Granulite Terranes and the Lower Crust of the Superior Province
- Robert F. Mereu,
- Stephan Mueller and
- David M. Fountain
Published Online: 9 APR 2013
Copyright 1989 by the American Geophysical Union
Properties and Processes of Earth's Lower Crust
How to Cite
Percival, J. A. (1989) Granulite Terranes and the Lower Crust of the Superior Province, in Properties and Processes of Earth's Lower Crust (eds R. F. Mereu, S. Mueller and D. M. Fountain), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM051p0301
- Published Online: 9 APR 2013
- Published Print: 1 JAN 1989
Print ISBN: 9780875904566
Online ISBN: 9781118666388
Granulites are a common component of the lower crust but the study of surface granulites can provide information on the contemporary lower crust only in certain rare examples. For example, granulite terranes of the Archean Superior Province formed in three distinct tectonic environments which governed their burial and uplift history: 1) ancient terranes, such as the Minnesota River Valley gneiss terrane, metamorphosed at modest pressure (4.5–6.5 kbar) in the granulite facies, possibly representing a continental collision environment; 2) greenstone-granite terranes, with granulitic (7.5–9 kbar) lower crust, that formed in magmatic arc environments; and 3) metasedimentary belts, with small to large. 4.5–6.5 kbar granulite occurrences, that represent accretionary wedges, tectonically thickened and subsequently metamorphosed during uplift. Collisional and accretionary settings lead to the rapid exposure of high-grade metamorphic rocks through tectonic thickening, heating and consequent erosion; however, thickening through magmatism rarely results in exhumation of deep crustal rocks. the Kapuskasing and Pikwitonei terranes of the Superior Province represent basal magmatic arcs, exposed late in their metamorphic history by Proterozoic faults, based on characteristics attributed to exposed crustal crosssections, including association with faults, gradational metamorphic zonation, high maximum metamorphic pressures and retarded cooling rates.
Granulite formation is an integral part of the process of production of stable continental crust in the Superior Province. Information on the nature of the contemporary lower crust can be inferred only from faulted granulite terranes although similar petrogenetic processes are recognized in all terrane types.