SW Jordan Research Articles

The timing of migmatization in the northern Arabian–Nubian Shield: Evidence for a juvenile sedimentary component in collision‐related batholiths

AbstractCollision‐related granitoid batholiths, like those of the Hercynian and Himalayan orogens, are mostly fed by magma derived from metasedimentary sources. However, in the late Neoproterozoic calcalkaline (CA) batholiths of the Arabian–Nubian Shield (ANS), which constitutes the northern half of the East African orogen, any sedimentary contribution is obscured by the juvenile character of the crust and the scarcity of migmatites. Here, we use paired in situ LASS‐ICP‐MS measurements of U–Th–Pb isotope ratios and REE contents of monazite and xenotime and SHRIMP‐RG analyses of separated zircon to demonstrate direct linkage between migmatites and granites in the northernmost ANS. Our results indicate a single prolonged period of monazite growth at 640–600 Ma, in metapelites, migmatites and peraluminous granites of three metamorphic suites: Abu‐Barqa (SW Jordan), Roded (S Israel) and Taba–Nuweiba (Sinai, Egypt). The distribution of monazite dates and age zoning in single monazite grains in migmatites suggest that peak thermal conditions, involving partial melting, prevailed for c. 10 Ma, from 620 to 610 Ma. REE abundances in monazite are well correlated with age, recording garnet growth and garnet breakdown in association with the prograde and retrograde stages of the melting reactions, respectively. Xenotime dates cluster at 600–580 Ma, recording retrogression to greenschist facies conditions as garnet continued to destabilize. Phase equilibrium modelling and mineral thermobarometry yield P–T conditions of ~650–680°C and 5–7 kbar, consistent with either water‐fluxed or muscovite‐breakdown melting. The expected melt production is 8–10 vol.%, allowing a melt connectivity network to form leading to melt segregation and extraction. U–Pb ages of zircon rims from leucosomes indicate crystallization of melt at 610 ± 10 Ma, coinciding with the emplacement of a vast volume of CA granites throughout the northern ANS, which were previously considered post‐collisional. Similar monazite ages (c. 620 Ma) retrieved from the amphibolite facies Elat schist indicate that migmatites are the result of widespread regional rather than local contact metamorphism, representing the climax of the East African orogenesis.

Detection and analysis of morphotectonic features utilizing satellite remote sensing and GIS: An example in SW Jordan

This study investigates the dominant orientations of morphological features and the relationship between these trends and the spatial orientation of tectonic structures in SW Jordan. Landsat 8 and hill-shaded images, constructed from 30m-resolution ASTER-GDEM data, were used for automatically extracting and mapping geological lineaments. The ASTER-GDEM was further utilized to automatically identify and extract drainage network. Morphological features were analyzed by means of azimuth frequency and length density distributions. Tectonic controls on the land surface were evaluated using longitudinal profiles of many westerly flowing streams. The profiles were taken directly across the northerly trending faults within a strong topographic transition between the low-gradient uplands and the deeply incised mountain front on the east side of the Dead Sea Fault Zone. Streams of the area are widely divergent, and show numerous anomalies along their profiles when they transect faults and lineaments. Five types of drainage patterns were identified: dendritic, parallel, rectangular, trellis, and modified dendritic/trellis. Interpretation and analysis of the lineaments indicate the presence of four main lineament populations that trend ~E–W, ~N–S, NE–SW, and NW–SE. Azimuthal distribution analysis of both the measured structures and drainage channels shows similar trends, except for very few differences in the prevailing directions. The similarity in orientation of lineaments, drainage system, and subsurface structural trends highlights the degree of control exerted by underlying structure on the surface geomorphological features. Faults and lineaments serve as a preferential conduit for surface running waters. The extracted lineaments were divided into five populations based on the main age of host rocks outcropping in the study area to obtain information about the temporal evolution of the lineament trends through geologic time. A general consistency in lineament trends over the different lithological units was observed, most probably because repeated reactivation of tectonism along preexisting deep structural discontinuities which are apparently crustal weakness zones. The reactivation along such inherited discontinuities under the present-day stress field is the most probable explanation of the complicated pattern and style of present-day landscape features in SW Jordan.

