第七章岩浆起源上升与侵位.ppt

* * * * * * Fig. 9. A map view of the sequential emplacement of the Tuolomne Intrusive Suite to form a set of nested plutons: nodiorite of Kune Crest, (b) (c) Half Dome Granodiorite, and (d) Cathedral Peak Granodiorite and Johnson Granite Porphyry (after Huber 1989). 复式岩体：多于两次侵入 带状岩体：中央偏酸性，外部偏基性 /articles/arj/v2/n1/radiohalos-in-yosemite-granites Fig. 10. Final stages in the development of the nested plutons of the Tuolumne Intrusive Suite (after Huber 1989). The Johnson Granite Porphyry represents the final phase of the suite that intruded the Cathedral Peak Granodiorite and erupted through a volcanic caldera at the earth’s surface above, spewing volcanic ash and debris across it. The volcanic deposit and much of the underlying rock were subsequently removed by erosion to create today’s land surface. * Figure 11-1. b. When a melt has a low dihedral angle the surface energy of the melt ? that of the minerals, and melt tends to “wet” the surfaces and form a continuous network c. Higher surface energy contrasts result in higher theta and isolated melt droplets Mafic systems theta 50o very small melt fractions should be extractable Rhyolitic melts may have higher angles (45-60o) Viscosity is also important in terms of segregation of a melt once a continuous network formed The critical melt fraction (or rheological critical melt percentage, RCMP): % melt at which a crystal-dominated, high viscosity granular framework gives way to a melt-dominated, lower viscosity suspension Theoretical system of spheres: RCMP = 26% melt Irregular shapes and variable sizes: RCMP may vary between 30-50% for static situations involving granitic compositions But other factors may play a role * * * * * * * * Altered oceanic crust begins to dehydrate at depths ~ 50 km or less, as chlorite, phengite, and other hydrous phyllosilicates decompose Further dehydration takes place at greater depths as other hydrous phases become unstable, including amphibole at about 3 GPa. The slab cr