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No ring fracture in Mono Basin, California

Hildreth, Wes and Fierstein, Judy and Ryan-Davis, Juliet (2021) No ring fracture in Mono Basin, California. Geological Society of America Bulletin, 133 (9-10). pp. 2210-2225. ISSN 0016-7606. doi:10.1130/b35747.1.

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In Mono Basin, California, USA, a near-circular ring fracture 12 km in diameter was proposed by R.W. Kistler in 1966 to have originated as the protoclastic margin of the Cretaceous Aeolian Buttes pluton, to have been reactivated in the middle Pleistocene, and to have influenced the arcuate trend of the chain of 30 young (62−0.7 ka) rhyolite domes called the Mono Craters. In view of the frequency and recency of explosive eruptions along the Mono chain, and because many geophysicists accepted the ring fracture model, we assembled evidence to test its plausibility. The shear zone interpreted as the margin of the Aeolian Buttes pluton by Kistler is 50−400 m wide but is exposed only along a 7-km-long set of four southwesterly outcrops that subtend only a 70° sector of the proposed ring. The southeast end of the exposed shear zone is largely within the older June Lake pluton, and at its northwest end, the contact of the Aeolian Buttes pluton with a much older one crosses the shear zone obliquely. Conflicting attitudes of shear structures are hard to reconcile with intrusive protoclasis. Also inconsistent with the margin of the ovoid intrusion proposed by Kistler, unsheared salients of the pluton extend ∼1 km north of its postulated circular outline at Williams Butte, where there is no fault or other structure to define the northern half of the hypothetical ring. The shear zone may represent regional Cretaceous transpression rather than the margin of a single intrusion. There is no evidence for the Aeolian Buttes pluton along the aqueduct tunnel beneath the Mono chain, nor is there evidence for a fault that could have influenced its vent pattern. The apparently arcuate chain actually consists of three linear segments that reflect Quaternary tectonic influence and not Cretaceous inheritance. A rhyolitic magma reservoir under the central segment of the Mono chain has erupted many times in the late Holocene and as recently as 700 years ago. The ring fracture idea, however, prompted several geophysical investigations that sought a much broader magma body, but none identified a low-density or low-velocity anomaly beneath the purported 12-km-wide ring, which we conclude does not exist.

Item Type:Article
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URLURL TypeDescription
Hildreth, Wes0000-0002-7925-4251
Fierstein, Judy0000-0001-8024-1426
Ryan-Davis, Juliet0000-0001-7048-5937
Additional Information:© 2021 Authors. This paper is published under the terms of the CC-BY license. Manuscript Received 7 May 2020; Revised Manuscript Received 8 December 2020; Manuscript Accepted 26 December 2020. We are grateful for spirited field assistance from Joel Robinson, Stuart Wilkinson, Fred Murphy, and Barney Hope. Mark Huebner provided sedulous lab support. Jared Peacock, Mae Marcaida, Marcus Bursik, and two anonymous reviewers provided helpful improvements. Associate editor Jocelyn McPhie was extraordinarily helpful in trimming and polishing the manuscript. The late Ron Kistler, an esteemed colleague for half a century, might have grumbled at this analysis, but he was not responsible for the bandwagon; we salute his Sierran studies and his contributions to the isotope geology of granitoids throughout the American West.
Issue or Number:9-10
Record Number:CaltechAUTHORS:20210225-151708501
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Official Citation:Wes Hildreth, Judy Fierstein, Juliet Ryan-Davis; No ring fracture in Mono Basin, California. GSA Bulletin 2021; 133 (9-10): 2210–2225. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108221
Deposited By: Tony Diaz
Deposited On:26 Feb 2021 00:16
Last Modified:13 Sep 2021 23:21

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