TY - JOUR
T1 - Analysis of the Wallowa-Baker terrane boundary
T2 - Implications for tectonic accretion in the Blue Mountains province, northeastern Oregon
AU - Schwartz, Joshua J.
AU - Snoke, Arthur W.
AU - Frost, Carol D.
AU - Barnes, Calvin G.
AU - Gromet, L. Peter
AU - Johnson, Kenneth
PY - 2010
Y1 - 2010
N2 - The Baker terrane, exposed in the Blue Mountains province of northeastern Oregon, is a long-lived, ancient (late Paleozoic-early Mesozoic) accretionary complex with an asso ciated forearc. This composite terrane lies between the partially coeval Wallowa and Olds Ferry island-arc terranes. The northern margin of the Baker terrane is a broad zone (>25 km wide) of fault-bounded, imbricated slabs and slices of metaigneous and metasedimentary rocks faulted into chert-argillite mélange of the Elkhorn Ridge Argillite. Metaplutonic rocks within tectonic units in this zone crystallized between 231 and 226 Ma and have low initial 87Sr/86Sr ratios (0.7033- 0.7034) and positive initial εNd values (+7.7 to +8.5). In contrast, siliceous argillites from the chert-argillite mélange have initial 87Sr/86Sr values ranging from 0.7073 to 0.7094 and initial εNd values between -4.7 and -7.8. We interpret this broad, imbricate fault zone as a fundamental tectonic boundary that separates the distal, Wallowa island-arc terrane from the Baker accretionary-complex terrane. We propose that this terrane boundary is an example of a broad zone of imbrication made up of slabs and slices of arc crust tectonically mixed within an accretionary complex, providing an on-land, ancient analog to the actualistic arc-arc collisional zone developed along the margins of the Molucca Sea of the central equatorial Indo-Pacific region.
AB - The Baker terrane, exposed in the Blue Mountains province of northeastern Oregon, is a long-lived, ancient (late Paleozoic-early Mesozoic) accretionary complex with an asso ciated forearc. This composite terrane lies between the partially coeval Wallowa and Olds Ferry island-arc terranes. The northern margin of the Baker terrane is a broad zone (>25 km wide) of fault-bounded, imbricated slabs and slices of metaigneous and metasedimentary rocks faulted into chert-argillite mélange of the Elkhorn Ridge Argillite. Metaplutonic rocks within tectonic units in this zone crystallized between 231 and 226 Ma and have low initial 87Sr/86Sr ratios (0.7033- 0.7034) and positive initial εNd values (+7.7 to +8.5). In contrast, siliceous argillites from the chert-argillite mélange have initial 87Sr/86Sr values ranging from 0.7073 to 0.7094 and initial εNd values between -4.7 and -7.8. We interpret this broad, imbricate fault zone as a fundamental tectonic boundary that separates the distal, Wallowa island-arc terrane from the Baker accretionary-complex terrane. We propose that this terrane boundary is an example of a broad zone of imbrication made up of slabs and slices of arc crust tectonically mixed within an accretionary complex, providing an on-land, ancient analog to the actualistic arc-arc collisional zone developed along the margins of the Molucca Sea of the central equatorial Indo-Pacific region.
UR - http://www.scopus.com/inward/record.url?scp=77950992705&partnerID=8YFLogxK
U2 - 10.1130/B26493.1
DO - 10.1130/B26493.1
M3 - Article
AN - SCOPUS:77950992705
SN - 0016-7606
VL - 122
SP - 517
EP - 536
JO - Bulletin of the Geological Society of America
JF - Bulletin of the Geological Society of America
IS - 3-4
ER -