Geol 456-556 Field Trip May 21-23, 2010 Accreted Terranes ... › ... › FT ›...
Transcript of Geol 456-556 Field Trip May 21-23, 2010 Accreted Terranes ... › ... › FT ›...
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Geol 456-556 Field Trip May 21-23, 2010
Accreted Terranes of Northern Cordillera
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This Field Trip:
Insular Terrane
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Insular Terrane Western Domain
Northwest Cascades System (NWCS) Nappes of Pz Mz eugeosynclinal strata EK blueschist Mostly shallow metamorphic dips
Darrington-Devils Mountain Fault Zone
Western and Eastern melange belts (WEMB):
Little metamorphosed Mesozoic marine rocks, lenses of Pz limestone, faut bounded Mz plutons (gabbro to tonalite) Bedding and cleavage steep
Straight Creek Fault Zone Crystalline Core
Lowergreenschist‐>Amphibolitefaciesschist,gneiss,migmatite,plutonsWenatcheeblock
recrystallizationstoppedby75Ma Entiat Fault
EoceneChiwaukumGrabenfluvial,lacustrine
ChelanBlockDeformati0nandrecrystallizationuntileT
Methow Domain
Methow Block: Little-metamorphosed Mz strata. East verging thrusts and folds
Ross Lake Fault Zone:
Rx of Methow block and Chelan block Oceanic greenstone, chert, argillite of Pz->Jr Hozameen group
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Cross Section of North Cascades
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Western Domain of North Cascades
P-T conditions of Skagit Gneiss Complex
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Ross Lake fault system
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Methow Terrane
Okanogan Batholith of Intermontane Terrane
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Pipestone Canyon Formation
Stratigraphy of Southern Can Cordillera
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SuperTerranes and faults
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Eocene Features of North Cascades
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In this region: accreted terranes are allochthonous tectonostratigraphic terranes juxtaposed along regional fault systems and intruded by Jurassic to Tertiary plutons Grouped into 2 superterranes separated by major zone of mK to T contractional deformation and plutonism:
Intermont ane superterrane (Stikinia, Cache Creek, Quesnellia terranes)
Insular superterrane- Wrangellia and Alexander terranes
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Focus on the Cretaceous-> Tertiary development of Cordillera Controversy: estimates of timing and magnitude of terrane displacement along margin:
-Large Translation: paleomagnetic data. Paleomagnetic data from stratified and plutonic rocks from Insular and
Intermontain suggest large northward translations between 90 and 55 Ma Intermontane: 1100 ±600 km between 70 and 55 Ma Insular : 3000±500 km between 80-55 Ma
-Small Translation: geologic data. Total translation: < 1000 km since mK. Terrane amalgamation at or slightly south of current location by mK
Insular : < 400 km dextral translation based on structural and stratigraphic field observations, stratigraphic correlations, and lab analyses