Nevada Petroleum and Geothermal Society (NPGS)
Canceled Speaker: Michael Say
Canceled Topic: Late Miocene transition between Basin and Range extension and Walker Lane tectonics, northern Pine Nut Mountains, Nevada: New insights from geologic mapping and 40Ar/39Ar geochronology
A message from NPGS: “The NPGS board has decided to cancel the April dinner meeting in light of the ongoing concerns surrounding the spread of the COVID-19 virus. While we always look forward to an engaging evening of great food and stimulating presentations and discussion, we know that the health and safety of our membership is far more important. We will be providing an update in due time about NPGS scheduling, including the May dinner meeting and other planned activities. Please feel free to reach out to any NPGS board member with any questions, concerns, or comments.
The scheduled speaker for the April dinner was Michael Say who is a second year, structural geology master’s student in the Department of Geological Sciences and Engineering at the University of Nevada, Reno. His research is focused on the transition from Basin and Range extension to Walker Lane right lateral shear in the northern Pine Nut Mountains through geologic mapping, geochemistry, and geochronology. He previously presented his work at the Geological Society of America conference in the fall and recently submitted a manuscript for publication to the Geological Society of Nevada Symposium that will be published this upcoming May. Michael’s future plans are to graduate in May of this year and apply his skills to the geothermal or mining industry. Michael graduated from the University of California, Los Angeles in 2017 and was recently an intern at Ormat Technologies, Inc.
Abstract: The westward encroachment of Basin and Range extension on the relatively stable Sierra Nevada block occurred during the Miocene. To better bracket the timing, magnitude, and kinematics of this transition, we conducted new geologic mapping, 40Ar/39Ar geochronology, and geochemical analyses in the northern Pine Nut Mountains, NV, which are the westernmost structural and topographic expression of the Basin and Range extensional province. Structural mapping suggests that north-striking normal faults developed during the initiation of Basin and Range extension and were later reactivated as northeast-striking oblique-slip faults following the onset of Walker Lane transtensional deformation in the Carson Domain. Newly obtained 40Ar/39Ar radiometric dates collected from 30-36° NW-dipping intermediate to felsic (~55-65% SiO2) volcanic and sedimentary rocks in the northern Pine Nut Mountains show that deformation initiated after 7.15 ± 0.10 Ma. Tilting of the range was accommodated by a major east-dipping normal fault that defines the eastern flank of the range. Extension magnitude recorded in the northern Pine Nut Mountains (14% extension) and westward towards the rigid Sierra Nevada is significantly less than the highly extended Singatse and Wassuk Ranges (~150-180% extension) to the east. Subsequently, Walker Lane transtension initiated and dextral shear in the Carson Domain induced clockwise rotation of structural blocks bounded by northeast-striking left-slip faults orthogonal to the dextral shear zone. This resulted in a northeast-striking oblique-slip and transtensional structure in the northern Pine Nut Mountains. Although this oblique left-slip normal fault system is covered by young alluvium and inactive today, we infer this structure may have served as a major kinematic component of left-lateral shear similar to other left-slip faults identified in the Carson Domain to the north and south. It may have become inactive because it became mechanically unfavorable as the Carson Domain rotated and slip was accommodated on the other parallel left-slip faults. Recently active, north-striking east-dipping curvilinear faults on the western flank of the range show dip-slip to oblique right-slip normal kinematics that may have accommodated some dextral shear as conjugate Riedel shears of the Carson Domain.
Message from John Casteel: It remains to be seen if Michael will have an opportunity to present his work to NPGS at a future dinner meeting, however he is scheduled to present the paper at the GSN symposium May 12-24 (currently still on schedule), so you might be able to catch him there if that event is not eventually canceled.
The scale and the magnitude of the impact this public health crisis is having has caught many of us off-guard and we will have to take a bit of a wait-and-see approach to how we schedule events going forward, starting next with the May dinner. The NPGS board hopes everyone remains safe and healthy during these coming weeks, and that we will be able to meet at least once more under better circumstances before the summer break. As always, please feel free to reach out to me or any NPGS board member with any questions, concerns, or comments.