOC (altered oceanic crust)-rich melts that underwent significant crustal assimilation, while type II originates from mantle-rich melts with less significant crustal assimilation. The early stage of type II magma (PDC1–LF3) was considered a closed system, evolving basaltic andesite into andesite (55.0–60.2 wt% SiO₂) with a progressively increasing phenocryst (0.30–0.48[Math Processing Error]) and decreasing crystal size distribution (CSD) slope (from -3.9 to -2.9). The evidence of fluctuating silica and phenocryst contents (between 55.9–59.7 wt% and 0.25–0.41[Math Processing Error], respectively), coupled with the kinked and steep (from -5.0 to -3.3) CSD curves imply the interchanging condition between open (i.e., magma mixing) and closed magmatic systems during the middle stage (LF4–LF6). Finally, it underwent to closed system again during the final stage (LF7–LD2) because the magma reached dacitic composition (at most 68.9 wt% SiO₂) with abundant phenocryst (0.38–0.45].

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DOI: 10.1007/s11631-024-00673-7

Source: https://link.springer.com/article/10.1007/s11631-024-00673-7