Recent isotopic and biochronologic dating has demonstrated that the Gets
nappe contains remnants of the oldest part of the oceanic crust of the
Alpine Tethys. The ophiolites are associated with deep sea sediments,
platform carbonates and continental crustal elements suggesting a
transitional environment between continental and oceanic crust.
Therefore, the ophiolites from the Gets nappe provide the opportunity to
assess the nature of mantle source and the magma evolution during the
final rifting stage of the European lithosphere. Trace clement analyses
of mafic rocks can he divided into two sets: (1) P, Zr and Y contents
are consistent with those of mid-ocean ridge basalts and REE patterns
have a P-MORB affinity. (2) P,Zr Ti and Y contents are compatible with
within-plate basalts and are characterized by REE spectra similar to
that of T-MORB. Both have Nd isotopic compositions similar to those of
synrift magma of the Red Sea and to the Rhine Graben. The model ages are
in agreement with an LREE-enriched subcontinental mantle source derived
from depleted mantle 800 to 900 Ma ago. Minor, trace element and Sm-Nd
compositions suggest that these rocks are basaltic relies of an earliest
stage of oceanic spreading i.e. an embryonic ocean. Comparison between
REE patterns, Nd and Sr isotope compositions, isotopic and
biochronologic ages from different Alpine Tethys ophiolites shows that
samples with enriched LREE are from the older ophiolitic suites and are
relies of the embryonic ocean floor. Later phases of ocean spreading are
characterized by basalts that are depleted in LREE.