The document summarizes a seminar on subduction and abduction zones. It defines subduction as the process where one tectonic plate moves under another at a convergent boundary. Abduction is the overthrusting of oceanic crust onto continental crust at these boundaries. The document describes different types of abduction mechanisms including upwedging in subduction zones, compressional telescoping onto continental margins, and abduction occurring during continental collisions when oceanic crust is trapped between converging continents.
The name ophiolite derived from Greek root which means
Ophio : snake or serpent Litho : Stone
The green colour, structure and texture of sheared ultramafic rocks is similar to some serpents
Economically :
Massive Sulphide
It founded within pillow lava most of massive Sulphide associated in ophiolites have well developed Gossans (bright colored iron oxide, hydroxides, and sulfides) which is very rich in gold.
Chromite
Stratiform (be tabular or pencil shape) or podiform (irregular shape) within ultra-mafic rocks
These deposits are developed on serpentinite peridotite
Laterites (nickel and iron)
Asbestos
Talc
Magenesite
ophiolite sequence :
Sediments
Pillow Lavas
Dykes
Gabbros
Layered Gabbro
Layered Peridotite
Upper mantle
Hi I'm Misson Choudhury , A Post Graduate student, Graduated from Utkal university and Now pursuing my m.sc in applied geology at Bangalore university, Bangalore, i love geological mapping,drawing,hill climbing and tracking..
The name ophiolite derived from Greek root which means
Ophio : snake or serpent Litho : Stone
The green colour, structure and texture of sheared ultramafic rocks is similar to some serpents
Economically :
Massive Sulphide
It founded within pillow lava most of massive Sulphide associated in ophiolites have well developed Gossans (bright colored iron oxide, hydroxides, and sulfides) which is very rich in gold.
Chromite
Stratiform (be tabular or pencil shape) or podiform (irregular shape) within ultra-mafic rocks
These deposits are developed on serpentinite peridotite
Laterites (nickel and iron)
Asbestos
Talc
Magenesite
ophiolite sequence :
Sediments
Pillow Lavas
Dykes
Gabbros
Layered Gabbro
Layered Peridotite
Upper mantle
Hi I'm Misson Choudhury , A Post Graduate student, Graduated from Utkal university and Now pursuing my m.sc in applied geology at Bangalore university, Bangalore, i love geological mapping,drawing,hill climbing and tracking..
This tacklesabout locating epicenter,3 typesof plate boundaries hotspot.
A ppt presentation for module 1 in 1st quarter in grade 10sciencein the Philippines.
Feel free tomessage mefor any corrections/suggestions forimprovement.
that is associated with broad upwarping of the overlying litho.docxmattinsonjanel
that is associated with broad upwarping of the overlying lithosphere (figure 5.1 iA). As a result, the lithosphere is stretched, causing the brittle crustal rocks to break into large slabs. As the tectonic forces continue to pull the crust apart, these crustal fragments sink, generating an elongated depression called a continental rift (figure 5.1 ib).
A modern example of an active continental rift is the East African Rift (figure s. i 2). Whether this rift will eventually result in the breakup of Africa is a topic of continued research. Nevertheless, the East African Rift is an excellent model of the initial stage in the breakup of a continent. Here, tensional forces have stretched and thinned the crust, allowing molten rock to ascend from the mantle. Evidence for recent volcanic activity includes several large volcanic mountains including Mount Kilimanjaro and Mount Kenya, the tallest peaks in Africa. Research suggests that if rifting continues, the rift valley will lengthen and deepen, eventually extending out to the margin of the landmass (r;<;ur.E 5.1 ic). At this point, the rift will become a narrow sea with an outlet to the ocean. The Red Sea, which formed when the Arabian Peninsula split from Africa, is a modern example of such a feature. Consequently, the Red Sea provides us with a view of how the Atlantic Ocean may have looked in its infancy (figure 5.1 id).
QEOD^
Forces Within sSWHBe Plate Tectonics
New lithosphere is constantly being produced at the oceanic ridges; however, our planet is not growing larger—its total surface area remains constant. A balance is maintained because older, denser portions of oceanic lithosphere descend into the mantle at a rate equal to seafloor production. This activity occurs along convergent (con = together, vergere = to move) boundaries, where two plates move toward each other and the leading edge of one is bent downward, as it slides beneath the other.
