The pre-lecture dinner (5:30 pm in GeoCorner Room 320-109) requires reservation no later than 10/06/06, and is $30 regular, $5 for students; however no-shows owe full price.
Abstract
The age and origin of high-grade rocks of the Sredinniy Range,
Kamchatka have been the subjects of a long and controversial debate.
Leading interpretations argue based on geochronologic data and its
association with a collage of accreted oceanic terranes that the
Sredinniy metamorphic rocks represent an accreted Precambrian
microcontinent. In this contribution, we develop a new hypothesis
that the Sredinniy metamorphic rocks represent part of the
Cretaceous-Paleocene sedimentary margin of northeast Russian that was
overridden and metamorphosed during Eocene obduction of the
Olyutorsky arc at the Russian margin. This interpretation is based on
new mapping and structural observations along the northern and
eastern flanks of the Sredinniy Range complemented by SHRIMP zircon
and monazite U-Th-Pb age data from 15 key samples. These new isotopic
data demonstrate that paragneissic units were formed from sediments
with depositional ages locally no older than Late Cretaceous to
Paleocene. Further, the statistical similarity of zircon U/Pb
grain-ages from the Kamchatka Schist with very low-grade turbidite
sandstones of the Ukelayat and Khozgon Groups indicate that
metasediments of the Sredinniy Range are upgraded stratigraphic
equivalents of northeast Russian marginal strata. The timing of peak
metamorphism is well-constrained by in situ analysis of zircon
overgrowths and monazite extracted from migmatite and gneiss to ~ 52
Ma -- broadly synchronous with the early stages of the Olyutorsky
arc-continent collision event. Heating and cooling rates over this
interval are apparently extremely rapid, approaching 90 degrees C/Ma.
We conclude that metamorphism and structural burial occurred during
Early Eocene arc-continent collision. Rapid heating rates are
attributed to syn-collisional, subduction-related magmatism.
Exhumation and resultant rapid cooling of the Sredinniy Range are
interpreted to result from diapiric ascent of a low-density
low-viscosity continental material beneath a dense structural lid of
the obducted island arc.
About the Speaker
http://www.diggles.com/pgs/2006/jeremy.jpg (photo of Jeremy)
Jeremy Hourigan is an Assistant Professor of Earth Sciences at the
University of California, Santa Cruz. His expertise includes
thermochronology, structural geology and tectonics. His teaching
interests include Structural Geology and Field Methods. He received
his B.A. in Russian from the University of Vermont, a B.S. in Geology
from the University of Vermont, and his Ph.D. in Geology from
Stanford University. He did a Postdoc at Yale University and U.C.
Santa Barbara. Visit Jeremy's faculty site at
<http://es.ucsc.edu/personnel/Hourigan/>http://es.ucsc.edu/personnel/Hourigan/
