INTRODUCTION
The Oman ophiolite is the largest ophiolite, extending over 600km in a NW-SE direction with a maximum width of 130 km, and is considered to be a fragment of Cretaceous Tethyan oceanic lithosphere (Tamura & Arai, 2006). The Oman ophiolite is a harzburgite ophiolite and is comprised of 12 separate tectonic blocks [Figure 1] whose internal structures imply inter-plate independence during their tectonic emplacement (Tamura, Arai, 2006). The Oman ophiolite has been thoroughly researched because it is well preserved and, particularly in the north, the entire sequence of ophiolite stratigraphy, from the upper mantle to oceanic sediments, is exposed. Within the ophiolite, there co-exists mid-ocean-ridge basalt (MORB)-type extrusive rocks as well as ‘arc signature’ extrusive rocks suggesting that the entire ophiolite was not formed at a mid ocean ridge (MOR) as was previously thought. The following essay will present evidence to support the theory that the Oman ophiolite formed in a MOR environment and could subsequently have experienced a supra-subduction zone (SSZ) setting as well.
Figure 1: Map of the Oman ophiolite with the twelve tectonic plates labelled in black. (Figure 1 Godard et al 2003)
The Oman Ophiolite consists of various layers that constitute the oceanic crust and upper mantle. From top to bottom, the oceanic crust comprises of lavas, a sheeted dyke complex and gabbros, both non-layered and layered. The uppermost part of the mantle includes gabbroic sills, chromitite and dunite in a large deposit of harzburgite. [Figure 2] For this essay emphasis will be placed on the lavas, gabbros and chromitites.
Figure 2: The crustal layers and up...
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...lite. Earth and Planetary Science Letters, 251, 52-65.
• Godard M, Dautria J, Perrin M. (2003) Geochemical variability of the Oman ophiolite lavas: relationship with spatial distribution and paleomagnetic directions. Geochemistry Geophysics Geosystems an electronic Journal of the Earth Sciences, 4, 1-15
• Tamura A, Arai S. (2006) Harzburgite-dunite-orthopyroxenite suite as a record supra-subduction zone setting for the Oman ophiolite mantle. Lithos, 90, 43-56
• France L, Ildefonse B, Koepke J. (2009) Interactions between magma and hydrothermal system in Oman ophiolite and in IODP Hole 1256D: Fossilization of dynamic melt lens at fast spreading ridge. . Geochemistry Geophysics Geosystems an electronic Journal of the Earth Sciences,10. 1-30
• Nicolas, A. (1989). Structure of Ophiolites and Dynamics of Oceanic Lithosphere. Dordrecht: Kluwer Academic Publishers.
Marshak, S. (2009) Essentials of Geology, 3rd ed. New York: W.W. Norton & Company, ch. 11, p. 298-320.
The shelf-edge includes carbonate-to-clastic facies transition and tectonic uplift and erosion of the carbonates followed by deposition of the clastics. The Saint Peter Sandstone is a well-sorted, almost pure quartz arenite deposited during a major mid-Ordovician low stand. Clastics spread across an exposed carbonate platform by transportation. This is shown by the well-rounded, frosted texture of the quartz grains.
The coastal belt of the Franciscan Complex is composed of the youngest and least deformed units and makes up the western quarter of all Franciscan rocks. The rocks of the coastal belt are composed of arkosic sandstones, andesitic graywackes, and quartzofeldspathic graywackes interbedded with radiolarian chert (turbidite deposits) (Blake and Jones, 1981). These sedimentary rocks suggest a depositional environment of deep-sea fan systems with both oceanic and continental provenance. Parts of the belt show evidence of later metamorphism, principally due to subduction. Low-grade blueschist mineral facies are indicated by the presence of minerals such as laumonite and prehnite-pumpellyite (Blake and Jones, 1981). All rock units show evidence of thrust (imbricate) faulting due to the compressional forces of subduction. Ages of the coastal belt run from as little as 40 Ma (Eocene) to as old as 100 Ma (middle Cretaceous).
