5-1-TMI and RTP Magnetic Map
The TMI map (Fig. 3) reveals that, the TMI-values are ranging from − 100 nT to 130 nT. These values are known the existence of various sources of numerous configurations, depths and trends. Magnetic values can be shown into various colors, as indicated by their amplitudes. First, the blue and its degrees, ranging from − 40 nT to -100 nT, is categorized by low magnetic anomalies, which extended and striking in the NE–SW and NW-SE directions. The intermediate-scale colors, ranging from 0 nT to -40 nT, their majority cover the southwestern, central and western parts. Besides, the high amplitudes, which range from 0 nT to 130 nT, cover the midpoint of the examined area and strike in the NE–SW trend (Fig. 3).
The TMI data were reduced to RTP, by using a 2-D wave number filter and utilizing the known inclination vector and declination of the study area (Youssef, 2010). It was used to overcome the inclination problems. On this map, the magnetic anomalies were centered directly above the causative sources (Baranov, 1957& 1975; Baranov and Naudy, 1964 and Bhattacharyya, 1965 & 1967). The RTP magnetic map (Fig. 4) can be divided into two zones, according to the magnetic characters, frequencies and amplitudes of the magnetic readings, as well as the shapes of the inherited magnetic anomalies The first zone (Z1) contains two-sub zones (Z1a and Z1b), that represented the high amplitude and dense frequency of magnetic field. Z1a is represented by mafic or ultramafic igneous rocks, unexposed on the surface, which lie at many parts, as the southeastern, northeastern and northwestern, as well as the westcentral parts of the studied area. These mafic and ultramafic igneous rocks are considered as the main source of the acidic magma (granitic rocks) and overlapped through the basal sandstone in the studied area. Meanwhile, the Z1b sub-zone is related to sets of basic dykes at the northwestern, eastcentral and southeastern parts, and trending NNE-SSW direction (parallel to the Gulf of Aqaba). The high magnetism of Z1b is related to the magnetic iron oxides, which occurred in the hydrothermal solutions invading these rocks through the faults and fractures, which dissecting these country rocks upward.
The second zone (Z2) is mostly striking in the NNE-SSW and NNW-SSE directions in the central part of the prospected area. Z2 has a broad contour shape, with low amplitude, that can be interpreted as basement complex deeper in this zone than the adjacent shallower zone. This zone can be easily considered as a downthrown block and it’s bounded by a system of faults, that dissected the area in the NNE-SSW direction. Z2 zone is located at the southwestern corner, as well as the southeastern and northcentral parts of the map. A part of this zone (Z2b) is recorded over the basal sandstone and alluvial sediments during the magmatic intrusions episodes.
5-2- Vertical and Horizonal Derivatives, and Analytical Signal method (As)
The first target of theses derivatives and analytical approaches is for the location of the basaltic igneous rocks in the subsurface. Figures (5, 6 and 7) show the derivatives and analytical signal maps, which are used to define the local contacts of the basic igneous rocks in the subsurface, as Z1 (Z1a and Z2b) and Z2.
Figure (5) shows the VDR map of the ground RTP magnetic data. Z1a features (of the northwestern, northeastern and southeastern parts) represent the locations of large invasive magma in the subsurface, while the Z1b anomalies at the eastern part, treading NNE-SSW) are the boundaries of intrusive basic dykes in the subsurface, that represented by positive anomalies. Moreover, the negative anomalies, such as the Z2 sub-zones, are clearly shown at the northeastern and southeastern parts of the study area. Figures (6) exhibits the THDR map of the ground RTP magnetic data, that emphasis the locations of positive and negative bodies in either the Z1 (Z1a and Z2b) and Z2 zones.
Figure (7) reveals the AS map of the magnetic data. This map designates that, the high-values of the AS are detected at the northwestern, eastcentral and southeastern parts, as well as few of the peak-values at the southwestern part of the investigated area. The lineament pattern resulted from the AS map is in the NNE–SSW trend, in accordance with the Gulf of Aqaba rifting.
