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Copper mineralization in the Lower Paleozoic sedimentary cover of the Anti-Atlas (Morocco) is continually being revised not only to improve its mining capacity, but also to determine its origin, which remains a matter of debate. As evidenced by the various models proposed, the related research is fragmented, localized, and confusing. The origin of the Anti-Atlas Lower Paleozoic copper mineralization is shared between synergistic and epigenetic processes or a superposition of the two processes. Based on new tectono-magmatic data and a reinterpretation of the ore structural arrangement, we propose a link between the last concentration of copper deposits and the Late Triassic–Early Liassic CAMP (Central Atlantic Magmatic Province) tectono-thermal event, as evidenced by the significant concentration of copper mineralization in the three NE–SW corridors affected by extensional faults, some of which are filled with dolerite CAMP magma. The heat flow generated by the mafic dykes within these reactivated corridors causes mineralized fluids to up well into the sedimentary layers, depositing material rich in juvenile or leached copper, or even a mixture of the two. In some cases, these fluids are trapped by fracture systems that accompany passive folds initiated on normal faults. In other cases, these fluids can infiltrate bedding planes, and even karst caves, formed during carbonate exhumation. Notably, extensive NE–SW faults systematically cover the early Hercynian structures, suggesting that they belong to a post-Hercynian extensional episode. During the Late Triassic, the global fragmentation of the Pangaea supercontinent was manifested by the stretching of the continental crust at the margin of northwest Africa, with the simultaneous opening of the Central Atlantic Ocean and emplacement of CAMP magmatism. This last and often overlooked tectonothermal event must be considered in the remobilization and reconcentration of copper mineralization and other mineralization in Morocco.

The Saharan Metacraton is a poorly known tract of pre-Neoproterozoic continental crust that occupies the area between the juvenile Arabian Nubian Shield, in the east, and the Tuareg Shield to the west. Neoproterozoic orogenesis (i.e. Ouban guides and East African orogenies) affect the west, the south and the east of the metacraton, respectively, which led to deformation, emplacement of igneous bodies, and localised episodes of rift-related magamatism. Details about interior regions of the Saharan Metacraton are poorly known, with much of it covered by Phanerozoic rocks. The basement outcrops in Sudan, Chad, Algeria and Libya have been the subject of few modern geochronological studies. Here we present results from the first zircon geochronology and in-situ zircon hafnium isotope investigations from both the Sudanese Butana and central Chad. The terranes in Butana, formed to the east of pre-Neoproterozoic continental crust of the Saharan Metacraton, with the oldest juvenile magmatism (ƐHf(t) of +4.89 to +7.89) at ca. 839 Ma, followed by subsequent magmatism at ca. 787 Ma. The ca. 787 Ma event (seen elsewhere in the East African Orogen) is interpreted to represent volcanic-arc collision and accretion with the kernel of the Saharan Metacraton. The ca. 839 Ma magmatism is contemporaneous with the accretion of the Tonian (ca. 850 Ma) arc terranes of the Arabian Nubian Shield and marks subduction to the east of the Saharan Metacraton. The magmatic history of the Ouaddaï region in Chad begins in the late Mesoproterozoic, with localised rifting, resulting in the emplacement of juvenile granites (ca. 1030 Ma). The Cryogenian and Ediacaran in the Saharan Metacraton reveal a complicated history of magmatism and deformation. Age data from Chad show the emplacement of granites (from melting of Mesoproterozoic crust: ƐHf(t) = +2.04 and −4.07) at ca. 665–654 Ma, coeval with the main East African Orogeny and accretion of the other ANS terranes to the Saharan Metacraton at ca. 650–580 Ma. The youngest tectonothermal event within the Saharan Metacraton is recorded by emplacement of granites between 580 and 550 Ma (ƐHf(t) values of −17 to −31) in southern Chad. Refereed/Peer-reviewed

Geological mapping and investigation of the mountain chain in Dronning Maud Land (DML) has been carried out by a number of geologists from South Africa, Japan, India, Germany, Russia and Norway over the last 40-50 years. The produced geological maps of these teams are, for a large part, based on fairly old data which makes these maps inhomogeneous. The maps are at different scales, contain different levels of details, and the standards for classification of the rock units may also differ between the maps. This limits the ability to use these maps to draw an overview tectonic model of the evolution of Dronning Maud Land.In this contribution, we present a newly compiled geological map and GIS database of the Dronning Maud Land. The map will be available soon as an open-access database, but the readers can test a test version of it at: https://geokart.npolar.no/Html5Viewer/index.html?viewer=Geology_DML. The geological importance of the Dronning Maud Land to understanding the evolution of the southern parts of the Gondwana supercontinent was the main motivation factor as the DML is considered as the missing link between the geology of South Africa, Australia and Indian subcontinent.The new database covers the area between 20o W and 45o E and was compiled at a scale level of 1:250 000. However, the database provides another scale level of 1:5 000 000 to put the DML in the regional framework of the Gondwana. The geological map is descriptive based on the new topographic dataset of the Landsat 8. The project was based at the Norwegian Polar Institute from 2014 to 2018 and supported by a research grant from the Ministry of Foreign Affairs, Norway.

