The Structural Geology of the Tectonized Ultramafic Suite of the Table Mountain Massif, Bay of Islands Complex, Newfoundland
Table Mountain is the northernmost massif in the Bay of Islands Ophiolite. It represents a continuous, approximately 7 kilometer thick, section of residual harzburgite tectonites capped by a nearly flat-lying assemblage of deformed and undeformed cumulate rocks. The notable mesoscopic structural fea...
| Summary: | Table Mountain is the northernmost massif in the Bay of Islands Ophiolite. It represents a continuous, approximately 7 kilometer thick, section of residual harzburgite tectonites capped by a nearly flat-lying assemblage of deformed and undeformed cumulate rocks. The notable mesoscopic structural features of the massif include a zone of penetrative deformation extending upsection from the tectonized harzburgites approximately 500 meters into the dunites and basal cumulates. The orientation of the foliation and associated lineations as well as the inferred shear sense within the zone is consistent with that affecting the harzburgites. Highly deformed dunite lenses which range in thickness up to 300 meters and up to 5 kilometers in lateral extent lie beneath the plagioclase-bearing cumulates. They have a gradational contact with the harzburgites. Throughout the harzburgite section compositional layering, defined by variations in enstatite concentration, is parallel or nearly parallel to the S1 foliation., The layering may either have limited lateral extent (associated with transposed intrusives) or it occurs in clusters of layers traceable as a group for several kilometers. The inclination of both the foliation and the layering relative to the essentially flat-lying contact between the cumulate and residual suites becomes progressively more shallow at deeper levels within the harzburgite. Petrographic examination of the massif indicates the presence of clinopyroxene and altered plagioclase (now hydrogarnet and sericite) in the upper 50 to 200 meters of harzburgite adjacent to the dunite lenses. Trace amounts of subhedral clinopyroxene occur throughout the harzburgite, typically associated with polycrystalline enstatite clots. Petrofabric analyses of olivine fabrics of samples from the harzburgite section indicate that the [100] maxima strengthen with increasing depth from the cumulate carapace. Fabric asymmetries relative to the trace of the foliation and spinel lineation indicate a dominantly sinistral shear ... |
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