Your SlideShare is downloading. ×
The Geology Of the Dibba Zone Durham University
Callum Thurley 1 of 50
The Geology of the Dibba Zone, Hajar Mountains, Uni...
The Geology Of the Dibba Zone Durham University
Callum Thurley 2 of 50
Abstract
The Dibba Zone studied shows a North East ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 3 of 50
Contents
Abstract – P.1
Acknowledgments – P.4
Intro...
The Geology Of the Dibba Zone Durham University
Callum Thurley 4 of 50
ii) Lithology 2 – Serpentinite – P.23-4
i) Mineralo...
The Geology Of the Dibba Zone Durham University
Callum Thurley 5 of 50
Acknowledgements
This project could not have been c...
The Geology Of the Dibba Zone Durham University
Callum Thurley 6 of 50
Introduction
This study was carried out in July - A...
The Geology Of the Dibba Zone Durham University
Callum Thurley 7 of 50
This chapter will describe all of the sediments in ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 8 of 50
The dark colour of the rock on a fresh surface is a...
The Geology Of the Dibba Zone Durham University
Callum Thurley 9 of 50
between this lithology and wadi conglomerates were ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 10 of 50
reduction in the oxygen minimum zone, a rise in th...
The Geology Of the Dibba Zone Durham University
Callum Thurley 11 of 50
Sub-lithology (i)
Observations:
Starting from the ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 12 of 50
Sub-lithology (ii)
Observation:
Above this litholo...
The Geology Of the Dibba Zone Durham University
Callum Thurley 13 of 50
beds are not consistent with their thicknesses, th...
The Geology Of the Dibba Zone Durham University
Callum Thurley 14 of 50
slope instability and can cause turbidity currents...
The Geology Of the Dibba Zone Durham University
Callum Thurley 15 of 50
conchoidal fracture and are composed of quartz. Th...
The Geology Of the Dibba Zone Durham University
Callum Thurley 16 of 50
Sub-lithology (v)
Observation
The following lithol...
The Geology Of the Dibba Zone Durham University
Callum Thurley 17 of 50
Sub-lithology (vi)
Observations
The top of the seq...
The Geology Of the Dibba Zone Durham University
Callum Thurley 18 of 50
Figure 8 (Sedimentary Log of the Turbidite Smarl /...
The Geology Of the Dibba Zone Durham University
Callum Thurley 19 of 50
There may have been a sustained period of high pro...
The Geology Of the Dibba Zone Durham University
Callum Thurley 20 of 50
Interpretation
This is another deep-water facies C...
The Geology Of the Dibba Zone Durham University
Callum Thurley 21 of 50
impermeable rocks due to intense heating and there...
The Geology Of the Dibba Zone Durham University
Callum Thurley 22 of 50
Chapter 2 - Igneous and Metamorphic Geology
Some k...
The Geology Of the Dibba Zone Durham University
Callum Thurley 23 of 50
Harzburgite is a type of peridotite that forms whe...
The Geology Of the Dibba Zone Durham University
Callum Thurley 24 of 50
Lithology 2 - Serpentinite
Observations
This litho...
The Geology Of the Dibba Zone Durham University
Callum Thurley 25 of 50
 10% - Dark red/brown elongate mineral, with a wa...
The Geology Of the Dibba Zone Durham University
Callum Thurley 26 of 50
The Contact between Serpentinite and Harzburgite.
...
The Geology Of the Dibba Zone Durham University
Callum Thurley 27 of 50
the anhydrous Harzburgite by seawater depends on p...
The Geology Of the Dibba Zone Durham University
Callum Thurley 28 of 50
Lithology 3 - Mélange
Observations
This lithology ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 29 of 50
mega breccia. This lithology may also have been se...
The Geology Of the Dibba Zone Durham University
Callum Thurley 30 of 50
Chapter 3 – Structural Geology
The Dibba Zone has ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 31 of 50
Figure 14(sketches to show the types of normal fau...
The Geology Of the Dibba Zone Durham University
Callum Thurley 32 of 50
Interpretation
The fact that normal faults were on...
The Geology Of the Dibba Zone Durham University
Callum Thurley 33 of 50
Thrust Faults
Observations
The main type of struct...
The Geology Of the Dibba Zone Durham University
Callum Thurley 34 of 50
the relationship with contours would be a cross cu...
The Geology Of the Dibba Zone Durham University
Callum Thurley 35 of 50
Emplacement of the Samail Ophiolite
The Samail Oph...
The Geology Of the Dibba Zone Durham University
Callum Thurley 36 of 50
The area is near the most northerly part where the...
The Geology Of the Dibba Zone Durham University
Callum Thurley 37 of 50
Folding – Ductile Deformation
Observations
The stu...
The Geology Of the Dibba Zone Durham University
Callum Thurley 38 of 50
a shale. The Chert was also
regularly seen folded,...
The Geology Of the Dibba Zone Durham University
Callum Thurley 39 of 50
Figure 20 of STERONETS
The Geology Of the Dibba Zone Durham University
Callum Thurley 40 of 50
Deformation of sediments
Observations
The Green Ch...
The Geology Of the Dibba Zone Durham University
Callum Thurley 41 of 50
of the mapping area, (Figure 21), which would mean...
The Geology Of the Dibba Zone Durham University
Callum Thurley 42 of 50
horizons/planes.Therefore allowing faulting and de...
The Geology Of the Dibba Zone Durham University
Callum Thurley 43 of 50
Figure 22, (A Field photograph, showing the sense ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 44 of 50
speculated that this was once an ocean continent t...
The Geology Of the Dibba Zone Durham University
Callum Thurley 45 of 50
Oblique Slip faults
Observations
A few strike slip...
The Geology Of the Dibba Zone Durham University
Callum Thurley 46 of 50
Mélange, and shear sense indicators
Observations
C...
The Geology Of the Dibba Zone Durham University
Callum Thurley 47 of 50
Chapter 4 – Economic Potential
Hydrocarbon Potenti...
The Geology Of the Dibba Zone Durham University
Callum Thurley 48 of 50
Chapter 5 - Geological History
The geological hist...
The Geology Of the Dibba Zone Durham University
Callum Thurley 49 of 50
Cenozoic
The most recent form of deformation is st...
The Geology Of the Dibba Zone Durham University
Callum Thurley 50 of 50
Bibliography
1. Alleman, F., and Peters, T. 1972, ...
The Geology Of the Dibba Zone Durham University
Callum Thurley 51 of 50
Geological Society of London,issue 11, ISBN: 06320...
Upcoming SlideShare
Loading in...5
×

Dissertation d ibba_thurley_ct

1,264

Published on

Published in: Technology, Education
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
1,264
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
13
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Transcript of "Dissertation d ibba_thurley_ct"

  1. 1. The Geology Of the Dibba Zone Durham University Callum Thurley 1 of 50 The Geology of the Dibba Zone, Hajar Mountains, United Arab Emirates. Callum Thurley Department of Earth Sciences Durham University 2012/13 This dissertation is submitted in partial fulfilment of the requirements of the degree “Geology.”
  2. 2. The Geology Of the Dibba Zone Durham University Callum Thurley 2 of 50 Abstract The Dibba Zone studied shows a North East to South West trending section consisting of deep-water facies sediments ranging in age from the late paleozoic and Mesozoic. These units are comprised of a carbonate black shale (Mayah Formation), inter-bedded Chert and Carbonate Smarls (Nayid Formation), bedded fine-grained Chert and Glauconitic Chert (Sid‟r Formation). The depositional environment for these rocks is likely to be in deep water, at a very similar depth to the lysocline, in order to produce carbonate and chert interchanges at a high frequency. These lithologies have undergone at least three stages of structural deformation, firstly by extension from a spreading ocean during the evolution of the Tethys in the Paleozoic and early Mesozoic. Secondly compressional deformation from the emplacement of the Hajar Ophiolite in the late Cretaceous, which lead to thrusting with easterly dipping faults, and tectonic transport of the sediments from East to the West. Thirdly, more recently and even current day strike slip deformation from the Dibba Fault, which shows a sinistral offset trending approximately North East to South West through the centre of the map. The emplacement of the Hajar Ophiolite occurred 65-70Ma by marginal basin spreading, and has been interpreted as an oblique obduction, due to lithological heterogeneities in the Green Glauconitic Chert (Sid‟r Formation).Partial serpentinization of the ophiolitic harzburgite, around its perimeter suggests that the hydration of the harzburgite and the two main thrust faults are closely related.