The majority of geological investigations that deal with the Arabian-Nubian Shield are concerned with the processes of ocean closure, subduction, orogenesis and crustal growth, in relation to the assembly of Gondwanaland in the late Neoproterozoic. Other valuable published works deal with the earlier development of the Arabian-Nubian Shield in the light of the configuration of Rodinia (assembly and rifting) and the Mozambique Ocean. Progress in modern geochronological and structural data from the Arabian-Nubian Shield reveals that some of the Arabian-Nubian Shield rocks were derived from older crustal material and were affected by tectonic events of the early ensimatic stage of the Mesoproterozoic Rodinia breakup. The studies of Arabian-Nubian Shield ophiolites and related melange rock units, representing remnants or fragments of earliest simatic (mafic-ultramafic) lithosphere, provide essential constraints on the oceanic realm predating the accretionary and collisional stages of the Arabian-Nubian Shield (~780–600 Ma). Understanding the complete tectonic evolution of the Arabian-Nubian Shield requires providing special attention to the structural, petrological, geochemical and geochronological characteristics of its early primitive stage during the Rodinia breakup.

The metamorphic rocks of the Sinai Peninsula cover about one-third of the Precambrian basement exposures and are preserved in four isolated metamorphic complexes (Feiran–Solaf, Kid, Sa’al-Zaghra, and Taba metamorphic complexes), separated by large volumes of granitic intrusions. The metamorphism and structural setting of these complexes are well studied, though their geochronology, and consequently their tectonic evolution, remains a matter of controversy. This chapter documents the ongoing efforts to establish correlations between the Sinai metamorphic complexes, in order to clarify their interrelations and reveal the stages of tectonic evolution of the Sinai Peninsula in the northern Arabian–Nubian Shield. Previous works dealing with the petrology, metamorphism, deformation phases, and radiometric dating are discussed and used to present a complete tectonic model for the Precambrian of the Sinai Peninsula. This tectonic model is divided into five stages of evolution, lasting almost 500 Myr, from the foundering of the Rodinia supercontinent to the lithospheric delamination stage that occurred during a late stage of the Pan-African orogeny. The first tectonic stage is the Rodinia breakup (1100–838 Ma) which is recorded in the Sa’al-Zaghara metamorphic complex as S1 extension-related shear zones heated to upper amphibolite facies conditions by syn-kinematic red granite intrusions. The second tectonic stage is represented by formation of two distinct volcanic arcs—the Feiran volcanic arc and the Taba volcanic arc, which were developed in the interval 805–745 Ma, as a result of the closing of the Mozambique Ocean. The third tectonic stage is an arc–arc collision stage (632–620 Ma), during which the Feiran–Solaf and Taba metamorphic complexes achieved peak metamorphic conditions at crustal depths of 28–30 km, in a compressional tectonic setting. Escape tectonics characterized the fourth tectonic stage (630–610 Ma), involving Najd Fault-related exhumation of the metamorphic rocks to depths of about 14 km. Later in this stage the metamorphic complexes were intensively intruded by large volumes of calc-alkaline and alkaline granites, followed by crustal cooling. In conjunction with the tectonic evolution of the Najd Fault System, lithospheric delamination and slab break-off occurred during the fifth tectonic stage (620–593 Ma), leading to opening and subsequent closing of a back-arc basin in the Kid complex. The thermal event associated with the formation of the back-arc basin resulted in an anticlockwise P-T metamorphic history and eruption of ~600 Ma bimodal volcanics.