Convergent boundaries are also called subduction zones, because they are sites where lithosphere is descending (being subducted) into the mantle. Subduction occurs because the density of the descending tectonic plate is greater than the density of the underlying asthenosphere. In general, oceanic lithosphere is more dense than the asthenosphere, whereas continental lithosphere is
(
Upwarping
figure 5.11
Continental rifting and the formation of a new ocean basin.
A.
The initial stage of con tinental rifting tends to include upwelling in the mantle that is associated with broad doming of the lith-osphere.Tensional forces and buoyant uplifting of the heated lithosphere cause the crust to be broken into large slabs.
b.
A
s the crust is pulled apart, large slabs of rock sink, generating a rift valley.
C.
Further spreading generates a narrow sea, similar to the present-day Red Sea.
D.
Eventually, an expansive ocean basin and ridge system are created.
)less dense and resists subduction. As a consequence, only oceanic lithosphere will subd ...
introduction of plate tectonics leading to finding the epicenter.
Divergent plate boundary is alsoincluded in the ppt. Search the activity sheet on this topic also uploaded here
Sedimentary basins are the depressions in the earth's crust where loose particles accumulate and finally lithified to form sedimentary rocks. Basins are particularly attractive to geoscientists from time immemorial due to the wealth hidden here in the form of oil, gas, coal etc. In this document you will find the types of basins, basin-fill types, methods of basin analysis and so on.
The Art Pastor's Guide to Sabbath | Steve ThomasonSteve Thomason
What is the purpose of the Sabbath Law in the Torah. It is interesting to compare how the context of the law shifts from Exodus to Deuteronomy. Who gets to rest, and why?
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
This is a presentation by Dada Robert in a Your Skill Boost masterclass organised by the Excellence Foundation for South Sudan (EFSS) on Saturday, the 25th and Sunday, the 26th of May 2024.
He discussed the concept of quality improvement, emphasizing its applicability to various aspects of life, including personal, project, and program improvements. He defined quality as doing the right thing at the right time in the right way to achieve the best possible results and discussed the concept of the "gap" between what we know and what we do, and how this gap represents the areas we need to improve. He explained the scientific approach to quality improvement, which involves systematic performance analysis, testing and learning, and implementing change ideas. He also highlighted the importance of client focus and a team approach to quality improvement.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
Ethnobotany and Ethnopharmacology:
Ethnobotany in herbal drug evaluation,
Impact of Ethnobotany in traditional medicine,
New development in herbals,
Bio-prospecting tools for drug discovery,
Role of Ethnopharmacology in drug evaluation,
Reverse Pharmacology.
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
We all have good and bad thoughts from time to time and situation to situation. We are bombarded daily with spiraling thoughts(both negative and positive) creating all-consuming feel , making us difficult to manage with associated suffering. Good thoughts are like our Mob Signal (Positive thought) amidst noise(negative thought) in the atmosphere. Negative thoughts like noise outweigh positive thoughts. These thoughts often create unwanted confusion, trouble, stress and frustration in our mind as well as chaos in our physical world. Negative thoughts are also known as “distorted thinking”.
3. INTRODUCTION
Plate tectonics is a scientific theory that describes the large-
scale motions of Earth's lithosphere.
The lithosphere is broken up into tectonic plates. On Earth,
there are seven or eight major plates and many minor plates.
Where plates meet, their relative motion determines the type
of boundary: convergent, divergent, or transform.
In geology, subduction is the process that takes place
at convergent boundaries by which one tectonic plate moves
under another tectonic plate and sinks into the mantle as the
plates converge. Regions where this process occurs are
known as subduction zones.
5. SUBDUCTION
When two oceanic plates collide, the younger of the two
plates, because it is less dense, will ride over the edge of the
older plate. [Oceanic plates grow more dense as they cool
and move further away from the Mid-Ocean Ridge]
The older, heavier plate bends and plunges steeply through
the asthenosphere, and descending into the earth, it forms a
trench that can be as much as 70 miles wide, more than a
thousand miles long, and several miles deep.
The Marianas Trench, where the enormous Pacific Plate is
descending under the leading edge of the Eurasian Plate, is
the deepest sea floor in the world.
