Life cycle of oceanic crust spreading ridges Ophiolites

1. LIFE CYCLE OF OCEANIC
CRUST
SPREADING RIDGES
OPHIOLITES
Geo-
Tectonics

2. KHAWAJA UMAIR MAJEED
ROLL NO 38
SECTION: MORNING
SEMESTER: 7TH
Dr. Raja
Jhanzaib

3. LIFE CYCLE OF
OCEANIC CRUST
Oceanic crust is continuously being created at mid-ocean ridges. As plates diverge at
these ridges, magma rises into the upper mantle and crust. As it moves away from
the ridge, the lithosphere becomes cooler and denser, and sediment gradually builds
on top of it. The youngest oceanic lithosphere is at the oceanic ridges, and it gets
progressively older away from the ridges.
As the mantle rises it cools and melts, as the pressure decreases and it crosses
the solidus. The amount of melt produced depends only on the temperature of the
mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very
slow spreading ridges (<1 cm·yr−1 half-rate) produce thinner crust (4–5 km thick) as
the mantle has a chance to cool on upwelling and so it crosses the solidus and melts
at lesser depth, thereby producing less melt and thinner crust.

5. SPREADING RIDGES
A spreading ridge is the fracture zone along the ocean bottom where molten mantle
material comes to the surface, thus creating new crust. This fracture can be seen
beneath the ocean as a line of ridge that form as molten rock reachs the ocean bottom
and solidifies.
Mid oceanic ridges perfectly falls in this category.

6. MID OCEANIC RIDGE
A long mountain range on the ocean floor, extending almost continuously through
the North and South Atlantic Oceans, The Indian Ocean and the South Pacific
Ocean. A deep rift valley is located at its center, from which magma flows and forms
new oceanic crust. As the magma cools and hardens it becomes part of the mountain
range.

8. DEEP SEA TRENCHES
Deep-sea trench, also called oceanic trench , any long, narrow, steep-sided
depression in the ocean bottom in which occur the maximum oceanic depths,
approximately 7,300 to more than 11,000 meters (24,000 to 36,000 feet). They
typically form in locations where one tectonic plate subducts under another. The
deepest known depression of this kind is the Mariana Trench, which lies east of
the Mariana Islands in the western North Pacific Ocean; it reaches 11,034 meters
(36,200 feet) at its deepest point.

10. OPHIOLITES
An Ophiolite is a section of the Earth's oceanic crust and the underlying
upper mantle that has been uplifted and exposed above sea level and often emplaced
onto continental crustal rocks. Ophio is Greek for snake, and lite means stone from
the Greek lithos , after the often-green-color rocks (spilites and serpentines) that
make up many ophiolites.
The term ophiolite was originally used by Alexandre Brongniart for an assemblage
of green rocks (serpentine subgroup, diabase) in the Alps; Gustav Steinmann later
modified its use to include serpentine, pillow lava, and chert ("Steinmann's trinity"),
again based on occurrences in the Alps.

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