Wadi Ghadir ophiolite in the Egyptian Eastern Desert, which forms the northern part of the Nubian Shield, is considered as one of the best-preserved segments of the Neoproterozoic oceanic lithosphere on Earth. Primary melt calculations and thermodynamic modeling of new geochemical data for the Wadi Ghadir pillow lavas and dike complexes, integrated with comprehensive petrographic investigations, are here employed to unravel the geodynamic evolution of this ophiolitic section. Whole-rock geochemical and clinopyroxene data indicate that the pillow lavas and sheeted dike complexes preserve geochemical signatures of N-MORB, E-MORB and OIB-like basalts. Less abundant, discrete dikes have a distinctly LILE-enriched island arc tholeiite (IAT) composition. The pillow lavas and sheeted dike complexes replicate mixed liquid lines of descent, whereas the discrete dikes exhibit a calc-alkaline differentiation trend. The pillow lavas were produced by limited (5–7%) mantle partial melting as a result of isothermal decompression over a wide pressure range (5 – 19 kbar) and restricted mantle potential temperatures (Tp ≈ 1260–1300 °C), suggesting ponding of rising melts from depths of ∼60 to 15 km in dry mantle. Primary melts of the sheeted dike complexes were produced by 9–11% partial melting at P ≈ 9.7 ± 2.5 kbar, Tp ≈ 1290 °C, and P ≈ 14.7 ± 1.4 kbar, Tp ≈ 1325 °C, suggesting a role of varying hydrostatic pressure. The magma source for the discrete dikes occurred at 10.7 ± 0.6 kbar and Tp of 1230–1300 °C by 11–13% partial melting of a metasomatized mantle region. The calculated Tp ranges for the different melts are consistently lower than temperatures of sub-ridge ambient mantle. Together with the variable concentrations of K2O and other incompatible elements, the estimated low temperatures of melt generation emphasize mixed sources and wet peridotite melting. The modeled primary melts designate crustal growth during back‐arc basin opening and closure. During the basin opening, decompression melting of mildly enriched mantle produced high-Ti tholeiitic (pillow lavas) and transitional (sheeted dike complexes) melts, whereas subduction initiation during basin closure promoted melt-peridotite interaction. Lowering of the solidus by subduction-related components triggered melting of a spinel lherzolitic mantle and produced low-Ti calc-alkaline melts that sourced the discrete dikes. The mixed MORB and SSZ geochemical characteristics of the studied volcanic rocks, coupled with the various modeled melts and lack of significant thermal anomalies in the mantle conditions, are here interpreted as manifestations of mantle source heterogeneity in a marginal oceanic basin during the accretionary stages of the Arabian-Nubian Shield.

The East-West Gondwana collision (0.75–0.5 Ga), by oblique convergence, was likely accompanied by high hydrothermal fluid flux and dispersed orogenic gold in the Arabian-Nubian Shield. Gold-bearing quartz veins along steep-dipping shear zones bordering or cutting through the ophiolitic and island arc rocks in the central Allaqi-Heiani belt in Wadi Defeit area deserved the interest of ancient miners. Field and remote sensing data revealed the structural and lithological controls of gold-bearing quartz veins, providing means of exploration for new targets in the larger Wadi Allaqi environ. The auriferous shear zones are attributed to D3 (a non-coaxial continuation of early NE-SW compression regime), and D4 (slip reactivation by E-W compression and transcurrent deformation). Microscopic investigations of quartz veins reveal the association of gold blebs and specks with fissure-filling galena-spahlerite-tetrahedrite assemblage and deformed Fe-As-sulfides (pyrite and arsenopyrite). As a gold-only province with abundant, variably deformed and carbonated metabasic rocks, metamorphic devolatilization is suggested to explain the discrete gold occurrences by fluid focusing in complex shear intersections. The available fluid inclusion data affirm the low salinity aqueous-carbonic composition of the ore fluids and mesothermal conditions of ore deposition, consistent with metamorphic devolatilization. Structures related to late ductile deformation in the post-accretionary stages of the evolution of the shield are, therefore, considered high priority zones for future exploration programs.

The assembly and disruption of Gondwana supercontinent involve several complex processes that induce major changes in chemical structures of the Arabian-Nubian Shield mantle reservoir. These processes include melting, depletion and metasomatic refertilization of the upper mantle peridotites. The geodynamic evolution of these processes is addressed based on petrological, mineral chemistry and geochemical data from a selected set of ophiolitic serpentinized peridotites from the Eastern Desert of Egypt (G. El-Maiyit, Um El-Saneyat and W. Atalla). The examined rocks represent mantle residual harzburgites after different degrees of partial melting. The most intact Cr-spinel cores and whole-rock trace and rare earth elements data show that mantle protoliths of the studied peridotites underwent different partial melting degrees of ∼23% to 35% (G. El-Maiyit rocks), ∼15% to 20% (Um El-Saneyat rocks) and ∼18% to 25% (W. Atalla rocks). The variations of partial melting degrees between different areas suggested mantle heterogeneity beneath the Arabian-Nubian Shield. The melt extraction took place under oxidizing conditions. All the studied samples are enriched in light rare earth elements (LREEs) relative to the middle (MREEs) and the heavy (HREEs) which is attributed most probably to induction of serpentinization-related hydrothermal fluids. The data conclude that the studied peridotites have different tectonic settings, including the forearc for G. El-Maiyit, mid-ocean ridge for Um El-Saneyat and mid-ocean ridge-arc transition setting for W. Atalla. The coexistence of the mid-ocean ridge peridotites with those of the supra-subduction zone reflects the transitional evolutionary history of the Neoproterozoic Mozambican oceanic lithosphere beneath the Eastern Desert of Egypt. A similar geodynamic evolution is recognized for the Mesozoic ophiolitic mantle peridotites which concludes that the construction of the Neoproterozoic mantle in the Eastern Desert of Egypt is might be similar to those of the younger age.

