Shrimp dating zircon
Geochemically, the older granitoids are metaluminous and exhibit characteristics of I-type granites and most likely formed in a convergent margin (arc) tectonic environment.On the other hand, the younger granites are peraluminous and exhibit the characteristics of A-type granites; these are post-collisional granites.Together with other studies we suggested that the collision of ocean and continent plates may occur at the early Caledonian in this area, forming the eclogite, and the collision of continent and continent plates at the late Caledonian, forming the Qaidamshan granite with the zircon SHRIMP age of 446 Ma.There is an increasing evidence for the involvement of pre-Neoproterozoic zircons in the Arabian-Nubian Shield, a Neoproterozoic crustal tract that is generally regarded to be juvenile. If your browser does not accept cookies, you cannot view this site.
Dr Ashwal added: "The fact that we found the ancient zircons in rock, corroborates the previous study and refutes any suggestion of wind-blown, wave-transported or pumice-rafted zircons for explaining the earlier results.”Published in the journal Nature Communications, the scientists theorise there are multiple fragments of the continent scattered throughout the Indian Ocean.
The source and significance of these xenocrystic zircons are not clear.
In an effort to better understand this problem, older and younger granitoids from the Egyptian basement complex were analyzed for chemical composition, SHRIMP U-Pb zircon ages, and Sm-Nd isotopic compositions.
The U-Pb SHRIMP dating of zircons revealed the ages of magmatic crystallization as well as the presence of slightly older, presumably inherited zircon grains.
The age determined for the older granodiorite is 652.5 ± 2.6 Ma, whereas the younger granitoids are 595-605 Ma.
of Geoscience, Madison, Wisconsin 53706, USA 2 Observatorio Volcanológico de los Andes del Sur (OVDAS) and SERNAGEOMIN, Chile, and Universidad de Concepción, Chile 3 Observatorio Volcanológico de los Andes del Sur (OVDAS) and SERNAGEOMIN, Chile 4 University of Alberta, Dept.