Triassic to early Liassic continental rifting chronology and process at the southwest margin of the Alpine Tethys (Middle Atlas and High Moulouya, Morocco); correlations with the Atlantic rifting, synchronous and diachronous

摘要: In Morocco from Triassic to Early Liassic times, continental Atlantic and Tethys rifting processes have interfered ([fig. 1][1]). On the future southwest tethyan margin, “Atlasic”, rift formation was recorded in “Middle Atlas” “High Moulouya” basins (MAHM) within central part of Moroccan Atlasic domain. The study their sedimentary infilling relationships with tectonic volcanism, Upper Trias Lower Lias, enables distinguish several major steps process on this tethysian margin segment. Successive ( [fig. 2][2] [5][3]) R1, Carnian-Norian first generation (G1). opening intracontinental (SE Tazekka, Kerrouchen,) resulted extensive along some sutures (NMAF SMAF). These half grabbens consist syn-rift series made detritic deposits (see [plate I, ph. 1-2][4]): piedmont conglomerates arkoses, fluvial sandstones argillaceous siltstones. Later, whole domain covered rather homogeneous lagunal-marine sediments corresponding a slight sea water rising and/or subsidence associated post-rift relaxation. Nevertheless, throughout period, number faults remained active generating more subsiding zones clays evaporites stable siltstones 3][5] [6A][6]). R2, Triassic-Liassic basaltic trapps 5C][3]), synchronous crustal fractures. emplacement all over atlasic coeval beginning Central magmatic province. studied area, trapp sequence (up 150 m), ([pl. 3-4][4]) include about twenty aerial subaqueous (fresh water, exceptionally water) lava-flows (5 m 10 thickness). R3, volcano-sedimentary second (G2). At that time, emerged. Continental erosion became close old new faults. A or transtensive event lead dislocation four 5D][3]). This “second generation” 6B][6]) either superposed “first (Boufekrane; 4B][7]) lagunal–marine sedimentation, could be independent strictly (Taggounite, Bou Tkoubay, Ahouli). formed basins. They always included positive megasequence proximal deposits, then fluvio-lacustrine and, at last, supratidal carbonates 5 7][4]). Within megasequence, when sedimentation fine, pyroclastic products interstratified. consisted ash lapilli tufs tuffites II][8]), which means volcanic explosions were subaerial while subaquatic sometimes reworked 4A][7]). craters proximal, localized probably fault crosscutting. following marine 5E][3]) began during Sinemurian Carixian times. Correlations 7][9]) At scale Morocco, three-step evolution is dramatically different southwestern domain, includes both westwards (Telouet, Haut Atlas de Marrakech) edge (Argana, occidental). Indeed eastwards MAHM pre-trapp (G1) only one (probably Trias), whereas sequences (Upper Permian Trias) successively westwards. R1 occurred later than western Tethyan domain. The post-trapp (G2) du MAHM, where explosive are known area. By fact, sites witnesses relaxation, basins, eruptions, individualizing eastwards. Thus also eastwards, as (R3) went but below level. Conclusions Our evidences Middle High Moulouya domains, phase eruptions after enormous fissural before transgression. necessarily polyphased Lias two syn-rifts periods R3 separated by dramatic eruptive R2. The comparison Trias-Lias geological highlights points: 1– genesis rifts synchronously times. times; 2– fact hold huge effusive until Jurassic transgression, specificity eastern parts rift. Besides, activity level time Jurassic. It comes long (Middle Moulouya) margin. [1]: #F1 [2]: #F2 [3]: #F7 [4]: #F4 [5]: #F3 [6]: #F8 [7]: #F5 [8]: #F6 [9]: #F9