Data analysis of a revisited exploration geochemical dataset of quartz porphyrites from SW Jordan using GIS techniques

The spatial distribution of Cu and its pathfinder elements in quartz porphyrites along Wadi Araba was studied in order to gain an insight about the geologic framework of Cu mineralization in the area. A geochemical exploration data set of 242 samples was revisited. Multivariate statistical and geostatistical analysis were performed on the data set. The objectives of the study were to define Cu relationships with its possible pathfinder elements and to figure out whether geostatistical treatment of exploration data would help telescoping already existing Cu mineralization in Wadi Araba, SW Jordan. Factor analysis and hierarchical cluster analysis were performed on the data set. The results of which indicate that seven elements, namely, Ba, Cr, Mn, Ni, Sc, Sr and V can be considered as pathfinder elements for Cu. Significant correlations do exist between Cu and these elements. The encountered experimental semivariograms of the defined pathfinders were fit to exponential models with varying nugget effects with the exception of Mn which was fit to the spherical model. Ordinary kriging was found to be most appropriate to generate geochemical exploration maps. The applied methods succeeded in deriving valuable information and visualizing the already existing Cu mineralization in Wadi Abu Khusheiba area.

Geochemical Exploration for Gold and the Association of As-Cu-Pb-Sn-Zn-Li in the Upper Proterozoic Granitoids of the Wadi Rumman Area, Southwest Jordan

The geochemical studies were conducted in an area covering about 15 km2 of the south side of the Wadi Rumman area, SW Jordan. The study area included a part of a basement of complex exposed rocks in southwestern Jordan. The complexes comprised igneous and metamorphic suites, mostly from the late Proterozoic age. A systematic geochemical sampling was conducted using rock and heavy mineral-panned concentrate of geochemical samples. Fifty rock samples were collected from the granitic rocks, simple pegmatite dyke, quartz veins and alteration zone, which covered the area. Next, 45 heavy mineral-panned concentrate samples were collected from the alluvium in the stream sediment within the catchment area, and the dray was sieved to less than 1 mm grain size. The geochemical samples were analyzed for their trace elements and gold by using Ione Conductive Coupled Plasma Emission Spectroscopy (ICP-AES) and the Atomic Absorption Spectrometer (AAS) at Natural Resources Authority (NRA) Labs. The results of the geochemical analysis indicated the presence of gold and heavy minerals in the study area, a result considered abnormal in the rock samples. A strong positive correlation was recorded of Au with As, Cu and W (r = 0.82, 0.7 and 1.0), as with Mo (r = 0.83), Cu with Pb (r = 0.83), Sn with Mo (r = 0.73), Mo with W (r = 0.97), Zn with W (r = 0.71), and Li with Bi (r = 0.7). These correlations revealed gold associated within the hydrothermal alteration, quartz veins and pegmatite dyke. Abnormal metals such as As and Bi were good path-finders to find Au. The HM samples showed low positive linear correlations among the concentrations of Au with As, Zn and Li, and negative linear correlations of Au with Pb, Sn, Bi and W. The combination of both rock and heavy mineral concentrate samples shows four geochemical anomalous areas of gold and heavy minerals. The geochemical signatures of Au and As in the Wadi Rumman appear to be in the hydrothermal alteration, quartz veins and pegmatite dyke, respectively. Heavy mineral concentration sampling delineated the Au geochemical anomaly in area 1 specificities with the rock geochemical anomaly of area 1.

