Petrogenesis of the jotunite unit at the Morin Complex, Grenville Province, Quebec: A field, mineralogical and chemical study.

摘要

There has been an ongoing controversy in igneous petrology regarding the relationship between massif anorthosites and Fe-Ti-rich, mafic to intermediate rocks that are associated with them, herein termed jotunite and mangerite. In the many models that have been developed to explain its formation, jotunite has been genetically related to anorthosite, mangerite, both or neither. Although jotunite seems to play an important role in the formation of anorthosite complexes, few studies have examined the nature of this rock type in detail. This study focuses on jotunite, and to a lesser extent, mangerite, from the Morin Complex, Quebec, in order to determine the field, petrographic and chemical characteristics of these rocks, and to develop a petrogenetic model that can describe their formation.;I have identified two suites of Fe-Ti-rich rocks within the jotunite unit. Both suites contain plagioclase + orthopyroxene + clinopyroxene ;Given the gradational nature of the contacts between the two units, the systematic progression of mineral compositions from jotunite to mangerite, and shared whole rock chemical characteristics, it seems clear that jotunite and mangerite are genetically related. To test this hypothesis, I have developed a "liquid line-of-descent" model that relates jotunite and mangerite through the progressive removal of a series of cumulate assemblages. The validity of such a process has been checked by modelling the behavior of a number of trace elements by Rayleigh fractional crystallization. The model predicts the behavior of ferromagnesian and large ion lithophile elements well, but cannot account for the behavior of high field strength elements.;Fine-grained enclaves found in both jotunite and mangerite strongly resemble their host rocks in mineral assemblage and mineral composition. Furthermore, these enclaves are similar in most respects, including whole rock composition, to fine grained varieties of jotunite and mangerite elsewhere in the Morin Complex. I conclude that these enclaves are autoliths of their hosts.