Timing and modes of granite magmatism in the core of the Alboran Domain, Rif chain, northern Morocco: Implications for the Alpine evolution of the western Mediterranean

Abstract

The Betic-Rif orogen forms the western termination
\nof the Alpine orogenic system in the Mediterranean
\nregion. The precise timing, structural evolution,
\nand distribution of high-grade metamorphic units
\n(Alpine versus pre-Alpine) in the inner zones of the orogen
\n(Alboran Domain) remain controversial issues. In
\nthis paper we report occurrence of distinct generations
\nof peraluminous granitic bodies intruded within Beni
\nBousera peridotites and their amphibolite-to-granulite
\nfacies envelope, in the core of the Alboran Domain of
\nthe Rif chain (northern Morocco). These granitic bodies
\nare central to the reconstruction of the high-grade evolution
\nof the Alboran Domain because they provide
\nfirst-order structural markers to assess the P-T-t-deformation
\nhistory of the high-grade terranes. Here we
\ndocument the petrography and structural relationships
\nwith the host rocks and constrain the timing of granite
\nemplacement using laser ablation.inductively coupled
\nplasma.mass spectrometry U-Pb zircon and/or monazite
\ndating, complemented by 40Ar/39Ar dating. The
\nresults indicate that granite emplacement occurred
\nin two major episodes of anatectic magmatism, during
\nthe Hercynian (circa 300 Ma) and Alpine (circa 22 Ma)
\nperiods, respectively. These data (1) provide conclusive
\nevidence for an important phase of Hercynian magmatism
\nand high-grade metamorphism in the Alboran
\nDomain and (2) permit a revaluation of the significance
\nof the high-grade early Miocene event documented in
\nthe Alboran Domain in terms of a late stage, thermal
\npulse that reworked a polymetamorphic (Hercynian
\nand Alpine) nappe pile. These results provide new
\nconstraints for construction of a feasible tectonometamorphic
\nmodel for the Alpine evolution of the western
\nMediterranean.