Petrography, Geochemistry and Petrogenesis of the Basalt Flow at Al Azraq Al Shamali Area, East Jordan ()
1. Introduction
Basalts are aphanitic igneous extrusive volcanic rocks formed by the rapid cooling of lava, composed of fine grains of plagioclase, pyroxene, olivine, hornblende and less than 20% quartz [1]. The basalt is the most common rock in the earth’s crust; it forms from the melting of the upper mantle and its chemistry closely like the upper mantle’s composition. The magma erupt in wide variety of tectonic environments on earth such as mid-ocean ridges, island arcs, back-arc basins, intraplate oceanic islands, large igneous provinces and intra-continental rifts [2]. According to chemical and mineralogical compositions of basalt there are two main types of basalt rocks; tholeiites which are silica saturated-oversaturated and alkali basalts that are silica under saturated. Huge eruption of basalts invariably takes the forms of lava flows, two Hawaiian words are used to describe the two main types of basaltic lava flows are (pahoehoe) lava which is characterized by a smooth or ropy surface and (a’a) lava described by jagged or rough surface [2] [3]. Basalt that forms from magma that extrudes into ocean water forms a type of basalt called “pillow lava” or “pillow basalt”.
Basalt in Jordan is a part of the Arabian plateau basalt, which covers a large area from Syria to Yemen through Jordan and Saudi Arabia [4] (Figure 1). It comprises one of the world’s largest alkaline volcanic provinces named the Arabian Harrat Province, and covers an area of 180.000 km2 [5]. The volcanism in Harrat Ash Shaam started about 24 million years ago (Miocene to Pleistocene) and continued to recent times with a volcanic hiatus (gab) of several million years between 13 and 7 Ma (a quiescent interlude in volcanic activity) in the northern part of the Harrat Ash Shaam [6] - [13]. Based on K-Ar dating, [6] [14] and [10] have divided the volcanic activity of Jordan into three major episodes: Oligocene to early Miocene (26.23 - 22.17 Ma), middle to late Miocene (13.97 - 8.94 Ma), and late Miocene to Pleistocene (6.95 Ma to <0.15 Ma).
The basalt in Jordan occurs as sporadic small volcanic centers along the eastern side of Dead Sea boundary and as a large area of volcanic field to the northeast of the plate boundary [11]. The N-S striking of Dead Sea Transform (DST) was accompanied by substantial horizontal sinister displacement and by sinisterly fan-like rotation of Arabian plate. These tectonic activities led to opening ways (fissure systems) for the ascent of magmas [15]. The fissure systems trending E-W and NW-SE direction along the eastern margin of the DST, on the large
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Figure 1. Distribution of intraplate volcanic fields of the Arabian Plate and Location of study area, modified after [4].
basaltic plateau [6]. The Cenozoic basaltic rocks in Jordan are nearly occupy 18% of Jordan area; and they are distributed in three main regions: 1) basalts relating to the DST (e.g. Zara basalt), 2) central Jordan (e.g. El-Lajjoun Basalt), and 3) NE-Jordanian Harrat (with an area 11,400 km2) which is a part of the largest Harrat Ash Shaam. The central Jordan basalt is found mainly in six places, El-Lajjoun, Jabal Shihan, Tafila, Wadi Dana, Jurf Al-Darawish and Ghor Al-Katar. They occur either as plateau basalts, or as local flows (e.g., Wadi fills) or as individual volcanic bodies (cones, plugs, sills, and dikes) [16]. The southern Jordan basalt is very limited, but there are some studies that have been carried out, such as the study of the origin of the Miocene Mudawwara-Quwayra Basaltic Dike [17]. The study area Al Azraq Al Shamali basalt flow which is a part of Harrat Ash Shaam area, located in the eastern part of Jordan within 36˚47'31" to 36˚51'03" longitudes and 31˚51'36" to 31˚54'35" latitudes. The main objectives of this study evaluate the mineralogy, petrography, and geochemistry features of the basalt flow by using different techniques.
2. Geological Setting
The study area (Al Azraq Al Shamali), situated on the eastern part of Jordan roughly 75 km east of Amman City. The study area covered by sedimentary and volcanic rocks Figure 2. The sedimentary rocks represented by superficial deposit within quaternary age, exposed in the central part of Al Azraq area. These deposits include alluvial mudflats, fluviatile, colluviums and Wadi sediments [18]. The volcanic rocks are represented with Abed Olivine Phyric Basalt Formation (AOB). These formation (AQB) is one of the three formations of the Safawi group, widespread and dominant in the Al Azraq Al Shamali area, comprises several basaltic flood lava and feeder dike systems. It comprises massive flows up to 10 m thick with a total thickness of up to 100 m, the formation is Late Miocene in age [18].