It curves northward from near the island of Guam and its
bottom lies close to 36,000 feet below the surface of the
Pacific Ocean.
7. ABDUCTION
Abduction is the overthrusting of continental crust by oceanic crust or
mantle rocks at a convergent plate boundary
This process is uncommon as the denser oceanic lithosphere usually
subducts underneath the less dense continental plate.
Abduction occurs where a fragment of continental crust is caught in a
subduction zone with resulting overthrusting of oceanic mafic and
ultramafic rocks from the mantle onto the continental crust.
Abduction often occurs where a small tectonic plate is caught between two
larger plates, with the crust (both island arc and oceanic) welding onto
an adjacent continent as a new terrane.
8. When two continental plates collide, abduction of the
oceanic crust between them is often a part of the
resulting orogeny.
Abduction is a process involving several mechanisms.
These may include up wedging, compressional
telescoping, gravity sliding or transformation of a
spreading ridge to a subduction zone.
Most abductions appear to have initiated at back-arc
basins above the subduction zones during the closing
of an ocean or an orogeny
10. TYPES OF ABDUCTIONS
1 Upwedging in subduction zones
2 Compressional telescoping onto Atlantic-type continental margins
3 Gravity sliding onto Atlantic type continental margins
4 Transformation of a spreading ridge to a subduction zone
5 Interference of a spreading ridge and a subduction zone
6 Obduction from rear-arc basin
7 Obduction during continental collision
11. UPWEDGING IN SUBDUCTION ZONES
• This process is operative beneath and behind the inner walls of
oceanic trenches (subduction zone) where slices of oceanic crust
and mantle are ripped from the upper part of the descending plate
and wedged and packed in high pressure assemblages against the
leading edge of the other plate.[1]
• Weakening and cracking of oceanic crust and upper mantle is likely
to occur in the tensional regime. This results in the incorporation of
ophiolite slabs into the overriding plate.[2]
• Progressive packing of ophiolite slices and arc fragments against
the leading edge of a continent may continue over a long period of
time and lead to a form of continental accretion.
12. COMPRESSIONAL TELESCOPING ONTO
ATLANTIC-TYPE CONTINENTAL
MARGINS
Figure 1: A, B, C. Obduction of an ophiolite sheet by the partial
subduction of an Atlantic type continental margin. D, E, F, G.
Obduction of an arc-trench gap ophiolite sheet by the collision of an
Atlantic type continental margin with a volcanic arc. 1=Continental
crust, 2= Oceanic Crust, 3= Mantle, 4= Continental rise sediments,
5=oceanic sediments, 6= Volcanogenic sediments,
7=silicic/intermediate volcanics, 8=low-velocity zone.
The simplest form of this type of obduction may follow from the
development of a subduction zone near the continental margin
shown in figure 1A. Above and behind the subduction zone, a welt
of oceanic crust and mantle rides up over the descending plate. The
ocean, intervening between the continental margin and the
subduction zone is progressively swallowed until the continental
margin arrives at the subduction zone and a giant wedge or slice
(nappe) of oceanic crust and mantle is pushed across the
continental margin. (Fig 1B)[citation needed]
Because the buoyancy of the
relatively light continental crust is likely to prohibit its extensive
subduction, a flip in subduction polarity will occur yielding an
ophiolite sheet lying above a descending plate. (Fig 1C) [3]
If however, a large tract of ocean intervenes between the
continental margin the subduction zone, a fully developed arc and
back arc basin (Fig 1D) may eventually arrive and collide with the
continental margin. Further convergence may lead to overthrusting
of the volcanic arc assemblage (Fig 1E, 1F) and may be followed by
flipping the subduction polarity. (Fig 1G)
According to the rock assemblage as well as the complexly
deformed ophiolite basement and arc intrusions, the Coastal
Complex of western Newfoundland may well have been formed by
this mechanism.
13. GRAVITY SLIDING ONTO ATLANTIC TYPE
CONTINENTAL MARGINS
• This concept involves the progressive uplift of
an actively spreading oceanic ridge, the
detachment of slices from the upper part of
the lithosphere and the subsequent gravity
sliding of these slices onto the continental
margin. This concept was advocated by
Reinhardt for the emplacement of the Semail
Complex in Oman and argued by Church and
Church and Stevens for the emplacement of
the Bay of Islands sheet in western
Newfoundland.
