Collaborative Research: Locating the Mantle Component in Granite

缅因海岸岩浆省（CMMP）的花岗质岩体通常显示出戏剧性的场关系，记录了显著不同成分（化学和同位素）和物理性质的岩浆之间的相互作用。源自地壳的硅质岩浆房接收了密度更大的基性岩浆的流入，这些基性岩浆沿着这些岩浆房的底部扩散，产生了一种被称为基性和硅质层状侵入（MASLI）的成分分层。最近的研究很好地记录了不同岩浆类型之间界面附近的壮观的场关系和大的成分变化。相比之下，在接受基性岩浆流入的岩浆室底部与上覆的硅质岩浆之间的物理和化学耦合程度仍然知之甚少。为了解决这一重要问题，研究人员选择了CMMP中三个已知或推测的MASLI岩体，即Vinalhaven， Deer Isle和Mt Waldo花岗岩。具体来说，是什么过程和其他因素决定了不同岩浆类型之间热量和物质交换的程度？热量和质量随后是否分布到腔室的上部？通过结合对分带斜长石和附属矿物的结构、成分和同位素研究（使用电子和离子探针技术），以及来自每种花岗岩的岩浆包裹体的数据，可以评估来自单个矿物结晶的岩浆成分变化的相对时间和程度。相邻矿物颗粒之间的内部变化的比较将用于限制材料在腔室内重新分布的相对程度。此外，这样的研究将增强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岩石成因中的贡献，并评估大陆岩石圈生长和演化的模式。

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.