The study area is located between two NW-SE trending major faults these are 1) Fuluq Fault system (NW-SE) is a normal fault system with downthrown to the southwest and characterized by strike-slip movement; 2) as Sirhan Fault Zone (NW-SE) the As sirhan fault is the western boundary of the sirhan basin, it consists of a series of NW-SE faults; 3) Al Bayda Fault (NW-SE) which represents the border of the main mudflat in the northeastern; 4) al Baqawiyya fault (SW-NE) which may have a horizontal component, it forms the southeastern edge of Qa Al Azraq [19].
3. Sampling and Analytical Techniques
A total of 16 representative rock chip samples were collected from the outcropping of Abed Olivine Basalt Formation (AOB) in eastern Jordan (Figure 2). The
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Figure 2. Geological Map of the study area and showing the rock sample locations modified after [20].
samples are crushed and powdered using a stainless steel Jaw Crusher and an Agate Ball Mill machine to obtain a grain size (less than −80μ). The samples were quartered to get a statistically representative (splitter) fraction and powdered using two geochemical techniques at the labs of Al al-Bayt University. The major and trace elements were analyzed on fused glass discs-like pellet (bead) using a pressed pellet using X-Ray Fluorescence Spectrometry (ARL ADVANT’X Intelli Power) model in the laboratories of Jordan Phosphate Mines Company (JPMC) and by Philips XRF (MAGIX PRO PW 2440) model in the laboratories of The Water Environment and Arid Region Research Center Lab at Al al-Bayt University. Using 8.0 gram from each grinded sample and 1.2 grams of grinded cellulose binder were added together on an analytical balance and mixed for approximately one minute. The resulting mixture were put in crucible and putted in oven at 70˚C for 2 hours. The resultant fine powder samples were pressed by press with pressure pumped to (4 tons) for (1 min) in (40 mm) mold (unified) to get the clear disc-like pellet at laboratories of Jordan Phosphate Mines Company. Thin section prepared at the Al al-Bayt University lab, and the photomicrographs of the thin sections were carried out using a LEICA-DMEP Canon camera in the petrography unit at Ministry of Energy and Minerals Resources. The geochemical data processed and pictorially represented by using the computer programs Excel, Igpet 32 and GCD kit and CIPW Norm program for [21].
4. Results and Discussion
4.1. Petrography and Mineralogy
The basaltic rocks samples taken from Al Azraq Al Shamali lava flows are dark, fine-grained to aphanitic rocks with few vesicular samples. The average modal percentage mineral composition of the samples is 60% plagioclase, 15% pyroxene, 13% olivine, 6% opaque minerals (mainly iron oxide), 4% vesicles and 2% secondary minerals such as Iddingsite, calcite and clay. The main common texture of the studied samples was porphyritic, glomeroporphyritic, intergranular, ophitic to sub-ophitic, Radiate, intergranular, seriate, vesicular and amygdaloidal texture.
4.1.1. Plagioclase
Plagioclase crystals are the predominant minerals in thin sections of all samples, forming about 60% of the rock and occur as lath-like shape, subhedral to euhedral tabular shape, and range in size from fine to coarse grain, simple and multiple twining is common. Oscillatory zoning is also noted in some crystals (Figure 3(a)). Some crystals displaying inclined extinction. Plagioclase crystals are elongated and occurs with ophitic to sub-ophitic texture enclosed in clinopyroxene crystal and show slight alignment exhibited orientation to olivine and pyroxene crystals. The Ternary Classification Ab-An-Or for feldspars shows that plagioclase minerals of the AZS basalt rocks are plot within the labradorite field (Figure 4(a)).
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Figure 3. Photomicrograph showing (a) Oscillatory zoning of plagioclase (XPL), magnification, 4×. sample 8. (b) Ophitic texture, where plagioclase laths are completely enclosed by pyroxene mineral (XPL), magnification 10×, sample No. 13. (c) Glomeroporphyritic texture, where the Phenocrysts (Plagioclase and olivine) are found to occur as clusters of crystals (XPL magnification, 4×, Sample No. 13. (d) Corona and Iddingsite texture (XPL), magnification 4×, Sample No.9. Where 4× = 0.1 mm, 10× = 0.25 mm, (Ol: Olivine; Plag: Plagioclase; Opq: Opaque minerals).
