Geochronologic and isotopic evidence for involvement of pre-Pan-African crust in the Nubian shield, Egypt

Journal Article · Wed Aug 01 00:00:00 EDT 1990 · Geology; (USA)

DOI:https://doi.org/10.1130/0091-7613(1990)018<0761:GAIEFI>2.3.CO;2· OSTI ID:6357255

Sultan, M; Chamberlain, K R; Bowring, S A; Arvidson, R E ^[1]; Abuzied, H ^[2]; El Kaliouby, B ^[3]

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1. Washington Univ., St. Louis, MO (USA)
2. Cairo Univ. (Egypt)
3. Ain Shams Univ., Abassia, Cairo (Egypt)

Two Late Proterozoic granitic bodies from the Eastern Desert of Egypt, the ca. 578 Ma Nakhil and the ca. 595 Ma Aswan granites, provide insights into processes of crust formation in the Arabian-Nubian shield. Evidence for involvement of an older crustal component in the formation of the Nakhil granite includes (1) U/Pb zircon data that establish a crystallization age of 578 {plus minus} 15 Ma and indicate the presence of inherited zircons possibly as old as 1.6 Ga; (2) an elevated model initial {sup 87}Sr/{sup 86}Sr (0.7136); and (3) an elevated initial {sup 207}Pb/{sup 204}Pb (15.561) relative to model mantle compositions at 578 Ma. Evidence for involvement of an older crustal component in the Aswan granite comes from the elevated initial {sup 207}Pb/{sup 204}Pb (15.611). In contrast, extensive crustal contamination is not reflected in the high initial {epsilon}{sub Nd} (+5.7) for the Nakhil and the low initial {sup 87}Sr/{sup 86}Sr (0.7029) for the Aswan granite. The contrasting inferences from the different isotopic systems can be explained by the high whole-rock Nd and Sr concentration for the the Nakhil (87 ppm Nd) and the Aswan (173 ppm Sr) granites, respectively, that suggest that the Nd and Sr isotopic composition of the older component has been overshadowed by the more primitive material. Similar contrasts in Pb, Sr, and Nd isotopic data from the eastern and western shield margins can be interpreted in the same manner and might suggest widespread involvement of older crustal components in the formation of the Late Proterozoic Arabian-Nubian shield.

• OSTI ID: 6357255
• Journal Information: Geology; (USA), Vol. 18:8; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CONTINENTAL CRUST
AGE ESTIMATION
EGYPTIAN ARAB REPUBLIC
CRYSTALLIZATION
EARTH MANTLE
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GRANITES
ISOTOPE DATING
ISOTOPE RATIO
LEAD 204
LEAD 207
NEODYMIUM ISOTOPES
PRECAMBRIAN ERA
STRONTIUM 86
STRONTIUM 87
URANIUM ISOTOPES
ZIRCON
ACTINIDE ISOTOPES
AFRICA
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
BETA DECAY RADIOISOTOPES
CHEMISTRY
DEVELOPING COUNTRIES
EARTH CRUST
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
HEAVY NUCLEI
HOURS LIVING RADIOISOTOPES
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LEAD ISOTOPES
MINERALS
NUCLEI
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
RADIOISOTOPES
ROCKS
SECONDS LIVING RADIOISOTOPES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
STRONTIUM ISOTOPES
TRANSITION ELEMENT COMPOUNDS
YEARS LIVING RADIOISOTOPES
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences