Isr. J. Earth Sci.; 48: 113-120 The youngest igneous event in the crystalline basement of the Arabian-Nubian Shield, Timna Igneous Complex Michael Beyth and Ariel Heimann Geological Survey ofIsrael, 30 Malkhe Yisrael Street, Jerusalem 95501, Israel (Received 22 June 1999; accepted 5 July 1999) ABSTRACT Beyth, M., Heimann, A. 1999. The youngest igneous event in the crystalline basement of the Arabian-Nubian Shield, Timna Igneous Complex. Isr. J. Earth Sci. 48: 113-120. The doleritic dike of Mt. Timna intrudes relatively homogeneous alkali granite that was previously fractured and intruded by rhyolitic, andesitic, and andesitic-rhyolitic composite dikes. The doleritic dike directly underlies the sandstone of the Amudei Shelomo Formation of Early Cambrian age. The sandstones do not exhibit any sign of contact metamorphism. Similar doleritic dikes were found intruding the Neopro- terozoic volcanic rocks of Mt. Amram, 13 km south of Mt. Timna. Radiometric dating of the doleritic dikes using the K-Ar method yielded a mean age of 546.3 ± 10.1 Ma for Mt. Timna (two samples) and 508.9 ± 9.2 Ma for a sample at Mt. Amram. An 4°Ar/ 39 Ar plateau age of 531.7 ± 4.6 Ma represents 67% of the 39 Ar that was released during the analysis. This is the best estimate for the formation age of the doleritic dike at Mt. Timna. Since the dikes intruded the youngest Precambrian units and did not affect overlying Cambrian sediments, they represent the youngest magmatic event in the crystalline basement of the northern part of the Arabian-Nubian Shield and are of Cambrian age. INTRODUCTION The CambrianlNeoproterozoic boundary has strati- graphic and tectonic global importance (Dalziel, 1997). In a review, Tucker and McKerrow (1995) defined this boundary at 545 Ma. An age older than 544 Ma was also suggested by Landing et al. (1998) for the CambrianiNeoproterozoic boundary. In the Arabian-Nubian Shield (ANS), a peneplain separates the Neoproterozoic northern crystalline basement from Early Cambrian sediments. Jarrar et at. (1993) compiled an age of 530 ± 10 for this Late Proterozoic/ Cambrian peneplain boundary in the northern ANS. In the present paper, the upper boundary of this crystal- line basement is precisely defined and dated based on mapping of the magmatic rocks and on new age deter- minations in Mt. Tirnna (Fig. 1) and in Mt. Arnram (preliminary age only), located 13 km south of Mt. Tirnna. The ages determined are younger than 545 Ma and therefore indicate that igneous events continued into the Cambrian. Consequently, the peneplain for- mation is also suggested to be a Cambrian event. E-mail: mbeyth@mni.gov.il © 1999 Laser Pages Publishing Ltd. 0021-2164/99 $4.00