The significance of plagioclase textures in mid-ocean ridge basalt (Gakkel Ridge, Arctic Ocean)
The significance of plagioclase textures in mid-ocean ridge basalt (Gakkel Ridge, Arctic Ocean)
复制标题
大洋中脊玄武岩（北冰洋加克尔海岭）中斜长石结构的意义
DOI：
10.1007/s00410-019-1587-1
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发表时间：
2019-06-01
影响因子：
3.5
通讯作者：
Cashman, Katharine, V
中科院分区：
文献类型：
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作者：
Bennett, Emma N.;Lissenberg, C. Johan;Cashman, Katharine, V
矿物的结构和组成可以用来推断岩浆系统中存在的物理化学条件。鉴于斜长石在许多岩浆系统中是一个丰富的阶段，了解结构和过程之间的联系是至关重要的。本文利用Gakkel ridge （Arctic Ocean）洋中脊玄武岩中>1800个斜长石晶体的结构和成分数据，探讨了斜长石结构和成分形成的物理化学条件和过程。Gakkel玄武岩具有高模态晶体含量（高达50%）。晶体货物是复杂的，个体斜长石和肾小球在晶体习性、分带和再吸收方面都表现出很大的变化。最常见的分区类型是反向和不完整的；我们将斑块分区归因于骨骼生长或吸收后的填充。岩浆再吸收丰富，在单晶中普遍存在多次再吸收事件，是岩浆充注和减压共同作用的结果。与淬火结晶不同的强烈过冷期，由成熟的骨架晶体和吸收后正常分布的富含熔体包裹体的薄带表示。单个样品通常含有不同的结构和成分的斜长石群。此外，大多数斜长石与其宿主熔体不处于平衡状态。最后，一些肾小球的多孔开放结构表明它们代表了携带的破碎的糊状物。我们的解释是，这表明晶体货物在起源上通常不是斑晶的。相反，在以糊状为主的管道系统的不同部分形成的斜长石晶体被带入上升的熔体中。单个晶体的结构是它们各自（欠）冷却、岩浆混合和减压历史的函数。斜长石晶体中熔体包裹体的形态与特定的寄主晶体结构有关，表明斜长石结晶过程与熔体包裹体之间存在联系。本文提出的斜长石数据库可以作为解释其他岩浆系统中斜长石结构的模板。
Textures and compositions of minerals can be used to infer the physiochemical conditions present within magmatic systems. Given that plagioclase is an abundant phase in many magmatic systems, understanding the link between texture and process is vital. Here, we present a database of textural and compositional data for>1800 plagioclase crystals in mid-ocean ridge basalt from the Gakkel Ridge (Arctic Ocean) to investigate the physiochemical conditions and processes that govern the formation of plagioclase textures and compositions. The Gakkel basalts have high modal crystal contents (up to 50%). The crystal cargo is complex, with both individual plagioclase and glomerocrysts showing large variations in crystal habit, zoning and resorption. The most common types of zoning are reverse and patchy; we attribute patchy zoning to infilling following either skeletal growth or resorption. Resorption is abundant, with multiple resorption events commonly present in a single crystal, and results from both magmatic recharge and decompression. Periods of strong undercooling, distinct to quench crystallisation, are indicated by matured skeletal crystals and thin normally zoned melt inclusion-rich bands following resorption. Individual samples often contain diverse textural and compositional plagioclase groups. Furthermore, most plagioclase is not in equilibrium with its host melt. Finally, the porous open structures of some glomerocrysts suggest that they represent pieces of entrained disaggregated mush. We interpret this to indicate that the crystal cargo is not generally phenocrystic in origin. Instead, plagioclase crystals that formed in different parts of a mush-dominated plumbing system were entrained into ascending melts. The textures of individual crystals are a function of their respective histories of (under)cooling, magma mixing and decompression. The morphologies of melt inclusion trapped in the plagioclase crystals are associated with specific host crystal textures, suggesting a link between plagioclase crystallisation processes and melt inclusion entrapment. The database of plagioclase presented herein may serve as a template for the interpretation of plagioclase textures in magmatic systems elsewhere.