Petrogenesis of Pyroxenites and Melt Infiltrations in the Ultramafic Complex of Beni Bousera, Northern Morocco

Abstract

HREE fract. (metam. grt); pos. Eu and Sr anomalies (magm. Plag); neg. HFSE; Nb/Ta fract. high CaTs, Na and Al variations (cpx); Al-rich metam. sp; Mg-rich grt; slight fract. LREE and HREE to the MREE, pos. Eu and Sr anomaly, low HFSE (cpx); pos. Eu anomaly, low HREE (grt). metam. Grt and cpx Graphite pseudomorph after diamond garnet clinopyroxenites (PSD) show a similar band geometry and geochemistry to specific IIIA garnet clinopyroxenites. Modal composition mineralogy consists of:

Orogenic, Ophiolitic, and Abyssal Peridotites

“…In Ronda, these pyroxenites are considered to derive from subduction-related magmatism, lending support to the scenarios involving a back-arc setting for the evolution of the Alboran Sea (Marchesi et al, 2012). The Beni Bousera peridotite contains replacive and deformed Al-poor pyroxenites that are compositionally comparable to the veins from Ronda and were also ascribed to subduction magmatism during the evolution of the Alboran domain (Gysi et al, 2011). Low-alumina pyroxenite dikes are also frequent in the ophiolitic harzburgite sequences.…”

“…Refractory peridotites may be volumetrically significant (up to 30-40%), while the mafic layers generally do not exceed 5%. Several orogenic peridotites contain accessory lithologies resulting from the segregation and migration of partial melts or from the interaction between mantle rocks and melt/fluid (e.g., Bodinier et al, 1988Bodinier et al, , 1990Bodinier et al, , 2008Borghini et al, 2007;Boudier and Nicolas, 1977;Garrido and Bodinier, 1999;Gysi et al, 2011;Mazzucchelli et al, 2009;Obata and Nagahara, 1987). Rock types related to melt/fluid processes include a variety of dikes, veins, and veinlets representing magma conduits now filled with garnet and/or amphibole pyroxenites, hornblendites, glimmerites (mica-clinopyroxene), orthopyroxenites or gabbros, and diffuse facies of pyroxene-rich or amphibole (AEphlogopite)-bearing peridotites resulting from interactions between peridotites and percolating melt/fluid.…”

“…Several studies were also performed on the Beni Bousera peridotite (Morocco), including pioneering and advanced geochemical studies of mafic layers (Blichert-Toft et al, 1999;Gueddari et al, 1996;Kumar et al, 1996;Kornprobst et al, 1990;Allègre, 1979, 1982;Pearson and Nowell, 2004;Pearson et al, 1989Pearson et al, , 1991aPolvé and Allègre, 1980). Recent studies on Ronda and Beni Bousera were mostly focused on deciphering the significance of the different types of pyroxenites and further constraining the mechanisms of lithospheric melting and related melt ingress and refertilization Crespo et al, 2006;El Atrassi et al, 2011;Gysi et al, 2011;Marchesi et al, 2010Marchesi et al, , 2012Morishita et al, 2009a;Soustelle et al, 2009). …”

“…In the first case, these rocks may be used to investigate the geochemical composition of primary mantle melts and the mechanisms of melt segregation from partially molten peridotites (Loubet and Allègre, 1982;Obata and Nagahara, 1987;Pearson et al, 1993;Reisberg and Lorand, 1995;Suen and Frey, 1987) or the subsequent evolution of melt compositions due to HP fractional crystallization and/or reaction with lithospheric peridotites (Bodinier et al, 1987a,b;Downes et al, 1991;Garrido and Bodinier, 1999;Gysi et al, 2011;Kumar et al, 1996;Marchesi et al, 2012;Rivalenti et al, 1995;Takazawa et al, 1999). In the second hypothesis, the peridotite massifs are considered as analogs for the source region of oceanic basalts, and the mafic layers are considered as the cause of the recycling isotopic and trace-element signature in oceanic basalts (e.g., Prinzhofer et al, 1989;Hauri, 1996;Hirschman andStolper, 1996, Pearson andNowell, 2004).…”

Partial melting of secondary pyroxenite at 1 and 1.5 GPa, and its role in upwelling heterogeneous mantle

“…MM3 (Falloon et al 1999(Falloon et al , 2008 DMM1 ( We considered two outermost mantle sources with pyroxenite mass fractions of 5 and 50%. Although the pyroxenite proportion into the mantle is commonly assumed to be around 2-10% (e.g., Hirschmann and Stolper 1996;Pertermann and Hirschmann 2003b), field evidence from orogenic and ophiolitic massifs indicates that the extent of pyroxenites in mantle sequences might be locally significantly higher than 10% (e.g., Gysi et al 2011). This is for example the case of some outcrops of the External Liguride mantle sequences, in which secondary pyroxenite abundance can reach a proportional ratio of 1:1 to the associated peridotites (Borghini et al 2013(Borghini et al , 2016.…”