Paper No. 5
Presentation Time: 8:00 AM-12:00 PM
TECTONIC RECONSTRUCTIONS BASED ON REGIONAL CROSS SECTIONS TO INCREASE UNDERSTANDING OF METALLOGENY AND FLUID FLOW IN THE NORTHERN GREAT BASIN
A complex series of regional to local geologic events, beginning in the Archean and continuing to the present, have resulted in the formation of the world-class mineral endowment in the northern Great Basin. Understanding the links between regional tectonic and metallogenic events necessitates the construction of the geologic framework in 2- and 3-dimensions. To this end, a series of regional cross sections have been constructed across the northern Great Basin to help understand the geologic events that led up to, were synchronous with, and followed major periods of mineralization. These sections extend to depths of at least 5 km in order to portray crustal structures that may have localized multiple episodes of deformation, magmatism, regional fluid flow, and hydrothermal activity. The top of pre-Cenozoic rocks in the cross sections is based on inversion of gravity data. Regional stratigraphic trends and aeromagnetic, magnetotelluric, geochronologic, geobarometric, and conodont CAI data constrain the deeper parts of the sections. One of the purposes of creating the cross sections, which portray the present-day three-dimensional geometry, is to remove the effects of younger events, allowing reconstruction of the geologic setting through time. For instance, to understand the structural and stratigraphic setting during the metallogenically important late Eocene, the effects of late Cenozoic extensional deformation are removed by restoring fault offset, as constrained in part by the distribution, thickness, and provenance of Neogene and Paleogene sedimentary and volcanic rocks. The effects of Late Paleozoic to Early Tertiary contractile deformation are removed by understanding the age and distribution of lithotectonic terranes and through the reconstruction of Paleozoic facies trends. The resulting geologic models show the regional controls on and locations of deformation, sedimentation, magmatism, and hydrothermal activity and frame numerical models of fluid flow, and mass transport during each event. Thus far, geologic sections for the present, mid-Miocene, and late Eocene have been coupled with fluid flow models that are calibrated to temperature, stable isotopes, and silica saturation to improve understanding of active geothermal systems, low sulfidation Au-Ag, and Carlin-type Au deposits.