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Jeanpaul Liegeois - One of the best experts on this subject based on the ideXlab platform.
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the latea metacraton central hoggar tuareg shield algeria behaviour of an old Passive Margin during the pan african orogeny
Journal of African Earth Sciences, 2003Co-Authors: Jeanpaul Liegeois, Louis Latouche, Mustapha Boughrara, Jacques Navez, Michel GuiraudAbstract:Historically, the Tuareg shield is divided into three parts bordered by mega-shear zones with the centre, the Central Polycyclic Hoggar, characterized byArchaean and Palaeoproterozoic lithologies. Nearly10 y ears ago, the Tuareg shield was shown to be composed of 23 displaced terranes (Geology22 (1994) 641) whose relationships were deciphered in A € i to the SE (Precambr. Res. 67 (1994) 59). The Polycyclic Central Hoggar terranes were characterized by the presence of well preserved Archaean/Palaeoproterozoic and Neoproterozoic lithologies. We show here that the terranes from Central Hoggar (Laouni, Azrou-n-Fad, Tefedest, Eg��e belonged to a single old Passive Margin, to which we gave the acronym name LATEA, which behaved as a craton during the Mesoproterozoic and the Early- Middle Neoproterozoic but was partlydestabilized and dissected during the Late Neoproterozoic as a consequence of its involvement as a Passive Margin in the Pan-African orogen. An earlyPan-African phase consisted of thrust sheets including garnet-bearing lithologies (eclogite, amphibolite, gneiss) that can be mapped and correlated in three LATEA terranes. In the Tin Begane area, P -T -t paths have been established from >15 kbar--790 � C (eclogite) to 4 kbar--500 � C (greenschist retrogression) through 12 kbar--830 � C (garnet amphibolite) and 8 kbar--700 � C (garnet gneiss), corresponding to the retrograde path of a Franciscan-type loop. Sm-Nd geochronology on minerals and laser ablation ICP-MS on garnet show the mobilityof REE, particularlyLREE, during the retrograde greenschist facies that affects, although slightly, some of these rocks. The amphibolite-facies metamorphism has been dated at 685 ± 19 Ma and the greenschist facies at 522 ± 27 Ma. During the thrust phase, the Archaean-Palaeoproterozoic basement was onlylocallyaffected bythe Pan- African tectonics. LATEA behaved as a craton. Other juvenile terranes were also thrust earlyonto LATEA: the Iskel island arc at � 850 Ma to the west of LATEA, the Serouenout terrane in the 700-620 Ma age range to the east. No subduction-related magmas have intruded LATEA during this epoch, which behaved as a Passive Margin. During the main Pan-African phase (625-580 Ma), LATEA was dissected bymega-shear zones that induced several hundreds km of relative displacement and allowed the emplacement of high-K calc-alkaline batholiths. Smaller movements continued till 525 Ma, accompanied bythe emplacement of subcircular plutons with alkaline affinity. Here is dated the Ounane granodiorite (624 ± 15 Ma; 87 Sr/ 86 Sri ¼ 0.70839 ± 0.00016; 6WR, MSWD ¼ 0.87) and the Tisselliline granite (552 ± 15 Ma; 87 Sr/ 86 Sri ¼ 0.7074 ± 0.0001; 5WR, MSWD ¼ 1.4). Nd isotopes indicate a preponderant Palaeoproterozoic crustal source for these two plutons: eNd ¼� 14 to )21 at 624 Ma and TDM ¼ 1650-2320 Ma for Ounane and eNd ¼� 13 to )15 at 555 Ma and TDM ¼ 1550-1720 Ma for Tisselliline. Our model links these intrusions to a linear lithospheric delamination along mega-shear zones, allowing the hot asthenosphere to rise, melt by adiabatic pressure release and inducing the melting of the Palaeoproterozoic and Archaean lower crust.
