Cao lead author of paper on the melting of eclogite for Precambrian Research journal

Department of Geology and Environmental Sciences Assistant Professor Wentao Cao is the lead author of a paper that has been accepted for publication in Precambrian Research, a peer-reviewed scientific journal covering the geology of the Earth and its planetary neighbors.

The paper, “Partial Melting due to Breakdown of Phengite and Amphibole in Retrogressed Eclogite of Deep Precambrian Crust: An Example from the Algonquin Terrane, Western Grenville Province, Canada,” addresses a petrological question of partial melting of eclogite (a.k.a. “Christmas rock”) in a mountain belt (Grenville Province) more than one billion years ago.

In deep roots of a large mountain belt, conditions could be reached to partially melt even mafic (ferromagnesian) rocks (which tends to have a higher partial melting temperature than other crustal rocks). However, how and under what conditions mafic rocks partially melt has been poorly studied.

In this study, Dr. Cao and his co-authors documented detailed petrographic textures in the studied eclogite and interpreted them as evidence of previous melting. The authors applied thermodynamic modeling to these samples and determined that the samples were exhumed from approximately 55 to 60 km below the surface and reached a peak temperature of 920 degrees Celsius at approximately 40 km. Integrating petrographic textures, mineral assemblage and thermodynamic modeling, the authors determined that two hydrous minerals, phengite and amphibole, are major minerals that contributed to the partial melting.

Since the mafic rocks have been partially melted, other crustal rocks at the same level could have been melted at a higher degree, which indicates extensive melting in the middle to lower crust of the orogen (i.e. mountain belt). The authors argue that the partial melting in the mountain root may have triggered the collapse of the large orogenic belt in Precambrian time.

The paper is from a new project that Cao started after arriving at Fredonia. The fieldwork and the project were generously supported by various funding sources and individuals, and the authors sincerely appreciate the funding and contributions. Funding sources include internal funding from the department, the college and Research, Scholarship and Creative Activities (RSCA) grants and a research grant from China University of Geosciences (Beijing).

Two Fredonia graduates, Emily Guest ('20, Geology, minor in Geographic Information Systems) and Ashley Wertz (‘19, Geology), conducted initial examination of the samples using petrographic microscopes and scanning electron microscopes (SEM) at the University at Buffalo. Peter Bush, from the State University at Buffalo, provided technical support of the SEM to the undergraduate researchers. The authors also benefited technical support, discussion and comments from colleagues at other institutions.

The paper is current under copyediting and will be in an issue soon. See the online journal page for the introduction of paper.