  3. 3. The Geology Of the Dibba Zone Durham University Callum Thurley 3 of 50 Contents Abstract – P.1 Acknowledgments – P.4 Introduction – P.5 Chapter 1 – Sedimentology - P. 6-20 i) Lithology 1 – Mayah Formation P. 6-7 ii) Lithology 2 – Sidr Formation P 7-9 iii) Lithology 3 - / Nayid Formation P. 9 -17 i) Sub-lithology 1 – P. 10 ii) Sub-lithology 2 – P. 10-2 i. Likely cause of Turbidity Currents – P. 12 iii) Sub-lithology 3 – P. 13 iv) Sub-lithology 4 – P..13-4 v) Sub- lithology 5 – P.15 vi) Sub-lithology 6 – P. 15-6 vii) Overall Interpretation Nayid Formation – P.16 i. Sedimentary Log of Nayid Formation – P17 iv) Lithology 4 - Brown Chert –P. 17-8 i. Possible formation hypotheses – P.17-18 v) Lithology 5 – Dendritic Chert – P. 18-9 vi) Lithology 6 – Wadi Conglomerate – P.19-20 vii) Chapter Conclusion – P.20 Chapter 2 – Igneous & Metamorphic Geology – P. 21-8 i) Lithology 1 – Harzburgite – P.21-2 i) Mineralogy from field observation – P.21 ii) Mineralogy under thin section – Appendix i
  4. 4. The Geology Of the Dibba Zone Durham University Callum Thurley 4 of 50 ii) Lithology 2 – Serpentinite – P.23-4 i) Mineralogy – P.23-4 iii) The Contact between Serpentinite and Harzburgite – P. 25-6 i) Mineralogy from thin section – Appendix ii iv) Lithology 3 – Mélange – P.27-8 v) Lithology 4 - Serpentinized intrusion – P.28 Chapter 3 – Structural Geology P. 29-45 i) Normal Faults – P.29-31 ii) Thrust Faults – P.32-3 i) Emplacement of the Samail Ophiolite P. 33-4 iii) Folding - P. 36-38 a. Stereonets, Figure 20 – P. 38 iv) Deformation of Sediments – P. 39-41 i) Possible interpretations – P.39-40. ii) Further research – P. 41 v) Strike Slip Faults – P.41- 43 vi) Oblique Slip Faults – P. 44 vii) Mélange and shear sense indicators – P. 45 Chapter 4 – Economic Potential – P.46 i) Hydrocarbon Potential – P.46 ii) Mining Industry – P. 46 Chapter 5 – Geological History – P.47-48 Bibliography – P 49-50
  5. 5. The Geology Of the Dibba Zone Durham University Callum Thurley 5 of 50 Acknowledgements This project could not have been carried out without the generous help given by various individuals. Thanks must go to Ali Mohammed Ahmed Qasim, head of Fujairah Department of Natural Resources. The whole mapping project would not have happened without the permission he granted. The hard work put in by Vanessa Jackson in organising meetings with the government in order to obtain permission forms, which was greatly appreciated. Paul Oliver must also be thanked for providing us with accommodation and relief from the heat. Geological advice from two geologists (Sheikh Ali and Edgar Akobyan) from Crescent Petroleum was also extremely helpful. Whilst out in the field, the general welcoming attitude and kindness of farmers in the mountains by allowing us to park on their land and offers of water was very much appreciated. Gulf Rock must also be thanked for their support, help in obtaining permission forms, and advice on the geology of the region. Dr Mark Allen who agreed to be supervise the project, supported us and allowed us to undertake this mapping project and has given his advice on any geological questions. Joao Trabucho-Alexandre has also aided this project by giving his opinion on Sedimentological issues that were encountered. Ben Jackson must finally be thanked for being my field partner for the duration of the mapping project.
  6. 6. The Geology Of the Dibba Zone Durham University Callum Thurley 6 of 50 Introduction This study was carried out in July - August 2012 and focused upon the Dibba Zone in the Hajar Mountains located in the Eastern United Arab Emirates. The Dibba Zone is to the west of Ghub and Dahir, and approximately 15km away from the town Dibba (see Figure 1 below). This region has not been extensively studied, apart from one major study by the British Geological Survey in 2003-5 and another by Mike Searle in the 1970‟s. An integral geological feature of the Dibba Zone is the Semail Ophiolite, which was obducted 65-70Ma and stretches for approximately 600km along the east coast of the United Arab Emirates and Oman. It is the largest and best exposed ophiolite in the world (M.P.Searl et al 1990). Beneath and in front of the Semail Ophiolite are thrust sheets composed of distal deep sea sediments, the Hayibi and Hawasina Complexes. During the course of this study, the Hawasina Complex was observed, which is composed of distal Limestones, Calciturbidites and Cherts, all of which have been faulted and folded during the ophiolite emplacement. The specific mapping area is highlighted in red below (Figure 1). Figure 1 (Location Map, Google Earth Copywrite) Chapter 1 – Sedimentology 3km150km
  7. 7. The Geology Of the Dibba Zone Durham University Callum Thurley 7 of 50 This chapter will describe all of the sediments in the area stratigraphically, starting from the basal units and working upwards. Lithology 1 - Mayah Formation Observations This is the lowest stratigraphic unit in the area and is an organic rich carbonate (Figure 2). This rock is well sorted, grey in colour, on a weathered surface, dark in colour on a fresh surface and very fine grained. There is a distinct lack of evidence of past life, with no fossils present. This limestone is calcareous, evidenced by the classic honeycomb weathering patterns and pits seen on the surface, as well as the reaction documented upon the addition of hydrochloric acid. This lithology was also in beds that ranged from approximately 10cm to 1m in thickness. After observation under thin section, it was still apparent that this was very fine grained, with little other than a single spongue spicule (exoskeleton) being seen. Figure 2. (Locality 1, showing the carbonate black shale, North facing). Interpretation 10m
  8. 8. The Geology Of the Dibba Zone Durham University Callum Thurley 8 of 50 The dark colour of the rock on a fresh surface is an indicator that the rock has a high organic content. It is likely that it was deposited in a deep water environment under an area of high productivity in order to yield sufficient organic matter to produce such a dark colour, therefore it can be classified as a pelagic deposit. The organic matter is likely to be comprised of Coccolithopores and Foraminfera, which fell through the water column as “marine snow” (Mike Leeder,2011) or as faecal pellets from animals at higher trophic level. This paleoenvironment is also likely to be anoxic, as hinted by the presence of organic material, the lack of oxygen means that there are no scavengers, therefore preserving the organic material. Therefore this may be described as a Sapropel, which is a term commonly associated with organic rich lithologies. Due to the distinct lack of fossil assemblages (apart from a singular Spongue Spicule) it can be interpreted that this is a distal Carbonate, and may even be described as Carbonate Black Shale. The fact that this rock contains carbonate, and fizzes under the application of hydrochloric acid indicates that this rock was deposited above the Calcite Compensation Depth and is therefore likely to be a Lime Mudstone. This has been deposited on the outer carbonate ramp, as a calcareous ooze, which was then buried and lithified. Searle et al 1990 suggests that the area underwent high amounts of slumping due to steep slopes, however no evidence of this was seen in the mapping area. The Mayah formation is part of the Sumeini Duplex, which is found stratigraphically below the Hawasin Complex. Lithology 2- Sid‟r Formation Observations The second lithology, was very fine grained, friable, green in colour, did not contain any fossils and did not react upon the application of hydrochloric acid. This lithology was found running along the base of one wadi sampled within the study. Angular unconformities
  9. 9. The Geology Of the Dibba Zone Durham University Callum Thurley 9 of 50 between this lithology and wadi conglomerates were scattered all over the mapping area (Figure3). Figure 3(Field photograph showing an angular unconformity between folliated Green Chert and Wadi Conglomerate, South Facing). Interpretation This lithology was deposited in a low energy, deep-water environment, with a low rate of sedimentation. The green colour could be attributed to the mineral Glauconite, which also supports the hypothesis that there was a slow rate of sedimentation (H.S Chafetz & A Reid, Oct 2000). Due to the fineness of the grains and the fact that there was no reaction with hydrochloric acid, this is a distal silica rich lithology. This lithology is quite similar to the lithology found at the bottom of the Turbidite Smarl / Nayid Formation. Due to the lack of any Carbonate, the depositional environment was below the calcite compensation depth. Therefore the depositional environment was underneath an area of an upwelling of silica rich organisms (Radiolarians and Diatoms). This is likely to have led to there being a 70cm
