GEOLOGY AND MINERAL OCCURRENCES OF THE TATLAYOKO LAKE MAP AREA ( 92 N / 8 , 9 and 10 )
Agreement,  was initiated in 1992  with  geological mapping of the Mount Tatlow map area (Riddell et al., 1993a,b). No fiddwork was done in 1993, but the project was continued 'In 1994 with geological mapping of the Tatlayoko Lake map area, reported on here. The project's objectives are to update the geological database for the eastem Coast Belt in portions of the Mount Waddington and  Taseko  Lakes  map areas, and to integrate the structural and stratigraphic relationships established within this area with rapidly evolving concepts regarding the tectonic anti stratigraphic framework of the region. This will provide an improved geological framework for understanding the settings and controls of known mineral
Tatla Lake Metamorphic Complex: An Eocene Metamorphic Core Complex on the southwestern edge of the Intermontane Belt of British Columbia
The Tatla Lake Metamorphic Complex (TLMC), which lies on the southwest side of the Intermontane Belt (IMB) in British Columbia, has characteristics typical of a metamorphic core complex: anticlinorial amphibolite-grade gneissic and migmatitic core underlying a 1− to 2.5+-km-thick zone of mylonite and ductilely sheared metamorphic rocks which is in fault contact beneath an upper plate of low-metamorphic-grade cover rocks of the 1MB. Ductile shearing in the TLMC involved tonalitic to granodioritic orthogneiss and structurally overlying amphibolite-grade metasedimentary rocks and greenschist-grade chlorite-actinolite-albite schist. Structures observed throughout the ductilely sheared rocks include a gently dipping mylonitic foliation (Ss), containing a mineral lineation (Ls) which trends toward 280° (100°) ± 20°. Minor folds of variable trend (Fs), almost exclusively confined to metasedimentary rocks, are interpreted as synductile shear. Vergence of these folds defines a movement sense and direction of top toward 290° ± 20°. Kinematic indicators from rocks not deformed by synductile shear folds indicate a tops-to-the-west sense of shear, while those within metasedimentary rocks (deformed by Fs folds) yield conflicting results, with a tops-to-the-west sense predominating. Calculated a directions from Fs folds which deform Ls lineations indicate nearly horizontal Ds movement, subparallel to 290°–110°. The entire metamorphic core of the TLMC has been deformed by upright, west to west-northwest trending, shallowly plunging map-scale folds (F3). The steeply dipping, northwest trending Yalakom fault cuts all units and forms the southwestern margin of the TLMC. U-Pb zircon geochronology has documented the existence of Cretaceous (107–79 Ma, in the core) and Eocene 55–47 Ma, (in the mylonitic zone) deformation and metamorphism in the TLMC. K-Ar dates for biotite and hornblende of 53.4–45.6 Ma record the uplift and cooling of the TLMC. During early and middle Eocene time (55–47 Ma) metamorphic rocks of the TLMC were carried to higher crustal levels along the footwall of the TLMC normal ductile shear zone. Final uplift and development of F3 folds (post-47 Ma) are possibly related to dextral motion along the Yalakom fault The TLMC has structural style and timing of deformation similar to other metamorphic core complexes in southeastern British Columbia. Local and regional evidence is consistent with the formation of the TLMC in a regional extensional setting within a vigorous magmatic arc. Similar interlayered gneisses with near-horizontal layering and foliation may underlie the entire southern IMB.
Sedimentology of a Melange: Franciscan of Trinidad, California: REPLY
ABSTRACT A study of layer features within coarse proximal-exotic sediment gravity-flow deposits of the Jurassic(?) Franciscan Formation and Patricks Point metasedimentary unit of the Trinidad quadrangle reveals the following common layer sequence: I--massive fine to medium-grained or inversely graded pebbly sandstone, II--pebbly sandstone or conglomerate with or without preferred clast orientation, III--coarse tail and/or content normally graded pebbly sandstone, IV--diffusely laminated and/or cross-stratified pebbly sandstone, V--massive fine to medium-grained sandstone, and VI--diffuse to sharply laminated fine to medium-grained sandstone which may contain dish and pillar structures. This sequence is developed vertically and laterally during a single flow event. It reflects transitions from rain support by dispersive pressure to fluid turbulence which occur as a sediment gravity-flow progresses downslope and the entrained grain population becomes finer. The sequence may therefore be used to recognize individual flow events in a vertical sequence and to determine proximality of deposition on the inner submarine fan or suprafan. Franciscan Formation sedimentary rocks were deposited chiefly on an inner fan, whereas those of the Patricks Point unit were deposited on an outer fan downfan from a suprafan lobe. The Patricks Point unit is either allochthonous and of a different age than the Franciscan Formation, or was severed, metamorphosed and emplaced east of the Trinidad Franciscan during melange formation.