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the latea metacraton central hoggar tuareg shield algeria behaviour of an old Passive Margin during the pan african orogeny
Journal of African Earth Sciences, 2003Co-Authors: Jeanpaul Liegeois, Louis Latouche, Mustapha Boughrara, Jacques Navez, Michel GuiraudAbstract:Historically, the Tuareg shield is divided into three parts bordered by mega-shear zones with the centre, the Central Polycyclic Hoggar, characterized byArchaean and Palaeoproterozoic lithologies. Nearly10 y ears ago, the Tuareg shield was shown to be composed of 23 displaced terranes (Geology22 (1994) 641) whose relationships were deciphered in A € i to the SE (Precambr. Res. 67 (1994) 59). The Polycyclic Central Hoggar terranes were characterized by the presence of well preserved Archaean/Palaeoproterozoic and Neoproterozoic lithologies. We show here that the terranes from Central Hoggar (Laouni, Azrou-n-Fad, Tefedest, Eg��e belonged to a single old Passive Margin, to which we gave the acronym name LATEA, which behaved as a craton during the Mesoproterozoic and the Early- Middle Neoproterozoic but was partlydestabilized and dissected during the Late Neoproterozoic as a consequence of its involvement as a Passive Margin in the Pan-African orogen. An earlyPan-African phase consisted of thrust sheets including garnet-bearing lithologies (eclogite, amphibolite, gneiss) that can be mapped and correlated in three LATEA terranes. In the Tin Begane area, P -T -t paths have been established from >15 kbar--790 � C (eclogite) to 4 kbar--500 � C (greenschist retrogression) through 12 kbar--830 � C (garnet amphibolite) and 8 kbar--700 � C (garnet gneiss), corresponding to the retrograde path of a Franciscan-type loop. Sm-Nd geochronology on minerals and laser ablation ICP-MS on garnet show the mobilityof REE, particularlyLREE, during the retrograde greenschist facies that affects, although slightly, some of these rocks. The amphibolite-facies metamorphism has been dated at 685 ± 19 Ma and the greenschist facies at 522 ± 27 Ma. During the thrust phase, the Archaean-Palaeoproterozoic basement was onlylocallyaffected bythe Pan- African tectonics. LATEA behaved as a craton. Other juvenile terranes were also thrust earlyonto LATEA: the Iskel island arc at � 850 Ma to the west of LATEA, the Serouenout terrane in the 700-620 Ma age range to the east. No subduction-related magmas have intruded LATEA during this epoch, which behaved as a Passive Margin. During the main Pan-African phase (625-580 Ma), LATEA was dissected bymega-shear zones that induced several hundreds km of relative displacement and allowed the emplacement of high-K calc-alkaline batholiths. Smaller movements continued till 525 Ma, accompanied bythe emplacement of subcircular plutons with alkaline affinity. Here is dated the Ounane granodiorite (624 ± 15 Ma; 87 Sr/ 86 Sri ¼ 0.70839 ± 0.00016; 6WR, MSWD ¼ 0.87) and the Tisselliline granite (552 ± 15 Ma; 87 Sr/ 86 Sri ¼ 0.7074 ± 0.0001; 5WR, MSWD ¼ 1.4). Nd isotopes indicate a preponderant Palaeoproterozoic crustal source for these two plutons: eNd ¼� 14 to )21 at 624 Ma and TDM ¼ 1650-2320 Ma for Ounane and eNd ¼� 13 to )15 at 555 Ma and TDM ¼ 1550-1720 Ma for Tisselliline. Our model links these intrusions to a linear lithospheric delamination along mega-shear zones, allowing the hot asthenosphere to rise, melt by adiabatic pressure release and inducing the melting of the Palaeoproterozoic and Archaean lower crust.