Quartzite is a non-foliated metamorphic rock. This rock is intrusive and forms when exposed to extreme amounts of heat and pressure. Over a billion years ago, there was an ocean where Kamiak Butte is. This ocean floor was made of sand, as time went on oceans receded and the exposed sand underwent processes that turned it into sandstone – or as we learned in class the process of lithification. Years later, this sandstone would morph into the quartzite that is present now.2
Plummer, C.C., McGeary, D., and Carlson, D.H., 2003, Physical geology (10th Ed.): McGraw-Hill, Boston, 580 p.
and Metamorphic rocks can be found. There are also a lot of crusted plates, and violent
“There are three types of hydrovolcanoe’s that are formed by basaltic hydro magmatic eruptions; maars, tuff rings, and tuff cones” (Brand, 2009). In summation, tuff rings form when rising magma interacts violently with abundant water near the ground’s surface, and explodes. Tuff cones are different than tuff rings because they have smaller craters with steeper beds, but a larger height to width ratio.
The Hadean era ranges from 4.6 billion years ago to 3.8 billion years ago. Included in this period was a time of major changes in the Earth’s formation. It involves the origin of the atmosphere, volcanic outgassing, and H2O, H2, HCL, CO, CO2, N2, and sulfur gases. Little or no free oxygen was present in this period. The evidence that supports the oxygen theory include: Urbanite and pyrite are readily oxidized today, in modern times, but are found unoxidized in sediments from here, chemical “building blocks” could not have formed in the presence of oxygen and the simplest living organisms have an anaerobic metabolism and would have been killed by oxygen. It also included the origin of the continental crust. Most of the early crust was mafic and the continental developed secondary to that.
... used to be a sea (Beaumont,1978). As mountain-building forces continued for several million years it created a big fold or anticline as it squeezed the rocks. These same pressures continued and overturned the fold which eventually caused them to break along a great low-angle fault (Beaumont,1978). The western limb of the fold was driven upward and eastern placing older layers of rock on top of younger ones. The younger layers of rock include cretaceous shales and sandstones. The slice of crust has been moved more than 15 miles toward the east, the surface it moved through is called the Lewis Overthrust. (Dyson,1957). Years of erosion finally exposed the fault which was buried throughout its early years. Erosion then separated several remnants, Chief Mountain is the best known which consists of Altyn limestone, exposed on its base is the Lewis Overthrust fault.
Recently in the Bismarck Sea there have been discoveries of rich minerals imbedded in the sea floor such as gold, lead, cobalt, silver, copper and zinc. We only have a short time left of gold, 16 years. There are several volcanoes located around the Bismarck Sea, which means there are many mineral deposits coming out from under the sea floor leaving deep pockets rich in coal and minerals. As the tectonic plates are moving they are activating volcanic eruptions, releasing minerals into the sea floor. With the tectonic plates continuously moving, the minerals and metal ores are shifting into the sea floor pockets causing the volcanoes to erupt coal and ores. The edge of the tectonic plates run directly under this site, subsequently releasing minerals from the magma below into the ocean floor.
Hidden below the Pacific ocean, about 300 miles off the coast of Oregon, lies the Axial Seamount. It is located on the plate boundary between the Pacific tectonic plate and the Juan de Fuca tectonic plate. The plate boundary is a divergent plate boundary, meaning that the two plates are slowly pulling away from each other. This causes a gap to be left behind in the ocean’s crust. Magma from deep below races to fill in the gap. Once the magma reaches the ocean water, it is cooled into a solid
Deposits of carbonate sediment and marine organisms that were deposited from the Tethys Sea (Late Triassic to Early Cretaceous), make up the oldest exposed rocks of western Sicily. During this time, the area’s structural setting was largely dominated by transtentional plate movements which resulted in fault block morphologies with alternating horst and graben structures and east-west trending normal fault systems (Hsu and Bernoulli, 1978; Nigro and Renda, 2002). The structural setting had a strong impact on the depositional environments including: shallow-water elongate platforms, seamounts, and deep water basins.
Tarbuck E., Lutgens F., Tasa D., 2014, An Introduction to Physical Geology, 5th Ed, Pearson Education, Upper Saddle River, New Jersey.
Since this time, the term uniformitarianism has been manipulated, altered, and redefined to mean a variety of different meanings spanning various fields of science. However, in the field of geology, uniformitarianism (or actualism) means something very specific. The term does not denote that every process we see before us now has been going on for eons, rather it stand for the chemical and physical laws that govern today’s processes. Evidence shows that the ancient atmosphere of the earth is extremely different from the one we can see today. There fore, the means by which erosi...
inferred for the reservoir (4). The magma ascent to the surface occurred through a conduit of possibly 70 to 100 m in diameter (5). A thermal model predicts that such a reservoir should contain a core of partially molten magma (6) that can be detected by high-resolution seismic tomography.