Peridotite in advanced stage of serpentinization - Onion Camp complex, Oregon

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

The serpentinized peridotite of the Onion camp complex, which is in contact with the variably serpentinized Josephine peridotite, is described by Yule et al. (2006)* as "highly serpentinized and sheared dunite, harzburgite, and sparse websterite....".  In the center of the image above, a pyroxene grain has been pseudomorphosed, probably by an amphibole mineral, with the chain structure preserved as parallel strands of the replacement mineral. A large serpentine pseudomorph after olivine occupies the center of the left side of the image, and a less obvious pseudomorph is at the upper right. Elsewhere in the image, serpentine is ubiquitous. Klamath Mountains, Josephine County, southwest Oregon. XPL. Digital mosaic, imaged area 3.6 mm x 6 mm.

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

Hand samples of serpentinized peridotite of the Onion Camp complex. Smaller sample on right has been rough polished on cut surface. Note hematite coating on left sides of both samples. Scale in centimeters.


*Yule, J. D., Saleeby, J. B., and Barnes, C. G., 2006, A rift-edge facies of the late Jurassic Rogue-Chetco arc and Josephine ophiolite, Klamath Mountains, Oregon, in Snoke, A. W. and Barnes, C.G., eds., Geological studies in the Klamath Mountain province, Californa and Oregon: A volume in honor of William P. Irwin: Geological Society of America Special Paper 410, p. 53-76.

Pseudomorphs after pyroxene in ancient (1.2 Ga) metaperidotite

Click on the image to enlarge.      Sample: Jeff Chiarenzelli; Photo: Dan Snyder

A small body of highly-metamorphosed rocks jn the Adirondack lowlands has been interpreted as metaperidotite because of its CIPW normative mineralogy (harzburgite) and because pseudomorphs after ferromagnesian minerals have been found there (Chiarenzelli et al., 2011)*. The protolith has been dated at ~1.2 Ga using detrital zircons. In this image, two pseudomorphs after pyroxene, now probably consisting of an amphibole mineral, can be seen at left center and top center. Pyrites Complex, St. Lawrence County, northern New York. XPL. Imaged area 1.3 mm x 2 mm.

Thanks to Dr. Jeff Chiarenzelli, of St. Lawrence U., for the loan of this and many other thin sections.

* Jeff Chiarenzelli, Marian Lupulescu, Eric Thern, and Brian Cousens (2011), Tectonic implications of the discovery of a Shawinigan ophiolite (Pyrites Complex) in the Adirondack lowlasnds, Geosphere, 2011;7;333-356