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the moroccan anti atlas the west african craton Passive Margin with limited pan african activity implications for the northern limit of the craton
Precambrian Research, 2001Co-Authors: Nasser Ennih, Jeanpaul LiegeoisAbstract:Abstract The Moroccan Anti-Atlas region, located south of the South Atlas Fault, has been viewed traditionally as containing two segments separated by the Anti-Atlas Major Fault. These two segments are said to consist of: (a) 600–700 Ma Pan-African segment located in the northeast; and (b) ∼2 Ga Eburnian segment situated to the southwest. On the basis of observations in the Zenaga and Saghro inliers and of a recent literature review, we suggest that this subdivision is inappropriate in that Eburnian and Pan-African materials occur throughout the Anti-Atlas region: the entire Anti-Atlas is underlain by Eburnian crust, unconformably overlain by a lower Neoproterozoic Passive Margin; allochthonous Pan-African ocean crustal slices were thrust onto the West African craton (WAC) Passive Margin sequence ∼685 Ma ago as a result of Pan-African accretion tectonics; high-level high-K calc-alkaline and alkaline granitoids locally intruded the Anti-Atlas sequence as a whole at the end of the Pan-African orogeny at 585–560 Ma; the intervening 100 m.y. interval was marked by quiescence. This succession of events can be related to the behaviour of one single rigid cratonic Passive Margin during an orogeny and correlated to the Pan-African events that occurred to the east in the Tuareg shield and to the north in Avalonian terranes. This model implies that the actual northern limit of the WAC is located at the South Atlas Fault (SAF) and not at the Anti-Atlas Major Fault (AAMF). We propose that the AAMF corresponds to the southwestern boundary of an aulacogen that formed along the northern Margin of the WAC during early Neoproterozoic times. This is consistent with the development of the Gourma aulacogen on the eastern side of the WAC. This model further suggests that the northeastern boundary of the WAC occurs north, and not south, of Ougarta (Algeria). Support for this model is provided by geological and geophysical evidence.
Paulian Dumitrica - One of the best experts on this subject based on the ideXlab platform.
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cambrian eocene pre rift pulsed rift Passive Margin and emplacement processes along the northern Margin of the southern neotethys evidence from the antalya complex in the alanya window s turkey
Journal of Asian Earth Sciences: X, 2020Co-Authors: Alastair H F Robertson, Osman Parlak, Tim Kinnaird, Kemal Tasli, Paulian DumitricaAbstract:Abstract Sedimentary rocks in the Alanya Window document pulsed Permian-Triassic rifting in a proximal basin setting, adjacent to the Tauride continental unit (Geyik Dag). Late Cambrian-Early Ordovician clastic sediments accumulated along the north Margin of Gondwana on a variable shallow-marine shelf. Above an unconformity related to rift-shoulder uplift, Late Permian facies document shallow-marine to evaporitic environments during regional tectonic subsidence (first main rift pulse). Above a second unconformity (both extension and sea-level controlled), Early Triassic carbonates and mudrocks accumulated on an unstable, gently subsiding shelf. Mudrocks, sandstones and lithoclastic debris-flows, derived from the underlying succession, accumulated during the Middle Triassic (Anisian-early Ladinian), implying strong tectonic subsidence and flank uplift (second main rift pulse). Radiolarian mudstones accumulated during late Middle Triassic-early Late Triassic in a well-oxidised, organically productive, but relatively quiescent, deep-water basin above the carbonate compensation depth (CCD). Thick (100s m) lithoclastic sandstone turbidites (commonly plant-rich) and localised debris-flows accumulated during the Late Triassic (Carnian), together with detached blocks of underlying lithologies (third main rift pulse), combined with regional uplift. Alkaline basaltic sills were intruded locally. Final continental break-up to create the Southern Neotethys took place regionally during the Late Triassic (Carnian). Latest Triassic-Late Cretaceous deposition records Passive Margin subsidence. Variable low-grade metamorphism and two-stage tectonic emplacement (southwards(?) then northwards) took place during latest Cretaceous and Eocene, respectively. The tectonic-sedimentary development of the Antalya Complex provides insights into rift/continental break-up processes that differ from the recently well-documented Alpine-North Atlantic region.
Osman Parlak - One of the best experts on this subject based on the ideXlab platform.
