Geochemical characterization of the Oman Crust-Mantle transition zone,
OmanDP Holes CM1A and CM2B
Abstract
The transition from the gabbroic oceanic crust to the residual mantle
harzburgites of the Oman ophiolite has been drilled at Holes CM1A and
CM2B (Wadi Tayin massif) during Phase 2 of the International Continental
Scientific Drilling Program (ICDP) Oman Drilling Project (OmanDP) (Nov.
2017-Jan. 2018). In order to unravel the formation processes of
ultramafic rocks in the Wadi Tayin massif (CM) crust-mantle transition
zone and deeper in the mantle sections beneath oceanic spreading
centers, our study focuses on the whole rock major and trace element
compositions (together with CO2 and H2O concentrations) of these
ultramafic rocks (56 dunites and 49 harzburgites). Despite extensive
serpentinization and some carbonation, most of the trace element
contents (REE, HFSE, Ti, Th, U) record high temperature, magmatic
process-related signatures. Two major trends are observed, with good
correlations between (1) Th and U, Nb and LREE on one hand, and between
(2) HREE, Ti and Hf on the other hand. We interpret the first trend as
the signature of late melt/peridotite interactions as LREE are known to
be mobilized by such processes (‘lithospheric process’), and the second
trend as the signature of the initial mantle partial melting
(‘asthenospheric process’), with little or no overprint from melt/rock
reaction events.