Description

Location: Reno Aces, Greater Nevada Field Upstairs

Contact: gsn@gsnv.org

GSN MEMBERSHIP MEETING—JANUARY 21, 2022*

Guest Speaker: Drew Levy, Ph.D. Candidate

Nevada Bureau of Mines & Geology, University of Nevada, Reno

 Title:  “New geochronologic insight into the structural and metamorphic evolution of the Basin and Range:  Ruby Mountains-East Humboldt Range metamorphic core complex, Elko County, Nevada”

Date:   FRIDAY, JANUARY 21, 2022

Time:  Drinks @ 6 pm, Dinner @ 6:30 pm, Talk @ 7:15 pm

WhereRENO ACES BALL PARK, 250 Evans St., Upstairs at the 250 Lounge/Good Hops Restaurant

Abstract:

Large-magnitude regional extension in the Basin and Range of eastern Nevada initiated at 16 Ma, however high-strain rocks in the metamorphic core complexes record an earlier episode of Eocene-Oligocene ductile thinning. Thermochronologic cooling ages and the lack of thick pre-16 Ma syn-extensional basins have been used to argue against large-magnitude extension during the Eocene-Oligocene, which motivates a deeper understanding of the mechanisms that drove ductile deformation in the core complexes. The Ruby Mountains-East Humboldt Range metamorphic core complex features a 1 km-thick ductile shear zone that developed between 29-17 Ma based on the existing zircon U-Pb and 40Ar-39Ar ages of cross-cutting intrusions. Within the shear zone, deformed 40 Ma diorite and 29 Ma monzogranite intrusions are abundant, yet at the same stratigraphic levels in adjacent ranges, Eocene diorites and Oligocene monzogranites are rare. To further understand the role of these intrusions in the development of the core complex, as well as their role in the regional tectonic evolution of the Basin and Range, we conducted new geochronology of intrusive rocks and metamorphic rocks at each structural level. Zircon U-Pb geochronology yields 100-70 Ma dates from the abundant pegmatitic leucogranites across the core complex. Diorites and monzogranites yield 42-36 Ma and 34-28 Ma zircon dates, respectively. A younger generation of leucogranites crosscut Oligocene monzogranites and yield metamorphic zircon dates as young as 26 Ma. Monazite and titanite U-Th-Pb geochronology from metapelitic schists and gneiss yield a broad range of dates recording Late Jurassic-Early Cretaceous, Late Cretaceous and Eocene-Oligocene metamorphic events. Late Cretaceous and Eocene-Oligocene monazite and titanite dates overlap with zircon U-Pb dates from intrusive rocks. Trace element geochemistry from monazite and titanite record recrystallization during an episode of high temperature metasomatism at 40 Ma, followed by retrograde breakdown of garnet from 40-30 Ma. Collectively, these new analytical results and our field observations suggest the Cenozoic development of the Ruby Mountains-East Humboldt Range metamorphic core complex was initiated by the intrusion of mafic, mantle derived magmas at 40 Ma during initial slab-rollback magmatism. The intrusion of these mafic melts into a pre-existing melt network heated, remobilized, and hybridized with the Late Cretaceous leucogranites. Remobilized melts distributed heat and less dense granitic intrusions throughout the core complex. The crystallization of these melts likely released abundant fluids, which fluxed through the middle crust driving retrograde metamorphic reactions. This magmatic-metamorphic-metasomatic event led to a hot, weak, and buoyant middle crust. We argue these conditions promoted buoyant, diapiric ascent of a broad gneiss dome, which was accommodated by ductile attenuation of the overlying ductile shear zone during the Oligocene. The development of high strain mylonitic fabrics created a mechanically weak layer that localized later normal faulting during the middle Miocene.  This research was supported by a generous award from the Geological Society of Nevada Great Basin Scholarship Fund.

 

Drew Levy Bio:

Drew Levy is a 5th year Ph.D. Candidate at the University of Nevada, Reno studying the tectonic evolution of the Basin and Range province with Dr. Andrew Zuza. His Ph.D. research applies structural geology, metamorphic petrology and geochronology to investigate the mechanisms and timing of post-orogenic extension in northeast Nevada. Before moving to UNR, Drew completed his Geology B.S. at UCLA in 2016, where he led geology field trips across southern California and researched the neotectonics of Owens Valley. After falling in love with the Eastern Sierra, Drew decided to stay close to the mountains and join the energetic geology program at UNR in 2017 to work with Andrew Zuza and Stacia Gordon. As a Ph.D. student, he has studied Paleozoic to Holocene tectonics across the Basin and Range, with his intellectual home base located in the Ruby Mountains and East Humboldt Range of Elko County, NV.