U–Pb detrital zircon provenance of the Saramuj Conglomerate, Jordan, and implications for the Neoproterozoic evolution of the Red Sea region

The latest stage in the evolution of the northernmost Arabian-Nubian Shield is characterized by the development of volcano-sedimentary successions. In Jordan the Saramuj Conglomerate Formation is considered to be one of these post-tectonic basins. It is polymict and poorly sorted with wide range of clast compositions, roundness and size. We present the first SIMS U–Pb dating of detrital zircons from two sandstone samples representative for the conglomerate matrix and of four clasts from the Saramuj Conglomerate for provenance and age determinations. The relative probability curve for the matrix samples indicates a major contribution (85%) from c. 600 to 650Ma, subclusters at 624 and 640Ma, a minor source from 700 to 750Ma, and a clear gap between 650 and 700Ma. These ages are consistent with those obtained from andesitic, rhyodacitic, granitic and gneiss clasts (624, 642, 650 and 734Ma respectively). In contrast to the adjacent volcano-sedimentary successions in the Elat area, Sinai and the Eastern Desert, no ages older than 750Ma were found. The good match between the known ages of the nearby exposed basement with the matrix ages and the immature nature of the sediments implies that the principal input was locally derived erosional detritus. The age of the youngest 10 detrital zircons at c. 615Ma represents the maximum age of deposition, which is consistent with the stratigraphic position of the Saramuj Conglomerate. Clast ages of 642Ma and 650Ma are interpreted as evidence for a magmatic source that has not been recognized in SW Jordan. This study implies that the volcano-sedimentary successions in the northernmost Arabian-Nubian shield may be broadly coeval but have distinct provenance and therefore evolved as isolated basins. Furthermore, U–Pb zircon provenance analysis allows us to recognize igneous products that are no longer preserved and/or exposed in the region.

Uplift and denudation history of the eastern Dead Sea rift flank, SW Jordan: Evidence from apatite fission track thermochronometry

AbstractThe Dead Sea rift (DSR), developed along the Dead Sea transform plate boundary, is characterized by salient flanks and morphotectonic asymmetry. Apatite fission track thermochronology (AFT) along ~1200 m high vertical profiles in Neoproterozoic basement and overlying Cambrian sandstone in southwestern Jordan is used to reconstruct timing, magnitude, and rate of uplift and denudation of the eastern DSR flank and examine its relationship to rift development and its flank landscape. Time‐temperature models based on AFT data suggest three major Phanerozoic heating and cooling episodes, Late Paleozoic, Early Cretaceous, and Oligocene. The latest episode, on which this study focuses, indicates uplift of ~3.8±0.3 km under a moderate paleogeothermal gradient. About 40% of the uplift was tectonically driven with the remainder attributed to isostatic rebound in response to denudation and erosion. Models suggest that uplift commenced in the Oligocene with a considerable part occurring prior to development of the DSR, despite being ~200 km from the Red Sea‐Gulf of Suez rift margin. Uplift is probably part of a regional rearrangement along the western Arabian platform margin occurring at the time of Red Sea rift initiation. Transition from primarily sedimentary layer stripping, most likely by scarp retreat, to one of dominantly incision of the underlying crystalline basement occurred in Late Miocene‐Pliocene time following enhanced subsidence and development of a low base level in the DSR. Consequently, the magnitude of uplift by isostatic rebound due to incision exceeded lowering by surface truncation and increased summit elevation and riftward flexing of the flank.

Geochemistry and P–T–t evolution of the Abu-Barqa Metamorphic Suite, SW Jordan, and implications for the tectonics of the northern Arabian–Nubian Shield

