As discussed in detail by Vernon (1986) and summarized by Vernon (1999) and Vernon and Paterson (2002), the following criteria favor a magmatic origin for K-feldspar megacrysts: (1) euhedral shapes of the megacrysts, compared with typical xenoblastic shapes of K-feldspar porphyroblasts in metamorphic rocks (Figure 3a, b); (2) simple twinning, which is rare to unobserved in metamorphic K-feldspar; (3) oscillatory zoning (especially Ba), which to our knowledge, is unreported for metamorphic K-feldspar; (4) normal zoning with Ba-rich cores, as expected for melt crystallization; (5) concentrically arranged inclusions (e.g., biotite and plagioclase) parallel to crystallographic planes, as opposed to inclusion trails unrelated to K-feldspar crystallography in metamorphic K-feldspar (Figure 3a, b); (6) euhedral plagioclase inclusions, as opposed to rounded plagioclase inclusions in metamorphic K-feldspar; (7) fractured megacrysts in which the fractures truncate zoning and the megacryst is surrounded by other crystals grown from a melt (Figure 3a, b); (8) evidence that already grown megacrysts were physically accumulated during flow in melt (Figure 4 - 10), as discussed later in the paper; and (9) overprinting of megacryst accumulations by a magmatic foliation. All of these observations are readily applied to megacrysts in the TB (Figure 3, 4).
Figure 4. K-feldspar megacryst accumulation in general clusters
CP-179 (UTM: 0287557 4194677) Cluster of K-feldspar megacrysts, nearly all of which are independent, euhedral, zoned crystals, without molding. The cluster has no obvious boundary. 15 cm ruler for scale; (View).
CP 766 (UTM: 0280769; 4211678) Normal distribution of k-feldspars and planar cluster of K-feldspar megacrysts, some of which touch but without molding. The cluster has no obvious boundary. Brunton for scale; (View).
CP-Z-294 ( UTM: 0297260;4207191) Clusters inside and outside local schlieren zone. Clusters elongate parallel to schlieren zone. Late aplite dike cuts clusters and schlieren. ~25 cm hammer for scale; (View).
CP-280 (UTM: 0298065 4206296): Megacryst cluster in CP near eastern margin with metavolcanic host rock. metavolcanic xenoliths, which have rotated with respect to the host rock, also occur. 15 cm ruler for scale; (View)
CP-281 (UTM: 0298025 4206295) Tiling of K-feldspar megacrysts in a cluster in CP phase where it has intruded metavolcanic host rocks. Molding relationships are again absent. 15 cm ruler for scale; (View).
CP-804 (UTM: 0281644 4210647) K-feldspar megacrysts and local megacryst cluster in mafic (hornblende-rich) layer in CP . 15 cm ruler for scale; (View).
HD-CP 640 (UTM: 0288529 4198378) Looking N along strike of contact that dips steeply to right between HD and CP granodiorites: thus cliff face is approximately parallel to contact. An accumulation of K-feldspar megacrysts in CP immediately at contact. Height of face approximately 7 m; (View).
HD-CP 641 (UTM: 0288567 4198416) Horizontal face near photo Fig. 4g, showing same contact between CP and HD phases. K-feldspar clusters from CP, one with accumulation of enclaves, occur in HD and are now detached from CP. ~36 cm hammer for scale. (View).
