SHARAD MASTER 503 Pangaean megalineaments: geophysical indications for the existence of Laurentian counterparts of the 6000 km Trans-SaharanTibesti Lineament, and implications for lithospheric tectonics and mineral deposits Sharad Master Economic Geology Research Institute, School of Geo.sciences, University of the P. Bag 3, Wits 2050, Johannesburg, Soutli Africa, e-mail: masters@geosciences.wits.ac.za © 2006 December Geoloj^cal Society of South Africa ABSTRACT A major (lOiJO-km long west-nonhwesl to easl-southeast-irentling 'i'r;in.s-S;ih;ir;in lineament, extending iVotn Kenya to Moroca), referred tu as the TibesU Lineameni, has been described by GuiniLid el al. (2(K)()). Thi.s lineamem shows up on satellite images, air-photo masaics and terrain elevation imxiels. as swarms of pamllel liiiilcs. It corresponds lo n major discontinuity of surface wave velocities in the mantle, suggesting thut it deeply affects the lithosplierc. The highest heat (low measurements in the Wesi Afritan sliield are found adjacent lo (he Tihesti Lineameni in the northern Hoggar uplift. Geophysical, geological, and geomorphologk-al evidence suggests thai the Tilu'sti lineament may have continued into North America (Laiirenria>. which collidiid witJi northwest Afric;i during the Appalachian-Miiuritanidc orogeny, coinciding with the late Palaeozoic assembly of the ,su|)ercontinent Pangaea. Tlie contiguous Uureniian lineaments which may lie extensions of the Tibesti Lineament, are the here newly recognised Chesierfieid irUet Lineament and the Cabm SiT^jit Lineament, lx>th of which are situated in Canada, These lineaments are defined as linearpatterrt breaks in processed aeromagnt-tic ammuiiy maps of Canada. ,Some jToriions of them also can be detected in refraction and reflection seismic survey data (e.g.. under Hudon Hay), and in a lesser exieni. in (he liouguer gravity anomaly map of Canada. Hie lineaments have present-day Cneotectonic) surface expressions in the form of inlets, submarine channels, straight river segments, and strings of linear lakes, exiendlng over 37(KI km. from Nunavut Province northwest of Hudson Ray. across Queliec and Newioundland, and to the Caliot Strait separating Newfoundland from Nova Scotia. The highest heal flow in the Canadian Maritimes is found in the Cabot .Strait. The Tibesti-Cabot-Strait-Chesteifieid Inlet lineaments reflect deep-sealed fracturing of (he North African and North American lithusphere, involving lioth the crust and rigid upf>er mantle. These lineaments cut right across Ihe grain of numerous orogenic lielts dating from the Palaeoproterozoic, Late Mesoprolerozoic. and Palaeozoic. By analogy with other large transcontinental lineaments which contain ore deposits, the.se newly identified megalineaments may Iw prospective for economic niineial deposits, such as hydrothemial gold and base metal mineralization, and diamondiferous kimberlites. Introduction Evidetice ha.s recently been presented for the existence of a major 6000-km long we.si-nonhwest to east- nonhcast-trending Trans-Saharan lineament, extending frorn Kenya to Morocco, refetred to :i.s the Tihesti Lineament (Giiiraud et al., 2000). On regional and continental .scales, the Tibesti Lineament .shows up on compo.site satellite image mosaics of North Africa, and on digital terrain elevation models, wliile on a local scale, the lineament shows up as .swarm.s of parallel faults, rather than as a single fault zone (Guiraud et al., 2000), Plate-scale geophysical .studies have shown a major discontinuity of the seismic SH (.surface) wave velocities in the mantle corre.sponding to the approximate location of the Tibesti Lineament, suggestitig that tlie discontinuity deeply affects the litho.sphere (Hadiouche and Jobert, 1988: Guit^ud f/ al., 2000). Heat flow measurements in the Saliara indicate that the highest heat flow in West Africa (>100 mWm") occurs at the north end of the Hoggar uplift, where it is bounded by the Tibesti Lineament (Lucazeau et al., 1991). Tlie Til^esti lineament is one of several major lineaments that cross Africa, including tlie Felusium lineament, Guineo-Nubian Lineament, the Central African Shear Zone, and the Taoudeni Lineament (Neev et al., 1982; Comacchia and Dars. 1983; Guiraud etal, 1985, 2000), Geophysical, geological, and geomorplujlogical evidence suggests that Uie Tibesti lineament may have continued into North America (Laurentia), which collided with northwest Africa during the Appalachian- Mauritanide orogeny (Pique, 1981; Villeneuve and Dallmeyer, 1988; Lecorche et al., 1989). coinciding with the late Palaeozoic assembly of the superconlinent Pangaea. The contiguous Laureniian lineaments which may be extensions of tlie Tibesti Lineament, are the here newly recognised Chesterfield Inlet Lineament and the Cabot Strait Lineaments, which are situated in Canada, The Chesterfield Inlet and Cabot Strait Lineaments In the Nunavut Province of Canada, on the northwestern side of Hudson Bay, there is a narrow 200-km long west- northwest-striking inlet known as Chesterfield Inlet, which forms a prominent lineament (Figure 1; for regional location, see inset in Figure 2). The lineament continues for another 680 km to the west-northwest, having a physiographic expre.ssion through a string of lakes, incKitling Hakcr, A!>erdeen and Beverly lakes, and continuing through the west-northwest4tending part of tlie Back River, towards Nose Lake, untii it meets tlie SOUTH AFRICAN JOURNAL OF GEOLOGY, 2006,VOLt;M^ 109 PAGE '5O,1-51( liMlkuu.