AGU Abstract Fall 1996 T71E-09

AN: T71E-09TI: A dextral, Orogen Parallel Transcurrent Shear Zone at     the Eastern Margin of the Quottoon Pluton, Coast Orogen,     British Columbia.AU: Chris AndronicosAF: Dept of Geol and Geophys Sci Princeton University Princeton New Jersey    08544EM: cla@princeton.eduAU: Cameron DavidsonAF: Dept of Geolgy Beloit College Beloit WI 53511 EM: davidson@beloit.eduAU: Lincoln HollisterAF: Dept of Geol and Geophys Sci Princeton University Princeton New Jersey    08544EM: linc@geo.princeton.eduAB:     An important question in the study of mountain belts is the     relative importance of orogen normal and orogen parallel     motions.  This question is particularly germane in the     Canadian Cordillera where paleomagnetic and paleontologic     studies suggest there may have been significant northward     transport of outboard terranes.  However, the structures     responsible for this displacement remain largely     unidentified.  We report evidence for an orogen parallel     strike slip shear zone from within the Coast Orogen of the     Canadian Cordillera.        A dextral transcurrent shear  zone with a dip-slip component     has been identified at the eastern margin of the Quottoon     pluton.  The shear zone is 3 kilometers wide and has a     minimum length of 25 kilometers.  The north-south extent of     the shear zone is currently unknown.  The zone trends to the     north-northeast, sub-parallel to the eastern  margin of the     pluton, although the intrusive contact with country rocks is     discordant at a map scale.  Kinematic indicators are     ubiquitous within the shear zone and include S-C fabrics,     shear bands, synthetic and antithetic shears, asymmetric     porphyroclasts, asymmetric boudinage, and tension vein     arrays.  Transport direction for the shear zone determined     from S-C fabrics plunges 2 degrees toward 022 on a moderate     to steeply west dipping fabric.  This contrasts with the     movement direction inferred from lineations, with a mean     lineation oriented 31 degrees toward 340. The apparent     disparity in transport direction determined by lineations     and S-C fabrics may be due to partitioning of strain and/or     rotation of lineations. In the southern mapped portion of     the shear zone lineations have steeper plunges, and fabrics     dip steeply to the east and west.  Dextral shearing was     synchronous with the formation of sheath folds with fold     axes parallel to the mineral stretching lineations in this     area.  The overall inferred transport direction plunges less     than 40 degrees, accommodating predominately transcurrent     displacement.        Movement on the shear  zone overlapped final crystallization     of the 58 Ma Quottoon pluton.  However, intense deformation     of the country rocks suggests that movement on the shear     zone largely preceded intrusion of the Quottoon pluton.     The magnitude of displacement on the shear zone is currently     unconstrained, but, the 3 km width of the shear zone,     and intensity of fabrics developed within the shear zone,     suggest a minimum displacement on the order of tens of     kilometers.       SC: UDE: 8110DE: 8035MN: Fall Meeting 1996