Late Precambrian intrusive rocks in the Arabian–Nubian Shield emplaced within and around the Najd Fault System of Saudi Arabia feature a great compositional diversity and a variety of degrees of deformation (i.e. pre-shearing deformed, sheared mylonitized, and post-shearing undeformed) that allows placing them into a relative time order. It is shown here that the degree of deformation is related to compositional variations where early, usually pre-shearing deformed rocks are of dioritic, tonalitic to granodioritic, and later, mainly post-shearing undeformed rocks are mostly of granitic composition. Correlation of the geochemical signature and time of emplacement is interpreted in terms of changes in the source region of the produced melts due to the change of the stress regime during the tectonic evolution of the Arabian–Nubian Shield. The magma of the pre-shearing rocks has tholeiitic and calc-alkaline affinity indicating island arc or continental arc affinity. In contrast, the syn- and post-shearing rocks are mainly potassium rich peraluminous granites which are typically associated with post-orogenic uplift and collapse. This variation in geochemical signature is interpreted to reflect the change of the tectonic regime from a compressional volcanic arc nature to extensional within-plate setting of the Arabian–Nubian Shield. Within the context of published geochronological data, this change is likely to have occurred around 605–580 Ma.

The southeastern sector of the Hafafit Metamorphic Complex, southern Eastern Desert of Egypt comprises infrastructural orthogneisses of tonalite and syenogranite parentage, amphibolites, and a volcano-sedimentary association. These are overthrust by an obducted suprastructural ophiolite nappes via the Nugrus thrust. The protolith of the biotite–hornblende-gneisses was formed during island-arc accretion, while that of the garnet–biotite gneisses were formed in a within-plate regime, consistent with a transition to a post-collisional setting. The volcano-sedimentary association comprises interbedded and intercalated highly foliated metapelitic schists, metabasites, and leucocratic gneisses, deposited in a back-arc basin. The metapelites and the leucocratic gneisses originated from immature Fe-shales and arkoses derived from intermediate-mafic and acidic igneous rocks, respectively, via weak chemical weathering in a tectonically active island arc terrane. The intercalated amphibolites were derived from tholeiitic basalts generated in a back-arc setting. The volcano-sedimentary association was metamorphosed under upper-amphibolite facies conditions with pressures of 9–13 kbar and temperatures of 570–675 °C, as derived from conventional geothermobarometry and pseudosection calculation. A steep, tight clockwise P–T path is constrained and a geothermal gradient around 20 °C/km is estimated for the peak metamorphism. We assume that deformation and metamorphism are due to crustal thickening during the collision of East and West Gondwana, where peak metamorphism took place in the middle to lower crust at 33 km average crustal depth. This was followed by a subsequent quasi-isothermal decompression due to rapid exhumation during wrench tectonics. Sinistral transcurrent shearing with extensional denudation resulted in vertical ductile thinning that was accompanied by heat input from magmatism, as indicated by a higher geothermal gradient during retrograde metamorphism and exhumation of the complex. U–Pb data from magmatic zircons yields protolith ages of 731 ± 3 Ma for the biotite–hornblende gneisses and 646 ± 12 Ma for the garnet–biotite gneisses. Conforming to field evidence, our geochronology data point to a depositional age of the volcano-sedimentary cover at around 650 Ma. The age of metamorphism is constrained by a low Th/U ratio of a zircon grain crystallized at an age of 597 ± 6 Ma.

In active tectonic regions, shear zones play an important role in re-configuring the structure of the lithosphere. One of the largest shear zones on Earth is the Najd Fault System of the Arabian–Nubian Shield. The main active phase of this shear zone was during the last stages of the Pan-African Orogeny (ca. 630–540 Ma). Six samples of intrusive rocks that were emplaced into the shear zone at different stages during its active phase are used to illustrate the progressive evolution of the Ajjaj shear zone. A sample of coarse-grained diorite, with an intercept U–Pb zircon age of 696 ± 6 Ma, shows very weak deformation. Two samples from deformed granodiorite–tonalite intrusions at the border of the Ajjaj shear zone show conspicuous degrees of deformation, and define two U–Pb clusters of concordia ages at 747 ± 12 Ma–668 ± 8 Ma and 742 ± 5 Ma–702 ± 12 Ma. Two samples of granites show mylonitic foliation with flattened quartz and biotite parallel to the trend of the shear zone. These samples yield U–Pb ages of 601 ± 3 Ma–584 ± 3 Ma. Another granite sample is undeformed and shows cross-cutting relations with the shear foliation of the Ajjaj shear zone. It yields a concordia age of 581 ± 4 Ma. The metamorphic rocks of the Hamadat complex host the Ajjaj shear zone, and have been useful in determining the metamorphic P-T conditions attending the activity of the shear zone. The peak metamorphism of the Hamadat Complex is 505–700 °C at two ranges of pressure 8–11 and 14.5 ± 2 kbar. New data confine the activation of the Ajjaj shear zone in a limited period of time between 604 Ma and 581 Ma and the operation at different crustal levels with a maximum depth of 58 km.

