ABSTRACT
Figure 10.1 (Continued) is fine-grained titanite. Notice how the garnet has overgrown an earlier folded foliation, indicated by the blue dashed line in A. Though not visible here, some garnets contain green hornblende in their cores, recording an earlier, lower pressure part of the metamorphic history. C, D) Blueschist that is transitional to eclogite facies, having the assemblage glaucophane – garnet – omphacite – epidote – phengite. The P-T conditions for the transition from blueschist to eclogite depends on both and fluid and rock compositions. Extending from the left side of the center garnet, toward the upper left and lower right, is a vein (yellow arrows) containing phengite, epidote, minor quartz, and glaucophane that has concentric color zoning (red arrow). These veins were deposited by flowing fluid, that appears as a network of irregular, gray to white lines on the outcrop surface. E, F) This rock is a volcanic breccia containing basaltic clasts (upper left) in a lighter-colored fragmental matrix (lower right). While at first glance images E and F (and the rock itself) look like a fine-grained mess, look carefully and you can see the texture of randomly-oriented lath-shaped crystals in the basalt fragment. In basalt the laths were plagioclase, but now they have been replaced by blue glaucophane. Somewhat larger glaucophane crystals are visible in the matrix, along with epidote and phengite. In the field, the minor amount of glaucophane gave the whole rock a blue-gray appearance, subtly contrasting it with other glaucophane-free rocks. Abbreviations: E, epidote; G, garnet; Gl, glaucophane; O, omphacite; P, phengite.