  10. 10. The Geology Of the Dibba Zone Durham University Callum Thurley 10 of 50 reduction in the oxygen minimum zone, a rise in the calcite compensation depth and all Carbonate tests being dissolved prior to deposition. The upwelling of silicate organisms led to the deposition of silicate biogenic ooze, which underwent diagenesis and was lithified into a “Green Glauconitic Chert.” Lithology 3 - Calciturbidite Smarl Formation/ Nayid Formation The third lithology studied was a Calciturbidite sequence, consisting of a sequence of inter- bedded limestones, smarls, and thinly bedded cherts (see Figure 4). Each lithology within the sequence has been separated into sub-lithologies and observed and interpreted. It has been described chronologically from the bottom to top of the sequence. Figure 4. (Field photograph, showing the inter-bedded Chert and Carbonate, SW Facing). 15cm
  11. 11. The Geology Of the Dibba Zone Durham University Callum Thurley 11 of 50 Sub-lithology (i) Observations: Starting from the bottom of the sequence, there is a finely bedded (1/2cm thick) smooth green rock type and this contained approximately 10% muscovite crystals. Abundant dendrites were observed along the bedding planes of this lithology. This rock is also dark on a fresh surface, indicating that there is a high organic content. This rock did not react upon the application of hydrochloric acid.There is a distinct lack of any fossils within the rock and the only sedimentary structure shown is planar bedding. Interpretation: Due to the fact that there was no reaction upon the application of hydrochloric acid, and is very finely grained, this rock does not contain any carbonate and is a silicate, clay rich rock. The green colour of this lithology may be caused by the presence of the mineral Glauconite. The planar bedding, fineness of the grains and the potential presence of Glauconite indicate that this was deposited in a low energy marine environment, in deep wateron the continental shelf, with a low rate of sedimentation (H.S Chafetz & A Reid, Oct 2000). Dendrites are the result of a chemical change during diagenesis,, the dendrites that have been studied look as if they are composed from Manganese. It can also be hypothesised that this rock was deposited below the calcite compensation depth due to the lack of carbonate in the rock. This rock is Glauconitic Shale and it looks as if it could be similar to the Green Glauconitic Shale.
  12. 12. The Geology Of the Dibba Zone Durham University Callum Thurley 12 of 50 Sub-lithology (ii) Observation: Above this lithology there is a carbonate, which shows a slight coarsening upward sequence from fine silt to very fine sand. This lithology showed planar bedding, with the beds varying in thickness between 20-45cm. Once again this rock was black/dark grey on a fresh surface and therefore also has a high organic content. Chert nodules were observed within the beds of this carbonate, and thin beds of chert were present, which were not consistent in their thickness (Figure 4). Flutecasts petruded from the base of the beds as seen in Figure 5, with a rough orientation of 040°. (Figure 5).Some quartz overgrowths were also seen. Figure 5(A field photograph illustrating Flute Casts on the base of a carbonate bed.) Interpretation: The presence of Chert nodules in the carbonate may suggest that the deposition of this Carbonate was in a shallower water paleoenvironment. The reason for the Chert nodules may be diagenetic unmixing or segregation of originally mixed biogenic ooze. (João Trabucho Alexandre et al Nov 2011). From looking at Figure 3it can be seen that the Chert 30cm
  13. 13. The Geology Of the Dibba Zone Durham University Callum Thurley 13 of 50 beds are not consistent with their thicknesses, these look like pinch and swell structures (boudinage), which formed by extension, where the more competent rock (Chert) breaks up and is stretched into a long thin shape (Hans Ramberg,1955). Flute casts form from erosion by turbidity currents, which are vortexes of water during submarine avalanches which produce triangular shaped structures that open out in the direction of the paleocurrent(Figure 6). The presence of flute casts indicates that there were submarine avalanches, and the fact that this is a carbonate means that it may have been deposited on a Carbonate Turbiditic Apron. The presence of quarts overgrowths, means that diagenesis occurred in a warm wet, oxic environment. This can be called a fine grained Cherty Carbonate. Figure 6(Rose Diagram Showing flute cast orientations). Likely Cause of Turbidity Currents The likely cause of turbidity currents may be attributed to various processes. Build of sediment in one area can cause overloading and slope instability, which then leads onto submarine avalanches. It is quite likely that earthquakes in the region caused slope failure, and turbidity currents. Decay of organic material within these organic rich lithologies leads to the release of methane gas into the pore spaces in the rocks. This exerts a pressure, and eventually, this pressure may exceed the internal strength of the rock. This leads to
  14. 14. The Geology Of the Dibba Zone Durham University Callum Thurley 14 of 50 slope instability and can cause turbidity currents when the slope fails and the material fall downs as a submarine avalanche. Sub-lithology (iii) Observations: The next lithology in this sequence of beds is beige in colour and is extremely finely bedded on a millimetre scale, powdery and clay rich. This rock fizzed under the application of hydrochloric acid, has a dark grey colour on a fresh surface indicating once again a high organic content, and shows planar bedding. Suggesting that the environment of deposition was one of low energy. The entire bed of this marl is only approximately a metre in width. Interpretation: Due to the fineness of the grains, the presence of clay and the small scale of the bedding, this may have been deposited in a deep water environment with a low rate of sedimentation. It can also be reasonably determined that is rock is a carbonate, due to the reaction witnessed after the addition of hydrochloric acid. Due to the high percentage of silicate minerals within the carbonate, determines this rock as a Smarl(João Trabucho Alexandre et al Nov 2011. Sub-lithology (iv) Observation: Above the bed described in sub-lithology iii there is another fine grained Siltstone which contains Chert nodules (Figure 7) in the lower section of the bed with a small band of Chert in the upper part of the bed, which also showed planar bedding. Flute casts were observed, with an average orientation of 030° and this therefore gives us evidence for submarine avalanches. These chert nodules in a smarl carbonate are typically named flint, which show
  15. 15. The Geology Of the Dibba Zone Durham University Callum Thurley 15 of 50 conchoidal fracture and are composed of quartz. The veins that run through the chert here are comprised of calcite as they fizzed under the application of hydrochloric acid and were easily scratched with a fingernail. Figure 6(Field photograph showing a Chert/flint Nodule) Interpretation: The fact that both beds and nodules of Chert/Flint are present, within the same lithology, suggests that the deposition may have occurred at or around the Lysocline. This means this was deposited during a period of high productivity, when there was an upwelling of silica richorganisms (Radiolarians).Therefore there was an increase in the oxygen minimum zone and a decrease in the Calcite Compensation Depth. This means that all calcite-containing tests, such as Foramonifera and Coccolithopores would be dissolved at this depth, and none would be preserved. This would lead to the deposition of silica rich rocks and most namely chert. However during the periods where there was not high productivity, the calcite compensation depth would be deeper, and therefore some of the calcium carbonate tests would be preserved, and ensuringthe preservation of a carbonate rock with some clay minerals rather than a pure silicate, this can also be described as Smarl. 5cm
  16. 16. The Geology Of the Dibba Zone Durham University Callum Thurley 16 of 50 Sub-lithology (v) Observation The following lithology in the sequence represents a fining upward sequence from coarse to medium sand. This is matrix supported and has lithic fragments of size ranging from 1- 3mm. It is black on a fresh surface and it fizzed under the application of hydrochloric acid. Under thin section we could see Ooids, circular structures and a cubic mineral which showed some clear fabric. Some smaller circular structures that were darker in colour than the ooids were also observed. Interpretation This is a carbonate mudstone, more specifically an Oolitic Micrite. Micrite has formed as diagenetic cement and therefore forms the matrix. Some of the Ooids are difficult to distinguish because they are also composed of micrite. The presence of Ooids indicates that this was originally a higher energy environment on the carbonate ramp, towards the offshore during periods of lower energy. This can be interpreted due to its occurrence with other ramp carbonate facies. Other inclusions of dolomite show that dolomitisation has occurred, which is a diagenetic change typical of dry arid environments. The small pellets are a form of carbonate material, maybe faecal pellets from organisms higher up in the water column. The pyrite seen indicates that during diagenesis this was an iron rich anoxic environment.
