Geotectonic evolution of the Great Basin William R. Dickinson Department of Geosciences, Box 210077, University of Arizona, Tucson, Arizona 85721, USA ABSTRACT dimmer as earlier and earlier geologic time (2) precipitation or fi xation of those elements at frames are considered. The purpose of this paper the site of an ore deposit. Setting an element in The crust of the Great Basin has occupied is to provide an overview of Great Basin geotec- motion from some suitable reservoir is a nec- a range of tectonic settings through geologic tonics through geologic time as background for essary but insuffi cient factor for ore genesis, time. Archean and Paleoproterozoic crustal discussions of Great Basin metallogeny in subse- because no ore deposit is formed so long as the genesis preceded residence of Laurentia quent papers of this special issue. element keeps on moving. Thermomechanical within the Mesoproterozoic supercontinent conditions for mobilization and for precipitation Rodinia, which rifted in the late Neopro- TECTONICS AND METALLOGENY are diametrically opposed, yet both are required terozoic to delineate the Cordilleran fl ank of for ore genesis. Many metallic elements may Laurentia. Successive stages of Phanerozoic To understand metallogeny, one must know be set in motion through some segment of the evolution included (1) early to middle Paleo- the geologic sources of the constituents in ore crust during a given tectonic regime, but only zoic miogeoclinal sedimentation along a pas- minerals, appreciate the structural preparation those induced thermochemically to stop moving sive continental margin, (2) late Paleozoic to of rock masses for ore deposition, and under- will occur in a given ore deposit. The source of earliest Mesozoic thrusting of oceanic Antler stand the mechanisms for ore transport and pre- metals may be of secondary interest for metal- and Sonoma allochthons over the continental cipitation. Tectonics lies at the root of all these logeny, with site conditions that encouraged ore margin in response to episodic slab rollback issues. Potential sources of metals in the crust deposition of primary importance. beneath an offshore Klamath-Sierran island- and mantle vary with tectonic setting, structural arc complex, (3) Mesozoic to mid-Cenozoic conditions within the crust are a function of tec- GREAT BASIN TECTONIC HISTORY arc-rear and backarc thrusting, together tonic evolution, and fl uid fl ow through the crust with pulses of interior magmatism, associated is dictated by ambient tectonic environments. The Great Basin forms the widest segment with development of the Cordilleran mag- Few regions of the world have had as varied a of the vast Basin and Range taphrogen, which matic arc to the west where subduction and tectonic history as the Great Basin, and its geo- extends for >2500 km from the Pacifi c North- arc accretion expanded the continental mar- logic complexity challenges interpretations of west to central Mexico (Fig. 1). From the Colo- gin, and (4) middle to late Cenozoic crustal metallogeny to the utmost. rado Plateau on the east to the Sierra Nevada on extension, which involved initial intra-arc The nature of potential metal sources in the the west, and from the Snake River Plain on the to backarc deformation and later transten- deep mantle changed over time as lithospheric north to the Garlock fault and the Mojave block sional torsion of the continental block inland plates moved over asthenosphere. The composi- on the south, the Great Basin occupies a 600 km from the evolving San Andreas transform tion of the crust and the immediately subjacent by 600 km tract of rugged internal topography. system. Potential metallogenic infl uences lithospheric mantle were modifi ed over time The bulk of the Great Basin lies within the state on Great Basin tectonic evolution included as mantle magmatism and associated metaso- of Nevada (state outlines are shown on accom- transfer of substance from mantle to crust by matism added materials that were previously panying paleotectonic maps), but it extends also magmatism and associated metasomatism, absent, and extraction of crustal melts and into western Utah and the eastern fringe of Cali- and reworking of crustal materials by both leaching by rising fl uids removed materials once fornia. The Oregon Plateau segment of the Basin magmatism and intracrustal fl uid fl ow, the present. Ground preparation by structural defor- and Range taphrogen (Fig. 1) is in part internally latter of which was induced both by thermal mation in the Great Basin refl ects the effects of drained, and it can be considered an appendage effects of magmatism and by reconfi guration multiple tectonic episodes of contrasting struc- of the Great Basin proper. of fl uid-bearing rock masses during multiple