Accepted manuscript version, licensed CC BY-NC-ND 4.0. The bedrock of Mühlig-Hofmannfjella, central Dronning Maud Land in eastern Antarctica, is part of the high-grade Maud Belt and comprises a deep-seated metamorphic-plutonic complex. The P-T-t evolution of anatectic supracrustal gneisses has been recovered through a study of mineral assemblages, textural relationships and U-Pb ID TIMS geochronology on zircon and monazite followed by pseudosection modelling. Peak conditions reached granulite facies conditions (T ≥ 810–820 °C) at moderate crustal depths (P = ca. 8 kbar) and resulted in partial melting. Peak-pressure conditions were followed by isothermal decompression at elevated temperatures. After exhumation to crustal levels of about 4–5 kbar, the area underwent a final near-isobaric cooling, which is documented by a secondary growth of garnet. Zircons indicate a period of growth at 570–566 Ma, whereas monazite ages range from 610 to 525 Ma. A likely heat source for the granulite facies metamorphism is decay of radioactive heat-producing elements in the core of the orogen. The combined geochronology and metamorphic data indicate a prolonged, clockwise P-T path, which reflects collision and formation of a long-lived orogenic plateau.

A petrological and metamorphic comparison of Mesoproterozoic metabasic rocks was conducted on the eastern margin of the Archaean Kaapvaal–Grunehogna Craton and the adjacent westernmost Maud Belt (western H.U. Sverdrupfjella), across a major structural discontinuity known as the Pencksokket–Jutulstraumen Discontinuity. Thermodynamic phase diagram modelling of the low- and high-grade metabasaltic assemblages on either side of the discontinuity revealed a difference in peak metamorphic conditions from T = 340 ± 25 to 700 ± 30°C and P = 0.29 ± 0.08 to 0.90 ± 0.10 GPa over an extrapolated orthogonal distance of 32 km across the strike of the discontinuity. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of titanite in a hornblende–plagioclase–quartz corona around garnet yielded a late Pan-African age of 491 ± 27 Ma for high-grade metamorphism in the western H.U. Sverdrupfjella of the Maud Belt. The new petrological and geochronological constraints indicate that peak upper amphibolite-facies conditions were achieved in the western H.U. Sverdrupfjella at c . 500 Ma; namely, c . 70–80 Ma after peak eclogite–high-pressure granulite-facies metamorphism in the eastern H.U. Sverdrupjella. The U–Pb age data argue against previous models that invoke only late Mesoproterozoic ( c . 1060–1030 Ma) granulite-facies metamorphism in the western H.U. Sverdrupfjella and Kaapvaal–Grunehogna Craton margin, and support the concept of a major diachronous Pan-African orogenic episode. A new geodynamic model is presented for western Dronning Maud Land, involving earliest Pan-African eclogite–high-pressure granulite- and upper amphibolite-facies metamorphism in a separate eastern H.U. Sverdrupjella terrane between c . 565 and 540 Ma, followed by later diachronous tectonic accretion of the eastern H.U. Sverdrupjella arc segment onto the western H.U. Sverdrupfjella crustal segment (including the easternmost Kaapvaal–Grunehogna Craton margin) that involved only upper amphibolite-facies metamorphism at c . 500 Ma. The new petrological data indicate that the inferred sub-glacial boundary (Pencksokket–Jutulstraumen Discontinuity) between the Kaapvaal–Grunehogna Craton and the western H.U. Sverdrupfjella region represents a major cratonic Pan-African thrust, which was subsequently reactivated by normal faulting during Gondwana break-up. Supplementary materials: Analytical details, representative mineral compositions, and geothermometry and geobarometry results are available at http://www.geolsoc.org.uk/SUP18832.

