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12 hits

  • Thumbnail for ERB-0X3

    In this sample, a spaced, anastamosing schistoscity defined by biotite, garnet, hornblende and opaques wraps around deformed feldspar lenses which display undulose extinction and bent growth as well as deformation twins. Polyganized quartz and feldspar mantles the feldspar porphyroclasts. Quartz ribbons are prevalent throughout this sample. The sense of shear is ambiguous.

  • Thumbnail for ERB-23

    Intergrown, subhedral two-pyroxene gabbro with hornblende and poikilitic plagiclase with deformation twins and abundant pyroxene inclusions.

  • Thumbnail for ERB-03

    In this mylonitized sample, biotite, sillimanite, and the opaques define a spaced schistoscity overprinting a background matrix of seriate-interlobate quartz and feldspar. The foliation wraps around polymineralic porphyroclasts with fish-like shapes. The sense of shear is ambiguous. A lineation is defined by aligned sillimanite and biotite.

  • Thumbnail for ERB-06a

    This thin section contains two distinct populations. The background 'matrix' consists of seriate-interlobate feldspar and quartz, with both phases exhibiting microstructures indicative of strain. A decussate fabric of biotite, chlorite, kyanite, and opaques are distributed in pods throughout the quartz and feldspar 'matrix'. Close examination of these pods reveals poikiloblastic host mineral, presumably k-feldspar, which is almost entirely obscured by inclusions. Zircons with radiation halos are extensive within this poikilobastic phase.

  • Thumbnail for ERB-02

    This sample is a strongly mylonitized pelitic schist with a continuous schistoscity defined by strongly alligned biotite, fibrous sillimanite, and opaques and interspersed with discontinuous quartz and k-feldspar ribbons. K-feldspar is strongly sericitized. The sense of shear is ambiguous.

  • Thumbnail for ERB-12

    This two-pyroxene, hornblende-bearing gabbro is highly fractured and has a much finer-grained population of pyroxenes growing in the interstices between larger pyroxene grains. A thin band of finer-grained pyroxne and plagioclase cross-cuts the sample.

  • Thumbnail for ERB-09b

    This metamorphosed granite has a weak spaced foliation defined by moderately aligned elongate minerals and slight compositional layering. The opaque phases are segregated into two discrete bands, along which, large quartz grains show a crystallographically preferred orientation, causing them to appear nearly isotropic. Alternatively, this nearly isotropic phase could be untwinned leucite, however, an the lack of twins and association with the remaining phases is unlikely. The chlorite and muscovite phases appear to be collectively pseudomorphing a preexisting phase, as evidenced by dark, elongate inclusions within the chlorite grains.

  • Thumbnail for ERB-09a

    Grain boundaries between the quartz and feldspar phases in this sample are consistently lobate, often with finer-grained subgrains rimming each crystal. Quartz in undulatory. The mica phases are subhedral and often resorbed, with kink bands causing undulose extinction along the length of the grain. Along one edge of the thin section is a seam dominated by clinozoisite. A hematite stain gives a dusty orange appearance to the feldspars and fractures within the sample contain higher concentrations of the phase.

  • Thumbnail for ERB-01

    Anastamosing spaced schistocity defined by aligned elongate minerals including biotite, hornblende, garnet, and opaques. Foliation wraps quartz and k-feldpsar porphyroclasts with core-mantle textures and subgrain development in the old grains. K-feldspar is strongly sericitized. The sense of shear is ambiguous.

  • Thumbnail for ERB-08

    This thin section contains two main zones. One half contains subhedral grains of k-feldspar, quartz, orthopyroxene, biotite and opaques. Kink bands, deformation twins, and core-mantle structures (fine-grained felspar rimming the older grain) in the the feldspars show evidence of strain accomodation. Aggregates of finer-grained serieate-lobate quartz grains with thickened grain boundaries and uniform extinction show evidence of grain boundary migration. Larger quartz grains with undulose extinction and deformation lamellae also indicate strain accomodation. The opaque mineral(s) have rounded, anhedral grain shapes and tend to cluster with biotite and orthopyroxene. Biotite is subhedral, with kink bands and undulose extinction; it is generally found in the intersticies between grains, most commonly adjacent to orthopyroxene grains. Orthopyroxene is subhedral and occasionally embayed. The other half of the thin section is dominated by two porphyroclasts of feldspar. This portion of the thin section abounds with symplectic intergrowths of quartz and feldspar as well as much subgrain development in both mineral. Growing normal to the rims of opaques and biotite grains is a poplulation of acicular aluminosilicate.

  • Thumbnail for ERB-07a

    This coarse-grained sample is dominated by subhedral to anhedral k-feldpsar and subhedral garnet, with pockets of quartz aggregates clustering near the feldspar grains and less abundant biotite and orthopyroxene grouped with the garnet phase. Symplectic growth concentrates along boundaries between garnet and k-feldspar. Contacts between garnet are typically host to a mixture of chlorite and biotite. The orthopyroxene grains are strongly fractured and embayed.

  • Thumbnail for ERB-24

    This sample has a weak spaced foliation defined by aligned, euhedral and subhedral biotite. The varied pleochroism and grain shape in the biotite grains suggests two phases of biotite growth, one of which occurred post-deformation. The garnets are skeletal and intergrown with biotite; their frequently 'strung-out' appearance helps contribute to the foliation development. K-feldspar is dominated by deformation twins. Quartz aggregates are alternately polygonal and granoblastic