5-3- SPI or LWM Depth Estimation
The second target is the depth estimation of the basaltic igneous rocks in the subsurface by the SPI or LWM technique. Figures (8) shows the depth evaluation, using the SPI or LWM approach, that demonstrates the depth ranges of the shallow structures, up to -20 m and for the deeper structures, that lie between − 50 m and − 120 m. The basement depths of the magnetic sources, from the SPI or LWM-technique, shown for the area (Table 1). Table 1 reveals that, the depths of shallow structures (Z1a and Z1b) and the depths of deeper structures (Z2) are also extended down to -100 m.
Table 1
The interpreted depth results of the different magnetic bodies and basic dykes for the investigation area, using the SPI or LWM.
Zone
|
Location
|
No. of data
|
A simple
Description
|
Depth Range(m)
|
Mean depth
(m)
|
Standard Deviation
|
CV (%)
|
Minimum
|
Maximum
|
Z1
|
Z1a
|
North western
|
98
|
Shallow Positive magnetic body
(30 to 150 nT)
|
-6
|
-102
|
-33
|
22
|
65
|
North eastern
|
21
|
-7
|
-99
|
-33
|
20.8
|
61.7
|
South eastern
|
24
|
-7
|
-26
|
-12
|
4.6
|
36.2
|
Z1b
|
North western
|
13
|
Shallow Positive magnetic Basic dike
(30 to 120 nT)
|
-6
|
-21
|
-11
|
4.6
|
40.3
|
Z1c
|
North western
|
55
|
-6
|
-34
|
-16
|
6.5
|
40.1
|
Z1d
|
Central
|
47
|
-7
|
-41.8
|
-18
|
6.9
|
37.4
|
Z1e
|
North eastern
|
65
|
-7.4
|
-33.7
|
16.6
|
5.6
|
35.1
|
Z1f
|
South eastern
|
|
-7
|
26.6
|
-14
|
4.7
|
33.1
|
Z2
|
|
Central eastern
|
126
|
Deeper negative magnetic body
(-50 to
-100 nT)
|
-6.6
|
-141
|
-38.3
|
27.5
|
71.9
|
|
South eastern
|
138
|
-6
|
-103
|
-29
|
23.4
|
80.1
|
|
South Western
|
17
|
-7.4
|
-49
|
-17.6
|
9.5
|
53
|
5-4-Tilt angle edge detection
The third aim is to infer the edge detection of the basaltic igneous dykes in the subsurface by the tilt angle (TDR), Theta map, ETilt and ETHDR maps. Figures (9) shows the tilt angle map, which is used to define the edges of the horizontal and vertical contacts of the basic igneous dykes in the subsurface section, with symbolizes for their locations. The Z1a locations and Z1b locations are appeared clearly. Also, the deeper negative magnetic bodies are shown on the TDR map (Fig. 9). Theta map (Fig. 10) illustrates shows the sensitivity of this approach to the deeper bodies, rather than the shallower ones, where the Z2 bodies appear clearer in their locations than the Z1 bodies. Figures (11) shows the Etilt map as shallow positive magnetic bodies (Z1a), shallow positive basic dykes (Z1b) and deeper negative magnetic bodies (Z2), as sharp edges over their locations. Figures (12) reveals more enhanced total horizontal derivatives than of the Etilt (ETHDR), that comprises more edge detection to all the implied bodies, either shallower or deeper in the study area.
5-5- 2.5 D forward modelling
Finally, the diligence to determine the different depth ranges across the basic intruded dykes and their surroundings in the east central part of the study area. A 2.5 D geomagnetic model has been done, as forward modelling, in which the locations of the models are shown in the RTP map (Fig. 13A). The depths to the basement surface and the basement relief of the models are ranging from 15 to 55 m in a magnetic model (Fig. 13B). The magnetic susceptibility of the sedimentary cover is assumed 0.002 cgs for the surrounding of the basic dykes, while the magnetic susceptibility of the basic dykes is 0.01 cgs.
