Geochemical and Sr-Nd isotopic constraints on the petrogenesis and geodynamic significance of the Jebilet magmatism (Variscan Belt, Morocco)

Abderrahim Essaifi, Scott Samson, Kathryn Goodenough

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

In the Variscan fold belt of Morocco, the Jebilet massif is characterized by Palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic-granitoid bimodal association and peraluminous granodiorites emplaced c. 330 Ma, intruded by younger leucogranites c. 300 Ma. The mafic-ultramafic rocks belong to a tholeiitic series, and display chemical and isotopic signatures consistent with mixing between mantle-derived and crust-derived magmas or assimilation and fractional crystallization. The granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of A2-type granites. The peraluminous, calc-alkaline series consists mainly of cordierite-bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths. Detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust (<30 km) by partial melting of tonalitic sources at high temperatures (up to 900°C) and by partial melting of metasedimentary protoliths at relatively low temperatures (c. 750°C), respectively. Mixing between the coeval mantle-derived and crust-derived magmas contributed to the large variation of initial Nd values and initial Sr isotopic ratios observed in the granitoids. Further contamination occurred by wall-rock assimilation during ascent of the granodioritic plutons to the upper crust. The ultramafic-granitoid association has been intruded by leucogranites that have high initial Sr isotopic ratios and low initial Nd values, indicating a purely crustal origin. The heating events that caused emplacement of the Jebilet magmatism are related to cessation of continental subduction and convective erosion/thinning of the lithospheric mantle during plate convergence.

Original languageEnglish (US)
Pages (from-to)666-691
Number of pages26
JournalGeological Magazine
Volume151
Issue number4
DOIs
StatePublished - Jul 2014

Keywords

  • Bimodal magmatism
  • Morocco
  • Peraluminous granite
  • Sr-Nd isotopes
  • Variscan orogeny

ASJC Scopus subject areas

  • Geology

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