4.1.2. Pyroxene
Pyroxene occurs as colorless to grayish brown in color with anhedral crystals, comprising about 15% of the rock, the crystals have sizes between 0.3 to 0.5 mm, and they show perfect two set of cleavage intersect at ~90˚ in the cross-section. The clinopyroxene intersected with plagioclase crystals to form ophitic to sub-ophitic textures (Figure 3(b)). The classification scheme of Morimoto (1988), clinopyroxene is fall in the augite field near the Diopside/Hedenbergite boundary (Figure 4(b)). The clinopyroxene intersected with plagioclase crystals to form ophitic to sub-ophitic textures
4.1.3. Olivine
The olivine Phenocrysts occurs as single or clustered subhedral to anhedral crystals, and forming ~13% of the rock, high relief and ranging between 0.02 and 0.75 mm in diameter displaying seriate texture. Moreover, when plagioclase and olivine Phenocrysts are found to occur as clusters of crystals exhibit glomeroporphyritic texture or aggregated within the intergranular spaces between plagioclase laths (Figure 3(c)). Olivine high degree of alteration to Iddingsite. The
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Figure 4. (a) Ab-An-Or ternary plot for plagioclase compositions of AZS samples, all the ample plotted within Labradorite field, modified after [22]. (b) Pyroxene Classification from the AZS basalts, the sample plotted within augite field, modified after [23]. Wo: Wollastonite; En: Enstatite; Fs: Ferrosilite.
crystals are fractured slightly to moderately, Iddingtization are also noted particularly along the edge (rim) and fractures of the crystals, some crystals were partially to completely pseudo morphed to brown Iddingsite and corona texture (Figure 3(d)).
4.1.4. Secondary Minerals
Secondary minerals resulting from introduced or substituted during the processes of alteration, metamorphism, or weathering that changes in the primary or original mineral constituents of the rock [1]. The microscopic investigations of samples show that these processes include alteration of olivine to produced Iddingsite. Opaque minerals (mainly iron oxide) were commonly found in thin sections, range in size from 0.03 mm to 0.05 mm, forming about 6% of the rock, opaque minerals common with anhedral shape, most of them occurred as hematite dispersed between plagioclase, pyroxene and olivine crystals (Figure 3(c) and Figure 3(d)) calcite and clay minerals then we called the texture amygdaloidal, the long axis of these vesicles ranges from 0.05 to 0.35 mm and formed about 4% of the rock.
4.2. Geochemistry
4.2.1. Major Oxides
Al Azraq Al Shamali (AZS) basalt have been investigated by Sixteen rock samples, were analyzed the major oxides (SiO2, TiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O and P2O5 (wt%)) and trace elements V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Ce, Nd and Ba (ppm) is listed in Table 1. The content of SiO2 varies from 44.4 wt% to 48.9 wt% with an average of 46.4 wt%, which is within the average value reported by several authors for alkali basalt and basanite [24] [16] [11] [25] [26] , and it can be classified as basalt to Trachy basalt using the Total Alkalis Vs. Silica classification scheme [27] and [28] (Figure 5(a) and Figure 5(b)). The total alkali-silica diagram, with the [29] show that AZS basalt samples
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Figure 5. (a) TAS diagram, after (Le Bas et al. 1986), shows the AZS sample located within basaltic to Trachy basalt field. (b) SiO2 vs. Na2O + K2O (TAS) diagram after [28] , showing the classification of volcanic rocks from AZS. All the rock samples were plotted within basalt field. (c) The total alkali-silica diagram, with the [29] boundary line which show that AZS basalt samples dominantly plot within alkaline field.