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cambrian eocene pre rift pulsed rift Passive Margin and emplacement processes along the northern Margin of the southern neotethys evidence from the antalya complex in the alanya window s turkey
Journal of Asian Earth Sciences: X, 2020Co-Authors: Alastair H F Robertson, Osman Parlak, Tim Kinnaird, Kemal Tasli, Paulian DumitricaAbstract:Abstract Sedimentary rocks in the Alanya Window document pulsed Permian-Triassic rifting in a proximal basin setting, adjacent to the Tauride continental unit (Geyik Dag). Late Cambrian-Early Ordovician clastic sediments accumulated along the north Margin of Gondwana on a variable shallow-marine shelf. Above an unconformity related to rift-shoulder uplift, Late Permian facies document shallow-marine to evaporitic environments during regional tectonic subsidence (first main rift pulse). Above a second unconformity (both extension and sea-level controlled), Early Triassic carbonates and mudrocks accumulated on an unstable, gently subsiding shelf. Mudrocks, sandstones and lithoclastic debris-flows, derived from the underlying succession, accumulated during the Middle Triassic (Anisian-early Ladinian), implying strong tectonic subsidence and flank uplift (second main rift pulse). Radiolarian mudstones accumulated during late Middle Triassic-early Late Triassic in a well-oxidised, organically productive, but relatively quiescent, deep-water basin above the carbonate compensation depth (CCD). Thick (100s m) lithoclastic sandstone turbidites (commonly plant-rich) and localised debris-flows accumulated during the Late Triassic (Carnian), together with detached blocks of underlying lithologies (third main rift pulse), combined with regional uplift. Alkaline basaltic sills were intruded locally. Final continental break-up to create the Southern Neotethys took place regionally during the Late Triassic (Carnian). Latest Triassic-Late Cretaceous deposition records Passive Margin subsidence. Variable low-grade metamorphism and two-stage tectonic emplacement (southwards(?) then northwards) took place during latest Cretaceous and Eocene, respectively. The tectonic-sedimentary development of the Antalya Complex provides insights into rift/continental break-up processes that differ from the recently well-documented Alpine-North Atlantic region.
Alastair H F Robertson - One of the best experts on this subject based on the ideXlab platform.
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cambrian eocene pre rift pulsed rift Passive Margin and emplacement processes along the northern Margin of the southern neotethys evidence from the antalya complex in the alanya window s turkey
Journal of Asian Earth Sciences: X, 2020Co-Authors: Alastair H F Robertson, Osman Parlak, Tim Kinnaird, Kemal Tasli, Paulian DumitricaAbstract:Abstract Sedimentary rocks in the Alanya Window document pulsed Permian-Triassic rifting in a proximal basin setting, adjacent to the Tauride continental unit (Geyik Dag). Late Cambrian-Early Ordovician clastic sediments accumulated along the north Margin of Gondwana on a variable shallow-marine shelf. Above an unconformity related to rift-shoulder uplift, Late Permian facies document shallow-marine to evaporitic environments during regional tectonic subsidence (first main rift pulse). Above a second unconformity (both extension and sea-level controlled), Early Triassic carbonates and mudrocks accumulated on an unstable, gently subsiding shelf. Mudrocks, sandstones and lithoclastic debris-flows, derived from the underlying succession, accumulated during the Middle Triassic (Anisian-early Ladinian), implying strong tectonic subsidence and flank uplift (second main rift pulse). Radiolarian mudstones accumulated during late Middle Triassic-early Late Triassic in a well-oxidised, organically productive, but relatively quiescent, deep-water basin above the carbonate compensation depth (CCD). Thick (100s m) lithoclastic sandstone turbidites (commonly plant-rich) and localised debris-flows accumulated during the Late Triassic (Carnian), together with detached blocks of underlying lithologies (third main rift pulse), combined with regional uplift. Alkaline basaltic sills were intruded locally. Final continental break-up to create the Southern Neotethys took place regionally during the Late Triassic (Carnian). Latest Triassic-Late Cretaceous deposition records Passive Margin subsidence. Variable low-grade metamorphism and two-stage tectonic emplacement (southwards(?) then northwards) took place during latest Cretaceous and Eocene, respectively. The tectonic-sedimentary development of the Antalya Complex provides insights into rift/continental break-up processes that differ from the recently well-documented Alpine-North Atlantic region.
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mesozoic deep water slope rise sedimentation and volcanism along the north indian Passive Margin evidence from the karamba complex indus suture zone western ladakh himalaya
Journal of Asian Earth Sciences, 1998Co-Authors: Alastair H F Robertson, Ian R SharpAbstract:Abstract Mesozoic deep-water sedimentary and basic volcanogenic rocks, defined as the Karamba Complex, are exposed within the Indus suture zone of Western Ladakh (N India). The Karamba Complex originated as part of the North-Indian Passive Margin in its entirety, and does not include exotic melange or accreted oceanic units, as recently suggested. The complex preserves younger, more distal equivalents relative to more proximal deep-water slope (Lamayuru Complex) and shelf (Zanskar) successions of the North-Indian Passive Margin. The Karamba Complex is mainly inverted, youngs to the NNW, and includes many outcrop-scale folds that face NNW. The Complex was initially emplaced onto the Zanskar Shelf as three main thrust slices probably in the latest Cretaceous, and later inverted, faulted and sheared during mid–late Tertiary NW backthrusting that accompanied uplift of the High Himalaya. Sedimentation in the Karamba Complex began in the Mid–Late Triassic, with mainly siliciclastic turbidites derived from the Indian basement, together with redeposited limestones and minor basic volcanics. Mixed radiolarian sediments, siliciclastic turbidites and redeposited shelf-derived calciturbidites accumulated in Early–Mid Jurassic, accompanied by eruption of alkaline volcanic rocks, mainly in the Mid Jurassic. The probable cause of the Jurassic volcanism was a pulse of crustal extension along the continent–ocean transition zone, triggered by late-stage rifting of India from Gondwana, as a precursor to its northward drift. Quartzose sandstone turbidites accumulated on the upper slope in the Early Cretaceous, whereas sedimentation on the lower slope/rise was pelagic, marked by depositional hiatuses and sediment redeposition. During the Late Cretaceous a switch to mainly calcareous pelagic deposition took place, interspersed with radiolarian accumulation on the lower slope/rise. Initial thrust emplacement onto the Zanskar Shelf in the latest Cretaceous is suggested by the absence of post-Upper Cretaceous sediments within the Karamba Complex.
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radiolarian evidence for the stratigraphy and palaeo oceanography of the deep water Passive Margin of the indian plate karamba formation indus suture zone ladakh himalaya
Marine Micropaleontology, 1997Co-Authors: Taniel Danelian, Alastair H F RobertsonAbstract:Abstract New radiolarian biostratigraphical information sheds light on the Mesozoic sedimentary, tectonic and palaeoceanographic evolution of a south-Tethyan Margin in northern India. Radiolarian cherts studied here form part of deformed deep-water successions within the Indus Suture Zone (Ladakh Himalaya); these are defined as the Karamba Formation and interpreted as the stratigraphically higher and palaeogeographically more distal parts of a Passive Margin (Lamayuru Group). This formation includes radiolarites, pelagic carbonates, redeposited limestones, ferruginous shales, sandstones, and abundant mafic extrusive rocks. Radiolarian assemblages of early and late Middle Jurassic, mid-Cretaceous (mid-Albian to Cenomanian) and Late Cretaceous (Santonian) age were obtained from four measured sequences. Results indicate: (i) long, intact Jurassic-Cretaceous successions, rather than disrupted melange, are present in the Karamba Formation; (ii) extensive basic volcanism took place during the Middle Jurassic and can be correlated with an extensional phase affecting the NW Indian continental Margin; (iii) non-calcareous radiolarian-rich sediments accumulated during the Middle Jurassic, reflecting the influence either of a broad Jurassic equatorial upwelling zone, or a more localised coastal upwelling system. After drowning of the Zanskar clastic shelf in the late Albian, sedimentation on the distal shelf and upper slope was restricted by bottom current activity. Late Albian-Cenomanian radiolarites of the Karamba Formation are contemporaneous with stratigraphie gaps and glauconite-phosphorite deposition on the Zanskar shelf. A well-developed eastward boundary current off the northern Margin of India may have persisted until near the end of the Late Cretaceous. During the late Albian-Cenomanian, current activity and coastal upwelling were probably strong and radiolarian-rich sediments accumulated on the distal Margin beneath the CCD. Pelagic limestones accumulated during the Turanian over the entire Margin, possibly related to eustatic sea-level rise and consequent reduction in bottom current activity. Intense oceanic circulation apparently was renewed during the Coniacian-Santonian, as indicated by sedimentary hiatuses in the Zanskar shelf succession and accumulation of carbonate-free radiolarian ooze in the Karamba Formation.
