By: magic-gigapans
Image: Callan Bentley, Mid-Atlantic Geo-Image Collection
License: Creative Commons Non Commercial ⧉

Uploaded: 22 Apr 2020
Last Updated: 15 Jul 2020

1.13 gigapixels
40,380 x 27,968 pixels
134.6 in X 93.2 in at 300dpi
5,646 pixels per inch

EPCC suite of rock types in thin-section-sized chips, polished up nice and pretty. Top, L-R: Campus Andesite, Red Bluff Granite, Mundy Breccia Bottom, L-R: Thunderbird Rhyolite, Castner Marble, Red Bluff Pegmatite, unknown (possibly part of a Waulsortian crinoid mound) Campus Andesite: Large emplacements of andesitic plutons mark the end of Laramide deformation in the El Paso region. Geophysical studies suggest that these bodies were placed in the El Paso region due to the fact that a segment of the Farallon Plate was subducting at a lower-than-normal angle so that the subducting slab did not get deep enough or hot enough to melt until it reached further inland (El Paso) unlike normal Andean model subduction zones. GigaPan of a related (same source) andesite intrusion known as Campus Andesite: https://viewer.gigamacro.com/view/IzTTya5Z9LSxL9dy Red Bluff Granite: Red Bluff Granites (5 total) are a suite of petrographically distinct granite phases that range from .98 -1.0 billion in age. The riebeckite pegmatite is one of these granites that contains large (>2cm) crystals of quartz, feldspar, and riebeckite with their characteristic black, blade-shape crystals. Other rare minerals are also present but in less quantity and quality. The sample shows changing crystal size from fine (small-closer to the cooler host rock) to courser (large- nearer to the hotter center of the magmatic dike). Gigapan of the Red Bluff Granite Micro-Granite phase: https://viewer.gigamacro.com/view/KeKHgD6ry7mXKAit GigaPan of the Red Bluff Granite phaneritic phase: https://viewer.gigamacro.com/view/P0081yxubSDiRDwF Mundy Breccia: Part of the Pre-Cambrian suite of rocks in the Franklin Mountains the Mundy Breccia is a unit that consists of boulder-like masses of basalt embedded in a fine-grained mafic matrix. The Mundy sits on top of the 1.2-1.4 billion year old Castner Fm. Since no lava source for the Mundy has been found the origins of this unit is thought to be one of three possibilities: 1)it's a volcanic debris flow (lahar) that occurred on top of an uplifted and exposed Castner Fm. 2) The Mundy is a volcanic lava flow that spread as molten lava that occurred on top of an uplifted and exposed Castner Fm. or 3) the Mundy is a under-water lava flow of pillow basalts encased in lava cooled by the ocean's waters. Gigapan of the Mundy Breccia in contact with a granitic dike. https://viewer.gigamacro.com/view/yfm72l1ANGiG5wu0 Thunderbird Rhyolite: Part of the Precambrian suite of rocks in the El Paso is the Thunderbird Group. It is younger (953-980 m.y.o) than the Red Bluff Granite indicating that the two rock units are related and that the Red Bluff magma was the source of the Thunderbird Rhyolites. GigaPan of another example of the Thunderbird Group: https://viewer.gigamacro.com/view/MFYSmkD8FpKTvUY6 Castner Marble: One of the more spectacular units on the Franklin Mountains is the Castner Fm. It is a 1400 ft thick exposed xenolith of marble inside the Red Bluff Granite complex. The Castner contains its original bedding planes and has several minerals in it due to metamorphism. These minerals include: garnets (shown in gigapan), tremolite, serpentine, and apatite. The Castner also contains the oldest fossils in the El Paso region which are stromatolites which are mounds of blue-green algae or cyanophytes called Collenia frequens. GigaPan of Castner Stromatolite: https://viewer.gigamacro.com/view/C2EcftJsGD3d3XsU Red Bluff Pegmatite: GigaPan of a larger section of the Red Bluff pegmatite: https://viewer.gigamacro.com/view/WPu5H8VptWUxosDE Unknown: Lower Permian limestone that is thoroughly metamorphosed by intrusives of probable Tertiary age. The limestone contains bivalves, crinoids, bryozoa, and some corals, which are indicative of a of shallow-water shelf environment.