Active Projects:

Tectonic analysis of the Olds Ferry - Baker terrane boundary zone, Idaho and Oregon
The paleogeography, timing, and kinematic characteristics of terrane accretion in the northwestern United States remain fundamental issues concerning the Mesozoic tectonic evolution of the North American continent. Because a regionally extensive blanket of Cenozoic volcanic and sedimentary cover limits the exposure of these terranes, resolving their evolution depends critically on detailed characterization of the structure, petrology, and field relationships where exposure is available. At present, much of the area in western Idaho where these terranes are exposed has yet to be mapped in detail (1:24,000 scale or smaller). The need for geologic mapping as a foundation for understanding the Mesozoic crustal assembly and younger tectonic modification in the region provides the principal scientific motivation for this research. 
    The main objectives of the current phase of the project are to: (1) document the geometry and movement history of the complex fault system between the Baker and Olds Ferry terranes in western Idaho and eastern Oregon; (2) to explore the relationships between the inherited Mesozoic structural architecture and Cenozoic deformation along this boundary zone; and (3) to determine the role of the terrane boundary  in the active regional strain field (it separates a microseismically active domain to the NW from a microseismically quiescent domain to the SE). To accomplish these objectives, an extensive field project (including me, two graduate students, and six undergraduate students) will begin to delineate the structural architecture and kinematic evolution of the Baker - Olds-Ferry  terrane boundary during the 1999 field season.  This research will involve a combination of geologic mapping, structural analysis, geomorphology, and geochronology.

Structure and timing of thrust emplacement of the Golconda Allochthon, western Nevada
Classically, the emplacement of the Golconda allochthon onto the western margin of North America has been attributed to the Sonoma Orogeny in Permo-Trassic time.  Critical evaluation of the available timing constrains, however, allows east-directed transport of the allochthon to have occurrred as late as the middle Jurassic -- perhaps 75 My later than currently envisioned.  So, when did Golconda thrusting occur, and how does it fit into the Paleozoic-Mesozoic tectonic framework of western North America?  These questions form the focus of this project and are being adressed through a multidisciplinary synthesis of geologic mapping, structural analysis, stratigraphy, and geochronology.

On the Horizon:

The Scandinavian Caledonides
The Scandinavian portion of the Caledonian-Appalachian mountain belt offers a fantastic opportunity to investigate tectonic processes at middle to deep levels of a continent-continent collision zone. Siluro-Devonian collision of Baltica and Laurentia resulted in the emplacement of a crustal-scale allochthon onto the western margin of the Baltic craton. Subsequent erosion has removed much of the original nappe stack, and the present-day mountain belt consists of a relatively thin veneer of the original allochthon lying over autochthonous structural basement. Because the present erosional surface essentially follows the basal thrust of the nappes, the contact between the underthrust Baltic craton and the over-riding Caledonian nappes can be studied and compared at a variety of locations and paleodepths. I plan to continue my work in Scandinavia in the near future, and hope also to begin a new project in western Ireland, looking at the evolution and juxtaposition of terranes in this portion of the Caledonian Mountain Belt.

Precambrian Basement
Several new projects to study the Archean and Proterozoic basement of the western United States are in the planning stages.  One focus of this work will be to characterize the western margin of the Wyoming craton -- the nature of this margin is important not only from the perspective of Archean tectonics, but also because it provides a template for identifying the continental block that rifted away from the western margin of the U.S. in latest Proterozoic time.

The Uralian Orogen
The Uralian Orogen played a fundamental role in the assembly of the Eurasian portion of Pangaea in late Paleozoic to early Mesozoic time, yet the detailed timing, paleogeography, and kinematic evolution of this collisional system are not well established.  Furthermore, from the perspective of orogenic development, the Urals exhibit a number of unusual characteristics compared to other mountain belts.   Remarkable features include: (1) the limited amount of shortening in the foreland fold-thrust belt; (2) the geometry of the foreland basin; (3) the relatively narrow width of the tectonized zone; and (4) the lack of a significant syn- to post-tectonic high-grade metamorphic core along the axis of the orogen.  Collectively, these characteristics suggest that Uralian orogenesis involved much less post-collisional convergence, shortening, and crustal thickening than other zones of collision.  At least two hypotheses can be offered to explain the relatively minor amount of shortening. First, the Urals may have resulted from highly oblique collision, making orogen-orthogonal convergence less important than orogen-parallel transport. Second, Uralian orogenesis may have occurred in phases of short duration, preventing the accumulation of significant crustal deformation over time. These hypotheses make predictions about the timing and kinematic evolution of the Urals.  Our research team (C. J. Northrup, W. S. Snyder, T. A. Schiappa, V. I. Davydov, and students) will test them through the integration of stratigraphic, structural, kinematic, and geochronologic analyses in the southwestern portion of the Urals and its foredeep.

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