Combined Zircon/Apatite U-Pb and Fission-Track Dating by LA-ICP-MS and Its Geological Applications: An Example from the Egyptian Younger Granites

Sherif Mansour,Ashraf Y Elnaggar,Noriko Hasebe,Ehab Azab,Akihiro Tamura

doi:10.3390/min11121341

Sherif Mansour, Ashraf Y Elnaggar + Show 3 more

Open Access

https://doi.org/10.3390/min11121341

Copy DOI

Journal: Minerals	Publication Date: Nov 29, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: Port Said University, Taif University, Kanazawa University

Abstract

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is classically used in U-Pb dating to measure U and Pb isotopic concentrations. Recently, it has become frequently used in fission-track (FT) chronometry too. As an advantage, the U-Pb and FT double dating will enable efficiently determining the crystallization ages and the thermo-tectonic history concurrently as samples volume, analytical time, efforts, and cost will be greatly reduced. To demonstrate the validity of this approach, a Younger granite (Ediacaran age) sample from North Eastern Desert (NED), Egypt was analyzed for U-Pb and FT double dating. The integration of multiple geochronologic data yielded a zircon U-Pb crystallization age of 599 ± 30 Ma, after emplacement, the rock cooled /uplifted rapidly to depths of 9–14 km as response to the post-Pan African Orogeny erosional event as indicated by apatite U-Pb age of 474 ± 9 Ma. Afterwards, the area experienced a slow cooling/exhumation for a short period, most-likely as response to denudation effect. During the Devonian, the area was rapidly exhumed to reach depths of 1.5–3 km as response to the Hercynian tectonic event, as indicated by a zircon FT age of 347 ± 16 Ma. Then the studied sample has experienced a relatively long period of thermal stability between the Carboniferous and the Eocene. During the Oligocene-Miocene, the Gulf of Suez opening event affected the area by crustal uplift to its current elevation. This integration of Orogenic and thermo-tectonic information reveals the validity, efficiency, and importance of double dating of U-Pb and FT techniques using LA-ICP-MS methodology.

Highlights

The integration of different geochronological (e.g., U-Pb, K-Ar, Helium and FT dating) techniques provide useful information on the formation and development of the upper crust through geological time [1,2,3]
FTs in Cl-apatite are seemingly more resistant to thermal annealing if compared with tracks in F-apatite [7,8]. This feature can be especially observed during the dating of clastic samples which commonly contain partially reset to set apatite grains, factually Cl-rich ones, which may yield older FT ages as compared with F-apatite grains [9]
The granitic sample was crystallized at 599 ± 30 Ma

Summary

Introduction

The integration of different geochronological (e.g., U-Pb, K-Ar, Helium and FT dating) techniques provide useful information on the formation and development of the upper crust through geological time [1,2,3]. The preservation of FTs in minerals mainly depends on the temperature and cooling rate. FTs in Cl-apatite are seemingly more resistant to thermal annealing if compared with tracks in F-apatite [7,8]. This feature can be especially observed during the dating of clastic samples which commonly contain partially reset to set apatite grains, factually Cl-rich ones, which may yield older FT ages as compared with F-apatite grains [9]. 90 ◦ C and experience total annealing at temperatures higher than 160 ◦ C This implies that the PAZ in Cl-rich apatite is wider and hotter if compared with the PAZ in F-apatite. For FTs in zircon, the effective closure temperature ranging 240 ◦ C and 200 ◦ C depending on cooling rates [10]

Methods

Results

Conclusion