  17. 17. The Geology Of the Dibba Zone Durham University Callum Thurley 17 of 50 Sub-lithology (vi) Observations The top of the sequence is capped with a green coloured rock that fractured in a conchoidal manner, sugary texture and showed planar bedding. It is monomineralic microcrystalline quartz. Interpretation The likely depositional environment for this was probably around the lysocline, when there was an upwelling of silica producing organisms such as Radiolarians and Diatoms. This led to an increase in the oxygen minimum zone, therefore raising the Calcite Compensation Depth, resulting in the deposition of a silicate ooze which was lithified during diagenesis to form green Chert/Jasperite. The Green colouration may also be due to the presence of Glauconite. Overall interpretation of the depositional environment of this inter-bedded Turbidite Smarl Chert sequence This sequence represents a series of distal facies carbonates, shale, and cherts. They are deep-water facies and due to the Carbonate/Chert cyclicity they were deposited at or around the lysocline. Carbonate rocks were deposited during times of calm and chert or shale was deposited when there was an upwelling and high productivity. The presence of flute casts in some of the carbonate beds means that these were deposited on the continental slope where slope instability was prominent. This may have occurred during the closing of the Tethys Ocean 75-65 Ma (M.P.Searle et al 1990), leading to submarine avalanches on a turbiditic apron (reasons for submarine avalanches can be seen on P 13). The sedimentary Log of the Turbidite Smarl/Nayid formation can be seen below (Figure 8). These can be classified a Smarl due to that fact that they are a Silica rich Marl (J.Trabucho Alexandre et al 2011).
  18. 18. The Geology Of the Dibba Zone Durham University Callum Thurley 18 of 50 Figure 8 (Sedimentary Log of the Turbidite Smarl / Nayif Formation) Lithology 4 - Brown Chert Observations This lithology formed in uniform beds, which were approximately 10cm in width. The rock was brown in colour, did not react under the application of hydrochloric acid, showed conchoidal fracture and was microcrystalline. (A field photograph of this lithology can be seen in the structural section on page 30, Figure 15). Interpretation Due to the fact that the rock here is formed in beds, completely silica rich with carbonate present, we can conclude that this is a Chert deep-water facies. Possible Reasons for Formation The formation of chert, is one of sedimentologys greatest questions, however below here are some possible interpretations.
  19. 19. The Geology Of the Dibba Zone Durham University Callum Thurley 19 of 50 There may have been a sustained period of high productivity and upwelling of silica containing tests (Radiolarians & Diatioms). Although this is a feasible explanation, it is unlikely due to the extremely low sedimentation rates of these rocks. Also the upwelling would have to last for an unrealistic amount of time for this thickness of Pelagic Chert to be deposited. A marine transgression could have produced such a thick formation of Chert. A marine transgression would lead to the starvation of carbonate from the environment, due to the Calcite Compensation Depth being now at a shallower depth than the floor of the paleoenvironment. The most likely reason for the formation of this Chert however is Diagenetic Secondary Replacement. This has been localised to a narrow band of Turbidite Smarl and two other spots on the map, therefore leading to the formation of a band silicified Turbidite Smarl. During burial, there may have been a change in both temperature and pressure and maybe even the addition of some fluid that dissolved the calcite and left silica remaining. This silica may then have formed biogenic opal, which was then changed into microcrystalline Quartz. This localised diagenesis, explains the fact that there are two smaller groups of this lithology in the mapping area. This also explains why there is a small slice of Turbidite Smarl on the top of this mountain; primarily due to the fact that the diagensis / replacement has been localised and therefore hasn‟t fully silicified the whole formation. Lithology 5 – Dendritic Chert Observations This rock was dark red, orange and green in colour on a fresh surface, contained both thin (5cm) and thick (30cm) beds and shows conchoidal fracture. Dendrites were also identified and it was microcrystalline.
  20. 20. The Geology Of the Dibba Zone Durham University Callum Thurley 20 of 50 Interpretation This is another deep-water facies Chert lithology. The predominant mineral is probably quartz due to the hardnessand conchoidal fracture. The depositional environment once again is one of deep water with a low rate of sedimentation and below the Calcite Compensation Depth. This has been called Dendritic Chert on the Geological Map. Lithology 6 – Wadi Conglomerate Observations This lithology contains poorly sorted angular clasts, between 3-8mm and 20cm, cemented by finer grained but unstable sediment due to a lack of diagenesis and compaction, meaning that this rock is matrix supported. Horizontal bedding with zero dip is observed at many localities, and fining upward sequences are seen. This lithology is only found at the base of wadis, throughout the mapping area, laid down uncomformably above the green chert, and with the metamorphic rocks in the area Serpentinite and Harzburgite. The clasts within the rock are composed of rocks in the local area, for example there are large clasts of the metamorphic Serpentinite, Harzburgite, and many inclusions of the surrounding carbonates and silicates. Imbricate structures are present here, where the long axis of each clast has aligned to the direction of the paleo current, which was at a bearing of 244 degrees or in a West, South-West Direction. (See Figure 3 for a field photograph) Interpretation It can be hypothesised from the lack of structural deformation seen in the form of folds and faults throughout the mapping area, that this is a much more recent deposit and is unrelated to the deposition of the Carbonates and Cherts. This is a Wadi Conglomerate, deposited during a very high-energy event and is likely to have been deposited over a period of a few hours. This often occurs when there is heavy rainfall in an arid environment that has
  21. 21. The Geology Of the Dibba Zone Durham University Callum Thurley 21 of 50 impermeable rocks due to intense heating and therefore drying out or crystalline lithologies. This leads to an extremely rapid rise in the water level and results in a flash flood. These can be extremely powerful and can transport boulder-sized clasts, which are deposited first and then the finer grains are deposited, leading to a fining upwards sequence. The paleocurrent simply just runs in a direction down and out of the wadi. Chapter conclusion It can be concluded that all of the carbonates in the area are sapropellic, due to their black colouration on a fresh surface. All of the sediments except for the Wadi Conglomerate were deposited on the continental shelf of the Arabian platform or Musandam Shelf edge, some of which were above the Calcite Compensation Depth producing carbonate grainstones, and some below forming microcrystalline Chert lithologies. Most recently flash flood deposits have led to the deposition of Wadi Conglomerates, that outcrop uncomformably in the Dibba Zone.
