Deep crustal crystallization of tholeiitic melt: Insights from Manguao Basalt, Palawan, Philippines
Deep crustal crystallization of tholeiitic melt: Insights from Manguao Basalt, Palawan, Philippines
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DOI：
10.2465/jmps.191211
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发表时间：
2020-12
影响因子：
0.7
通讯作者：
James Cesar Avisado Refran;T. Ohba;C. Arcilla;T. Hoshide;M. Balangue-Tarriela
中科院分区：
文献类型：
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作者：
James Cesar Avisado Refran;T. Ohba;C. Arcilla;T. Hoshide;M. Balangue-Tarriela
曼瓜奥玄武岩是位于菲律宾巴拉望岛东北边缘的普里奥-更新世玄武岩熔岩流。巴拉望大陆块（PCB）周围没有活动的海沟，对该地区岩浆作用的性质和起源提出了挑战。这项研究展示了曼瓜玄武岩的岩石学和地球化学特征，并提供了对 PCB 下方熔体形成的见解。满瓜玄武岩样品为橄榄石状，含有少量辉石，镶嵌在以斜长石为主的微晶基质中。曼郭玄武岩的平均块岩主量元素组成与普通橄榄石玄武岩拉斑玄武岩相似。然而，斑晶的岩相观察显示，辉石在结晶序列中具有不同寻常的优先性。计算出的模态组合的地层温度和压力与早期辉石形成的想法一致。使用 MELTS 程序对地幔熔化的模拟显示了辉石饱和原始液体的形成。这些原始液体的演化与1230-1260℃的曼瓜玄武岩成分相似。平衡和分级结晶的模拟证明了橄榄石或斜方辉石作为第一晶体的形成。然而，在平衡条件下进行的模拟与观察到的曼郭玄武岩中辉石斑晶的矿物化学更加一致。因此，维持源和熔体之间的平衡对于复制观察到的辉石化学至关重要。 Magmatic 底镀提供了一个出色的模型，用于可视化 PCB 下方的熔化和结晶过程。该模型也与巴拉望岛北部其他岩浆单元（例如卡波阿斯花岗岩）的叙述一致。这项研究的重要发现有助于理解 PCB 的构造演化。
Manguao Basalt is a Plio–Pleistocene basaltic lava flow located on the northeastern edge of Palawan Island, Philippines. The absence of active trenches surrounding the Palawan Continental Block (PCB) poses a challenge regarding the nature and origin of magmatism in the region. This study presents the petrographic and geochemical character of Manguao Basalt, as well as provides insights to the melt formation beneath the PCB. Manguao Basalt samples are olivine–phyric with minor pyroxenes, set in a plagioclase–dominated microcrystalline groundmass. Average bulk–rock major element composition of Manguao Basalt shows similarities to common olivine basalt tholeiite. Petrographic observations of the phenocrysts, however, show the unusual precedence of pyroxenes in the crystallization sequence. Calculated formation temperatures and pressures of the modal assemblage are consistent with this idea of early pyroxene formation. Simulations of mantle melting using the MELTS program show the formation of pyroxene–saturated primitive liquids. The evolution of these primitive liquids reaches similarities with Manguao Basalt composition at 1230–1260 °C. Simulations of equilibrium and fractional crystallization demonstrate the formation of olivine or orthopyroxene as the first crystals. However, the simulations done at equilibrium conditions are more consistent with the observed mineral chemistry of pyroxene phenocrysts in Manguao Basalt. Hence, maintaining the equilibrium between the source and melt is crucial for replicating the observed pyroxene chemistry. Magmatic underplating provides an excellent model for visualizing the melting and crystallization processes beneath the PCB. The model is also consistent with the narrative of other magmatic units in northern Palawan (e.g., Capoas Granite). The significant findings of this study contribute to the understanding of the tectonic evolution of the PCB.