Structural and magmatic history of upper mantle peridotites in the Bay of Islands Complex, Newfoundland

• Main Author: Suhr, Gunter
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1991
• Subjects: Table Mountain; Newfoundland
• Online Access: https://research.library.mun.ca/6801/; https://research.library.mun.ca/6801/1/GunterSuhr.pdf; https://research.library.mun.ca/6801/3/GunterSuhr.pdf

The Bay of Islands Complex (BOIC) represents a lower Ordovician ophiolite located in western Newfoundland. In the northern part of the BOIC, a 6 km thick mantle section is exposed in the Table Mountain (TM) massif. The structural, micro-structural (including olivine lattice data), and geochemical variation within the mantle section were investigated in order to delineate the tectonic and magmatic history of the peridotites. -- The field structures indicate the presence of six structural units which are defined by distinct trends of the high temperature mineral stretching lineation of harzburgites, lherzolites, and dunites. On the basis of microstructural evidence, the formation of four of these units is assigned to spreading-related events, the remaining two to detachment tectonics. A high level and a low level zone preserving microstructural evidence for melt infiltration are present. The high level peridotites also show mineral chemical evidence for melt infiltration. -- Peridotite microstructures are classified into several 'type microstructures' interpreted to reflect differences in stress, accumulated strain, temperatures of deformation, and presence or absence of melt during deformation. The microstructural behaviour of orthopyroxene and spinel is investigated in more detail. The range of deformation mechanisms inferred from the morphology of orthopyroxene correlates largely with the temperature of deformation. In areas of lower accumulated strain, spinel grains, together with spatially associated phases, appear to preserve morphologies discriminating between different magmatic processes, i.e. spinel formed during partial melting, trapping of melt, and transient melt movement. -- The process of melt infiltration into peridotite is further investigated and two end-member processes can conceptionally be distinguished: (i) simple trapping of primitive melt; (ii) extensive flushing of melt through peridotite associated with fractionation of melt and reaction with the host. Mineralogical and geochemical trends ...