Extension in high‐grade terranes of the southern Omineca Belt, British Columbia: Evidence from paleomagnetism

M. T D Wingate, E. Irving

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    Abstract

    Paleomagnetic observations are used to construct a map of structural tilts in metamorphic and plutonic rocks of the southern Omineca Belt in southeastern British Columbia. During Eocene extension, midcrustal rocks were exhumed in footwalls of low to moderate angle normal faults that dip east and west in the eastern and western parts of the study area, respectively. Tilts (averaging 30° to 40°) are consistent over large areas and generally antithetic to the major faults. In the central part of the study area, however, the eastern half of the Coryell Pluton is untilted, and its western half, in the hanging wall of the east dipping Kettle River Fault, is tilted down‐to‐ the‐east, in the opposite sense to that expected. North of the pluton, these eastward tilted rocks are juxtaposed against westward tilted rocks. To explain the anomalous tilts, a major west dipping Eocene normal fault (Arrow Lake Fault) is inferred, and a revised kinematic history for the area proposed. Observations of magnetic polarity (86% normal), laboratory unblocking temperatures, and isotopic age data suggest that magnetizations in the west were acquired during chron 23n, and in the east, in chron 23n and/or chron 24n. Unless extension postdated the acquisition of magnetization, tilts would not be observed; thus it is argued that extension in the west occurred after 50.6 Ma, and in the east between 51.6 (possibly 53.3) and 50.6 Ma. These time intervals do not correspond to any known global plate reorganization event, indicating that the last phase of Eocene extension in the southern Omineca Belt was governed by regional rather than global processes.

    Original languageEnglish
    Pages (from-to)686-711
    Number of pages26
    JournalTectonics
    Volume13
    Issue number3
    DOIs
    Publication statusPublished - 1994

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