tilted middle tertiary ash-flow calderas and subjacent granitic plutons, southern stillwater range,...
Post on 21-Dec-2015
219 views
TRANSCRIPT
Tilted middle Tertiary ash-flow calderas and subjacent granitic
plutons, southern Stillwater Range, Nevada : Cross sections of
an Oligocene igneous center
By
David A. John
Introduction
Steeply tilted late Oligocene caldera system record a number of unusual features Extremely thick (>4-5.5 km) caldera related
deposits Lack of evidence of structural doming Preservation of compositional zoning Cogenetic plutonic rocks are exposed over
depth range of~10 km
Stillwater Caldera Complex
Job Canyon (29-28 Ma) Poco Canyon (25-23 Ma) Eleven Mile Canyon (25-23 Ma) Composite Freeman Creek pluton
Unusual features
Extreme thickness caldera related deposits (>4-5.5 km)
Unusual features continued
Preservation of compositional zoning
Caldera collapse
Miocene extension Basement rocks tilted 40°-90° Subvertical ring-fracture faults (>3-5 km)
depth Piston like blocks Lack of evidence of structural doming
Conclusions
Oligocene caldera complex in the southern Stillwater Range
Extremely thick caldera related deposits due to extreme subsidence
Cogenetic plutonic rocks over a depth range of ~10 km due to tilting during Miocene extension