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Hansen, V.L., 1987

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Hansen, V.L., 1987, Structural, metamorphic, and geochronologic evolution of the Teslin suture zone, Yukon : evidence for Mesozoic oblique convergence outboard of the northern Canadian Cordillera: University of California, Los Angeles, Ph.D. dissertation, xviii, 221 p., illust., maps.


Ductile deformation fabrics and synchronously-formed metamorphic mineral assemblages from the Teslin suture zone (TSZ), a portion of the Yukon-Tanana terrane (YTT), Yukon and Alaska, record deep-seated evolution of a Mz transpressional margin outboard the North American (NA) margin. The TSZ is composed of pre-Early JR rocks divisible into three lithotectonic assemblages: Layer 1 oceanic sediments; Layer 2 oceanic crust; and Layer 3 volcano-plutonic and continental sedimentary strata, which display a NNW-trending structural pattern. Tectonic movement within the TSZ began as penetrative dip-slip motion at a high angle to the NA margin (Le1), and locally evolved to right-lateral (Le2), boundary parallel translation along 1- to 3-km-wide steep, anastomosing shear zones. Coherent high P/T metamorphism (575-725 degrees C and 12 +/- 4kb) accompanied Le1 deformation as determined by quantitative geothermobarometry. These data, and amphibole compositions, are consistent with TSZ deformation within an ancient subduction complex. Le2 rocks re-equilibrated to 425-550 degrees C and 5-8 kb. A TSZ P-T-time-motion path indicates granite emplacement into metasedimentary rocks, and crystallization at 10-18 km depth at 360 +/- 16 Ma. Subsequent ductile deformation and metamorphism of TSZ tectonite ended by Mid-JR; dip-slip motion ended by 213 +/- 7 Ma, and strike-slip translation ended by 195 +/- 10 Ma. The TSZ was imbricated with, and thrust northeastward onto, NA cratonal margin strata in Middle-JR to mid-Cretaceous time. Based on integrated study of the TSZ, I develop a model in which the YTT and Slide Mountain (SMT) terranes, which exhibit certain lithotectonic disparities, are correlated within a unifying tectonic framework. Each terrane represents a different crustal level of the same late Pz-early Mz convergent margin in western NA. The SMT, comprised of unmetamorphosed to low-grade complexly telescoped Layer 1 oceanic strata, represents a late Pz-early Mz accretionary complex formed in conjunction with a west-dipping subduction complex and associated magmatic arc, together represented by the heterogeneously metamorphosed and ductilely deformed YTT. The TSZ, the high-P/T portion of the YTT, formed the decollement between the YTT-SMT composite terrane hanging wall and the descending NA footwall; therefore, TSZ structural relations provide insight into the kinematic interaction of this composite terrane with NA prior to its late-stage emplacement on NA.

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