dominantly plot within alkaline field (Figure 5(c)). These results have been documented by many authors such as [26] [30] [31] [32] [33] [34]. According to [35] , diagram for the alkali series into sodium, potassium and potassium-rich series, the AZS basalts samples were found to belong to the sodic series (Figure 6). The variation ranges of other major elements oxides such as Al2O3 content ranges from 16.7 wt% to 19.6 wt% with average of 18.2 wt%, Fe2O3 varies between 9.9 wt% and 10.6 wt% with average of 10.2 wt%. MnO range between 0.13 and 0.15 wt% with average of 0.14 wt%. MgO range between 4.1 wt% and 6.2 wt% with average of 4.9 wt% CaO range between 9.9 wt% and 12.9 wt% with average of 10.9 wt%. Na2O range between 3.3 wt% and 4.7 wt% with average of 4.2 wt%. K2O range between 0.6 wt% and 0.8 wt% with average of 0.7 wt% and P2O5 between 0.3 wt% and 0.9 wt% with average of 0.4 wt%. The Mg number (Mg#), defined as the molecular proportion of Mg2+/(Mg2+ + Fe2+) and usually used as a petrogenetic indicator for magma fractionation and its primitive volcanic rocks [36] [30]. The Mg# varies from 62 to 70 with average of 65 (Table 1).
The major elements concentrations were used to calculate the CIPW norm (Table 1). The Normative albite has higher concentrations than anorthite, which indicates the alkaline in nature of these rocks. Diopside and Nepheline are present in the AZS rock samples and low percent of apatite, perovskite and ilmenite respectively. Based on CIPW normative calculations and the classification scheme of alkali basalts proposed by [37] , the studied samples are plotted in the alkali olivine basalt field (Figure 7).
4.2.1. Trace Elements
The AZS basalt samples high concentration of Ni and Cr, range between 147 to 232 with average 192 ppm, Cr range between 432 to 590 with average 505 ppm, it is may indicate for derivation of parental magmas from a peridotite mantle
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Figure 6. K2O vs. Na2O diagram showing the study samples plotted within Sodic Series, after [38].
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Figure 7. Plots of normative olivine (wt%) against normative nepheline (wt%) compositions of AZS alkali basalt, after [39].
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Table 1. Chemical analysis of the AZS basaltic sample studied.
An: Anorthite; Or: Orthoclase; Ol: Olivine; Ab: Albite; Di: Diopside; Ap: Apatite; Il: Ilmenite; He: Hematite; Pf: perovskite; Ne: Nepheline.
source [40]. The high content of Cr and Ni indicated by the parental magma had been derived through partial melting of peridotite mantle source, and suggested that presence of olivine and clinopyroxene fractions in the AZS [3] [11] [26] [40]. The concentration of Sr and Zr, in the AZS rock sample study had relatively high contents. The Sr ranging between 283 to 2530 ppm with average of 764 ppm, Zr content between 40 to 143 ppm with average of 117 ppm, (Table 1). The Sr+2 is substitute for Ca in plagioclase minerals (Anorthite CaAl2Si2O8) and lesser extent was found in K-feldspar. Zr is found in accessory minerals such as Zirconium (ZrSiO4) [41] [42]. The Rare Earth Elements (REE) includes Nb and Y content ranging between 8 to 18 ppm with average 13, Nb range between 11 to 15 with average 15 ppm respectively. The REE were replacement of Ca+2 in accessory minerals such as Apatite Ca5(PO4) (OH, F, Cl) and Titanite (CaTiSiO5). Niobium (Nb5+) does not substitute for major elements because of its high charge, but it may substitute for titanium due to their similar ionic radii and valence state [42]. Vanadium concentration range between 168 to 202 with average 187 ppm. Vanadium and Titanium has a comparable behaviour in melting and crystallization processes, those elements provide a useful signal for of the fractionation of Fe-Ti oxides (such as ilmenite) [40]. The average ratio between Zr/Nb, Nb/Y and Zr/Y are 9.85, 0.86 and 8.0 respectively. These ratios were documented and reported by [32] [43] for the intercontinental alkali basalt.
5. Petrogenesis
The chemical analysis of major and trace elements for AZS basaltic rock samples study was used to construct the discriminate diagrams, which help to classification, nomenclature and interpretation of the tectonic setting of the AZS basalt. Ti-V diagram after [44] dependent on a variable valence state of vanadium and ranges in titanium abundances to delineate mid-ocean ridge, Ocean Island and volcanic-arc basalt. The study samples fall within the alkaline field (Figure 8). The ternary diagram for Ti-Zr-Y, after [45] , the studied samples fall within plate basalt field Figure 9(a). The Zr-Nb-Y diagram after [46] , shows all the study samples plotted and fall within the fields A and B, these indicating an intraplate tectonic setting (Figure 9(b)). The MnO-TiO2-P2O5 diagram after) [47] , all the studied samples are located within the (OIA) field, (Figure 9(c)).
