Timing of deformation in the early Mesozoic back-arc basin of the western U.S. Cordillera
1/15/97-12/31/99, $94,400, PI-Wyld
National Science Foundation EAR-9796174 (This grant represents the remainder of the one listed next, after transferring the project to the University of Georgia.)
1/1/96-12/31/98, $165,000
National Science Foundation EAR-9526129
(Rice University, joint with J.E. Wright )
This project focused on the structural evolution of a back-arc basin system in Nevada, from its inception as a sedimentary basin in the Triassic to its structural collapse later in the Mesozoic, during formation of the Luning-Fencemaker fold-and-thrust belt. Results of this study have yielded several important conclusions. First, the back-arc basin developed in response to extensional tectonism along the continental margin, not thermal or dynamic subsidence as had been previously proposed. Second, structural collapse of this basin to form the Luning-Fencemaker belt occurred via polyphase deformation that propogated from west to east across the basin, as the adjacent arc (located to the west) was first thrust over the back-arc, and the back-arc deposits were ultimately thrust over the continental shelf (to the east). Third, structural collapse of the basin occurred entirely in the Jurassic, and did not span the Jurassic to Cretaceous as had been previously proposed. Cretaceous deformation within these rocks post-dates Jurassic deformation by >50 m.y., and reflects a separate orogenic event that is unrelated to development of the Luning-Fencemaker belt. Finally, our studies of the metamorphic grade of rocks in the Luning-Fencemaker belt indicate that Jurassic crustal shortening resulted in structural burial of these rocks to depths of at least 7 km, followed by substantial uplift and erosion prior to the Early Cretaceous. These results have major implications for the structural and tectonic evolution of the western U.S. Cordillera in the Mesozoic Era. Project Summary (PDF) Publications resulting from Project (PDF)
Nature, timing and controls of Jurassic orogenesis in the western U. S. Cordillera
1/1/92-12/31/94, $98,052
National Science Foundation, Tectonics Division, EAR-9219268
(Rice University, joint with J. E. Wright).
This grant provided funds for work on the nature and timing of regional Jurassic shortening deformation in the early Mesozoic arc of the western U. S. Cordillera. Our studies document significant differences in the timing of regional deformation between three different parts of the arc (the Klamath Mountains of California, Pine Nut Range of west-central Nevada, and Black Rock Desert of northwest Nevada). We have demonstrated that the timing of deformation in each area corresponds closely to the timing of voluminous Jurassic plutonism. These relations suggest that arc plutonism plays an integral role in facilitating and localizing strain in the crust of an active arc system. Our work indicates that this is probably not the only factor controlling the timing of deformation, however. Thus, our data show that major Jurassic shortening deformation in the Black Rock Desert occurred in the Early Jurassic some 30 m.y. prior to Jurassic shortening in the Pine Nut Range, a contrast in timing which is far too long to be accounted for simply by natural variations in the time of voluminous plutonism between one part of the arc and another. Viewed on a larger scale, the record of Early Jurassic shortening deformation in the Black Rock Desert is completely at odds with the Middle to Late Jurassic age of shortening deformation documented in most other parts of the Mesozoic arc. These relations therefore suggest that plate boundary conditions may have been substantially different in the vicinity of the Black Rock Desert segment of the arc than elsewhere during the Early Mesozoic. This conclusion has substantial new implications for the Jurassic tectonic evolution of the western U.S. Cordillera. Publications supported by this grant are listed below. Project Summary (PDF) Publications resulting from Project (PDF)
Paleozoic and Mesozoic geology and geochronology of the Pine Forest Range, northwest Nevada
7/89-8/91, $39,523
American Chemical Society Petroleum Research Fund Grant (Stanford University).
This project (written by Wyld to support Ph.D. thesis research) was funded to support field-based stratigraphic, structural and geochronologic studies in metamorphosed and deformed Paleozoic to Mesozoic strata of the Pine Forest Range (PFR), northwest Nevada. The first part of the project concentrated largely on the stratigraphic framework and paleogeographic and tectonic setting of the PFR. The second part of the project concentrated mostly on the Mesozoic deformational and metamorphic history of the range, and the relationship between deformation, metamorphism and coeval plutonism. Project Abstract (PDF) Publications resulting from Project (PDF)