A group of intrusive and extrusive igneous rocks is located around Wadi Kariem, Central Eastern Desert. These rocks have diversed petrographic compositions ranging from gabbros to granites with their volcanic equivalents. They belong to four distinct Neoproterozoic units of the Eastern Desert, namely “metagabbros (MG), older granites (OG), metavolcanics (MV) and younger granites (YG)”. Both major and trace elements are compiled to deduce their genetic relationships. 1/Sr versus Rb/Sr and Rb/Ba versus Rb plots suggest that these rock units exhibit comparative magmatic relationships. The trace element data and the numerical modelling are treated according to the general equation of partial melting (Shaw 1970) and Rayleigh equation of fractional crystallization. These rock types favour complex petrogenetic processes during their generation. The magmatic model is based on “in-sequence” genesis between partial melting and fractional crystallization as well as assimilation and/or magma mixing processes in the late stage. It is evident that these rocks resulted from five essential stages during magmatic evolution of the area: (1) Meta-andesite (MV) was generated throughout partial melting (5 %) of the oceanic crust followed by fractional crystallization (25–50 %); (2) Gabbroic rocks (MG) were derived by partial melting (46 %) of the oceanic crust followed by fractional crystallization (20–40 %); (3) Granodiorite (OG) were derived throughout partial melting (6–6.5 %) of gabbroic parent followed by (5–20 %) fractional crystallization; (4) Alkali-feldspar granite (YG) was derived throughout (45–60 %) fractional crystallization of granodiorite (OG); And finally, (5) the recorded hybrid granodiorite rocks (HG) were generated by partial melting of granodiorite (OG) (24.5 %), assimilation and/or partial melting of metagabbros (MG) (11.7 %), followed by magma mixing and (35–55 %) fractional crystallization.

The Arabian–Nubian Shield is the largest tract of juvenile continental crust of the Neoproterozoic. This juvenile crust is composed of intra-oceanic island arc/back arc basin complexes and micro-continents welded together along sutures as the Mozambique Ocean was closed. Some of these sutures are marked by ophiolite decorated linear belts. The Sol Hamed ophiolite (808 ± 14 Ma) in southeastern Egypt at the Allaqi-Heiani-Onib-Sol Hamed-Yanbu arc–arc suture represents an uncommon example of rocks that might be less deformed than other ophiolites in the Arabian–Nubian Shield. In order to understand fluid–rock interactions before and during arc–arc collision, petrological, mineral chemistry, whole-rock chemistry and thermodynamic studies were applied to the Sol Hamed serpentinized ophiolitic mantle fragment. These studies reveal that the protolith had a harzburgite composition that probably originated as forearc mantle in the subducted oceanic slab. We propose that these rocks interacted with Ti-rich melts (boninite) in suprasubduction zone, which latter formed the Sol Hamed cumulates. Spinel’s Cr# associated with the whole rock V–MgO composition suggest that the harzburgites are highly refractory residues after partial melting up to 29%. The melt extraction mostly occurred under reducing conditions, similar to peridotites recovered from the subducted lithosphere. Protolith alteration resulted from two stages of fluid–rock interaction. The first stage occurred as a result of infiltration of concentrated CO 2 -rich fluid released from carbonate-bearing sediments and altered basalt at the subduction zone. The alteration occurred during isobaric cooling at a pressure of 1 kbar. The fluid composition during the isobaric cooling was buffered by the metamorphic reactions. The second stage of fluid–rock interactions took place through prograde metamorphism. The increase in pressure during this stage occurred as a result of thrusting within the oceanic crust. In this process the forearc crust was loaded by roughly 20–30 km of overthrust rocks.

The Cenozoic volcanism of western Saudi Arabia extends from southern Yemen to Jordan northward. They cover an area of nearly 180,000 km2. The rocks are dominated by alkali olivine basalts and olivine basalts. Al-Wahbah crater, a part of Harrat Kishb, represents a model occurrence to study the gneisses of these rocks. New mineral chemistry and isotopic data are presented. It aims to follow the isotopic, mineralogical, and thermobarometry variations among these volcanics. Amphiboles of the studied volcanics belong to the monoclinic calcic group. The chemistry of the amphibole crystals shows two ranges of pressure. They are 3.6–5.6 and 0.38–0.78 kbar. The Aliv values of the amphiboles are in the range of 1.202 and 1.407, indicating corresponding temperature condition of 820–920 and 620–720 °C, respectively. The feldspar of the studied samples has the composition of plagioclase, though some grains have sanidine composition. They are formed in temperature range of 975 and 400 °C. The coexisting amphiboles and plagioclases indicate two sets of pressure and temperature. They are 540–575 °C (3.5–4 kbar) and 510–525 °C (~2 kbar), respectively. Rb–Sr isochron of the whole rock yields an age of 0.867 ± 0.160 Ma with initial Sr87/Sr86 of 0.702 ± 0.00086. The low initial ratio of Sr87/Sr86 together with positive values of eNd today implies that the studied volcanics have mantle source. Meanwhile, the present isotopic data suggest extraction of juvenile magma from asthenosphere source. The present study shows that the Al-Wahbah crater rocks belong to Cenozoic basalts and indicate EM-I-like signature.