tural style, which resulted in superposed struc- The Great Basin evolved along the western episodes of Great Basin deformation. tural features and older structures overprinted fringe of Precambrian Laurentia through diverse by younger ones. chapters of Earth history, each if which had Keywords: Basin and Range, geologic history, Ore transport and deposition involve inher- potential but varying implications for metallog- geotectonics, Great Basin, Nevada. ent thermochemical variability diffi cult to eny (Fig. 2), including: infer because the fl uids and thermal conditions (1) Precambrian emergence of juvenile conti- INTRODUCTION that formed ore are recorded in the geologic nental crust from the mantle to form the Archean record only by subtle indicators that are dif- Wyoming Province and the Paleoproterozoic The broad outlines of Cordilleran plate tecton- fi cult to read without ambiguity. For relations Mojave Province; ics are now well understood (Dickinson, 2000, between tectonics and metallogeny, there are (2) Mesoproterozoic incorporation of the Pre- 2002, 2004), although disputes continue regard- two linked but separate facets of ore genesis to cambrian basement into the Rodinian supercon- ing the impetus for each stage of tectonic evolu- keep in mind: (1) mobilization of elements of tinent during an interval punctuated by incipient tion, and our mental picture grows progressively interest from mantle or crustal reservoirs, and Belt-age rifting; Geosphere; December 2006; v. 2; no. 7; p. 353–368; doi: 10.1130/GES00054.1; 9 fi gures. For permission to copy, contact [email protected] 353 © 2006 Geological Society of America Dickinson 130°W 120°W 110°W TTJ Fraser River- Straight Creek V a fault n Alberta-Montana c o thrust front u v e r e Is g la id n * R d a c u * 50°N eF OM nd C A N A D a * A u in J e a LCZ KFMS U S A g h n C a * Laramide R Rocky t * CRP G s Mountains F a Z o c C i n a * W c Idaho- l N * o BM Montana P V a * Segment d r e o g G id Yellowstone R * Oregon Plateau s KM * e Segment hotspot d a track c s 40°N * a (SRP) MTJ C Gorda Figure 1. Position of the Great Basin Plate * S in the western Cordillera (adapted a n G r e a t after Dickinson, 2002). Modern triple foot of continental B a s i n 40°N plate junctions: MTJ—Mendocino; slope A RTJ—Rivera; TTJ—Tofi no. Other n SN d S e g m e n t r e abbreviations: BM—Blue Moun- a LEGEND s C O L O R A D O tains; CRP—Columbia River Plateau (check pattern and red color denote subduction F extent of Columbia River Basalt a zone u P L A T E A U l lavas); KFMS—Kisenehn-Flathead- t Gf volcanic* arc Rio Mission-Swan extensional Paleogene stratocones Grande T Rift basins; KM—Klamath Mountains; ran sit LCZ—Lewis and Clark fault zone; ion Z triple plate on PNW—Pacifi c Northwest; RFZ— junctions e U Rivera Fracture Zone; SN—Sierra P M S A e x Nevada; SRP—Snake River Plain; 30°N i c core A o TMI—Tres Marias Islands (cross complexes C M U e S M x A pattern and red color denote extent of I G B i c F A u G e o bimodal volcanic suite). J l u s active I A f l e 30°N f t ridge crest C a oceanic o C E S f i crust <5 Ma A e C S x r O L r i C t e e a e I a n r F n M r C l s t a O i i a r f o d a r M E R o n e l N r a O ad boundary of n l A I c Basin & Range i c r A a e id Province N e P n O t r P a o r r l i o e v en n i v n c t i al n la c c v e Numic e e subtaphrogen N RTJ Basin ic if intrataphrogen and c a sill Range P e TMI t is taphrogen s a R E R i Trans-Mexico Piman ve subtaphrogen raP 20°N 0500 la volcanic belt RF te scale in km Z 120°W 110°W 354 Geosphere, December 2006 Great Basin geotectonics Time ScaleCalifornia Sierran G R E A T B A S I N Colorado Plateau & scale forearc arc break region terrane western central eastern Rocky Mtns. Q north P b a s i n - r a n g e t e c t o n i s m c M south i o San 25 migratory z Andreas mid-Tertiary o O transform magmatism s n o uthwest e migratory n E Laramide ortheast Laramide C 50 magmatism province Franciscan east P west lK subduction Sevier Sevier thrust foreland 100 complex Sierra belt basin eK Nevada backarc c satellite [uncertain tectonic setting] i plutons batholith plutons o 150 z o J arc LFT s accretion Utah- e basinal 200 Idaho red bed M foothills Shelfal trough (-erg) subduction deposits Tr complex TRUNCATION 250 LFT Shelfal Pm n Antler o A n c e s t r a l R o c k i e s h t h overlap 300 c b a s i n s & u p l i f t s Pn n o n l r l a e a r c sequence h T r t i a e r G i d o o S n Antler n M o h z n t c foreland basin r 350 l Antler orogen a intraoceanic e o o remnant arcs t n m island arcs and s G o e Pilot - Joana a i a l t l e K m a t r a n D o f e t T P a l 400 m M i Roberts p C o r d i l l e r a n d R S Mountains e s allochthon m i o g e o c l i n e O C 500 UMG/BCF nP Yreka-Trinity- Shoo Fly miogeoclinal rifting mP subduction (inc.