I'm conducting this NSF-funded study in collaboration with Jeff Vervoort at Washington State University. This is the central topic of Todd LaMaskin's PhD research, and he is taking the lead on many aspects of the project. We are using a multidsicplinary approach to test a new hypothesis for collisional tectonics and related basin development during Triassic and Jurassic time in the Blue Mountains Province of northeastern Oregon. Our interdisciplinary research combines detailed stratigraphy, field mapping, detrital zircon dating, and trace-element and isotope geochemistry. With this data we hope to reconstruct changes in basin geometry and provenance through time, and thus clarify the major driving forces and plate interactions that controlled the tectonic evolution of eastern Oregon and adjacent parts of the western U.S. Cordillera. The following figures are from a paper that Todd and I recently submitted to AJS, which reviews an extensive literature on the stratigraphy and tectonics of Mesozoic rocks in the Blue Mountains, and presents a new hypothesis for Late Triassic arc-arc collision followed by Jurassic arc-continent collision in eastern Oregon. We are interested in how these events may be related to other parts of the western U.S. and Canadian Cordillera, and their significance for understanding processes of crustal accretion and continental growth. Our working hypothesis is just the first step in this multi-year project. We have a series of tests lined up and expect things will look fairly different by the time lots of new data come in and get synthesized.
Figure 1. Generalized terrane map of the Blue Mountains Province (BMP), modified from Dickinson (1979), Mann (1989), Follo (1992), Vallier (1995), Gray and Oldow (2005). BC, Baker City; BMB, Bald Mt. batholith; H, Huntington; IB, Idaho Batholith; IM, Ironside Mt.; JM, Juniper Mt.; O, Oxbow; PL, Pittsburg Landing; CM, Cuddy Mt.; CH, Coon Hollow; SDM, Seven Devils Mts.; SRB, Salmon River Belt; WM, Wallowa Mtns. (and batholith); WISZ, Western Idaho Shear Zone.
Figure 2. Chronostratigraphic correlation chart for sedimentary and volcanic rocks in the Blue Mountains, compiled from multiple sources. The stratigraphy provides a record of basin evolution, provenance, and controling tectpnic processes, which we are investigating in this study. Our work would not be possible without many pioneering studies by some great geologists, some of which are cited above, that gave us our present knowledge of the geology and stratigraphy in the Blue Mountains.
Figure 3. Schematic diagrams illustrating hypothesis for Late Triassic to Late Jurassic arc-arc and arc-continent collision in the Blue Mountains Province (BMP) and related collisional basin evolution. Restoration of ~400 km of post-Jurassic dextral translation places the BMP outboard of the Black Rock (B.R.) arc and LFTB in NW Nevada (Wyld and Wright, 2001). A. Pre-collisional Wallowa (Wa) and Olds Ferry (OF) arcs; B. Doubly-vergent Molucca Sea-type arc-arc collisional complex (B = Baker terrane) with coarse olistostromes and gavel shed into flanking marine sub-basins (blue arrows); C. Early to Late Jurassic growth of Izee collisional basin and onlap of sediments onto older rocks and structures, deep subsidence possibly a flexural response to thrust loading in LFTB; D. Thrusting, uplift, and post-kinematic pluton emplacement related to initiation of new subduction zone. MS-1a, -1b, -2 indicate mega-sequences.
Link to the webpage for our Blue Mts Field Trip, March 24-29, 2007.
Blue Mts Seminar, Fall quarter, 2006.
Dorsey and LaMaskin (2006) and LaMaskin and Dorsey (2006) Anchorage GSA abstracts.
Our thinking about collisional tectonics and related basin evolution is fleshed out in a new "idea paper", which we submitted to AJS in November 2006. Please contact me if you would like a copy.
The above material is based upon work supported by the National Science Foundation (Grant No. EAR-0537691). Any opinions, findings or conclusions expressed herein are those of the authors and do not necessarily reflect the views of the National Science Foundation (NSF).
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This page was last updated March 2007, by Becky Dorsey.