The Abu Barqa Metamorphic Suite (ABMS) represents the oldest part of the Arabian–Nubian Shield in southern Jordan. It comprises tonalitic gneiss, metasediments including schist and paragneiss, and granitic gneiss, intruded by later granitic bodies. Geochemically, the majority of the schist samples have shale and Fe-shale protoliths, while the paragneisses represent metagreywacke. Tectonic discrimination diagrams indicate that the protolith of the ABMS was deposited at an active continental margin/island arc setting.U–Pb zircon (SIMS) ages from metamorphic and igneous rocks of the ABMS indicate that it evolved between ∼800 and ∼610Ma. A tonalitic gneiss has a crystallization age of 787±3Ma. Detrital zircon from the metasediment has a range of concordant ages from 680 to 860Ma. The entire metamorphic complex was intruded by calc-alkaline granitoids (∼615–610Ma) and quartz diorite dated (∼600Ma).Field and petrographic investigations of ABMS metasediment elucidate the development of three metamorphic zones, from north to south: (1) andalusite–staurolite (andalusite+staurolite+biotite+muscovite+plagioclase±garnet+quartz±chlorite+fibrolitic sillimanite+accessories), (2) garnetsillimanite (sillimanite+garnet+biotite+plagioclase+quartz+K-feldspar+cordierite (pinitized)±rutile±ilmenite), and (3) cordierite–sillimanite (sillimanite+biotite+plagioclase+cordierite+hercynite+quartz+accessories).The maximum metamorphic conditions (M1) were attained in the garnet–sillimanite zone (5–6kbar, ∼700°C), while peak conditions of ∼3.2kbar and 540°C were obtained for the andalusite–staurolite zone (using both forward-pseudosection modeling and inverse-modeling with multi-equilibrium approach). Compositional isopleth calculations of small relics of garnet yield about 3.5kbar and 600°C for the sillimanite–cordierite zone. These values are in agreement with results obtained by TWQ inverse modeling. The M1 event most probably occurred around ∼625 and was followed by a decompressional thermal phase (M2) contemporaneous with post-tectonic granitoid emplacement at ∼615–610Ma; and lastly went through a retrograde cooling phase (M3) accompanying uplift of the whole complex to the surface at ∼605Ma.

Optical dating of sediments in Wadi Sabra (SW Jordan)

At Wadi Sabra (SW Jordan) human occupation dates back to the Palaeolithic and Epipalaeolithic. Although there is stratigraphic correlation based on archaeological finds of Ahmarian origin, numerical age estimates are lacking. We applied single-aliquot optical dating of coarse grained quartz of wadi deposits and investigated the luminescence properties in detail to achieve more accurate age information about the time of human occupation. Weak luminescence signals and scattered dose distributions characterise the multi-grain aliquots. The residual doses of the investigated modern wadi sediment are between 0 and 7 Gy. Moreover, comparison of equivalent dose (De) values of 1 mm and 8 mm aliquots shows higher equivalent doses for the large aliquots. Both experiments indicate that the luminescence signal is partially bleached prior to deposition. The dose distributions of all samples are broadly scattered and have overdispersion values between 25 and 43%, some samples are significantly skewed. The shape of the dose distributions points to other sources of scatter, in addition to partial bleaching. Comparison of 1 mm multi-grain and single-grain data demonstrates that the luminescence signal of one multi-grain aliquot most likely is from a single grain. For this reason, variation in the number of photon counts due to the weak luminescence intensity and variations in beta microdosimetry have a bigger impact on the spread of dose distributions. However, we cannot quantify the particular impact of partial bleaching, weak luminescence intensity and beta microdosimetry. To account for the spread of the dose distribution, we use the central age model to calculate equivalent doses. Age calculations yield results in the range of 30–48 ka.

The effects of vegetation cover on the structure of bird communities in a hyperarid desert

The hyperarid deserts of Wadi Araba, SW Jordan, include a variety of habitats ranging from barren alluvial fans and sand dunes to arid acacia savannahs and salt marshes. The diversity of resident birds was highest in acacia stands growing on alluvial fans and stone plains. Although open sand dune habitats have a distinct bird community contributing to the overall diversity, the local diversity within these habitats is relatively small. In habitats with both rocky and sandy substrates, species richness, avian abundance and the diversity of feeding guilds increased locally with the density of shrubs and/or trees. Additionally, avian diversity was related to vertical structure and linked to the mean height of shrubs and trees. Ephemeral annual cover had no general effect on the diversity of the native bird community. Shrub and tree cover appear to be reliable habitat cues used by many bird species when choosing their breeding habitats, as the presence of shrubs and trees increases the diversity of food resources and of secure nesting sites.

