GSN Regular Membership Meeting – January 17, 2025

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Contact: gsn@gsnv.org

GSN REGULAR MEMBERSHIP MEETING—January 17, 2025

TIME: Drinks @ 6 pm, Dinner @ 6:30 pm, Talk @ 7:30 pm

WHERE: ATLANTIS CASINO RESORT, RENO, NV

Presenter: Dr. Jim Faulds, Associate Director of NBMG, Professor at UNR

Title:  “Nevada’s Dynamic Geologic Journey: Living on the Edge in a Long-Lived Orogenic Belt”

MEETING SPONSOR:  PREMIER DRILLING

DINNER COST:  $60 per person

ONLINE RESERVATIONS CAN BE MADE  BELOW.

PLEASE RSVP FOR DINNER NO LATER THAN MONDAY, JANUARY 13, 2025

Please contact Laura Ruud at the GSN office for more information:  gsn@gsnv.org

Abstract:

Nevada’s journey through time has produced some of the most intriguing geology on Earth, with terrain rich in natural resources and replete with geologic hazards. Our current rapidly evolving landscapes reflect an active tectonic environment but also record a rich geologic history spanning more than one billion years of tectonism along the western margin of North America.  The western North American plate margin originated during late Proterozoic rifting and breakup of a supercontinent, as marked by development of rift basins and local mafic volcanism.  A broad late Proterozoic-Paleozoic passive continental margin developed in the wake of late Proterozoic rifting.  Thick sections (commonly >10 km) of late Proterozoic to late Devonian, shallow marine miogeoclinal sedimentary strata accumulated on the continental shelf.  The passive margin began to breakup in the late Devonian-early Mississippian with the onset of the Antler orogeny, whereby east-directed thrusting placed deep-water sediments over portions of the continental shelf.  What followed was a long period of convergent tectonism that persisted into the early Tertiary and included both the accretion of exotic terranes and subduction of oceanic lithosphere (mainly the Farallon plate) with attendant arc volcanism.  Facilitated by abundant subhorizontal discontinuities, broad fold and thrust belts developed in the thick sections of miogeoclinal sediments, eventually transforming the subdued topography of the Paleozoic continental shelf into a broad mountainous terrane, perhaps rivaling parts of the present-day Andes. Varying rates of convergence and angles of subduction affected the style and distribution of magmatism across the region. Typical intermediate composition arc magmatism was then punctuated by voluminous felsic volcanism of the poorly understood ignimbrite flareup, which swept southward across Nevada in Eocene to Miocene time and locally adorned Paleozoic shelf carbonates with large quantities of disseminated gold, thus generating the Carlin type gold deposits.  Multiple calderas or super volcanoes spewed enormous amounts of ash-flow tuffs that flowed down and filled paleovalleys to the east and west from a high topographic divide in central Nevada. Some of these paleovalleys extended westward to the Pacific Ocean in what is now central California.

In mid-Tertiary time ~30 Ma, the North American and Pacific plates came into contact as the East-Pacific rise approached and much of the Farallon plate had been subducted beneath North America.  Relative motions between the North American and Pacific plates induced development of a transform-plate boundary, with the right-lateral San Andreas fault accommodating the bulk of this motion.  As the western Cordillera evolved from a convergent to a transform plate boundary, voluminous magmatism continued but was accompanied by major ~E-W extension across much of Nevada. Magmatism (including the ignimbrite flareup in some areas) continued and was partly induced by foundering of parts of the subducted Farallon plate and development of a slab gap, which placed relatively warm asthenosphere (previously insulated by the subducting slab) against the base of the lithosphere and triggered melting of mantle lithosphere.  Extension was driven by relaxation of compressional stress coupled with gravitational collapse of overthickened crust produced by mid-Paleozoic to early Tertiary shortening.  As North America continued to override more of the Farallon plate in Neogene time, the transform boundary increased in length and strike-slip deformation stepped inland, fully transferring parts of North America to the Pacific plate (e.g., Baja California) and initiating dextral shear on the east side of the Sierra Nevada in the Walker Lane.  As the transform boundary lengthened, volcanism eventually waned and retreated to the northwest, leaving most of Nevada devoid of volcanism since the Pliocene.  Since the early Miocene, more than 400 km of right-slip have accumulated on the San Andreas fault system while parts of Nevada have extended >100%.  Due to crustal extension, Nevada has been the fastest growing state for the past ~15 million years, and even today about 2 acres per year are added to the state thanks to regional extension. High geothermal gradients and abundant active normal faults resulting from regional extension bestow Nevada with huge amounts of geothermal resources, placing it at the center of one of the largest geothermal provinces on Earth.

Evolution of this long-lived plate margin is far from complete.  The Walker Lane in western Nevada currently accommodates >20% of the plate motion and may one day (~7-8 million years from now) become the primary plate boundary, as evidenced by the inland stepping inclination of the San Andreas. As this occurs, the Sierra Nevada block will be transferred to the Pacific plate, and the Gulf of California may propagate northward, leaving western Nevada with ample beachfront property.  The end result of Nevada’s rich history is the most mountainous, fastest growing (tectonically speaking), and third most seismically active state that contains more gold, lithium, and geothermal resources than any state along with hundreds of active faults that are continually modifying and enriching our landscapes.  Nevada is indeed an extraordinary place to call home.

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