The Petrological and Geochemical Evolution of Ediacaran Rare‐Metal Bearing A‐type Granites from the Jabal Aja Complex, Northern Arabian Shield, Saudi Arabia

Abstract

New fieldwork, mineralogical and geochemical data and interpretations are presented for the rare‐metal bearing A‐type granites of the Aja intrusive complex (AIC) in the northern segment of the Arabian Shield. This complex is characterized by discontinuous ring‐shaped outcrops cut by later faulting. The A‐type rocks of the AIC are late Neoproterozoic post‐collisional granites, including alkali feldspar granite, alkaline granite and peralkaline granite. They represent the outer zones of the AIC, surrounding a core of older rocks including monzogranite, syenogranite and granophyre granite. The sharp contacts between A‐type granites of the outer zone and the different granitic rocks of the inner zone suggest that the AIC was emplaced as different phases over a time interval, following complete crystallization of earlier batches. The A‐type granites represent the late intrusive phases of the AIC, which were emplaced during tectonic extension, as shown by the emplacement of dykes synchronous with the granite emplacement and the presence of cataclastic features. The A‐type granites consist of K‐feldspars, quartz, albite, amphiboles and sodic pyroxene with a wide variety of accessory minerals, including Fe‐Ti oxides, zircon, allanite, fluorite, monazite, titanite, apatite, columbite, xenotime and epidote. They are highly evolved (71.3–75.8 wt% SiO2) and display the typical geochemical characteristics of post‐collisional, within‐plate granites. They are rare‐metal granites enriched in total alkalis, Nb, Zr, Y, Ga, Ta, REE with low CaO, MgO, Ba, and Sr. Eu‐negative anomalies (Eu/Eu* = 0.17–0.37) of the A‐type granites reflect extreme magmatic fractionation and perhaps the effects of late fluid‐rock interactions. The chemical characteristics indicate that the A‐type granites of the AIC represent products of extreme fractional crystallization involving alkali feldspar, quartz and, to a lesser extent, ferromagnesian minerals. The parent magma was derived from the partial melting of a juvenile crustal protolith with a mantle contribution. Accumulation of residual volatile‐rich melt and exsolved fluids in the late stage of the magma evolution produced pegmatite and quartz veins that cut the peripheries of the AIC. Post‐magmatic alteration related to the final stages of the evolution of the A‐type granitic magma, indicated by alterations of sodic amphibole and sodic pyroxene, hematitization and partial albitization.

Geochemistry and Petrogenesis of Late Ediacaran Rare‐metal Albite Granites of the Arabian‐Nubian Shield

“…However, large differences in major and trace element concentrations and isotope ratios among various A-type granitic rocks in the ANS demand that a variety of processes and sources were responsible for their origins (e.g. Jarrar et al, 2008;Eyal et al, 2010;Ali et al, 2014Ali et al, , 2015Azer et al, 2014;Gahlan et al, 2016;Khalil et al, 2018;Abdallah et al, 2020). Theories for A-type granites in the ANS also fall into two distinct groups, those invoking extensive fractional crystallization of mantle-derived mafic magmas (e.g.…”

“…The ANS has been intruded by voluminous granitoids of various ages, geochemical characteristics and tectonic regimes (e.g. Qadhi, 2007;Küster, 2009;Ali et al, 2014;Moghazi et al, 2015;Khalil et al, 2018;Basta et al, 2017;Abdallah et al, 2020). One of the most striking features of the north ANS is the abundance of postcollisional granitic intrusions.…”

Tracking the transition from subduction‐related to post‐collisional magmatism in the north Arabian–Nubian Shield: A case study from the Homrit Waggat area of the Eastern Desert of Egypt

“…Pre-collisional and syn-orogenic calc-alkaline magmatism (650-620 Ma), characteristic of the subduction period of the north ANS, was succeeded by post-collisional magmatism (e.g., Jarrar, Manton, Stern, & Zachmann, 2008;Moussa, Stern, Manton, & Ali, 2008;Azer & El-Gharbawy, 2011;El Hadek, Mohamed, El Habaak, Bishara, & Ali, 2016;Sami et al, 2017;Azer, Gahlan, Asimow, & Al-Kahtany, 2019,Azer, Abdelfadil, & Ramadan, 2019Abdallah, Azer, & El Shammari, 2019) including high-K calc-alkaline and alkaline rocks.…”

“…Pre‐collisional and syn‐orogenic calc‐alkaline magmatism (650–620 Ma), characteristic of the subduction period of the north ANS, was succeeded by post‐collisional magmatism (e.g., Jarrar, Manton, Stern, & Zachmann, ; Moussa, Stern, Manton, & Ali, ; Azer & El‐Gharbawy, ; El Hadek, Mohamed, El Habaak, Bishara, & Ali, ; Sami et al, ; Azer, Gahlan, Asimow, & Al‐Kahtany, ,Azer, Abdelfadil, & Ramadan, ; Abdallah, Azer, & El Shammari, ) including high‐K calc‐alkaline and alkaline rocks. The post‐collisional granitoid rocks of the north ANS, including those outcropping in the Eastern Desert of Egypt, provide significant information on these late magmatic phases and their contributions to the growth of the upper continental crust.…”

The Geochemistry, Petrogenesis, and Rare-Metal Mineralization of the Peralkaline Granites and Related Pegmatites in the Arabian Shield: A Case Study of the Jabal Sayid and Dayheen Ring Complexes, Central Saudi Arabia

“…The magma composition was likely influenced by progressive chemical fractionation processes, which caused the development of peralkaline A-type granites and related pegmatites. The development of the Najd fault system is believed to have facilitated the ascent of magmas and the formation of peralkaline granitoids within the AS [9,[57][58][59][60][61]. This fault system provided pathways for the upward migration of magmas from deeper levels to shallower crustal levels, where they eventually crystallized and formed peralkaline granitoids.…”