Origin, age and petrogenesis of Neoproterozoic composite dikes from the Arabian‐Nubian Shield, SW Jordan

AbstractThe evolution of a Pan‐African (c. 900–550 Ma) suite of composite dikes, with latite margins and rhyolite interiors, from southwest Jordan is discussed. The dikes cut the Neoproterozoic calc‐alkaline granitoids and high‐grade metamorphic rocks (c. 800–600 Ma) of the northern Arabian‐Nubian Shield in Jordan and have been dated by the Rb‐Sr isochron method at 566±7 Ma. The symmetrically distributed latite margins constitute less than one‐quarter of the whole dike thickness. The rhyolite intruded a median fracture within the latite, while the latter was still hot but completely solidified.The dikes are alkaline and bimodal in composition with a gap in SiO2 between 61 and 74 wt%. Both end members display similar chondrite‐normalized rare earth element patterns. The rhyolites display the compositional signature of A‐type granites. The (La/Lu)N values are 6.02 and 4.91 for latites and rhyolites, respectively, and the rhyolites show a pronounced negative Eu anomaly, in contrast to the slight negative Eu anomaly of the latites. The chemical variability (e.g. Zr/Y, Zr/Nb, K/Rb) within and between latites and rhyolites does not support a fractional crystallization relationship between the felsic and mafic members of the dikes. We interpret the magma genesis of the composite dikes as the result of intrusion of mantle‐derived mafic magma into the lower crust in an extensional tectonic regime. The mafic magma underwent extensive fractional crystallization, which supplied the necessary heat for melting of the lower crust. The products of the initial stages of partial melting (5–10%) mixed with the fractionating mafic magma and gave rise to the latite melts. Further partial melting of the lower crust (up to 30%) produced a felsic melt, which upon 50% fractional crystallization (hornblende 15%, biotite 5%, feldspars 60%, and quartz 20%) gave rise to the rhyolitic magma. Copyright © 2004 John Wiley & Sons, Ltd.

Contributions to the flora of Jordan 4. A new species ofPycnocycla (Apiaceae)

Abstract Danin, A., Hedge, I. C. & Lamond, J. M.: Contributions to the flora of Jordan 4. A new species of Pycnocycla (Apiaceae). — Willdenowia 30: 77–81. 2000. — ISSN 0511-9618. Pycnocycla saxatilis from SW Jordan and NW Saudi Arabia is described as a species new to science and illustrated. It is a stem-assimilant subshrub related to P. tomentosa and confined to crevices of smooth-faced sandstone and similar habitats. Attention is drawn to another undescribed and related Pycnocycla taxon from further south in Saudi Arabia.

SANDSTONE OUTCROPS—A MAJOR REFUGIUM OF MEDITERRANEAN FLORA IN THE XERIC PART OF JORDAN

Plants growing in sandstone outcrops at the western escarpments of the Jordanian plateau, in the Tafila-Petra-Ras en Naqb area, represent a unique refugium for Mediterranean flora in an area receiving 100–300 mm of rainfall annually, located at the transition between desert and shrub-steppe vegetation of southwestern Jordan. The occurrence of large outcrops of smooth-faced hard sandstone and limestone cliffs at elevations from sea level to 1,200 m above sea level enabled the long persistence of various kinds of habitats that supported hundreds of Mediterranean relict plant species of all growth forms that survived from periods when the climate was moister. The continuity, in SW Jordan, of the refugium habitat enabled a rich Mediterranean flora to survive in the desert including many endemic species. The Jordanian refugia are much richer floristically than those of the Israeli and Sinai deserts.

