Pg dating rus
They furthermore argued that there was no structural break between the granitoid gneisses and adjacent amphibolite facies supracrustal rocks grading into low-grade metasupracrustals away from the orthogneisses.This interpretation is in conflict with the interpretations of most other workers, e.g.
These shear zones define together the boundaries of the gneiss complex.
Based on these postulated shear zones, they explained the gneiss complex as an exhumed gneiss dome resulting from orogen-parallel (NW–SE) extension caused by oblique collision, similar to the model proposed for the Meatiq gneiss dome (Abd Ell Wahed ) also reported NW–SE-trending open folds and subsequent NW–SE-directed extensional structures post-dating the NW thrusting, but emphasized that these structures pre-date development of semi-brittle to brittle strike-slip shear zones present in Wadi El-Shush (Fig.
Diapiric rise of late orogenic magmas is a third model which has been proposed to explain the Meatiq and El-Sibai gneissic complexes (Fritz and Messner The Meatiq and Megif-Hafafit orthogneiss-dominated complexes, also referred to as the infrastructure, are domal structures with a tectonic boundary separating medium- to high-grade gneisses in the footwall from low-grade metasediments and metavolcanics of island arc and oceanic affinity in the overlying allochthon or superstructure (e.g. ), however, have recently challenged this view and argued that the infrastructural gneisses in the El-Sibai complex represent granitoids intruding the island arc affined allochthon synchronously with top-to-the-NW thrusting during nappe assembly.
In this contribution we present new U–Pb ID-TIMS data from the El-Sibai complex, further adding to the growing amount of evidence showing that the Arabian–Nubian Shield in the Eastern Desert of Egypt is mainly juvenile, with no exposures of rocks formed prior to the Neoproterozoic East African orogeny.
) grouped these intrusives into (1) exhumation-related granites and (2) “late tectonic” granitoids based on a combination of field relations and geochemical characteristics.
Clearly post-dating the “late tectonic” granitoids are some gabbroic complexes, composed of leucogabbros, anorthosites and diorites, and alkaline granitoids (Akaad and Abu El Ela GPS positions of the different samples are given in parentheses.Accessory zircon and titanite are present.) from coarse-grained foliated granite with variably deformed large K-feldspar porphyroclasts.Although most of the feldspars are altered, relict magmatic growth zonation is observed in many of the plagioclase and K-feldspar grains.Chlorite is common, most likely replacing primary magmatic biotite.Titanite and zircon are present as accessory minerals.) and is a dark porphyritic rock with large plagioclase phenocrysts in a finer-grained matrix, and with less than 10% mafic phases. The rock also occurs as a coarse-grained equigranular variety.Appearance of a regionally extensive shear zone separating the low-grade island arc volcanics and volcaniclastic sediments from the underlying gneisses in the Central Eastern Desert indicates that this shear zone must either be (1) a crustal scale extensional shear zone or (2) represent a highly disturbed Neoproterozoic basement-cover contact.