5-6- Structural Lineaments Interpretation
The study area is mainly represented by varying trends and locations. Consequently, it is expected that, the RTP, VDR, THDR, AS, TDR, Etilt and ETHDR maps (Figs. 4, 5, 6, 7, 11 and 12, respectively) should reflect the gross structural pattern of the study area. The magnetic signatures of the various magnetic maps show various significant structural elements, such as the different types of faults, hidden dykes (Fig. 14) and exposed dykes (Fig. 2). Statistical analysis of the structural lineaments of the study area resulted in the number, length, and orientation of the interpreted lineaments. The statistical analysis shows that most of the well-developed structural lineaments are oriented mostly to NW, NE and N-S.
This significant structural frame is responsible for the tectonic development of the geologic setting of the area. The interpreted trends are represented by peaks exceeding the significant frequency on the rose diagram. The interpreted trends were grouped into three main categories, according to their directions from east to west. The NW-SE, NE-SW and N-S trends were proved to be significant, as far as the area under study is considered.
The NW (Gulf of Suez- Red Sea) trend is developed as a strong major trend. It was interpreted by Meshref, (1971) and Meshref, et, al, (1990), as one of the fracture systems that resulted from the forces of a couple associated with the Red Sea. In the study area, F1, F2 and F3 of the detailed geological map (Fig. 2) represent the main trend of the Gulf of Suez. The second major trend on all the maps, either at the near-surface or at the deep-seated levels is the NNE-SSW (Gulf of Aqaba) trend, which interpreted by Garfunkel, (1970). In this study, F4, F5 and F6 of the detailed geologic map (Fig. 2) represent the main trend of the Gulf of Aqaba. The last one, the N-S (Meridional) trend comes in the third order, as a major trend in the study area. The fault system of this trend is dislocated by the second order elements, which are directed to the WNW-ESE. Ghanem (1968) described the faults trending in the N-S direction as being developed after the emplacement of the Late Orogenic plutons.
The present authors, however, postulated model of northeastern Egypt during the Miocene, with special emphasis on the Gulf of Suez (Fig. 15). In this model, a NNW-SSE main tangential compression stress from southern Europe is acting on northern Africa, consequently on northern Egypt, with the start of the Miocene. This stress together with its southern antistress, created two complement y sets of first order shears (one NW-SE right lateral for Gulf of Suez and one NNE-SSW left lateral for Gulf of Aqaba). As a reaction of compressional stress, a tensile stress, with its anti-stress, area initiated in an ENE-WSW trend and formed two other sets of second order shears (one ESE-WNW right lateral and one NE-SW left lateral). The four sets of first and second regional shear faults are intersected at point. Nearly at Shadwan Island, the center of most of the strong earthquakes of the Red Sea and of the two gulf (Abu El-Ata, 1981).
It is worth mentioning that, with respect to the second order right lateral shears, there are four mega shears detect crossing the eastern (Abu Masarib and Wadi Al-Hamd shears) and Western (Duwi and Wadi Hafafit shears) coast of the Red Sea. There are other three Mega-shears (Wadi Araba, Ras Shukheir and Ras El-Bahar shears) related to the second order left lateral shears, and also delineated at the western coast of the Gulf of Suez.
Secondary compressional stress acting in the NW-SE direction is created giving by the same way of the third and fourth order shears, as shown by Moody and Hill, (1956) and modified by Badgley (1965),Uplifting occurred at the end of the Miocene, causing vertical movements along pre-established shear faults, giving rise to normal movements on the same faults, Accompanied with this later uplifting, two sets of normal faults are formed directly as a result of the principle and secondary compressional stresses and perpendicular to them. Among these orders of magnitudes, types of faults and trends of elements, it is possible to find an interpretation for any structural feature in this part of the con