Field evidence from the Baladiyah complex in the northern part of the Arabian^Nubian Shield of Saudi Arabia indicates several erosional unconformities separating different high- and medium-grade metasedimentary sequences. This suggests that the collision between East and West Gondwana involved several cycles of exhumation and burial, providing a unique opportunity to study the multiple stages of this orogeny. A mineral equilibria approach and thermodynamic modeling are used to place constraints on the formation conditions of each of these cycles. It is shown that the complex is characterized by three regional metamorphic events followed by a fourth metamorphic event related to shear heating owing to the thrusting of post-tectonic granites. During the first metamorphic event peak metamorphism was at around 705^7158C and 5·2^5·6 kbar followed by subsequent decompression to the Earth’s surface. Subsequently deposited sediments attained 635^6708C and 4·2^5 kbar during a second metamorphic event, followed by exhumation, erosion and deposition of molasse sediments. The rocks were then buried for a third time and metamorphosed to greenschist-facies metamorphic conditions (330 � 308C and 3·6^4·6 kbar) under the load of the molasse sediments. Finally, post-tectonic granites were intruded and thrust during the final Pan-African exhumation, causing a fourth metamorphic event (700 � 258C). Correlation of this metamorphic evolution with the deformation history shows that the first and the second metamorphic events occurred in a compressional regime (D1 and D2), interpreted to be related to the first (750 Ma) and the second (676 Ma) collision stages between East and West Gondwana, respectively. The third deformation phase began with a compressional regime causing the third metamorphic event, and then turned into an oblique transpressive regime, which led to escape tectonics and the development of the large-scale Najd strike-slip shear zone system.

Metamorphic core complexes are usually thought to be associated with regional crustal extension and crustal thinning, where deep crustal material is exhumed along gently dipping normal shear zones oblique to the regional extension direction. We present a new mechanism whereby metamorphic core complexes can be exhumed along crustal-scale strike-slip fault systems that accommodated crustal shortening. The Qazaz metamorphic dome in Saudi Arabia was exhumed along a gently dipping jog in a crustal-scale vertical strike-slip fault zone that caused more than 25 km of exhumation of lower crustal rocks by 30 km of lateral motion. Subsequently, the complex was transected by a branch of the strike-slip fault zone, and the segments were separated by another 30 km of lateral motion. Strike-slip core complexes like the Qazaz Dome may be common and may have an important local effect on crustal strength.

Recently published age data indicate that the Sa’al–Zaghra metamorphic complex in Sinai, Egypt contains the oldest rocks found in the northernmost Arabian-Nubian Shield, preserving evidence for a 1110–1030 Ma rift-related volcanic system formed during Rodinia break-up ( Be’eri-Shlevin et al., 2012 ). As such, its metamorphic evolution provides evidence for an important part of the geological history of the shield. Here we use petrographic, mineral chemistry and thermodynamic modeling, in combination with structural data from the field, to derive a P–T–D–t path for the complex. It is shown that the metamorphic rock of the complex equilibrated during an early deformation event that involves a flat lying fabric and is interpreted as an extensional event. P–T conditions attained during this event are between 370–420 °C and around 3 kbar. These conditions correspond to a geothermal gradient of 38–41 °C/km which is much higher than that documented elsewhere in the metamorphic complexes of Sinai (i.e. 25–27 °C/km). We suggest that this is because metamorphism in the Sa’al–Zaghra complex records an earlier stage of metamorphism and deformation during breakup of Rodinia, whereas the lower gradients documented elsewhere is related to the Gondwana collision. During the subsequent East-West-Gondwana collision, the Sa’al–Zaghra complex remained at shallow crustal levels (

Calc-alkaline and alkaline intrusions of the late Neoproterozic form essential part of the Arabian–Nubian Shield. They were formed during the collision between East- and West-Gondwana. Sharm El-Sheikh area, Sinai, includes wide compositional array of these intrusions that can be considered as a case study. Variations in both tectonic and thermobarometric condition for granitic intrusions are studied. Four mappable granitic types are recognized namely monzogranite, syenogranite, alkali feldspar granites, and riebeckite-bearing granites. The monzogranite and the syenogranite of the study area are mostly I-type, whereas the alkali feldspar granite and the riebeckite-bearing granite belong to A-type granitoid. The calc-alkaline intrusions were formed in compressional setting due to decompressional melting of mafic lower crust. Partial melting and anatexing of crustal rocks are suggested to explain the protolith of the alkaline intrusions. The transition from the calc-alkaline magma to the alkaline one occurred as a result of the tectonic transition from compression regime to tectonic relaxation (extension setting) during the last stage of the Pan-African Orogeny. The amphiboles of the studied granites are classified as calcic- and alkali-amphiboles. The calcic-amphiboles are ferro-edenite while the alkali-amphiboles are typically riebeckite. Both amphibole types are of magmatic nature. Coexisting amphiboles and plagioclases are used to estimate the physicochemical parameters of magma crystallization. The syenogranite underwent temperature and pressure of formation range of 520–730 °C

