Formed during the
Late Cretaceous period, approximately 95 million years ago,[4] the Samail Ophiolite represents a fragment of the
Tethyan Oceanic crust that was thrust over continental crust due to the convergence of the African and Eurasian
tectonic plates. This geological phenomenon, known as
obduction, makes it a site for studying the processes of oceanic crust formation,
subduction, and obduction.
It covers an area of around 100,000 square kilometers,[3] and is a complete and well-preserved
stratigraphic section. This includes layers from the Earth's upper mantle, along with cumulate rocks, gabbros, sheeted dike complexes, and volcanic sequences, providing a vertical profile of oceanic lithosphere. It is primarily made of
silicate rocks with (
SiO2) content ranging from 45–77 wt%.[5]
Geologic formations
The Arabian continental margin formed in the early
Paleozoic and possibly the late
Proterozoic. After that the thrust sheets are from low to high structurally: the
autochthonous units, and the
allochthonous units. The allochthonous units, from low to high structurally, are the Sumeini group, the Hawasina complex, the Haybi complex, the Ophiolite, and the Batinah complex.[6] From the Sumeini group to the Haybi Complex make up the
continental slope with an age range from Middle Triassic to Late
Cretaceous.[6] The ophiolite formed in the Late Cretaceous and consists of a basal
metamorphic sole (150–200 m),
peridotite tectonic (8–12 km),
igneous peridotite and
gabbro (0.5–6.5 km),
sheeted dikes (1–1.5 km), and
lavas (0.5–2.0 km).[6] The Batinah complex containing
continental margin sediments came from beneath the ophiolite during late-stage extensional faulting and then slid into the ophiolite late in the emplacement history.[6]
Metamorphic Sole
There are two locations where the metamorphic core of the ophiolite are exposed. These locations occur at the Sumeini Window and the Wadi Tayyin.[7] The Sumeini Window is lcoated in northern Oman at the base of the ophiolite. The Wadi Tayyin is located in southwestern Oman near the classic Green Pool locality. The metamorphic rocks include garnet and clinopyroxene-bearing granulite, hornblende and plagioclase amphibolite, epidote, and greenschist facies sediments that include cherts, marbles, and quartzites. Although there have been many theories about the pressure-temperature environment of these metamorphic soles, Cowan et al. suggest that the formational temperatures and pressure of the metamorphic being 770-900 degrees celsius and 11-13 kbar respectively are representative of a subduction zone that was present before the emplacement of the ophiolite.[7]
Formation
There are three different models that may explain how the Samail Ophiolite could form and overthrust a continental margin:
The gravity sliding model: A seven to 20 km thick ophiolitic terrane could slide onto a continental margin. This requires an elevated source region, which presents difficulties.[8]
The suprasubduction model: The
obduction of an arc-trench gap ophiolite due to the collision of a
volcanic arc and a passive continental margin (Fig. 2). Figure 2-A, older than 101 to 95 Ma the
mid-ocean ridge is spreading and the ocean
lithospheresubducted under the continental lithosphere on the right while the other side is overriding the oceanic lithosphere on the left. Also, that is where the proto Semail Ophiolite and volcanism starts to form a volcanic arc. Figure 2-B, from 95 to 87 Ma the mid-ocean ridge is spreading and a volcanic arc has formed. Figure 2-C, from 87 to 76 Ma the mid-ocean ridge is spreading and the ocean lithosphere being pushed and over thrust the continental lithosphere by the help of the volcanic arc.[3][9]
The obducting model: The oceanic lithosphere over thrust continental lithosphere (Fig. 3). Figure 3-A, older than 101 to 95 Ma the mid-ocean ridge is spreading and the oceanic lithosphere subducted under both continental lithosphere. The Samail Ophiolite initial place is marked on the right oceanic lithosphere. Figure 3-B, from 95 to 87 Ma the mid-ocean ridge stopped spreading and the intra-oceanic thrusting started. Where the left oceanic lithosphere subducted under the right oceanic lithosphere with the Samail Ophiolite, which are
accreted at
amphibolite facies conditions at the base of the Samail Ophiolite. Figure 3-C, from 87 to 76 Ma the Samail Ophiolite overthrusts the continental lithosphere and is emplaced onto the
craton, which are accreted at
greenschist-facies conditions at the base of the Samail Ophiolite. This model is more supported by geologists.[3][6]
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abcdefHacker, Bradley R. (April 1991). "The Role Of Deformation In The Formation Of Metamorphic Gradients: Ridge Subduction Beneath The Oman Ophiolite". Tectonics. 10 (2): 455–473.
Bibcode:
1991Tecto..10..455H.
doi:
10.1029/90TC02779.