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Weathered Metanorthosite, Roaring Brook, Adirondack Mountains by Ron Schott

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About This Gigapan

Taken by
Ron Schott Ron Schott
Explore score
0.42 Gigapixels
Date added
Oct 26, 2008
Date taken
Oct 26, 2008

Anorthosites metamorphosed to granulite facies underly most of the High Peaks region of the Adirondack Mountains in upstate New York. This sample illustrates beautiful examples of garnet coronas around pyroxenes.

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Gigapan Comments (2)

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  1. Ron Schott

    Ron Schott (September 08, 2011, 12:51PM )

    In this case, the plagioclase feldspars (off white and/or bluish) and the pyroxene (dark green) are primary igneous minerals and the garnet (red) is metamorphic. The plagioclase crystals almost certainly formed first based on their subhedral to euhedral shapes (crystallizing without impediment in the parental magma) and the pyroxenes crystallized at the end of the original igneous crystallization sequence as seen by their anhedral shapes (filling in the gaps between the well formed plagioclase crystals). In fact, the abundance of plagioclase in anorthosites (>90% by definition) is, in this instance, thought to be the result of early formed plagioclase crystals accumulating by floatation in a relatively dense ferrodioritic magma chamber. The pyroxenes are basically the interstitial last remanents of the slow crystallizing magma. The garnet is definitely a metamorphic mineral and thus formed post-igneous crystallization, though in this case my recollection is that the metamorphism was relatively soon after the magmatic event. Here's the official geochronology: the anorthosite crystallized ~1135Ma as part of the AMCG intrusions (anorthosite-mangerite-charnockite-gabbro) and was subsequently metamorphosed to granulite facies during the 1080-1050Ma Ottawan Orogeny of the Grenville Orogenic cycle (McLelland and Chiarenzelli, 1990).

  2. Chris Fastie

    Chris Fastie (September 08, 2011, 06:47AM )

    Is it possible to know which of the crystals grew when the intrusion first cooled a billion years ago, and which were formed a bit later during the events that metamorphosed this pluton?

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Stitcher Notes


GigaPan Stitcher version 0.4.3510 (Windows)
Panorama size: 417 megapixels (23095 x 18073 pixels)
Input images: 156 (12 columns by 13 rows)
Field of view: 1.3 degrees wide by 1.0 degrees high (top=0.1, bottom=-1.0)
All default settings
Original image properties:
Camera make: Canon
Camera model: Canon PowerShot S5 IS
Image size: 3264x2448 (8.0 megapixels)
Capture time: 2008-10-26 12:03:28 - 2008-10-26 12:12:31
Aperture: f/8
Exposure time: 0.0166667
ISO: 200
Focal length (35mm equiv.): 423.1 mm
Digital zoom: off
White balance: Fixed
Exposure mode: Manual
Horizontal overlap: 42.4 to 47.8 percent
Vertical overlap: 38.5 to 51.9 percent
Computer stats: 3261.98 MB RAM, 2 CPUs
Total time 1:43:30 (0:39 per picture)
Alignment: 40:13, Projection: 7:13, Blending: 56:03

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