Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006e%26psl.252..308h&link_type=abstract
Earth and Planetary Science Letters, Volume 252, Issue 3-4, p. 308-326.
Other
14
Scientific paper
The Bi'r Umq suture zone (BUSZ) in western Saudi Arabia comprises Neoproterozoic oceanic-arc plutonic, volcanosedimentary, and ophiolitic rocks that record some of the earliest magmatic and tectonic events of the East African Orogen in the Arabian Nubian Shield (ANS). New Nd isotopic analyses are combined with data on zircon inheritance and published isotopic studies to establish the case that pre-Neoproterozoic crust had a greater influence on the oceanic portion of the ANS than is appreciated. Highly positive initial ɛNd (+ 3.9 to + 8.5) and Nd model ages (560 830 Ma) that approximate crystallization ages (573 813 Ma) of BUSZ igneous rocks are comparable to upper crust in other parts of the ANS considered to be juvenile (mantle-derived) and to some xenoliths from the lower crust and lithospheric mantle. Overall, the data suggest that the 40-km-thick crust beneath much of the Arabian Shield is juvenile and that most of it was extracted from depleted mantle during the interval ˜ 740 830 Ma. Although much of the ANS is isotopically juvenile, some Neoproterozoic igneous rocks in the northern ANS contain zircon inherited from pre-Neoproterozoic sources. Samples from the BUSZ that show inheritance yield slightly lower initial ɛNd than contemporary samples that do not show inheritance, suggesting that some juvenile magmas assimilated older continental material. The age of that material is inferred to be largely early Neoproterozoic and Mesoproterozoic, with minor Paleoproterozoic and Archean components, based on U Pb ages of inherited zircon and Nd model ages for ANS upper crustal rocks and xenoliths of the lower crust and mantle lithosphere. Inherited zircon may have been assimilated from terrigenous sediment shed from nearby passive margins, and transported fluvially or by glaciers, or by assimilation of cryptic early Neoproterozoic to Archean basement that underlies the “juvenile” core of the ANS. Zircon morphologies are consistent with both sedimentary origins and in situ extraction from older basement, although inheritance in the Tharwah ophiolite argues for the latter (i.e. during rifting of pre-existing arc crust). Assuming a sedimentary origin, Paleoproterozoic Archean inherited zircon may be derived from basement of that age exposed in the ANS, but Mesoproterozoic sources do not occur anywhere in the shield.
Hargrove Ulysses S.
Johnson Randall P.
Kimura Jun-Ichi
Manton William I.
Stern Ronald J.
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