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The Late Eocene Eshamy Suite plutons (ESP) intrude turbidites of the Chugach-Prince William (CPW) terrane in western Prince William Sound. The Prince William Sound region of South-Central Alaska consists of the Chugach-Prince William Terrance (CPW), containing the Valdez and Orca Group separated by the Contact fault. The Valdez Group is Late Cretaceous in age and is characterized by a thick sequence of interbedded siltstone, greywacke, and pebble conglomerate likely deposited as turbidites on submarine fans (Tysdal and Plafker, 1978). South of the Valdez is the Orca Group of Paleocene to Eocene age, characterized by folded and faulted rocks that have been intruded by younger plutons (Davidson and Garver, 2017). The CPW has been traditionally interpreted as a Late Cretaceous to Paleocene accretionary wedge complex that was either formed in situ or was deposited farther south and subsequently transported a significant distance along the continental margin (cf. Cowan, 2003; Haeussler et al., 2003). The ESP is a bimodal suite of granites dominated by biotite granites and leucogranites with subordinate gabbro. Questions for the ESP include the crystallization ages for the plutons, their relationship to igneous rocks found farther inboard, and the nature of the tectonic setting. For this study, we examined a set of granites from Miners Bay and Cedar Bay to compare with the rocks from the Nellie Juan and Eshamy Bay plutons to the southwest (Fig. 1), and the Caribou Creek volcanics (CCV) that occur 200 km inland. Our results show that the Miners and Cedar Bay plutons fall within the age range of the CCV and are marginally older than the Nellie Juan (NJP) and Eshamy Bay plutons (EBP) (Cole et al., 2006; Johnson, 2012). However, preliminary geochemical data suggest that the ESP may not be directly related to the CCV and therefore may have formed in a different tectonic setting.
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Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt
The Wadi Al-Baroud area, in Egypt’s Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi Al- Baroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syn- tectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite mon- zogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are over- grown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated re- sidual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.
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- Award ID(s):
- 1947616
- PAR ID:
- 10514218
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of African Earth Sciences
- Volume:
- 207
- Issue:
- C
- ISSN:
- 1464-343X
- Page Range / eLocation ID:
- 105044
- Subject(s) / Keyword(s):
- Arabian-Nubian Shield Eastern Desert Post-collisional magmatism Lithospheric delamination Nb-Ta oxide minerals Granitoid compositions
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Journal Article:
- https://doi.org/10.1016/j.jafrearsci.2023.105044