Peter A Cawood - One of the best experts on this subject based on the ideXlab platform.
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the neoproterozoic southern Passive Margin of the sao francisco craton insights on the pre amalgamation of west gondwana from u pb and hf nd isotopes
Precambrian Research, 2019Co-Authors: Alice Westin, Peter A Cawood, Mario Da Costa Campos Neto, C J Hawkesworth, Bruno Dhuime, Helene DelavaultAbstract:Abstract Sedimentary basins are, in many cases, the only preserved record of the geological processes active through geological time. These deposits preserve age, isotopic and geochemical signatures of the source rocks, providing insights into tectonic setting. In this context, we investigate the lithostratigraphy, provenance and tectonic environment of the Carrancas Group, a meta-sedimentary sequence characterised by a basal psammitic unit (Lower Unit) passing up into interbedded psammo-pelites (Intermediate Unit), which are overlain by a further psammitic unit (Upper Unit). This succession, along with the Canastra, Paranoa and Vazante groups (Brasilia orogen), comprises a mature Passive Margin developed at the western-southern Margin of the Sao Francisco craton during the Neoproterozoic. Detrital zircon U-Pb ages and Nd-Hf isotope data enable revised stratigraphic correlations across the basin, highlighting variations in the source of detritus. Deposition began after 0.92 Ga, with the sedimentation of the Lower Unit, with input of juvenile ∼2.1 Ga detritus (eNdt = −0.1 to +3.2) derived from the Sao Francisco craton. A marine transgression characterises the transition to the Intermediate Unit, which gradually covered over juvenile ∼2.1 Ga terrains and rendered them unavailable as possible source rocks for detrital zircons. Evolved Archaean-Palaeoproterozoic basement rocks, the Espinhaco Supergroup and evolved Neoproterozoic granitoids, all belonging to the Sao Francisco craton, acted as sources for the Intermediate and Upper units (U-Pb = 2.7 Ga to 0.9 Ga; eNdt = −10.4 to +7.1). The Goias massif might also have acted as a source, providing juvenile Mesoproterozoic detritus. The sediments of the Upper Unit register a significant shift in source, with incoming of juvenile Mesoproterozoic and crustal 1.9 – 1.7 Ga detritus. This change in the ages of the detrital material may be related to exhumation of the Espinhaco Supergroup during the evolution of the Passive continental Margin basin. The whole-rock Nd TDM model ages become progressively younger from the base to the top of the sequence (Nd TDM = 2.6–1.8 Ga). The collisional events between Amazonian and Sao Francisco cratons and the Paranapanema block set the minimum age of deposition along this Passive continental Margin at around 0.67 Ga.
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provenance record of laurentian Passive Margin strata in the northern caledonides implications for paleodrainage and paleogeography
Geological Society of America Bulletin, 2007Co-Authors: Peter A Cawood, A A Nemchin, R A StrachanAbstract:Siliciclastic sequences accumulated along the eastern Margin of Laurentia during the late Neoproterozoic to early Paleozoic as a result of the breakup of Rodinia and formation of the Iapetus Ocean. Detrital zircon data show considerable variability in provenance of time-equivalent units that has implications for paleodrainage and paleogeography. Samples from northwest Scotland and northeast Greenland show detrital zircon U-Pb age groupings dominated by Archean and Paleoprotero-zoic populations consistent with derivation largely from the West Greenland segment of the North Atlantic craton. In Scotland, time-equivalent outboard sedimentary sequences show contrasting Archean and Proterozoic populations, including a substantial ca. 1.1–1.0 Ga component, indicative of derivation from the Grenville orogen to the southwest. These contrasting paleodrainage patterns, consistent with paleocurrent data, must have developed during the early phase of Passive-Margin thermal subsidence and may have been accentuated by remnant rift shoulders. In Newfoundland and the U.S. Appalachians, time-equivalent sedimentary sequences are located within the hinterland of the Grenville orogen and are dominated by ca. 1.1–1.0 detritus with very few pre-Mesoproterozoic grains. The Grenville deformation front in these areas may have constituted a drainage divide that limited sediment input from the cratonic interior.