1000-580Ma crustal evolution in the northern Arabian-Nubian Shield revealed by U-Pb-Hf of detrital zircons from late Neoproterozoic sediments (Elat area, Israel)

Morag N. ; Avigad D. ; Gerdes A. ; Harlavan Y. (2012)

Article

The final stages in the evolution of the Arabian-Nubian Shield (ANS) during the late Neoproterozoic include the deposition of sub-aerial volcano-sedimentary sequence above exhumed deep-seated plutonic-metamorphic rocks. In southern Israel the sediments in this sequence, known collectively as the Elat conglomerate unit, consist primarily of immature polymictic conglomerates whose composition closely reflects their underlying basement. U-Pb dating and Hf isotopic analysis of single zircons from two samples of the Elat conglomerate is used here to gain a complementary perspective on crustal evolution processes in the northern ANS. The U-Pb age spectra of the detrital zircons bear evidence for two major magmatic cycles separated by a lull; early island-arc magmatism occurred at 880-760Ma and peaked at ∼800Ma, whereas post-collisional granitoids and volcanics invaded the amalgamated arc crust between 660 and 580Ma and peaked at 610-630Ma. Integration with previously published data from Sinai suggests the aforementioned igneous cycles and the intervening lull are of regional significance. Although island-arc igneous activity in the ANS ranged mostly between 880 and 760Ma, the occurrence of detrital zircons with strongly positive e{open} Hf(t) values and U-Pb ages of up to 1.0Ga in the Elat conglomerate suggests that island-arc magmatism in the northern ANS started in the early Tonian, earlier than previously recognized. The youngest zircons in the Elat conglomerate constrain its deposition age to ∼580. Ma. No younger U-Pb zircon ages were obtained for crystalline rocks in this region, our data thus indicates that 580. Ma marks the cessation of igneous activity in the northern ANS. The great majority of detrital zircons in the Elat conglomerate display positive e{open} Hf(t) values, in line with the overall juvenile character of the Shield. Nonetheless, the relatively wide range of e{open} Hf(t) values in zircons representing island-arc magmatism (between +3.6 and +11.6), and the presence of zircons with pre-Neoproterozoic ages and/or negative e{open} Hf(t) values, suggest some contamination of the arc magmas by an older crustal component. The e{open} Hf(t) values in zircons representing the younger, post-collisional magmas are all positive (between +4.9 and 9.2) and resemble those in the preceding arc-derived zircons. This feature is consistent with both reworking of mafic island-arc crust and contribution from mantle-derived melts during the post-collisional stage. Thus, it cannot be deciphered whether the 1000-580Ma igneous activity in the northern ANS represents continuous juvenile crustal addition from the mantle, or subsequent recycling of early-formed arc crust during a later post-collisional phase. © 2012 Elsevier B.V.

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