The spider diagrams for Rock Primordial mantle are used to study for AZS basaltic rock samples (AZS). The study samples show enrichments with peaks at Nb and Sr, and depletions for the high field strength (HFS) elements of Zr, Ce and Ti, in addition to a little variation in Y contents. The negative (K) anomalies are obviously a common feature of Si-under saturated basic magmas and indicate for a smaller degrees of partial melting, also the strong positive Sr anomalies reflects the higher content of (Sr) element in the samples which is a feature inherited from the mantle source [48]. The presence of negative (P) anomaly indicates a crystallization of apatite [49]. The negative anomalies of HFS elements (Zr, Ce, Ti and Y) in primitive mantle-normalized diagrams (Figure 10), are incompatible with a fundamental involvement of continental crust in the genesis of AZS basaltic rocks (Doroozi et al. 2018). A slightly positive Nb peak is a
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Figure 8. Ti/1000 vs. V discrimination diagram after [44] , AZS basalt samples. Within Alkaline field, MORB: mid-ocean ridge basalt; BABB: back-arc basin basalt.
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Figure 9. (a) Ti-Zr-Y diagram of after (Pearce and Cann, 1973) for the AZS basalt samples, shows the studied samples fall in the (D)-within plate basalt field; (b) the Nb –Zr– Y diagram after [46] for the AZS basaltic samples, shows the studied samples within A and B fields; (c) TiO2-MnO-P2O5 diagram after [47] , for AZS basaltic samples plotted within OIT: ocean island tholeiites field.
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Figure 10. Primitive mantle-normalized incompatible trace element abundance patterns of the AZS basaltic rocks, after [54].
distinctive feature of continental and oceanic alkali basalts [50] , and considered a good indicator that the AZS is a product of the asthenosphere part of the mantle rather than the lithosphere [16]. It can be noticed, that the positive Ba and Sr anomalies and slight negative Zr and Ti anomalies reflect that the general multi-element distribution patterns of the AZS alkali basalt samples shows an OIB-like feature [51] [52] , except the trace element Sr, which has relatively higher contents (average ~ 764 ppm) than those of normal OIB (average ~ 660 ppm) [53].
The binary diagram for Zr-Nb plot after Bakhsh, 2015, Figure 11 explain the geochemical characteristics and petrogenetic studies of the AZS basalt have indicated that the magmas initially originated by a low partial melting (~ 10%) and the peridotite precursor was most probably spinel lherzolite rather than garnet.
6. Conclusions
The following present of the study area are:
1) All the samples mainly contain olivine, pyroxene, plagioclase and opaque with secondary mineral phases such as Iddingsite which is a result of the alteration processes of olivine.
2) Many types of textures have been observed in AZS samples such as porphyritic, glomeroporphyritic, vesicular, intergranular, radiate, and ophitic to sub ophitic texture.
3) Petrographically, we can classify AZS basalt samples as Alkali-olivine basalt.
4) Normative mineralogy by using CIPW norm showed that AZS basalt samples dominated by anorthite, albite, olivine, orthoclase, Diopside, hematite, nepheline, olivine and low percent of apatite, perovskite and ilmenite.
5) The chemical classification of AZS basalt samples classified as alkaline basalt
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Figure 11. Zr-Nb plot of AZS basalt samples, show that the peridotite precursor was most probably spinel lherzolite rather than garnet, with a small degree of melting, modified after [54].
and belongs to sodic series.
6) The tectonic setting for the discrimination diagram showed that the AZS samples are situated within plate basalt field.
7) The AZS basalts were produced by primary magmas, were mainly resulted by low degrees of partial melting of garnet-bearing peridotite within the asthenosphere at >I00 km depth, and underwent fractional crystallization of olivine, pyroxene and the plagioclase in the latest stage.
8) The geochemical characteristics and petrogenetic studies of the AZS basalt provide no clear evidence for crustal contamination being a major influence on these rocks.
9) The normalized trace elements spider diagrams (Primitive mantle) of AZS basalt suggest that the basalt is derivation from a depleted mantle source (precisely from asthenosphere part of the mantle).
Acknowledgements
The author is thankful to the laboratory of the University of Al al-Bayt University, Faculty of the Earth and Environmental Sciences for the geochemical and thin section preparation samples. Thanks to the Water Environment and Arid Region Research Center Labs at Al al-Bayt University, and Jordan Phosphate Mines Company (JPMC) for determine and analysis of the major and trace elements using X-Ray Fluorescence Spectrometry.