Structural and kinematic evolution of the teslin suture zone, Yukon: record of an ancient transpressional margin

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Abstract

The Teslin suture zone (TSZ), Yukon, which forms the fundamental boundary between rocks deposited along the ancient margin of North America, and allochthonous terranes to the west, preserves a complex history of pre-mid-Jurassic convergence and dextral strike-slip translation which is overprinted locally by late Cretaceous dextral strike-slip shear. The TSZ, comprised of a 15-20 km thick structural sequence of ductilely deformed sedimentary and volcanic strata, basalt, peridotite and granitoids, is divisible into distinct elongate structural domains based on the distribution of two well-defined but differently oriented stretching lineations, Lds and Lss, Lds and Lss both formed during non-coaxial ductile deformation; Lds trends E-W and plunges down-dip, whereas Lss trends NNW-SSE and plunges shallowly. Two 1-2 km wide, NNW-trending anastomosing shear zones of Lss cross-cut Lds structures, indicating Lss is younger. Other field relations indicate further that Lds began forming earlier than Lss, followed by a period of coeval Lds and Lss formation; latest motion was dominantly parallel to Lss. Synkinematic mineral assemblages associated with both Lds- and Lss-related structures record greenschist to albite-epidote amphibolite facies conditions. Lds tectonites record a complex movement history: to the west textural asymmetries indicate west-side-down, or normal shear, whereas in eastern domains top-to-the-east thrust-style asymmetries dominate. Lss tectonites consistently record dextral, or top-to-the-north, shear parallel to Lss. Tectonic motion began as chiefly penetrative dip-slip shear (Lds) at a high angle to the present trend of the TSZ, and evolved to dominantly dextral strike-slip shear (Lss) parallel to the trend of the zone. The geometry, kinematics and sequence of deformation in TSZ tectonites evoke a general model of terrane accretion during oblique plate convergence involving initial shortening at a high angle to the convergent margin and progression to margin-parallel translation.

Original languageEnglish (US)
Pages (from-to)717-733
Number of pages17
JournalJournal of Structural Geology
Volume11
Issue number6
DOIs
StatePublished - 1989

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