MIDDLE JURASSIC EXHUMATION ALONG THE WESTERN FLANK OF THE SELKIRK FANSTRUCTURE - THERMOBAROMETRIC AND THERMOCHRONOMETRIC CONSTRAINTS FROM THE ILLECILLEWAET SYNCLINORIUM, SOUTHEASTERN BRITISH-COLUMBIA

Citation
M. Colpron et al., MIDDLE JURASSIC EXHUMATION ALONG THE WESTERN FLANK OF THE SELKIRK FANSTRUCTURE - THERMOBAROMETRIC AND THERMOCHRONOMETRIC CONSTRAINTS FROM THE ILLECILLEWAET SYNCLINORIUM, SOUTHEASTERN BRITISH-COLUMBIA, Geological Society of America bulletin, 108(11), 1996, pp. 1372-1392
Citations number
108
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
11
Year of publication
1996
Pages
1372 - 1392
Database
ISI
SICI code
0016-7606(1996)108:11<1372:MJEATW>2.0.ZU;2-B
Abstract
New thermobarometric and thermochronometric data from the Illecillewae t synclinorium, a broad regional southwest-verging structure in the we stern flank of the Selkirk fan structure, indicate that accretion of t he Intermontane superterrane resulted in deep burial (20-25 km) of the outer margin of Ancestral North America and that subsequent southwest -verging folding and thrusting were accompanied by rapid exhumation. S outhwest-verging folding of lower Paleozoic rocks in the Illecillewaet synclinorium was initiated during regional peak-metamorphic condition s at 6-7 kbar, Crystallization of late-synkinematic granitoid plutons that intrude the Illecillewaet synclinorium also occurred at pressures of 6-7 kbar; however, equilibration of the contact aureoles of the pl utons occurred at 3-3.5 kbar, during the latter stages of the southwes t-verging deformation, Evidently, a decompression on the order of 3 kb ar occurred concurrently with southwest-verging folding and thrusting in the Illecillewaet synclinorium, Thermochronometric analyses further indicate that plutonic rocks from the Illecillewaet synclinorium cool ed rapidly between times of crystallization and times of Ar closure in biotite. Regional relationships indicate that the accretion of the In termontane superterrane to the edge of the North American margin in so utheastern British Columbia occurred between 187 and 173 Ma (Toarcian- Bajocian), Subsequent southwest-verging deformation occurred approxima tely between 173 and 168 Ma (Bajocian-Bathonian). Thus, the removal of at least 10 km of rocks from above the Illecillewaet synclinorium, in ferred from thermobarometric data, occurred approximately between 173 and 168 Ma, Rapid denudation of the Selkirk fan structure was probably the result of synorogenic extension (or extensional collapse) contemp oraneous with the development of southwest-verging structures at deepe r levels of the orogen. The data presented here indicate that all sign ificant deformation and most of the exhumation along the western flank of the Selkirk fan structure were complete by late Middle Jurassic ti me, After the Middle Jurassic, the Selkirk fan structure must have bee n transported passively northeastward along the basal decollement of t he Cordilleran foreland thrust-and-fold belt, together with the Interm ontane superterrane, as the fold-and-thrust belt tectonically overrode the margin of the North American craton.