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