Surface textures of quartz grains from arid continental environments (Wadi Araba area, SW Jordan)

Surface textures of quartz grains from arid continental environments (Wadi Araba area, SW Jordan)

Contributions to the flora of Jordan 2. A new species ofSatureja (Labiatae)and some new records

Abstract Danin, A. & Hedge, I. C.: Contributions to the flora of Jordan 2. A new species of Satureja (Labiatae) and some new records. — Willdenowia 28: 135–142. 1998. — ISSN 0511-9618. Satureja nabateorum is described as a species new to science and illustrated. It is confined to crevices of smooth-faced sandstone in SW Jordan (Edom) and closely related to S. thymbrifolia, a species restricted to the Judean Desert and belonging to S. sect. Zatarioideae. The different ecology of both species is discussed and their distribution mapped. Ten new records of interesting plants from Edom include the southernmost record of Arbutus andrachne from the Petra area. In this context also the new combination Bituminaria bituminosa var. brachycarpa is made.

Contributions to the flora of Jordan: new and interesting plants from Dana Nature Reserve, SW Jordan

Danin, A.: Contributions to the flora of Jordan: new and interesting plants from Dana Nature Reserve, SW Jordan. — Willdenowia 27: 161–175. 1997. — ISSN 0511-9618.Rubia danaensis, Micromeria danaensis, and Silene danaensis from sandstone and limestone outcrops of the Dana Reserve, SW Jordan, are described as species new to science, illustrated, and compared with their closest relatives. The heterogeneous Teucrium leucocladum is subdivided into three subspecies and two varieties, of which subsp. sinaicum, subsp. jordanicum and subsp. leucocladum var. glandulosum are described as new to science. Five taxa, i.e. Clypeola jonthlaspi subsp. microcarpa var. glabra, Hypericum sinaicum, Plantago sinaica, Veronica panormitana subsp. baradostensis, and V. polifolia are new records for the ‘Flora Palaestina’ area, and seven taxa, i.e. Alcea galilaea, Linum toxicum, Reaumuria negevensis, Saxifraga hederacea, Stachys zoharyana, Teucrium montbretii, and Typha elephantina are new records for Jordan.

Sedimentology and mineral composition of the Kurnub Sandstone in Wadi Qsieb, SW Jordan

The Kurnub Sandstone of Early Cretaceous age crops out in Wadi Qsieb (in the southwest of Jordan) with a thickness of 130 m. Moderately developed fining-upward cycles with irregular erosive bases, together with the presence of plant fragments and the absence of body or trace fossils, point to a fluviatile depositional environment, probably a river of intermediate sinuosity. Results of grain-size analysis confirm this interpretation. The sandstones are compositionally and texturally supermature quartz arenites formed mainly by recycling from Early Palaeozoc sandstones and less commonly by direct supply from the Arabian-Nubian Shield. The absence of feldspars and unstable heavy minerals is attributed to intense chemical weathering, attacking sands that were deposited with a low rate on a craton bordering the Tethys Sea. The thickness recorded here and the absolute absence of hornblende are in contradiction with what has been published by Nasir and Sadeddin (1989).

Multivariate statistical techniques in geochemical exploration applied to Wadi sediments' data from an arid region: Wadi Dana, SW Jordan

The well-known multivariate statistical techniques applied generally to studying stream sediments' data from humid regions were used to test their usefulness in studying stream sediments (Wadi sediments) from an arid region (Wadi Dana). 134 samples were collected along the course of Wadi Dana and its major tributaries. In this study, factor analysis, especially the R-mode, revealed a distinct and, for exploration purposes, useful simplification of the given data set. A four factor R-mode model explained 72.48% of the total information contained in the original data. Q-mode clustering technique pinpointed the MnCu mineralization sites, whereas spatial variability studies helped determining the spatial dependence of the inferred pathfinders. The results of this study indicate that the applied techniques serve also as good tools for geochemical exploration in arid regions.