Strain caps are one of a series of microstructures that typically form during deformation of a softer matrix around hard objects. However—in contrast to other microstructures around porphyroblasts, for example pressure shadows—strain caps are rarely described in the literature. Here we describe strain caps with particular focus on strain caps associated with growth of a new phase, not elsewhere present in the paragenesis. Examples from foliated, amphibolite facies, metapelitic schists from Alaska, Sinai and Bhutan are discussed. All examples show chlorite growth exclusively in strain caps formed around porphyroblasts. Porphyroblasts around which the strain caps grow are muscovite, staurolite and garnet, respectively. In all of these examples strain caps formed synkinematically, but the chlorite grew statically at a later stage. Three mechanisms can explain the formation of new phases in the strain cap region: (a) the strain cap region may have experienced different P-T conditions from the matrix; (b) the strain cap region has a different effective bulk composition from the surrounding matrix; (c) fluid flow that is preferentially focused parallel to the foliation planes causing only local adjustment to retrograde metamorphism in the strain cap region. We show that the third hypothesis is the most preferable mechanism. Indeed, the absence of chlorite outside the strain cap region allows a quantification of the amount of fluid that infiltrated the rock. It is shown that for Bhutan sample about 8.5 mole% more water must have been added to the rock during fluid infiltration to cause the strain cap formation.

Calc-silicates have proved to be important rock types to place constraints on the fluid behaviour in high grade metamorphic rocks. Here we describe amphibolite facies calc-silicate rocks of Wadi Solaf, Egypt which is one of the highest grade basement complexes of Egypt and was exhumed in close connection with the Najd fault system – one of the largest pre-Mesozoic fault systems on the Earth. Calc-silicates formed around 7–8 kbar in temperature range of 600–720 °C and can be classified into three groups (CS 1 , CS 2 and CS 3 ). CS 1 and CS 2 are characterized by the presence of garnet porphyroblasts which contain concentrically arranged wollastonite inclusions. CS 3 has a similar paragenesis but is characterized by the presence of clinozoisite/epidote and the absence of wollastonite as well as a pervasive late overgrowth of prehnite. Garnet in CS 1 lies along a grossular–andradite solid solution, while the garnet composition of CS 2 and CS 3 is hydrogrossular and hydroandradite. There is a positive correlation between Al 2 O 3 and Na 2 O as well as between Al 2 O 3 and Fe 2 O 3 from CS 2 through CS 1 to CS 3 possibly indicating a successive increase in fluid flow between the different calc-silicate types. During the peak metamorphism, the X CO 2 is 0.02–0.08 and 0.2–0.44 for the CS 1 and CS 3 , respectively. The mineral assemblage of CS 1 and CS 2 buffered the composition of the fluids along the reaction: q + cc = wo + CO 2 . During post-peak metamorphism the rocks were intruded by syn-tectonic granites. CS 2 records the contact metamorphic conditions. The rocks reached a peak contact metamorphism conditions at temperature 790–828 °C and X CO 2 = 0.22–0.41. Finally, the rocks reached a temperature range 296–311 °C during the cooling path.

The Feiran-Solaf metamorphic complex of Sinai, Egypt, is one of the highest grade metamorphic complexes of a series of basement domes that crop out throughout the Arabian-Nubian Shield. In the Eastern Desert of Egypt these basement domes have been interpreted as metamorphic core complexes exhumed in extensional settings. For the Feiran-Solaf complex an interpretation of the exhumation mechanism is difficult to obtain with structural arguments as all of its margins are obliterated by post- tectonic granites. Here, metamorphic methods are used to investigate its tectonic history and show that the complex was characterized by a single metamorphic cycle experiencing peak metamorphism at 700- 750 � C and 7-8 kbar and subsequent isothermal decompression to 4-5 kbar, followed by near isobaric cooling to 450 � C. Correlation of this metamorphic evolution with the deformation history shows that peak metamorphism occurred prior to the compressive deformation phase D2, while the compressive D2 and D3 deformation occurred during the near isothermal decompression phase of the P-T loop. We interpret the concurrence of decompression of the P-T path and compression by structural shortening as evidence for the Najd fault system exhuming the complex in an oblique transpressive regime. However, final exhumation from 15 km depth must have occurred due to an unrelated mechanism.