  22. 22. The Geology Of the Dibba Zone Durham University Callum Thurley 22 of 50 Chapter 2 - Igneous and Metamorphic Geology Some key features of this mapping dissertation were defined by the presence of igneous and metamorphic lithologies. All of these lithologies have got an ophiolitic origin. Lithology 1- Harzburgite Observations This lithology was black in colour, crystalline with Interlocking crystals, and very dense. Figure 9 shows a thin section. i) Mineralogy from field observation. 10% - Dark green, circular mineral, poor cleavage. Circular Pits with rust coloured residue in them. This mineral is Olivine, and the residue in the pits is known as Iddingsite, which is weathered olivine. 10% - Black elongate mineral, vitreous lustre, cleavage at approximately 120°. This mineral is amphibole. 10% - Bronze coloured mineral, platey with a metallic lustre, at least 2 directional cleavage. This mineral is called Bronzite, which is an Orthopyroxene. 70% - The finer grained material is all a dark mineral and in the field it is hard to identify, but maybe Augite. See appendix i for full mineralogical description of thin section. Interpretation Due to the very high density of this rock and the presence of these orthopyroxene mafic/ultramafic minerals such as Bronzite, this rock can be classified as Harzburgite. Bronzite is an iton rich weathered form of Enstatite (Encyclopedia Britannica (1911) Enstatite) whichis indicitive of this rock type. Harzburgite is found at the ophiolite sole. This is a cumulate rock, meaning that it forms by the accumulation of minerals.
  23. 23. The Geology Of the Dibba Zone Durham University Callum Thurley 23 of 50 Harzburgite is a type of peridotite that forms when Lherzolite is melted and the Clinopyroxene is lost, leaving a rock with Orthopyroxene and Olivine and a Harzburgitic content. In ophiolites, Harzburgite is the most common type of peridotite found. Figure 9(Thin section of True Harzburgite away from the apparently serpentinized zone in cross polarised light, see appendix i) 4mm
  24. 24. The Geology Of the Dibba Zone Durham University Callum Thurley 24 of 50 Lithology 2 - Serpentinite Observations This lithology is green in colour and has dark patches. It is medium grained, has a fibrous texture with interconnecting calcite veins. Dark inclusions can be up to 30 cm wide, and some darker minerals have a fabric and are aligned to a bearing of 113/293 degrees. A photograph of this lithology can be seen below (Figure 10). Figure 10 (A field photograph of Serpentinite, South East Facing) i) Mineralogy  10% - Dark elongate minerals with cleavage at approximately 120°, this is amphibole.  10% - Dark green, circular mineral, poor cleavage. Circular Pits with rust coloured residue in them. This mineral is Olivine, and the residue in the pits is know as Iddingsite, which is weathered olivine.  10% - Lighter green plated mineral, this mineral was also rounded and had a vitreous lustre, this mineral is Chlorite.  5% - A very small amount of a blue elongate mineral, which has 2 directional cleavage, this minteral is Glaucophane. 50cm
  25. 25. The Geology Of the Dibba Zone Durham University Callum Thurley 25 of 50  10% - Dark red/brown elongate mineral, with a waxy lustre. This may be Jasper.  10% - Crysotile Aspestos, although this varied from locality to locality.  Veins scratch easily with a steel knife, and weather like a limestone, therefore these are calcite veins. Interpretation This lithology is a metamorphic Serpentinite, probably with a Harzburgite protolith. It is formed by the low-grade metamorphism and hydration of the Harzburgite ophiolite sole, by the addition of water (Patricia Fryer,2002). Harzburgite is unstable at the earth‟s surface due to the fact that is formed in the mantle at vastly higher temperature and pressures. Therefore when these rocks were exhumed by thrusting, the addition of seawater and the change in physical conditions leads to metamorphosis. On a mineral scale, serpentinization occurred, this led to the hydration of ultramafic minerals such as Olivine and Orthopyroxene first and the formation of Serpentine. During metamorphosis there is only a relatively small change in temperature and pressure, and the minerals metamorphose in order to reach equilbrium with their environmental conditions. This may have occurred when subduction began. When the rocks were exhumed by thusting, the reduction in both temperature and pressure, along with the addition of sea water led to the serpentinization of the ultramafic Harzburgite, forming the serpentine minerals and the rock Serpentinite. The formation of this Serpentinite has a structural origin. (See next observation & Interpretation).
  26. 26. The Geology Of the Dibba Zone Durham University Callum Thurley 26 of 50 The Contact between Serpentinite and Harzburgite. Observations The contact between these two lithologies is not a distinct change, but a gradual one. There is a transition zone between these two major lithologies, where the rock seems to be of a higher density than the pure Serpentinite but less dense than the true ophiolite (Harzburgite). It seems to contain more serpentine minerals aswell, giving it more of a green colouration, but also contains some Bronzite minerals that are exclusively found in the Harzburgite. Some of the rocks found here are extremely rich in Bronzite minerals.(See below for a thin section Figure 11). Detailed mineralogical descriptions can be seen in appendix ii. (disc in at the back of the book). Figure 11(Thin section from the Harzburgite/Serpentinite transition zone in cross polarised light) Interpretation This is most likely to be some form of metamorphic contact and the serpentinization, doesn‟t extend very far into the Harzburgite. This may be due to the fact that hydration of 4mm
  27. 27. The Geology Of the Dibba Zone Durham University Callum Thurley 27 of 50 the anhydrous Harzburgite by seawater depends on percolation along a conduit such as a thrust/fault plane. (Patricia Fryer, 2002).Therefore seawater may not have been able to penetrate very far into the Harzburgite, and thus partial serpentinization has occurred (Figure 12). Serpentinite is weaker than the surrounding Harzburgite and so allows shearing to be focussed at the hydrous/anhydrous boundary. This hypothesis is supported by the fact that Sepentinite is found at lower altitudes, in wadis below and surrounding the Harzburgite. This has led to the separation of the two lithologies by a second thrust fault.The thrusting and tectonic activity may have stopped before the serpentinization was complete, therefore leaving some of the Harzburgite in its „pure‟ form whilst some of it was metamorphosed into Serpentinite. Figure 12(schematic diagram showing the segregation of hydrated Serpentinite and the anhydrous “pure” Harzburgite). Pure Harzburgite, is hasn’t been affected by the serpentinization process. The Serpentinite is hydrated Harzburgite. Sea water percolated along the floor thrust fault to create a narrow shear zone, and that is where the Serpentinite formed.
  28. 28. The Geology Of the Dibba Zone Durham University Callum Thurley 28 of 50 Lithology 3 - Mélange Observations This lithology was too small to map on a 1:10,000 scale map. It has the same fibrous texture as the Serpentinite and is brown in colour. Some very large inclusions that can be up to 50cm in size are present. It looks like a fragmental rock and the matrix looks as if it has flowed in a ductile manner, around the larger clasts. (see structural section for more on this). Some of the inclusions seem to consist of the underlying carbonates (Nayid Formation) whilst others seem to be composed of Serpentinite. This rock looks as if it is a large Breccia but on a larger scale (Figure 13), and looks as if it has also been serpentinized. Figure 13(Field photograph of Locality 41, showing the Mélange, North facing.) Interpretation This is a mega-breccia, in other words Mélange. Where the ophiolite has been thrusted over the Carbonates beneath and the lithologies have been tectonically sheared together into a 40cm
  29. 29. The Geology Of the Dibba Zone Durham University Callum Thurley 29 of 50 mega breccia. This lithology may also have been serpentinized during the exhumation of these rocks, just like the Harzburgite has been. Lithology 4 – Ultramafic Dyke Observations This lithology was also of a scale too small to map, however it should be noted as part of this study. It was a linear outcrop of emerald green and white rock on a weathered surface. The outcrop stands alone with scree on either side of it. It is a much darker green than the surrounding Serpentinite. In some places on a fresh surface this appeared to be white. Mineralogy o 20% - Dark green, circular mineral, poor cleavage, this mineral is Olivine. o 80% - Black Groundmass, it is hard classify in the field, however it may be some form of Augite or Amphibole. Interpretation This is an ultramafic dyke that has been serpentinized. It still looks like Serpentinite, however it is a different kind of Serpentinite to that of the majority. This may have come from a dyke that was more ultramafic or more Olivine rich than Harzburgite. It was found very near to an area that has been have interpreted as a thrust plane. Therefore this may have been where the hydrating fluid has been concentrated. This along with the fact that this is an ultramafic dyke could have led to this exceptional serpentinization. This may even be a Carbonatite, see Economic Potential, Metaliferous Mining on page 46 for more detail.
