PETROGENETIC STUDY OF RUTILE IN GRENVILLIAN ECLOGITES OF THE MANICOUAGAN IMBRICATE ZONE, NORTHEAST GRENVILLE PROVINCE

Throughout the Grenville Province, only a few localities of high pressure domains are documented. One of them is the Manicouagan Imbricate Zone (MIZ), where crustal rocks are thought to have reached eclogite facies metamorphic conditions (herein considered as Grt-Cpx-bearing without plagioclase irrespective of Cpx composition) during the Ottawan period of the Grenvillian orogeny (1090-1040 Ma).

The industrial transformation of ilmenite to synthetic rutile (Becher Process) mimics natural metamorphic process involving breakdown of ilmenite (or titanite) to form rutile, but generates many by-products. Thus, understanding rutile petrogenesis in metamorphic rocks, such as the eclogites of the Grenville Province, is of primary importance for the discovery of valuable mineral deposits. Subsequently, this could lead to cleaner titanium production.

The purpose of this study is to conduct a petrogenetic evaluation of rutile among the eclogite facies rocks of the MIZ. First, we want to identify the metamorphic reactions present in samples from various protolith of the MIZ. Then, determine the exhumation rate at which rutile retrogression can be prevented. Our methodology includes: (1) Field work done over the summer of 2017 (2) a petrographic study of textures and paragenesis under thin section and SEM (3) calculations of isochemical phase diagrams sections (IPDS), (4) X-ray compositional mapping and SEM quantitative analysis to further constrain the IPDS and (5) diffusion modeling.

Here, we present preliminary results of field work, textural analysis of thin sections and IPDS. Field observations suggest that the eclogites of the MIZ were subjected to extensive retrogression. This is supported by plagioclase rims around garnets, amphibolitisation of Cpx and symplectite textures observed under thin section. Also, rutile is present under various forms and stable with different paragenesis. So far, the petrographic analyses combined with IPDS partially unravel the key reactions guiding the formation and preservation of rutile in eclogites of the MIZ.