Collision related granitoid batholiths, like those of the Hercynian and Himalayan orogens, are mostly fed by magma derived from metasedimentary sources. However, in the late Neoproterozoic calcalkaline batholiths of the Arabian Nubian Shield (ANS), which constitutes the northern half of the East African orogen, sedimentary contribution is obscured by the juvenile character of the crust and the scarcity of migmatites. Here we use paired in-situ measurements of U-Th-Pb isotope ratios and REE contents of monazite and xenotime by LASS to demonstrate direct linkage between granites and migmatites in the northernmost ANS. Our results indicate a single prolonged period of monazite growth, 640-600 Ma, in metapelites, migmatites and per-aluminous granites of the Abu-Barqa (SW Jordan), Roded (S Israel) and Taba-Nuweiba (Sinai, Egypt) metamorphic suites. Distribution of monazite dates and age zoning in single monazite grains in migmatites suggest that peak thermal conditions and partial melting prevailed for ~10 Myr, from 620 to 610 Ma. REE patterns of monazite are well correlated with age, recording garnet growth and garnet breakdown in association with the prograde and retrograde stages of the melting reactions, respectively. Xenotime dates (n=40) cluster at 600-580 Ma recording retrogression to greenschist facies conditions as garnet continues to destabilize. Phase equilibrium modelling and mineral thermobarometry illustrate that melting occurred either by dehydration of muscovite or by water-fluxed melting at ~650-680°C and 57 kbar. The expected melt production is 814%, allowing melt connectivity network to form and eventually melt extraction and segregation. The crystallization time of peritectic melt retained in dia- and metataxites overlaps the emplacement time of a vast calcalkaline granitic flux throughout the northern ANS, which was previously considered post-collisional. Similar monazite ages (~620 Ma) of the amphilolite facies nonanatectic Elat schist indicate that migmatites are the result of widespread regional, rather than local contact metamorphism, representing the climax of East African orogenesis.
|Journal||Geophysical Research Abstracts|
|State||Published - 2017|