  30. 30. The Geology Of the Dibba Zone Durham University Callum Thurley 30 of 50 Chapter 3 – Structural Geology The Dibba Zone has undergone, atleast 3 phases of structural deformation, and there is still some strike slip deformation occurring today. The following structural features have been explained in chronological order, in terms of the apparent geological history. Normal Faults Normal faults were observed in all of the sedimentary sequences that were mapped (Figure 13/14/15). At locality 1, in the carbonate black shale, all of the normal faults observed had the southerly side downthrown. All of the faults observed showed fault drag and some smaller degrees of fault bend. In some areas the faults did seem to show an en-echelon pattern. Normal dip slip faults were seen on scales with offsets of up to 6.5m down to 3cm, see Figure 14 for schematic diagrams of the faults, see figures below. Other faults were seen to form in conjugate sets and some smaller faults showed a listric habit. (Figure 13). Figure 13(A normal fault, seen in the carbonate black shale, North East Facing). 10cm
  31. 31. The Geology Of the Dibba Zone Durham University Callum Thurley 31 of 50 Figure 14(sketches to show the types of normal faults seen) Figure 15(outcrop showing normal fault system in fine grained Chert, South Facing) 2m
  32. 32. The Geology Of the Dibba Zone Durham University Callum Thurley 32 of 50 Interpretation The fact that normal faults were only present in the sedimentary rocks in the area, suggests that the tensional deformation occurred prior to the ophiolite emplacement and the compressional deformation. This would have occurred when the Tethys Ocean was still spreading and the Carbonates and Cherts were still being deposited in the ocean basin during the Permain period (M P. Searle et al 1990). Due to the fact that some of the normal faults in the area show an en echelon pattern, this may suggest that this was a transtensional margin, or an “oblique rift” margin. (M P. Searle et al 1990). It has also been suggested that the normal faulting may have been caused by the subduction, a process known as “Marginal Basin Spreading.” This has been described and explained fully in the Obduction of the Semail Ophiolite section (Gary Feulner 2005). Due to the fact that the ophiolite and serprentinite were not visibly affected by normal faulting, it could be argued that this occurred before the ophiolite was obducted onto the Arabian continental margin. However, it may have happened in the early stages of subduction due to marginal basin spreading. Alternatively, spreading of a conventional manner in the Tethys Ocean could have been the cause of these tensional faults.
  33. 33. The Geology Of the Dibba Zone Durham University Callum Thurley 33 of 50 Thrust Faults Observations The main type of structural deformation in the Dibba Zone has been compression; all of the rocks in the area have been affected by the thrusting and therefore are all allochotonous units. The vast number of folds and tilted sedimentary sequences in the area reflects this. There are two main thrust faults in the area, one runs along the boundary between the Harzburgite, and the Serpentinite, the other between the Serpentinite and the Turbidite Limestone contact. Furthermore, the faults generally follow the contours of the mountains. Slicken lines and slickenfibre steps (Figure 16) were seen all along these contacts, and throughout the Serpentinite. Riedel shears were seen throughout the Serpentinite, and occasionally in the Green Chert. Figure 16(field photograph, showing a slickenside, and slickenfibre steps). Interpretation As we can see from the fair copy map the general direction of tectonic transport is from East to West and due to the fact that the faults generally follow the contours this means that we probably have a shallowly dipping thrust. If this was a steeply dipping thrust plane then 10cm
  34. 34. The Geology Of the Dibba Zone Durham University Callum Thurley 34 of 50 the relationship with contours would be a cross cutting one. Riedel shears are features that are associated with Strike or Oblique-Slip Faults. (Twiss Robert J,Moore Eldrige M, 2006) and thus this may indicate the presence of a transpressional deformation zone. The slickenfibre steps form from the reactivation of faults along the same plane and the direction of stepping up indicates the direction of tectonic transport. As demonstrated in Figure 16 the direction of transport is up the rock face. Finally, thrusting from the ophiolite emplacement has led to the tectonic transport of all sedimentary lithologies in the area. Therefore they are all allochtonous units, as they are not currently sat in the position that they were originally deposited. All of the pelagic and turbidic sediments in the area are part of an accretionary prism (Figure 17) where the sediments have been scraped off from the oceanic plate. This was formed during the ophiolite obduction, these are the deep water facies that immediately over-lie the oceanic plate. http://www.classroomatsea.net/general_science/images/acc_prism.jpg Figure 17 (a diagram to show the formation of an accretionary prism)
  35. 35. The Geology Of the Dibba Zone Durham University Callum Thurley 35 of 50 Emplacement of the Samail Ophiolite The Samail Ophiolite represents a section of the Tethyan Oceanic crust, formed by the spreading in the Cenomanian/Mid Cretaceous (Robert G Coleman 1981). The ophiolite exposure extends for approximately 600km and is made up of 12 blocks, separated by major faults (Lippard et al 1986). During the dispersal of Gondwanaland, the Arabian Plate drifted north and Eurasia and Africa rotated in an opposite direction. This led to the closing of the Tethyan Ocean during the Turonian and Campanian or end cretaceous period 65-70 Ma (M P. Searle et al 1990). The Ophiolite in the Mapping Area The ophiolite the studyarea is called the „Hajar Ophiolite‟ and it has been suggested by Gary Feulner that it was not obducted in the conventional manner. Due to the fact that the ophiolite has been aged between 90Ma and 100Ma, it would suggest that these rocks were obducted soon after their genesis. Gary Feulner has also implied that the ophiolite was not formed from a conventional spreading ridge, but from a process called „Marginal Basin Spreading‟ which takes place on an overriding plate close to the subduction zone. This is caused by physical tension in the overriding plate caused by rapid decent of the subducting plate. During the process frictional heating and the release of water vapor and other volatiles from the subducted slablead to the melting of the overriding plate. Marginal basin crust is thinner than true oceanic crust (due to a smaller source), this crust was young, buoyant and hot. Collectively these features facilitated the obduction of the Hajar Ophiolite (Gary Feulner 2005)It has been proven that this is method of obduction is correct due to the fact that the protoliths in the metamorphic sole are not the same age as the ophiolitic rocks above (Mike Searle & Jon Cox, 1999). Therefore the subduction can not have been initatied from a mid-ocean ridge.
