HR: 1340h
AN: V33C-1525    [Abstracts]
TI: Evidence for volcano-pluton connections in the distal volcanic record: Examples from the western United States
AU: * Christiansen, E H
EM: eric_christiansen@byu.edu
AF: Geological Sciences, Brigham Young University, Provo, UT 84602, United States
AU: Kowallis, B J
EM: bart_kowallis@byu.edu
AF: Geological Sciences, Brigham Young University, Provo, UT 84602, United States
AU: Britt, B B
EM: brooks_britt@byu.edu
AF: Geological Sciences, Brigham Young University, Provo, UT 84602, United States
AB: The supracrustal cover rocks of batholith belts are often rapidly eroded, leaving at best a fragmentary record of contemporaneous volcanism. A complementary record is often preserved as distal volcanic ash in sedimentary basins. This record is also incomplete and depends on deposition in favorable environments and on a structural history that first buries and preserves and then allows erosion to expose the record. When pieced together with near the source record, a more complete picture of the connection between plutonic and volcanic rocks can be constructed. For example, the Mesozoic and Cenozoic history of the western United States is marked by the development of plutonic belts of different ages and locations that migrated in response to geodynamic changes. For much of this time, favorable sedimentary environments existed in the back arc, hundreds or thousands of kilometers away from the plutonic belt. Analysis of of the existing sedimentary record and its enclosed volcanic components shows that episodes of volcanism and plutonism correspond closely in space and time. Magmatic pulses found in the plutonic record are generally obvious in the volcanic record-with abundant ash in the Triassic, Middle and Late Jurassic, Cretaceous, and late Paleogene and Neogene. However, less ash is found during the Middle Jurassic, even though sedimentary rocks are preserved behind the arc. This is consistent with the observation that much of the Middle Jurassic arc in California was submarine, hindering the eruption and widespread dispersal of volcanic ash behind the arc. Moreover, as the locus of plutonism migrated, so did the deposition of volcanic ash. During the Jurassic and middle Cretaceous ash is common in the Colorado Plateau and adjacent regions to the south. When the Idaho and Boulder batholiths developed, thick ash accumulated in Montana and Wyoming. Although it has been suggested that volcanism and plutonism are decoupled in space and time, we conclude that for most of the Mesozoic and Cenozoic, plutonism and volcanism were closely coupled in the western United States. Finally, the distal volcanic record is strongly biased toward preserving deposits from large eruptions formed when large volumes of molten magma existed in a chamber. Thus, the abundance of these ash deposits implies that batholith-size chambers (>10 km across) filled with magma existed across much of the Cordillera
DE: 8455 Tephrochronology (1145)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting