Petrographic, mineralogical and geochemical investigations were carried out on representative samples from the Mudawwara-Quwayra Dike (MQD) in southernJordan. The MQD intruded Paleozoic and Cretaceous rocks as sub-vertical basaltic plugs, striking NW-SE along a fault zone and extending for more than 100 km. The MQD forms irregularly positive features, and is represented by symmetrical, elliptical, elongated or circular hills. It comprises thin basaltic layers intercalated with pyroclastics and inclusions of different size and lithology, including limestone, sandstone, phosphate, quartzite, and marble. Petrographically, the rock exhibits phyric, porphyritic, vitrophyric and locally glomerophyritic textures manifested by plagioclase, clinopyroxene and rare olivine and set in a matrix of plagioclase, pyroxene, brown glass and opaque phases. Clinopyroxene and olivine phenocyrsts show disequilibrium textures such as reaction/resorbed rims in the forms of corroded ends. The paragenetic sequence shows that olivine is the first phase to be crystallized and coexisting with pyroxene at sometime, while pyroxene continues crystallization. Plagioclase might have crystallized in contemporaneous later than the pyroxene. The MQD rocks are classified as basalt and exhibit a narrow range of silica with a unique subalkaline affinity. This is most probably attributed to assimilation of the abundant siliciclastic inclusions by the ascending magma. Emplacement of the MQD is attributed to regional phase of magmatism in Jordan and Saudi Arabia, which is probably the peripheral extension of a large magmatic event widely exposed in the Red Sea realm.
Neogene-Quaternary volcanic rocks are mainly widespread in the northwestern part of the Arabian Plate including Jordan (
The K-Ar dating results of the MQD gave an age of 20 ± 0.23 Ma and were considered to be of Mio-Pliocene age [
Previous studies regarding the volcanic activity related to the MQD are scarce. It is the purpose of this study to provide a detailed description of the mineralogy, petrology and geochemistry of the MQD and its associated sedimentary inclusions, and to compare the MQD with the approximately synchronous Miocene volcanic rocks of the region. The new data allow a better understanding of the volcano-tectonic history of southern Jordan and the northern Arabian Plate.
The study area is located in south Jordan about 50 km south of the city of Ma’an (
More than forty representative samples were collected from different parts of the MQD for petrographic, mineralogical and chemical analyses. Fifty thin sections were prepared and petrographically investigated via polarizing microscope type Lica with different magnifications. Major, minor and trace elements were analyzed on representative samples using multi-channel XRF spectrometry by fused glass disks at the Natural Resources Authority of Jordan. For this aim rock powders were dried for two hours at 110˚C and ignited in an electric furnace at 1000˚C for one hour. Ignited samples were then mixed with sodium tetraborate (1:7) and fused in Pt crucibles
over gas burners for one hour. Melts were poured into a Pt mold creating 32 mm diameter glass disks. Na2O was determined by atomic absorption spectrometry (AAS), where dried samples were treated with HF acid, evaporated, and then dissolved in HCl-KCl solution. Trace elements were analyzed by inductively coupled plasma- mass spectrometry (ICP-MS) following a combined lithium metaborate fusion, multiacid dissolution technique.
The dike forms positive irregularly features and represented by a symmetrical, elliptical, elongated or circular plugs, domes and hills that varies in their sizes (
Field investigations of the MQD indicate presence of thin basaltic flows intercalated sometimes with pyroclastic material. Highly weathered basaltic bombs and crustal inclusions are common. Some parts of MQD plugs have no obvious chilled margin, whereas the wider parts of the MQD have more than 10 m macroscopic pale grey in color chilled zone. The basaltic rocks in the study area are variable in thickness and weathering character istics from dense to vesicular basalt. Dense basalt is with smooth surface, showing black to brown and greenish color. The basalt boulders range in size from 0.5 m to 3 m with irregular shape. Vesicles are cylindrical, elon-
Samples | N | E | Remarks | Elevation |
---|---|---|---|---|
QM-1 | 29 31.680 | 35 48.010 | 15 m wide, 5 m high, 300 m long | 869 m |
QM-2 | 29 29.534 | 35 49.998 | 5 m wide, 2 m high, 14 m long | 889 m |
QM-3 | 29 28.982 | 35 50.503 | 20 m wide, 30 m high, 100 m long | 858 m |
QM-4 | 29 28.033 | 35 51.388 | 20 - 30 m wide, 50 m high, 100 m long | 852 m |
gated and oval in shape and filled sometimes with either calcite or silica. Clustered vesicles up to 2 cm in size are present. Exfoliation of basalt boulders up to 5 m in diameter is common.
The MQD Megascopic study indicates that the basalt is fine to medium-grained, porphyritic and amygdaloidal. Dolerite is noticed in one locality which is composed of olivine phenocyrsts up to 0.5 cm in diameter. Plagioclase, pyroxene, olivine among other minerals are the essential minerals of the dike. Field studies show that the MQD hosts wide spectrum of upper crust inclusions with different diameters including different types of sandstone and limestone, phosphatic sandstone, quartzite and marble representing the stratigraphic column in the study area. The MQD intruded paleozoic and cretaceous sedimentary rocks as subvertical basaltic plugs (
The petrographical study of the basaltic rocks within MQD typically shows phyric, porphyritic, vitrophyric and locally glomerophyritic textures that dominated mainly by plagioclase and clinopyroxene and rare olivine and set in a matrix of plagioclase, pyroxene, brown glass and opaque phases (
basalts displays intergranular and seriate textures with a pilotaxitic texture which is mainly represented by acicular plagioclase laths, prismatic to anhedral pyroxene crystals, and some intergranular glass and magnetite (opaque) phases.
Plagioclase crystals are the predominant phase forming more than 45% of the basaltic phenocyrsts and microphenocyrsts. They occur in variety of forms and sizes, including subhedral to euhedral in shape and ranges in sizes from medium to fine phenocyrsts and to very fine acicular to needle microlites in the groundmass (
Clinopyroxene (cpx) is the second dominant phase with concentrations of about 30% - 35% that are generally represented by subhedral to anhedral forms of dusty beige to pale brown (probably Ti-rich) phenocryts. Most of the pyroxene crystals are corroded and superimposed by either plagioclase or replaced at the rims by Fe-Ti oxides. Some pyroxene is twinned. Finer size of the clinopyroxene crystals are confided to the groundmass. Very few pyroxene crystals show ophitic texture but mostly they are sub-ophitic with plagioclase.
Olivine (up to 5%) is anhedral to subhedral. It occurs mainly as micro-phenocryts that are slightly altered to iddingsite and chlorite in both rims. Some of the olivine crystals are replaced by dark yellowish brown mineral that could be saponite or iddingsite. Clinopyroxene and olivine phenocyrsts show disequilibrium textures such as reaction/resorbed rims in the forms of corroded ends.
The paragenetic sequence shows that olivine was the first phase to be crystallized and coexist with pyroxene at sometime, while pyroxene continues crystallization. Plagioclase might have crystallized in contemporaneous and later than the pyroxene. The ophitic and supophitic textures of plagioclase and pyroxene point to near-equi- librium conditions of coexisting plagioclase and pyroxene phases close and beyond cotectic crystallization point, under more static conditions of the magmatic melt. Some of plagioclase phenocryts cross cut both clinopyroxene and olivine rims which indicate that plagioclase continue crystallizing after olivine and pyroxene.
The accessory phases are mainly magnetite, ilmenite (Fe-Ti oxide), and +/− apatite and rarely spinel. They mainly occur as subhedral grains, although some of the fine iron oxides are elongated and filling intersertal spaces between phases. They may exhibit dendritic shapes (
Glass mainly yellowish-brown in color, is interspersed among the microcrystalline grains as a result of incomplete crystallization. They usually show a hyalopilitic texture, although the glass is usually replaced. Calcite amygdules are slightly common in the samples. The outer rind of some of glassy is a few millimeters thick and was produced by quenching of the hot magma against cold surface. Few are embedded sparse phenocyrsts of Fe- Ti oxide and +/− olivine that crystallized before extrusion on the surface. Few vesicles were observed and were partly filled by very fine cryptocrystalline secondary silica and rimmed by dark opaque Fe-Ti oxides. Vesicles increases within the more porphyritc basalt.
A few possible lithophysae inclusions of high silica content were noticed. One grain is ~7 mm in length and is angular. It is composed of very fine matrix of amorphous silica that includes coarser quartz grains (~1 mm) of rounded to semi-rounded in shape. This litho fragment is highly fractured. They are surrounded by feathery rim crystals of cryptocrystalline clinopyroxene and iron oxides that are apparently nucleated heterogeneously around the inclusion as the result of its reaction with the silica under saturated melt, during the rapid quenching and substantial under cooling of the melt (
Porphyritic textures observed among the sections represent polygenetic of these basaltic rocks that probably involves a multi-stage cooling history for the melt. The presence of a variety of plagioclase shapes and sizes may indicate different stages in the cooling history but rather more likely to be affected by the sudden changes in the degree of super cooling (∆T) or in the number of nuclei [
Inclusions from different rock types are present. Some evidences of heating of these inclusions were observed.
They are subjected to alteration by annealing. The inclusions as they transported to the surface by basaltic melt, they have been heated and altered in different ways. The presence of these inclusions gives some evidence of the composition of the crust below the MQD.
Sandstone and Quartzite inclusions are composed of fine- to medium-grained, poorly sorted, rounded to sub-rounded highly fractured quartz grains embedded in clay matrix. Sometimes clay minerals are laminated. In some cases, the matrix which supported the grains is made of microcrystalline calcite. Opaque minerals occur as black spots in some places. Ferruginous sandstone is with abundant iron oxide/hydroxide is also present.
Marble is made of recrystallized spary calcite with well developed druzy and mosaic texture. Calcareous phosphatic quartzite inclusions exhibit fine-grained, rounded, well sorted and fractured quartz grains. The major constituents are shell fragments, phosphatic pellets and apatite. Phosphatic limestone inclusions with packstone texture where calcite forms about 30%. They are composed of black color phosphatic pellets due to heating, partially silicified, intraclasts of micrite, shells, bone fragments that are made up of cellophane (isotropic phosphate).
Micro-granite inclusions are characterized by presence of quartz, orthoclase, plagioclase and biotite that are highly weathered to sericite. Secondary calcite fills the spaces between grains and cavities.
The results of major and trace element chemistry of volcanic rocks and inclusions is listed in
Al2O3 contents in the MQD samples vary from 12.23 to 14.93 wt%, meanwhile CaO varies between 6.82 and 9.05 wt%.
BD1 | BD2 | BD3 | BD4 | BD5 | BD6 | BD7 | BD8 | BD9 | BD10 | BD12 | DX2* | DX3* | DX5* | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Oxides % | |||||||||||||||
SiO2 | 49.28 | 49.32 | 50.30 | 51.48 | 49.30 | 48.92 | 49.44 | 51.78 | 51.28 | 51.59 | 50.09 | 67.90 | 76.30 | 73.00 | |
TiO2 | 2.42 | 2.83 | 2.74 | 2.95 | 2.56 | 3.37 | 3.36 | 2.92 | 2.93 | 2.90 | 3.20 | 2.00 | 1.00 | 0.90 | |
Al2O3 | 13.46 | 12.80 | 12.90 | 12.80 | 13.20 | 14.93 | 14.40 | 12.23 | 12.63 | 12.82 | 14.11 | 12.50 | 8.60 | 10.60 | |
Fe2O3 | 2.45 | 2.80 | 2.80 | 3.50 | 2.80 | 3.45 | 2.60 | 2.30 | 4.23 | 3.44 | 2.22 | 7.30 | 5.10 | 4.90 | |
FeO | 9.34 | 9.87 | 9.68 | 8.90 | 9.87 | 10.23 | 8.96 | 10.30 | 8.90 | 9.23 | 10.23 | 1.23 | 2.23 | 2.12 | |
MnO | 0.18 | 0.23 | 0.17 | 0.21 | 0.18 | 0.22 | 0.17 | 0.22 | 0.22 | 0.20 | 0.16 | 0.05 | 0.06 | 0.07 | |
MgO | 6.96 | 7.56 | 6.97 | 6.39 | 8.79 | 6.48 | 5.96 | 5.88 | 5.51 | 6.60 | 7.90 | 0.90 | 1.70 | 2.10 | |
CaO | 9.05 | 7.87 | 8.88 | 6.82 | 7.81 | 7.93 | 7.65 | 7.47 | 7.10 | 7.20 | 7.60 | 1.10 | 1.50 | 1.30 | |
Na2O | 2.34 | 2.88 | 2.12 | 2.75 | 2.23 | 2.88 | 3.12 | 2.81 | 2.77 | 3.12 | 2.89 | 1.20 | 2.10 | 1.70 | |
K2O | 0.59 | 0.48 | 0.55 | 0.59 | 0.48 | 0.67 | 0.68 | 0.69 | 0.48 | 0.40 | 0.50 | 0.70 | 0.80 | 1.90 | |
P2O5 | 0.50 | 0.53 | 0.54 | 0.53 | 0.74 | 0.59 | 0.59 | 0.82 | 0.78 | 0.75 | 0.58 | 0.11 | 0.12 | 0.15 | |
SO3 | 0.35 | 0.45 | 0.35 | 0.54 | 0.33 | 0.54 | 0.65 | 0.54 | 0.55 | 0.56 | 0.65 | 0.68 | 0.66 | 0.58 | |
LOI | 2.10 | 1.50 | 0.90 | 2.00 | 0.90 | 0.20 | 1.90 | 1.60 | 1.80 | 1.10 | 0.50 | 3.60 | 0.50 | 1.00 | |
Total | 99.02 | 99.12 | 98.90 | 99.46 | 99.19 | 100.41 | 99.48 | 99.56 | 99.18 | 99.91 | 100.63 | 99.27 | 100.67 | 100.32 | |
Mg# | 50.74 | 51.43 | 49.88 | 49.81 | 57.83 | 46.68 | 47.90 | 44.11 | 46.11 | 49.71 | 51.63 | ||||
Trace element (ppm) | |||||||||||||||
Ni | 91 | 88 | 98 | 100 | 87 | 101 | 96 | 96 | 97 | 86 | 86 | 60 | 51 | 70 | |