*GSN will continue to follow County, State and CDC Covid-19 requirements/guidelines and adapt as needed. At the time of this publication, face coverings are required in counties with substantial or high community transmission rates while in public indoor spaces regardless of vaccination status. All counties that host GSN events are currently considered to have substantial or high community transmission rates. The Executive Committee urges its members to strictly adhere to CDC guidelines and recommendations, such as receiving the vaccine as soon as eligible and wearing masks at all indoor GSN gatherings.  Please do not attend GSN events if you feel sick or have a known Covid-19 exposure.  For more information please visit: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html

 

 


Details

01/21/2022 18:00:0001/21/2022 21:00:00America/Los_AngelesGSN Regular Membership Meeting, Reno, NevadaGSN MEMBERSHIP MEETING—JANUARY 21, 2022* Guest Speaker: Drew Levy, Ph.D. Candidate Nevada Bureau of Mines & Geology, University of Nevada, Reno  Title:  “New geochronologic insight into the structural and metamorphic evolution of the Basin and Range:  Ruby Mountains-East Humboldt Range metamorphic core complex, Elko County, Nevada” Date:   FRIDAY, JANUARY 21, 2022 Time:  Drinks @ 6 pm, Dinner @ 6:30 pm, Talk @ 7:15 pm WhereRENO ACES BALL PARK, 250 Evans St., Upstairs at the 250 Lounge/Good Hops Restaurant Abstract: Large-magnitude regional extension in the Basin and Range of eastern Nevada initiated at 16 Ma, however high-strain rocks in the metamorphic core complexes record an earlier episode of Eocene-Oligocene ductile thinning. Thermochronologic cooling ages and the lack of thick pre-16 Ma syn-extensional basins have been used to argue against large-magnitude extension during the Eocene-Oligocene, which motivates a deeper understanding of the mechanisms that drove ductile deformation in the core complexes. The Ruby Mountains-East Humboldt Range metamorphic core complex features a 1 km-thick ductile shear zone that developed between 29-17 Ma based on the existing zircon U-Pb and 40Ar-39Ar ages of cross-cutting intrusions. Within the shear zone, deformed 40 Ma diorite and 29 Ma monzogranite intrusions are abundant, yet at the same stratigraphic levels in adjacent ranges, Eocene diorites and Oligocene monzogranites are rare. To further understand the role of these intrusions in the development of the core complex, as well as their role in the regional tectonic evolution of the Basin and Range, we conducted new geochronology of intrusive rocks and metamorphic rocks at each structural level. Zircon U-Pb geochronology yields 100-70 Ma dates from the abundant pegmatitic leucogranites across the core complex. Diorites and monzogranites yield 42-36 Ma and 34-28 Ma zircon dates, respectively. A younger generation of leucogranites crosscut Oligocene monzogranites and yield metamorphic zircon dates as young as 26 Ma. Monazite and titanite U-Th-Pb geochronology from metapelitic schists and gneiss yield a broad range of dates recording Late Jurassic-Early Cretaceous, Late Cretaceous and Eocene-Oligocene metamorphic events. Late Cretaceous and Eocene-Oligocene monazite and titanite dates overlap with zircon U-Pb dates from intrusive rocks. Trace element geochemistry from monazite and titanite record recrystallization during an episode of high temperature metasomatism at 40 Ma, followed by retrograde breakdown of garnet from 40-30 Ma. Collectively, these new analytical results and our field observations suggest the Cenozoic development of the Ruby Mountains-East Humboldt Range metamorphic core complex was initiated by the intrusion of mafic, mantle derived magmas at 40 Ma during initial slab-rollback magmatism. The intrusion of these mafic melts into a pre-existing melt network heated, remobilized, and hybridized with the Late Cretaceous leucogranites. Remobilized melts distributed heat and less dense granitic intrusions throughout the core complex. The crystallization of these melts likely released abundant fluids, which fluxed through the middle crust driving retrograde metamorphic reactions. This magmatic-metamorphic-metasomatic event led to a hot, weak, and buoyant middle crust. We argue these conditions promoted buoyant, diapiric ascent of a broad gneiss dome, which was accommodated by ductile attenuation of the overlying ductile shear zone during the Oligocene. The development of high strain mylonitic fabrics created a mechanically weak layer that localized later normal faulting during the middle Miocene.  This research was supported by a generous award from the Geological Society of Nevada Great Basin Scholarship Fund.   Drew Levy Bio: Drew Levy is a 5th year Ph.D. Candidate at the University of Nevada, Reno studying the tectonic evolution of the Basin and Range province with Dr. Andrew Zuza. His Ph.D. research applies structural geology, metamorphic petrology and geochronology to investigate the mechanisms and timing of post-orogenic extension in northeast Nevada. Before moving to UNR, Drew completed his Geology B.S. at UCLA in 2016, where he led geology field trips across southern California and researched the neotectonics of Owens Valley. After falling in love with the Eastern Sierra, Drew decided to stay close to the mountains and join the energetic geology program at UNR in 2017 to work with Andrew Zuza and Stacia Gordon. As a Ph.D. student, he has studied Paleozoic to Holocene tectonics across the Basin and Range, with his intellectual home base located in the Ruby Mountains and East Humboldt Range of Elko County, NV.
*GSN will continue to follow County, State and CDC Covid-19 requirements/guidelines and adapt as needed. At the time of this publication, face coverings are required in counties with substantial or high community transmission rates while in public indoor spaces regardless of vaccination status. All counties that host GSN events are currently considered to have substantial or high community transmission rates. The Executive Committee urges its members to strictly adhere to CDC guidelines and recommendations, such as receiving the vaccine as soon as eligible and wearing masks at all indoor GSN gatherings.  Please do not attend GSN events if you feel sick or have a known Covid-19 exposure.  For more information please visit: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html
   
[gravityform id="9" title="true" description="true"]
Reno, NV
Event StartsEvent Ends
01/21/202201/21/2022
All Day Event
6:00pm9:00pm