Geophysical Expression of the Northern Part of the Mono-Inyo Volcanic Chain, Mono Basin, California

Abstract

The Mono Domes are located at the northernmost end of the Mono-Inyo volcanic chain just north of the Long Valley Caldera and include more than 30 overlapping domes and coulees that follow an arcuate trend. A shallow basement high, possibly bounded by a fault, as suggested by potential-field models of data collected in Mono Basin, California, may have influenced the geometry and location of the Mono Domes. Over 320 new gravity stations and approximately 297 line-km of ground magnetic data were collected during the summer of 2010 to investigate the subsurface structure of the Mono Basin. Regional gravity data were collected throughout the basin, and ground magnetic data were collected on major roads along numerous transects throughout the region, one of which was coincident with a seismic refraction line. Gravity and magnetic data were compiled with pre-existing data from studies dating back to the 1960's to produce a new regional isostatic gravity anomaly map and ground magnetic profiles throughout the basin. Aeromagnetic and ground magnetic data revealed an anomalous ring-shaped magnetic high centered over Aeolian Buttes, whose eastern margin follows the arcuate trend of the Mono Domes. This magnetic high is essentially coincident with what Kistler (1966) inferred to be a ring-fracture. Two-dimensional forward modeling of potential field data along a profile across the basin suggests a basement high, or ridge, at roughly 700 m depth, the eastern edge of which lies beneath the Mono Domes. The basement ridge is probably fractured, as suggested by potential field data, indicating a possible preexisting fault beneath the Mono Domes. This fault is along the eastern edge of the basement ridge and could have served as a conduit for the Mono Domes feeder dike. vi ACKNOWLEGEMENTS This thesis project would not have been possible without the support of many people. My deepest appreciation goes to my thesis committee for their continued encouragement and support. I would like to thank Dr. Jonathan Miller for having confidence in me and giving me the opportunity to work on this project. I would also like to thank Dr. Maurizio Battaglia for taking me on as a student and providing invaluable guidance throughout the thesis. It is an honor to have had Dr. Maggie Mangan as a supervisor and mentor and to have her support and encouragement, and for introducing me to the GUMP group. I am very fortunate to have been under the supervision of such an amazing woman/scientist. I owe my deepest gratitude to Dr. Darcy McPhee and Dave Ponce for teaching me more than any potential field geophysics book or class could have ever taught me, and for opportunities I would have never had without their help. I cannot find the words to express my appreciation to Dave for his mentoring and advising through every aspect of this work and for his patience and understanding, no matter how small the question. It was a privilege to work with both Darcy and Dave and never in my dreams would I have expected a thesis project to be as fun and exciting as this w...

Imaging the magmatic system of Mono Basin, California, with magnetotellurics in three dimensions

“…The contact surface may structurally control the arcuate shape of Mono Craters. Gravity and magnetic data modeled along an east-west profile across North Coulée show an east dipping contact zone juxtaposing the distinct physical properties of the Aeolian Buttes pluton and those of the adjacent rocks [McDonell, 2013].…”

“…This low has been attributed to Cenozoic tuffs, lacustrine, and glacial deposits [ Pakiser et al , ]. An east‐west gravity profile cutting through North Coulée has been modeled by McDonell [], where an east dipping fault underlies the west side of the Mono Chain to a depth of a few kilometers. Shallow magnetic data images the eruption areas along the Mono Chain to be magnetic highs in the near surface despite being composed of tuff and rhyolite that have been measured to have low magnetic susceptibilities [ Pakiser et al , ].…”

Vertical Axis Rotation Across the Eastern Mono Basin and West‐Central Walker Lane Revealed by Paleomagnetic Data From the Jack Springs Tuff

“…Here we argue that the region between the Excelsior Mountains and White Mountains served, and continues to serve, as a “zone of weakness” to funnel deformation across the Mono Basin into the central Mina Deflection due to crustal anisotropy (Figure ). Recent and historic magnetic and gravity data in the area between Excelsior Mountain and the White Mountain structural blocks show gradients in both total field magnetic and isostatic residual gravity data (Bursik et al, ; Christensen et al, ; Gilbert et al, ; McDonell, ; Pakiser et al, ; Roberts & Jachens, ). A pronounced magnetic high occurs just west of the Adobe Hills (Adobe Flats) at the California‐Nevada border that increases rapidly into the western Mina Deflection just south of Huntoon Valley (Appendix Ca).…”

“…To the north, a magnetic low extends from north of Mono Lake well into western Nevada into the central Mina Deflection where the total field intensity drops from +250 to less than −230 nT (McDonell, ). In the same area, isostatic residual gravity data increase from ~20 mGal in the Adobe Flats to about 30 mGal in the area just south of Huntoon Valley; consistent with the magnetic data (McDonell, ; Appendix Cb). These rapid, abrupt changes in magnetic and gravity data may reflect a fundamental change in the shallow to midcrust between the Excelsior and White Mountain structural blocks.…”

“…A pronounced magnetic high occurs just west of the Adobe Hills (Adobe Flats) at the California‐Nevada border that increases rapidly into the western Mina Deflection just south of Huntoon Valley (Appendix Ca). The regional aeromagnetic anomaly map of the area (McDonell, ) shows a significant increase in total magnetic field from around +65 nT in the Adobe Flats to over +250 nT just south of Huntoon Valley across the Jack Springs Canyon sampling area (Appendix Ca). To the north, a magnetic low extends from north of Mono Lake well into western Nevada into the central Mina Deflection where the total field intensity drops from +250 to less than −230 nT (McDonell, ).…”