Cr | 110 | 112 | 127 | 115 | 110 | 115 | 129 | 118 | 120 | 130 | 110 | 91 | 71 | 91 | |
V | 94 | 120 | 130 | 99 | 135 | 128 | 129 | 100 | 113 | 114 | 147 | 45 | 4 | 9 | |
Cu | 50 | 79 | 780 | 1589 | 650 | 780 | 188 | 1069 | 1145 | 2600 | 83 | 1053 | 236 | 298 | |
Zn | 91 | 160 | 166 | 174 | 187 | 153 | 125 | 157 | 163 | 209 | 117 | 67 | 17 | 48 | |
Pb | 15 | 44 | 54 | 124 | 121 | 61 | 26 | 80 | 99 | 178 | 13 | 95 | 20 | 39 | |
Sr | 450 | 480 | 470 | 441 | 486 | 517 | 468 | 459 | 439 | 472 | 499 | 230 | 351 | 160 | |
Ba | 12 | 22 | 43 | 17 | 55 | 15 | 5 | 50 | 14 | 126 | 39 | 23 | 371 | 56 | |
Zr | 500 | 411 | 434 | 436 | 543 | 542 | 578 | 428 | 429 | 409 | 391 | 612 | 556 | 568 | |
Nb | 18 | 23 | 25 | 27 | 27 | 29 | 27 | 25 | 27 | 24 | 20 | 30 | 18 | 22 | |
Y | 22 | 25 | 22 | 24 | 23 | 27 | 26 | 25 | 26 | 24 | 24 | 22 | 27 | 24 | |
La | 21 | 27 | 23 | 27 | 28 | 27 | 25 | 28 | 26 | 24 | 21 | 42 | 56 | 38 | |
Ce | 35 | 26 | 30 | 40 | 32 | 33 | 37 | 36 | 42 | 32 | 27 | 79 | 89 | 79 | |
Co | 37 | 26 | 27 | 30 | 29 | 34 | 29 | 28 | 31 | 24 | 28 | 22 | 5 | 32 | |
Li | 51 | 25 | 34 | 15 | 24 | 17 | 34 | 16 | 17 | 36 | 16 | 15 | 14 | 6 | |
Be | 10 | 11 | 21 | 11 | 31 | 14 | 15 | 17 | 10 | 13 | 15 | 4 | 2 | 2 | |
As | 40 | 123 | 154 | 117 | 89 | 64 | 96 | 95 | 119 | 73 | 49 | 46 | 44 | 57 | |
Sn | 8 | 29 | 76 | 91 | 65 | 37 | 55 | 43 | 53 | 144 | 77 | 65 | 17 | 21 | |
W | 3 | 4 | 3 | 6 | 5 | 4 | 1 | 5 | 2 | 4 | 2 | 6 | 5 | 5 |
In the binary diagram (
The primitive mantle normalized trace elements is shown in
Early Miocene NW?SE dikes are well known from Jordan [
extension controlled melting where there was dominated by lithospheric trace element/isotopic signatures [
The NW-SE trending Mudawwara-Quwayra Dike (MQD) is a very important dike in terms of volcano-tectonic evolution of the south Jordan. The MQD is controlled by a major NW-SE trend fault system. They volcanic activity which is related to eruption of the MQD is attributed to regional phase of magmatism in Jordan and Saudi Arabia. This phase is probably the peripheral extension of a large magmatic event widely exposed in the Red Sea realm.
The MQD intruded Paleozoic and Cretaceous sedimentary rocks as sub-vertical basaltic plugs, extending for more than 100 km. This dike forms positive irregularly features and is represented by symmetrical, elliptical, elongated or circular domes and hills up to 20 m high, 150 m length and 100 m wide. Field evidences indicate the presence of thin basaltic layers intercalated with pyroclastic materials, volcanic bombs and inclusions of different size and lithology, including limestone, sandstone, phosphate, quartzite, and marble.
The petrographical and geochemical affinities of the MQD are unique if compared with intraplate basalts of Jordan and Saudi Arabia. The MQD is sublkaline basalt with high silica content and low alkalis. The unique petrographical and geochemical affinities of the MQD are most probably related to presence of abundant sedimentary inclusions which are partially assimilated by the ascending magma.
HaniAlnawafleh,KhaledTarawneh,KhalilIbrahim,KhitamZghoul,AwadTiti,RamiRawashdeh,KhaledMoumani,AhmadMasri,11, (2015) Characterization and Origin of the Miocene Mudawwara-Quwayra Basaltic Dike, Southern Jordan. International Journal of Geosciences,06,869-881. doi: 10.4236/ijg.2015.68071