Geochronology in the Southern Midyan Terrane: A Review of Constraints on the Timing of Magmatic Pulses and Tectonic Evolution in a Northwestern Part of the Arabian Shield

SGS-TR-2017-3 Wieslaw Kozdrój*, Allen K. Kennedy, Peter R. Johnson, Malgorzata Ziółkowska-Kozdrój, and Khalid A. Kadi
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The southern Midyan terrane is a composite Tonian to Ediacaran tectonostratigraphic crustal block in the northern Arabian Shield that prior to Red Sea opening was contiguous with coeval rocks in the Eastern Desert and Sinai. Ion microprobe (SHRIMP) dating of 12 rock samples described here and the results of other dating programs establish a clear timeframe for depositional, intrusive, and structural events in the region and provides a chronology of tectonism in this part of the Arabian-Nubian Shield.  Deposition of Zaam and Bayda group volcanosedimentary rocks and emplacement of mafic-ultramafic complexes and TTG-type diorite, tonalite, and granodiorite denote formation of the Tonian (780-710 Ma) Zaam arc and fore-arc ophiolite above a possible west-dipping subduction system in the southern part of the Midyan terrane.  Convergence with the Hijaz terrane farther south and obduction of ophiolite nappes resulted by ~700 Ma in development of the Yanbu suture.  Ongoing or a new subduction system led to a ~705-660 Ma Cryogenian pulse of magmatism represented by I-type calc-alkaline diorite, granodiorite, and granite that have volcanic-arc and syn-collisional granite affinities.  This was followed, after a brief end-Cryogenian hiatus, by a 635-~570 Ma period of Ediacaran magmatism marked by monzogranite, syenogranite, and minor gabbro and diorite.  These rocks are reported to have within-plate to volcanic-arc and syncollision chemical characteristics but their precise tectonic setting is uncertain.  Structurally, the intrusions are diapiric and were evidently emplaced in an extensional regime consistent with an overlap between intrusion and Najd faulting associated, at this time, with transpressional collision and northward extension through much of the ANS.  Terminal magmatism in the southern Midyan terrane post-dated cessation of Najd faulting at ~575 Ma and resulted in the emplacement of undeformed within-plate A-type alkali-feldspar granites and mafic (lamprophyre) and felsic dikes.



Kozdrój, W., Kennedy, A.K., Johnson, P.R., Ziółkowska-Kozdrój, M., and Kadi, K.A., 2017, Geochronology in the southern Midyan Terrane: A review of constraints on the timing of magmatic pulses and tectonic evolution in a northwestern part of the Arabian Shield: Saudi Geological Survey Technical Report SGS-TR-2017-3, 36 p., 7 figs., 3 tables.