TY - JOUR
T1 - Characterization of the crust of the Coast Mountains Batholith, British Columbia, from P to S converted seismic waves and petrologic modeling
AU - Calkins, Josh A.
AU - Zandt, George
AU - Girardi, James
AU - Dueker, Ken
AU - Gehrels, George E.
AU - Ducea, Mihai N.
N1 - Funding Information:
The Batholiths project was funded under the U.S. National Science Foundation's Continental Dynamics program , grant EAR-0309885 . The instruments used in the field program were provided by the PASSCAL facility of the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. Data collected during this experiment will be available through the IRIS Data Management Center. The facilities of the IRIS Consortium are supported by the National Science Foundation under Cooperative Agreement EAR-0004370 and by the Department of Energy National Nuclear Security Administration . Compositions of the rock samples used for forward modeling were determined by X-ray diffraction by Jeff Thole at Macalaster College, St. Paul, MN, 55105.
PY - 2010/1/15
Y1 - 2010/1/15
N2 - The late Triassic to early Tertiary Coast Mountains Batholith (CMB) of British Columbia provides an ideal locale to study the processes whereby accreted terranes and subduction-related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals. Seismic measurements, combined with calculated elastic properties of various CMB rock compositions, provide a window into the deep-crustal lithologies that are key to understanding the processes of continental growth and evolution. We use a combination of seismic observations and petrologic modeling to construct hypothetical crustal sections at representative locations across the CMB, then test the viability of these sections via forward modeling with synthetic seismic data. The compositions that make up our petrologic forward models are based on calculations using the free energy minimization program Perple_X to predict mineral assemblages at depth for the bulk compositions of exposed plutonic rocks collected in the study area. Seismic data were collected along two transects in west-central British Columbia: a southern line that crossed the CMB near the town of Bella Coola (near 52° N), and a northern line centered on the towns of Terrace and Kitimat (near 54° N). Along both transects, seismic receiver functions reveal high Vp/Vs ratios near the Insular/Intermontane terrane boundary and crustal thickness increasing from 26 ± 3 km to 34 ± 3 km (at the 1 sigma certainty level) from west to east across the Coast Shear Zone (CSZ). On the southern line, we observe an anomalous region of complex receiver functions and diminished Moho signals beneath the central portion of the CMB. Our petrologic and seismic profiles show that observed seismic data from much of the CMB can be well-matched in terms of crustal thickness and structure, average Vp/Vs, and amplitude of the Moho converted phase, without including ultramafic residual material in the lower crust.
AB - The late Triassic to early Tertiary Coast Mountains Batholith (CMB) of British Columbia provides an ideal locale to study the processes whereby accreted terranes and subduction-related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals. Seismic measurements, combined with calculated elastic properties of various CMB rock compositions, provide a window into the deep-crustal lithologies that are key to understanding the processes of continental growth and evolution. We use a combination of seismic observations and petrologic modeling to construct hypothetical crustal sections at representative locations across the CMB, then test the viability of these sections via forward modeling with synthetic seismic data. The compositions that make up our petrologic forward models are based on calculations using the free energy minimization program Perple_X to predict mineral assemblages at depth for the bulk compositions of exposed plutonic rocks collected in the study area. Seismic data were collected along two transects in west-central British Columbia: a southern line that crossed the CMB near the town of Bella Coola (near 52° N), and a northern line centered on the towns of Terrace and Kitimat (near 54° N). Along both transects, seismic receiver functions reveal high Vp/Vs ratios near the Insular/Intermontane terrane boundary and crustal thickness increasing from 26 ± 3 km to 34 ± 3 km (at the 1 sigma certainty level) from west to east across the Coast Shear Zone (CSZ). On the southern line, we observe an anomalous region of complex receiver functions and diminished Moho signals beneath the central portion of the CMB. Our petrologic and seismic profiles show that observed seismic data from much of the CMB can be well-matched in terms of crustal thickness and structure, average Vp/Vs, and amplitude of the Moho converted phase, without including ultramafic residual material in the lower crust.
KW - Coast Mountains Batholith
KW - forward modeling
KW - receiver function
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U2 - 10.1016/j.epsl.2009.10.037
DO - 10.1016/j.epsl.2009.10.037
M3 - Article
AN - SCOPUS:73149106170
VL - 289
SP - 145
EP - 155
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
IS - 1-2
ER -