  36. 36. The Geology Of the Dibba Zone Durham University Callum Thurley 36 of 50 The area is near the most northerly part where the ophiolite has been obducted and we have the rocks from the very base of the oceanic crust. Harzburgite, is found in the metamorphic sole and is a form of Peridotite. The other layers of Tethyan oceanic crust are found further south and east along the coast for example. The Aswad Block shows a complete ophiolite section from mantle harzburgites to the upper crustal Pillow lavas to the East(Goodenbough et al 2009). The ophiolitic rocks in the area of study are actually part of a klippe, which have been detached from the main ophiolite by erosion. (Figure 18).There are two smaller scale klippes in my area, both are in the North East section of the map, one of Harzburgite in the Serpentinite, and one of Calciturbidite Smarl in Serpentinite. Figure 18(schematic diagram showing the formation of a klippe in the Dibba Zone)
  37. 37. The Geology Of the Dibba Zone Durham University Callum Thurley 37 of 50 Folding – Ductile Deformation Observations The study area was dominated by folds, ranging from a few centimetres to tens of metres in scale. Many of the folds were open or closed, upright folds (Figure19)and were more recumbent, whilst a few cylindrical folds were spotted(Figure 19). Most of the fold hinges measured in the area measured have azimuths between 90 and 160 degrees or south-eastern direction and had an eastward vergence. From the photos to the left (Figure 19) at the top a “S” fold is observed, with low inter-limb angles, this is a closed fold. Below this a recumbent fold has formed with Cherty Siliceous rocks in the middle of the fold, with the carbonate Smarl Formation on the outside of the fold. Finally a cylindrical fold in the Mayah Formtion, this unit was heavily folded, possibly due to its low competency, due to being 1.5m 1m 5m 3m
  38. 38. The Geology Of the Dibba Zone Durham University Callum Thurley 38 of 50 a shale. The Chert was also regularly seen folded, sometimes very intricately as seen in the fourth photo down in Figure 19where Z folds are observed. Finally, in the last photo ofthere are another set of open folds that are fairly symmetrical, forming multiple anticline syncline folds. Recumbent folds (100m across) are found connected to eachother (See Figure 20 for detailed analysis PTO) that had an eastward vergence. Interpretation Due to the fact that the folds don’t seem to be cross cut by any of the faults, it can be concluded that they were produced at the same time as the ophiolite obduction.Folding is an example of ductile deformation, as opposed to faulting which is brittle deformation. These rocks have been deformed at depth and pressure, which allowed for them to behave in a ductile manner to form folds. Stereonets from the entire mapping area (Figure 20) give us evidence that the in general, the hinges of folds in the area are dipping in a southerly direction, and predominantly South East. This means that the deformation has originally come from the South West and North East producing a hinge dipping South East. The deformation in the form of folding seems to be fairly homogenous, as many folds are upright, with near verticle axial planes and are nearly symmetrical. Both S and Z folds have formed on either side of the same mountain in both Turbidite Smarl and Chert formations. Figure 19 (field photographs of folds seen in the area) 3m
  39. 39. The Geology Of the Dibba Zone Durham University Callum Thurley 39 of 50 Figure 20 of STERONETS
  40. 40. The Geology Of the Dibba Zone Durham University Callum Thurley 40 of 50 Deformation of sediments Observations The Green Chert lithology is not laterally homogenous, for example at the South Western tip of this unit qualities such as, high friability, foliaton and cleavage are seen. These are usually features that associated with metamorphic Schist. Elongate minerals were also seen in the South Western tip where the rock was heavily foliated and powdery and could be classified as chlorite. However, the North Eastern section of this unit is dominated by a greater number of finer grained, less folliated, and chlorite minerals than are seen to the South West. Generally most of the beddings seem to dipping in a Southeasterly direction. Interpretation The lack of consistency in cleavage and mineralogy throughougt this unit may suggest that there has not been a homogenous amount of deformation throughout the area of study. The rocks to the south west have experienced a higher degree of shearing than the rocks to the north east and have therefore led to heavy foliation of the rocks to the southwest.The bedding dipping to the South East suggests that the compression has come from that direction also. Robertson, A.H.F et al 1990 has suggested that there is a thurst contact beween the Mayah Formation and Hawasina complex. On the fair copy map map this runs along the boundary between the Mayah Formation and the Sid‟r formation. There was not time time to properly research this whilst out in Dibba, however below are a few potential causes for the intriguing heterogeneity in this lithology. Possible interpretations i) This could have been caused by an oblique convergence when the ophiolite was obducted. There may have been rotation hinged in the North Eastern part of section
  41. 41. The Geology Of the Dibba Zone Durham University Callum Thurley 41 of 50 of the mapping area, (Figure 21), which would mean that the rocks in the nothern area of the map have been translated much less than the rocks in the South West. Therefore less deformation has occurred here and so they show less evidence for shearing. Figure 21(schematic sketch to show an oblique convergence and possible rotation of the ophiolite) ii)The heterogeneity may have been caused by a small lithological or mineralogical change, allowing shearing to to be fully distributed throughout the entirety of the lithology to the south. Whereas in the North Western section of the map, the shearing has been concentrated in the narrow fault planes, and so the rocks arent as foliated. This heterogeneity may have been due to the fact that the rocks to the north had more clear cut
  42. 42. The Geology Of the Dibba Zone Durham University Callum Thurley 42 of 50 horizons/planes.Therefore allowing faulting and deformation to use these pre existing lines of weakness as a slip surface. Further research If the study was to continue in the Dibba Zone, a couple of tests could be run, in order to resolve this issue. i) Study the lithology more closely in both areas, and obtain more data. Take thin sections of the rocks from both localities and study them under the microscope to look for mineralogical differences. ii) Measure slickenline plunge and azimuths more in the areas to obtain see if there are any preferred orientations, this may give more information about how the ophiolite was obducted and direction of thrusting. Strike Slip Faults. Observations Many of the contacts in my area have been offset by faults, most of which showed no vertical offset whilst and others did. Eight major strike slip faults were seen in varying locations, most created offsets in the Serpentinite and Harzburgite thrust contacts. Indicators of shear sense and shear band fabrics were observed along fault planes (Figure 22). All of the faults apart from one seem to show an orientation between 090° and 170°.
  43. 43. The Geology Of the Dibba Zone Durham University Callum Thurley 43 of 50 Figure 22, (A Field photograph, showing the sense of a shear band fabric, where we can see the minerals aligning to the fault plane, the diagram to the right, shows the strain ellipsoids of the minerals across the fault plane). Interpretation Using the law of cross cutting relationships it can be said that, this is the most recent form of structural deformation based on the fact that many of the contacts in my area were offset by strike slip faults. This particular fault shows a dextral sense of shear and we can see that the strain ellipsoids are stretched to a prolate form along the fault plane and then plain strain on either side of the fault. On a Flinn Plot, the strain here would plot somewhere in the zone of apparent constriction. The minerals are rotated into parallelism with the shear plane, suggesting that the strain increases towards the centre of the shear zone. The strike slip faults that cross cut the thrust faults produce structures called “non-coplanar imbricate thrusts” (Robert J. Twiss, Eldridge M. Moore, 2006)(Figure 23.) Due to the South Easterly orientation of the faults in my area, this may suggest that there is a major strike slip fault running underground in the same direction through the centre of my study area. This may be the Dibba fault, which separates the ophiolites to the South and the mesozoic carbonates of the Musandam peninsula (P.D.Clift, D.Kroon, and J Craig, 2002) and it has been
  44. 44. The Geology Of the Dibba Zone Durham University Callum Thurley 44 of 50 speculated that this was once an ocean continent tranform fault between the Arabian plate and Tethys Ocean (A.S.Alsharam, A.E.M. Nairn, 1997). However, this may even be linked to the escape tectonics occurring in the Zagros region in Iran. This fault renders many of the potential oil and gas reserves in the region useless by providing a conduit for the petroleum to escape, leaving dry wells. Figure 23(Diagram of Non-Coplanar Imbricate Thrusts)
  45. 45. The Geology Of the Dibba Zone Durham University Callum Thurley 45 of 50 Oblique Slip faults Observations A few strike slip faults observed in my area showed both some horizontal and vertical offset. The main example of this was at locality 36, I found a contact that was offset horizontally by 30m and vertically by approximately 10m up-hill. (Figure 24) Figure 24, (Diagram of an oblique slip fault) Interpretation As we can see from Figure 24, this is an oblique slip fault, due to the fact that both horizontal and vertical displacement is shown. This fault that was observed showed some dextral sense of shear, which is anomalous for the area. In general the strike slip faults have a sinistral sense which may be due to the fact that it happened at the same time as the obduction of the Samail Ophiolite, rather than from the more recent strike slip faulting and as such this may have been an oblique convergent boundary.
