Constraints on the magmatic evolution of the oceanic crust from plagiogranite intrusions in the Oman ophiolite

Karsten M. Haase*, Sarah Freund, Christoph Beier, Jürgen Koepke, Martin Erdmann, Folkmar Hauff

*Corresponding author for this work

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

We present major and trace element as well as Sr, Nd, and Hf isotope data on a suite of 87 plutonic rock samples from 27 felsic crustal intrusions in seven blocks of the Oman ophiolite. The rock compositions of the sample suite including associated more mafic rocks range from 48 to 79 wt% SiO2, i.e. from gabbros to tonalites. The samples are grouped into a Ti-rich and relatively light rare earth element (LREE)-enriched P1 group [(Ce/Yb)N > 0.7] resembling the early V1 lavas, and a Ti-poor and LREE-depleted P2 group [(Ce/Yb)N < 0.7] resembling the late-stage V2 lavas. Based on the geochemical differences and in agreement with previous structural and petrographic models, we define phase 1 (P1) and phase 2 (P2) plutonic rocks. Felsic magmas in both groups formed by extensive fractional crystallization of olivine, clinopyroxene, plagioclase, apatite, and Ti-magnetite from mafic melts. The incompatible element compositions of P1 rocks overlap with those from mid-ocean ridges but have higher Ba/Nb and Th/Nb trending towards the P2 rock compositions and indicating an influence of a subducting slab. The P2 rocks formed from a more depleted mantle source but show a more pronounced slab signature. These rocks also occur in the southern blocks (with the exception of the Tayin block) of the Oman ophiolite implying that the entire ophiolite formed above a subducting slab. Initial Nd and Hf isotope compositions suggest an Indian-MORB-type mantle source for the Oman ophiolite magmas. Isotope compositions and high Th/Nb in some P2 rocks indicate mixing of a melt from subducted sediment into this mantle.

Original languageEnglish
Article number46
Pages (from-to)1-16
Number of pages16
JournalContributions to Mineralogy and Petrology
Volume171
Issue number5
DOIs
Publication statusPublished - 1 May 2016
Externally publishedYes

Keywords

  • Fractional crystallization
  • Mid-ocean ridge
  • Subduction

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