Petrography, Geochemistry and Petrogenesis of the Basalt Flow at Al Azraq Al Shamali Area, East Jordan

Al Azraq Al Shamali (AZS) basaltic rocks were investigated aiming to under-stand their mineralogy, petrography and geochemistry features, and to achieve that a total of sixteen representative rock samples were selected for both geochemical and petrographic analysis from several sites in the study area. Petrographic characteristics were analyzed by optical microscopy after preparation thin sections for representative rock samples, which show that all basalt samples have minerals comprising: olivine, plagioclase (labradorite), clinopyroxene (augite), opaque’s and some secondary minerals such as Iddingsite, however, the proportions of each mineral vary between samples. Normative mineralogy by using CIPW Norm showed that AZS basalt samples dominated by olivine, Diopside, and nepheline, and AZS basalt can be normatively classified as alkali olivine basalt. Some textures that may be evident on microscopic examination such as porphyritic, glomeroporphyritic, vesicular, intergranular, and ophitic to sub-ophitic texture. X- Ray Fluorescence was used for whole rock major elements analysis (SiO 2 , TiO 2 , Al 2 O 3 , Fe 2 O 3 , MnO, MgO, CaO, Na 2 O, K 2 O


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 km 2 [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 I. A. B. Yaseen, A. A. E. Al Smairan 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 km 2 ) 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.

Geological Setting
The study area (Al Azraq Al Shamali), situated on the eastern part of Jordan  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   [20]. International Journal of Geosciences 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 (

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.

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

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  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)).

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.  [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    [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).

Major Oxides
The variation ranges of other major elements oxides such as Al  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).

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   Niobium (Nb 5+ ) 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

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-TiO 2 -P 2 O 5 diagram after) [47], all the studied samples are located within the (OIA) field, (Figure 9(c)). 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   [46] for the AZS basaltic samples, shows the studied samples within A and B fields; (c) TiO 2 -MnO-P 2 O 5 diagram after [47], for AZS basaltic samples plotted within OIT: ocean island tholeiites field. International Journal of Geosciences 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.

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. . 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).