14. TRANSFORMATION OF A SPREADING RIDGE TO A
SUBDUCTION ZONE
• Many ophiolite complexes were emplaced as thin hot
obducted sheets of oceanic lithosphere shortly after
their generation by plate accretion. The change from a
spreading plate boundary to a subduction plate
boundary may result from rapid rearrangement of
relative plate motion. Transform moving from pure
strike slip to oblique compression fields could become
subduction zones, the side with the higher, hotter,
thinner lithosphere riding over the lower, colder
lithosphere. This mechanism would lead to obduction
of ophiolite complex if it occurred near a continental
margin.
15. INTERFERENCE OF A SPREADING
RIDGE AND A SUBDUCTION ZONE
• Figure 2: Various possible geometric relationships
resulting from the progressive interaction of a
subduction zone and a spreading ridge. 1=continental
crust, 2=oceanic crust, 3=mantle, 4=oceanic
sediments, 5=volcanogenic sediments,
6=silicic/intermediate volcanics, 7=low-velocity zone
• In the situation where a spreading approaches a
subduction zone, the ridge collides with the subduction
zone, at which time there will develop a complex
interaction of subduction related tectonic sedimentary,
and spreading related tectonic igneous activity. The left
over ridge may either subduct or ride upward across
the trench onto arc trench gap and arc terranes as a
hot ophiolite slice. These two mechanisms are shown
in figure 2 B and C.[10]
Two examples of this interaction
of a ridge colliding into a trench are well documented.
The first one is the progressive diminution of the
Farallon plate off California. Ophiolite obduction by the
above proposed mechanism would not be expected as
the two plates share a dextral transform boundary.
However, the major collision of the Kula/Pacific plate
with the Alaskan/Aleutian resulted in the initiation of
subduction of the Pacific plate beneath Alaska, with no
sign of either obduction or indeed any major
manifestation of a ridge being “swallowed”.[11]
16. ABDUCTION FROM REAR-ARC BASIN
• Dewey and Bird [12]
suggested that a common form of ophiolite obduction is related
to the closure of rear-arc marginal basins and that, during such closure by
subduction, slices of oceanic crust and mantle may be expelled onto adjacent
continental forelands and emplaced as ophiolite sheets. In the high heat-flow
region of a volcanic arc and rear-arc basin the lithosphere is particularly thin. This
thin lithosphere may preferentially fail along gently dipping thrust surface if a
compressional stress is applied to the region. Under these circumstances a thin
sheet of lithosphere may become detached and begin to ride over adjacent
lithosphere to finally become emplaced as a thin ophiolite sheet on the adjacent
continental foreland.[13]
This mechanism is a form of plate convergence where a
thin, hot layer of oceanic lithosphere is obducted over cooler and thicker
lithosphere.
17. ABDUCTION DURING CONTINENTAL
COLLISION
• Figure 3: Obduction of oceanic, arc-trench gap, ophiolite
sheets by the progressive convergence, collision, and
suturing of two continents. 1=continental crust,
2=oceanic crust, 3=mantle, 4=continental rise
sediments, 5=oceanic sediments, 6=volcanogenic
sediments, 7=silicic/intermediate volcanics, 8=exo-
geosynclinal flysch and molasse, 9=low velocity zone.
• Figure 3 shows the sequence of events illustrating the
obduction model following continental collision. As an
ocean is progressively trapped in between two colliding
continental lithospheres, the rising wedges of oceanic
crust and mantle rise are caught in the jaws of the
continent/continent vise and detach and begin to move
up the advancing continental rise. Continued
convergence may lead to the overthrusting of the arc-
trench gap and eventually overthrusting of the
metamorphic plutonic and volcanic rocks of the volcanic
arc. (Fig 3D) Following total subduction of oceanic tract,
continuing convergence may lead to a further sequence
of intra-continental mechanisms of crustal shortening.
This mechanism is thought to be responsible for the
various ocean basins of the Mediterranean region. The
Alpine belt is believed to register a complex history of
plate interactions during the general convergence of the
Eurasian plate and African plates.