Journal
JOURNAL OF STRUCTURAL GEOLOGY
Volume 39, Issue -, Pages 52-65Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsg.2012.03.007
Keywords
Along-strike growth of extensional provinces; Normal-fault tip propagation; Brothers fault zone; Northwest Basin and Range
Categories
Funding
- National Science Foundation grant from the Continental Dynamics Program [EAR-0506869]
- National Science Foundation grant from the Tectonics Program [EAR-0610064]
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New data indicate that northeast-directed extensional faulting characterizes slip across the Brothers fault zone (BFZ), which marks the northern limit of the northwestern Basin and Range (NWBR) extensional province in southeastern Oregon. Structural separation across individual north-northeast striking NWBR faults decreases to zero south of the BFZ. Field relationships and cross-sections demonstrate limited kinematic linkage and independent evolution of the two fault systems since similar to 7 Ma. West-directed extension accumulated on NWBR faults at 0.01 mm/yr and lengthened northward after 7.05 Ma. BFZ faults accumulated northeast-directed extension at rates of 0.01 mm/yr since 5.68 Ma. Deformation coincides with periods of heightened basaltic magmatism in the High Lava Plains, implying that volcanism weakened the crust and promoted extension in the BFZ. In a new model, we reconcile the observed northward diminishing rate and clockwise motion of the modern NWBR deformation field with regional geology. The BFZ defines a small circle about the pole of rotation and separates a stable block to the NE from the extending region to the south. Faults to the south are growing northward, consistent with the northward decrease in rate and magnitude of extension in the NWBR. (C) 2012 Elsevier Ltd. All rights reserved.
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