Collaborative Research: Locating the Mantle Component in Granite

缅因州沿海岩浆省的Hogan、Lux和GibsonEAR-0003417/0003660/0003694花岗岩通常表现出戏剧性的场关系，记录了成分(化学和同位素)和物理性质明显不同的岩浆之间的相互作用。源自地壳的硅质岩浆室接收了密度更高的镁铁质岩浆的流入，这些岩浆沿着这些岩浆室的底部扩散，产生了一种被称为马菲克和硅质层状侵入体(MASLi)的成分分层。最近的研究很好地证明了不同岩浆类型之间在界面附近壮观的场关系和巨大的成分变化。相比之下，接受镁铁质流入的洞穴底部与上面的硅质岩浆之间的物理和化学耦合程度仍然知之甚少。CMMP中的三个已知或推定的马斯利深成岩系，分别是维纳尔海文、鹿岛和芒特。沃尔多花岗岩被选中进行研究，以解决这一重要问题。具体地说，是什么过程和其他因素决定了不同类型的岩浆之间热量和物质交换的程度？热量和质量随后会被分配到气室的上游吗？通过结合对带状斜长石和副矿物的结构、成分和同位素研究(使用电子和离子探针技术)，以及每一花岗岩中岩浆包体的数据，可以评估岩浆成分与结晶矿物的相对时间和变化程度。相邻矿物颗粒之间的内部变化将被用来限制材料在腔内重新分布的相对程度。此外，这类研究将加深我们对岩浆房动力学和生长的认识，使我们能够认识到地幔和地壳成分在花岗岩成因中的贡献，并对大陆岩石圈的生长和演化模式进行评价。

Hogan, Lux, and GibsonEAR-0003417/0003660/0003694Granitic plutons of the Coastal Maine Magmatic Province (CMMP) commonly display dramatic field relations that record interaction between magmas of markedly different composition (chemical and isotopic) and physical properties. Silicic magma chambers, derived from the crust, received influxes of denser mafic magma that spread out along the floor of these chambers to produce a compositional stratification know as Mafic and Silicic Layered Intrusions (MASLI). The spectacular field relations and large compositional variation in the vicinity of the interface between contrasting magma types are well document by recent studies. In contrast, the extent of physical and chemical coupling between the base of the chamber, that receives mafic influx, and the overlying silicic magma remains poorly understood. Three known or presumed MASLI plutons in the CMMP, the Vinalhaven, Deer Isle, and Mt. Waldo granites, have been selected for study to address this important issue. Specifically, what processes and other factors determine the extent to which heat and material are exchanged between contrasting magma types? Is heat and mass subsequently distributed to the upper reaches of the chamber? By combining textural, compositional and isotopic studies of zoned plagioclase and accessory minerals (using electron and ion-microprobe techniques), along with data for magmatic enclaves from each of the granites, the relative timing and extent of variation in composition of the magma from with individual minerals crystallized can be assessed. Comparison of internal variations among adjacent mineral grains will be used to constrain the relative extent to which material is redistributed within the chamber. Furthermore, studies such as this will enhance our understanding of magma chamber dynamics and growth, enable recognition of the contribution of mantle and crustal components in granite petrogenesis, and evaluate models for the growth and evolution of continental lithosphere.