The Central Atlantic Magmatic Province (CAMP) in Morocco

Abstract

The Central Atlantic Magmatic Province (CAMP) is a large igneous province (LIP) composed of basic dykes, sills, layered intrusions and lava flows emplaced before Pangea break-up and currently distributed on the four continents surrounding the Atlantic Ocean. One of the oldest, best preserved and most complete sub-provinces of the CAMP is located in Morocco. Geochemical, geochronologic, petrographic and magnetostratigraphic data obtained in previous studies allowed identification of four strato-chemical magmatic units, i.e. the Lower, Intermediate, Upper and Recurrent units. For this study, we completed a detailed sampling of the CAMP in Morocco, from the Anti Atlas in the south to the Meseta in the north. We provide a complete mineralogical, petrologic (major and trace elements on whole-rocks and minerals), geochronologic (40Ar/39Ar and U–Pb ages) and geochemical set of data (including Sr–Nd–Pb–Os isotope systematics) for basaltic and basaltic–andesitic lava flow piles and for their presumed feeder dykes and sills. Combined with field observations, these data suggest a very rapid (<0·3 Ma) emplacement of over 95% of the preserved magmatic rocks. In particular, new and previously published data for the Lower to Upper unit samples yielded indistinguishable 40Ar/39Ar (mean age = 201·2 ± 0·8 Ma) and U–Pb ages (201·57 ± 0·04 Ma), suggesting emplacement coincident with the main phase of the end-Triassic biotic turnover (c.201·5 to 201·3 Ma). Eruptions are suggested to have been pulsed with rates in excess of 10 km3/year during five main volcanic pulses, each pulse possibly lasting only a few centuries. Such high eruption rates reinforce the likelihood that CAMP magmatism triggered the end-Triassic climate change and mass extinction. Only the Recurrent unit may have been younger but by no more than 1 Ma. Whole-rock and mineral geochemistry constrain the petrogenesis of the CAMP basalts. The Moroccan magmas evolved in mid-crustal reservoirs (7–20 km deep) where most of the differentiation occurred. However, a previous stage of crystallization probably occurred at even greater depths. The four units cannot be linked by closed-system fractional crystallization processes, but require distinct parental magmas and/or distinct crustal assimilation processes. EC-AFC modeling shows that limited crustal assimilation (maximum c.5–8% assimilation of e.g. Eburnean or Pan-African granites) could explain some, but not all the observed geochemical variations. Intermediate unit magmas are apparently the most contaminated and may have been derived from parental magmas similar to the Upper basalts (as attested by indistinguishable trace element contents in the augites analysed for these units). Chemical differences between Central High Atlas and Middle Atlas samples in the Intermediate unit could be explained by distinct crustal contaminants (lower crustal rocks or Pan-African granites for the former and Eburnean granites for the latter). The CAMP units in Morocco are likely derived from 5–10% melting of enriched peridotite sources. The differences observed in REE ratios for the four units are attributed to variations in both source mineralogy and melting degree. In particular, the Lower basalts require a garnet peridotite source, while the Upper basalts were probably formed from a shallower melting region straddling the garnet–spinel transition. Recurrent basalts instead are relatively shallow-level melts generated mainly from spinel peridotites. Sr–Nd–Pb–Os isotopic ratios in the CAMP units from Morocco are similar to those of other CAMP sub-provinces and suggest a significant enrichment of the mantle-source regions by subducted crustal components. The enriched signature is attributed to involvement of about 5–10% recycled crustal materials introduced into an ambient depleted or PREMA-type mantle, while involvement of mantle-plume components like those sampled by present-day Central Atlantic Ocean Island Basalts (OIB, e.g. Cape Verde and Canary Islands) is not supported by the observed compositions. Only Recurrent basalts may possibly reflect a Central Atlantic plume-like signature similar to the Common or FOZO components.

Deep CO2 in the end-Triassic Central Atlantic Magmatic Province

“…The geothermobarometer based on the equilibrium between clinopyroxene and a magmatic liquid 37 was applied using whole rock composition as proxy for the original magmatic liquid composition, because the MIs glass is in chemical disequilibrium with the host clinopyroxene. The calculated crystallization pressure ranges from 0.1 to 0.7 ± 0.2 GPa (at temperatures from 1150 to 1230 ± 27°C) and is consistent with previous estimates from clinopyroxene crystallization pressures (from 0.2 to 0.8 GPa) in basalts from the entire CAMP 23,[39][40][41] . These results suggest that the crystallization of clinopyroxene in the investigated CAMP samples occurred predominantly within the middle continental crust (on average ca.…”

“…The inferred depth of CO 2 exsolution and entrapment indicates that this volatile species has a deep origin (at least 12 ± 7 km on average). It therefore reveals that the entire CO 2 budget involved in CAMP emplacement could not have originated exclusively from assimilation and degassing of shallow intruded sediments 26 , because sediments in the circum-Atlantic basins only reach a thickness of 5 km in eastern North America 49 and <1 km in Morocco 23 and Portugal 39 . On the contrary, at least part of the CO 2 most probably derived from assimilation of deepto middle-crustal metasedimentary rocks (e.g., metacarbonates or graphite-bearing amphibolites/granulites) or from the mantle source of CAMP basalts (Fig.…”

“…The emplacement of CAMP (peak activity at 201.6-201.1 Ma) occurred during the early stages of the Pangaea supercontinent break-up, leading to the opening of the Central Atlantic Ocean, and is synchronous with the End-Triassic Extinction (ETE), one of the five most severe biotic crises during the Phanerozoic [19][20][21][22] . At least 3 × 10 6 km 3 of CAMP basaltic magmas were erupted or intruded into the continental crust over an area of 10 7 km 2 in brief pulses, from a few centuries to a few millennia each, characterized by high eruption rates 6,23 . Such short and powerful eruptions may have had a severe impact on global climate by limiting the time in which negative feedback processes, such as the weathering of Ca-Mg silicates, can abate warming and acidification.…”

Comment on “The Mesozoic Margin of the Maghrebian Tethys in the Rif Belt (Morocco): Evidence for Polyphase Rifting and Related Magmatic Activity” by Gimeno‐Vives et al.

“…(a) Primitive mantle‐normalized multielement diagrams of Central Atlantic Magmatic Province (CAMP) intrusive rocks of North‐West and West Africa compared with that of Bou Adel gabbros. The data (average of data) for the Anti‐Atlas (Morocco) and southwestern Algeria are respectively from Marzoli et al () and Chabou et al (), for the Kakoulima laccolith from Deckart et al (), for Freetown layered complex from Callegaro et al (), and for Bou Adel gabbros from Benzaggagh et al (). Normalizing values are from Sun and McDonough ().…”

“…Normalizing values are from Sun and McDonough (). (b) Th/Yb vs. Nb/Yb diagram (Pearce, ) for the Bou Adel gabbros (Benzaggagh et al, ) and the CAMP intrusive rocks of Morocco (Marzoli et al, ) and Mali (Verati et al, ).…”