  46. 46. The Geology Of the Dibba Zone Durham University Callum Thurley 46 of 50 Mélange, and shear sense indicators Observations Carbonate and Serpentinite inclusions were found in the Mélange, with some finer grained material that looked as if it had flowed around it in a ductile manner. (Figure 25) Figure 25, (A field photograph of a σ shear sense indicator) Interpretation Figure 25 shows aσ shear sense indicator(Robert J. Twiss & Eldridge M.Moores,2006) formed in a ductile shear zone during the thrusting of the ophiolite. It has formed due to ductile flow in a deformable matrix, and we can see this porphoryclast of a local carbonate carbonate. (Robert J. Twiss & Eldridge M.Moores,2006) Here we can see that the asymetric „tails‟ have been recrystallised from the edges of the porphoryclast itself. This particular example (Figure 25) shows a right lateral shear sense and this gives us supporting information that the ophiolite obduction did in fact have some component of dextral shearing as well as thrusting. This supports the hypothesis discussed in the interpretation of oblique slip faults.
  47. 47. The Geology Of the Dibba Zone Durham University Callum Thurley 47 of 50 Chapter 4 – Economic Potential Hydrocarbon Potential The carbonates in the area are perfect resevoir lithologies, due to their high porosity, permeability, high organic content, and presence of impermeable cap rocks Unfortunately the structural geology extinguishes their economic potential, due to the fact that this is a complicated fault zone and ensures that there are far too many routes of escape for potential hydrocarbons to be retained in traps. Mining Industry Principally, much of the limestone in the area is mined, where the lime is removed and used within the production of cement. Chippings of both Limestone and the ophiolite are also used for aggregate. i) Metaliferous mining Chromite is the main economic income in the metaliferous mining of Dibba, from the chrome-spinel in Harzburgite and other mafic/ultramafic lithologies. It is then used to induce hardness and chemical resistance in steel. Large bodies of Carbonatites are found within the metamorphic rocks beneath the Semail Ophiolite near to Dibba, which are associated with meta-volcanics and Radiolarian Cherts. (Alleman, F., and Peters, T. 1972.) Carbonatites contain the highest percentage of Rare Earth Elements (REE) of any other igneous rock type. The abundance of Niobium bearing minerals such as Phyrochlore make the Carbonatite economically viable for mining. It is then used in Iron and other alloys and occasionally jewelry. Tantalium is another REE that is mined from Carbonatites, both of these elements are used extensively within the high-tech industry. There was a small dyke observed, which is described in more detail on page 27 and this could have potentially been an intrusive Carbonatite.
  48. 48. The Geology Of the Dibba Zone Durham University Callum Thurley 48 of 50 Chapter 5 - Geological History The geological history of the Dibba Zone has been written in chronological order, from past to present. Paleozoic Deposition of the distal carbonate Mayah Formation in the spreading Neo-Tethys Ocean, this was a transtensional oblique rift margin in the Permian period. Mesozoic After this there was an upwelling of silica rich organisms, leading an increase in the oxygen minimum zone and lysocline and resulting in the deposition of a Glauconitic Chert. Tectonic activity and gas pressure caused submarine avalanches leading to density flows producing a Calciturbidite sequence (Nayid Formation). Fluctuations in the lysocline due to periods of high productivity caused the Nayid formation to be a section of inter-bedded Carbonates and Cherts. Normal faults from the spreading ocean penetrate sediments from the north western section of the map. In the late cretaceous 65-70Ma the Semail Ophiolite was obducted when the Neo-Tethys spreading rate slowed and the rate of subduction overcame this. This was an oblique obduction suggested by the presence of riedel shears, and the heterogeneity in the green chert. This compression principally came from the South West and North East, as the Arabian plate collided with the Eurasion plate. Compressional forces caused thrusting and folding of sediments during the ophiolite emplacement. During the obduction, interactions between seawater and Harzburgite, lead to the partial serpentinization of the ultramafic ophiolite sole. Most folds in the area have azimuths facing South East, therefore suggesting once again that the deformation was orientated South West / North East.
  49. 49. The Geology Of the Dibba Zone Durham University Callum Thurley 49 of 50 Cenozoic The most recent form of deformation is strike slip, offsetting the thrusts forming non- coplanar imbricate thrusts. These strike slips faults all seem to show a sinistral shear sense, hinting that they may have been caused by the Dibba Fault which runs underground in close proximity to the mapping area and is known to be a sinistral strike slip fault. The most recent sedimentology in the area is the deposition of Wadi conglomerated at the base of the Wadis forming unconformities with all lithologies. These have been deposited during flash floods, which occur when there is a heavy rainfall in an arid environment
  50. 50. The Geology Of the Dibba Zone Durham University Callum Thurley 50 of 50 Bibliography 1. Alleman, F., and Peters, T. 1972, The ophiolite-radiolaite belt of the northern oman mountains,Eclogolgy geology Helvitica 65, pp. 657-697, 2. Alsharam, A.S., Nairn, A.E.M., 1997. Sedimentary Basins and Petroleum Geology of the Middle East, 1st ed. Elsevier, Amsterdam. ISBN:0-444-82465-0. 3. H.S Chafetz & A Reid, October 2000, Syndepositional shallow-water precipitation of glauconitic minerals.Volume 136, Issues 1–2, October 2000, pp. 29–42 4. http://www.classroomatsea.net/general_science/images/acc_prism.jpg 5. Clift, P.D., Kroon, D., Gaedicke, C., Craig, C., 2002. The tectonic and climatic evolution of the Arabian Sea Region. Geological Society Special publication No. 195. The Geological Society, London. ISBN: 1-86239-111-4 6. Coleman Robert G 1981, Tectonic setting for ophiolite obduction in Oman, VOL. 86, NO. B4, P. 2497, doi:10.1029/JB086iB04p02497 7. Creid Jeffrey, Igneous rocks in thin section 8. http://www.jeffreycreid.com/petrography/pet_igneous.html. 9. Encyclopedia Brittanica, 1911, Enstatite. 10. Feulner, G., 2005. Geological Overview of the UAE, in: Hellyer, P., Aspinall, S. (ed.), The Emirates- A Natural History. Trident Press Limited. London . pp. 53-58. 11. Fryer, P., 2002. Recent Studies of Serpentinite Occurrences in the Oceans: Mantle-Ocean Interactions in the Plate Tectonic Cycle. Chemie der Erde – Geochemistry. 62(4), pp. 257-302. 12. Goodenough K M1, Styles M T2, Schofield D2, Thomas R J2, Crowley Q C3,*, Lilly R 11, M4, #, McKervey, J2, Stephenson, D1, Carney, J N2, Architechture of the Oman-UAE Ophiolite: Evidence for a Multi-phase magmatic history, Vol.3, Issue4, pp 439-458. 13. Leeder Mike, 2011, Sedimentology and Sedimetary Basins, ISBN: 978-1-4051-7783-2 14. Lippard, S.J.Shelton, A.W and Gass I.G 1986, The Ophiolite of Northern Oman. Memoir
  51. 51. The Geology Of the Dibba Zone Durham University Callum Thurley 51 of 50 Geological Society of London,issue 11, ISBN: 063201587X 15. Ramberg Hans,1955. Natural and Experimental Boudinage and Pinch and Swell Structures, The Journal of Geology, Vol.63, pp 512-526. 16. Robertson, A.H.F., Blome, C.D., Cooper, D.W.J., Kemp, A.E.S., Searle, M.P., 1990. Evolution of the Arabian continental margin in the Dibba Zone, Northern Oman Mountains. In: Robertson, A.H.F., Searle, M.P., Ries, A.C. (eds.), The Geology and Tectonics of the Oman Region. Geological Society Special Publication Vol. 49, The Geological Society, London. pp. 251-284. 17. Searle Mike &Jon Cox, 1999, Tectonic Setting, origin, and obduction of the Oman Ophiolite, vol.111, no.1, pp. 104-122, 18. Trabucho-Alexandre Joãoa,b,⁎, Alessandra Negri c,d, Poppe L. de Boer a , Early Turonian pelagic sedimentation at Moria (Umbria-Marche, Italy): Primary and diagenetic controls on lithological oscillations, Paleo. 311, 3-4 pp. 200-214 19. Twiss Robert J,Moore Eldrige M 2006, Structural Geology, ISBN:978-0-7167-4951-6

×