Eclogite from Norway

Click on image to enlarge.         Specimen: Oliver Pluemper; Photo: Dan Snyder

Eclogite hand specimen from Norway. Thanks to Oliver Pluemper, University of Oslo, for the specimen. Optical scan. Specimen width 9.42 cm, height 7.3 cm.

Click on image to enlarge.     Specimen: Oliver Pluemper     Photo: Dan Snyder

Garnet (large, dark forms) and pyroxene (small and very  small yellow  and brown forms) in eclogite specimen shown in hand sample image above. This specimen, from the western Gneiss belt of Norway, has undergone significant deviatoric stress, which the garnet has resisted more effectively than has the pyroxene. XPL. Imaged area 2.7 mm by 4 mm.

Eclogite pebble fragment

Click on image to enlarge.          Specimen: Michael Davis; Photo: Dan Snyder

A slice through a small eclogite pebble from San Onofre breccia. Red and brown garnet with green pyroxene. Thanks to Distinguished Professor Michael Davis, University of California - Riverside, for the specimen. Found as beach rock, Camp Pendleton (USMC), California. Optical scan of sawed surface. Long dimension of imaged area 33 mm.

Click on image to enlarge.          Photo: Dan Snyder

Reflected-light photomicrograph of a small portion of the above sample. 2x objective. Imaged area 2.7mm by 4mm.

Click on image to enlarge.          Photo: Dan Snyder

Higher-magnification image of left center of previous image. Subhedral pyroxene grains visible at right of large garnet grain. Black grains are rutile, a common accessory in eclogite. Reflected-light photomicrograph. 4x objective. Imaged area 1.3mm by 2mm.

Click on image to enlarge.         Photo: Dan Snyder

Photomicrograph of part of thin section of same specimen at same scale as previous image. Black forms are garnet grains, brightly colored grains are pyroxene. Note many inclusions in garnet. Beige triangular grain at right is amphibole. XPL. Imaged area 1.3mm by 2mm.

Metamorphosed pyroxene and plagioclase in Litchfield (meta)norite

Click on image to enlarge.          Photo © Daniel R. Snyder

Metamorphosed orthopyroxene (left, bottom, upper right, lower right) and plagioclase (center) in  norite. Pyroxene grains show varying degrees and types of metamorphism. Original linear structure of large pyroxene grain at left is detectable only as a weak lination imparted by dark specks. Plagioclase is more intact, but shows degradation (blurring) of twin lamellae. Mt. Prospect complex, Litchfield County, northwestern Connecticut. XPL. Imaged area 1.3mm x 2mm.

Click on image to enlarge.          Photo © Daniel R. Snyder

Higher-magnification image of replacement product (blue) in large orthopyroxene grain (left side of top photo). XPL. Imaged area 0.5mm by 0.8mm.

Click on image to enlarge.          Photo © Daniel R. Snyder

Higher-magnification (10x objective) image of heavily-altered orthopyroxene grain (lower right corner of top photo). Green areas are remnants of original mineral. Note linear (chain silicate) structure. Also note that small grains of opaque mineral, presumably an iron-oxide mineral, are preferentially concentrated in pyroxene remnants. XPL. Imaged area 0.5mm by 0.8mm.

Click on image to enlarge.          Photo © Daniel R. Snyder

PPL image of above, showing relict lineation and concentration of opaques in pyroxene remnants.

Click on image to enlarge.          Photo © Daniel R. Snyder

Higher-magnification (40x objective) image of cluster of opaques in center of photo above. Note that many of the "opaques" appear to be slightly translucent brown ovals, aligned to the lineation in the pyroxene. PPL. Imaged area 0.13mm by 0.2mm.

Hydrous minerals replacing plagioclase and pyroxene in metabasalt

T

Click on image to enlarge.          Photo © Daniel R. Snyder

Above: Ophitic-texture pyroxene and plagioclase in a metabasalt are being replaced by hydrous minerals of the greenschist facies. The large orange and brown cluster was a pyroxene grain enclosing the now-corroded plagioclase laths. The pyroxene has been replaced by uralite, a massive amphibole usually composed mainly of actinolite (less commonly of hornblende). The scattered plagioclase laths show varying degrees of replacement by epidote, and probably by other minerals too small to identify. Extensive replament has occurred in the two adjacent, parallel plagioclase laths at right of center (See second image below for greater detail). Greenstone cobble in glacial gravel, southeastern Michigan, Specimen No. 49. Provenance likely northern Ontario. XPL. Imaged area 1.3mm by 2mm.

Below: PPL image of above. Green color of uralite is characteristic of actinolite (as well as hornblende).

Click on image to enlarge.          Photo © Daniel R. Snyder

Below: Higher-magnification image of area right of center in top photo. Note the cluster of small epidote grains that have replaced much of the two adjacent plagioclase laths. The replacement of plagioclase by epidote in this location was likely speeded by a channel between the two grains (visible as a narrow strip of uralite) that provided access by percolating fluids. XPL. Imaged area 0.5mm by 0.8mm.

Click on image to enlarge.          Photo © Daniel R. Snyder

Text

Epidote-rimmed albite and sieve-textured hornblende in Buck Creek (NC) amphibolite.

Click on image to enlarge.          Photo © Daniel R. Snyder

Epidote (cyan and magenta) rimming albite grains (white or gray) and sieve-textured hornblende (stippled orange and brown grains: left center, bottom center, lower left, bottom right) in Buck Creek  amphibolite. Blue Ridge Mountains, Clay County, western North Carolina. XPL. Imaged area 1.3mm by 2 mm.

Below: Higher magnification PPL image of sieve texture in hornblende grain at bottom center of image above. Imaged area 0.27mm by 0.4mm.

Click on image to enlarge.          Photo © Daniel R. Snyder

Below: Epidote-rimmed albite in another area of the same thin section. XPL.  Imaged area 0.76mm by 1.14mm. Ab=albite, Hbl=hornblende, Mt=magnetite. Epidote, not labeled, is the high-birefringence mineral rimming the albite grains.

Click on image to enlarge.          Photo © Daniel R. Snyder

Below:  PPL image of above. Note green color of hornblende (stage is rotated to give a pale green color) and sieve texture in hornblende grain at left of image.

Click on image to enlarge.          Photo © Daniel R. Snyder

Pseudomorphs after pyroxene in greenstone

Click on image to enlarge.          Photo © Daniel R. Snyder

Above: Serpentine pseudomorphs after pyroxene. Greenstone, specimen No. 5. Pebble in glacial gravel, southeastern Michigan. Provenance likely northern Ontario. XPL. Imaged area 2.7mm by 4mm.
Below, as above. Imaged area 3.2mm by 3.5mm.

Click on image to enlarge.          Photo © Daniel R. Snyder

Below, as above. Imaged area 1.3mm by 2mm.

Epidote, pyrite, and titanite in greenschist.

Click on image to enlarge.          Photo © Daniel R. Snyder

Epidote (high-birefringence, high-relief mineral, at right), pyrite (opaque mineral grains at left), and titanite (brown mineral surrounding pyrite). Greenschist,  specimen No. 1. Pebble in glacial gravel, southeastern Michigan. Provenance likely northern Ontario. XPL above, PPL below. Imaged area 1.3mm by 2mm.

Click on image to enlarge.          Photo © Daniel R. Snyder