Termination of the northwestern Basin and Range province into a clockwise rotating region of transtension and volcanism, southeast Oregon
- 作者：David Trench ; david.trench@gmail.com ; Andrew Meigs meigsa@oregonstate.edu ; Anita Grunder grundera@oregonstate.edu
- 关键词：Along-strike growth of extensional provinces ; Normal-fault tip propagation ; Brothers fault zone ; Northwest Basin and Range
- 刊名：Journal of Structural Geology
- 出版年：2012
- 期刊代码：52_01918141
- 类别：ear
- 出版时间：June, 2012
- 卷：39
- 期：Complete
- 页码：52-65
- 文件大小：2730 K
摘要
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 鈭?聽Ma. West-directed extension accumulated on NWBR faults at 0.01聽mm/yr and lengthened northward after 7.05聽Ma. BFZ faults accumulated northeast-directed extension at rates of 0.01聽mm/yr since 5.68聽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.