Explain how the slab component is generated in island arc igneous rocks. Consider both the fore-arc and back-arc basin environments
Island arcs form as oceanic plate subducts under oceanic plate. Volcanism is concentrated in an arc of volcanoes, generally approximately located above the leading edge of the subducting plate. A trench often forms where the slabs meet and subduction begins. On the non subducting slab a series of basins form, with a fore-arc basin nearest the subduction/trench, then the main arc, and a back-arc basin on the far side (Mitchell and Reading, 1971; Frisch, Meschede and Blakey, 2010).
An island arc subduction zone. Modified from Frisch et al. (2010).
Magmas in island arc settings consist primarily of components from two different origins, the slab component, and the mantle wedge. The mantle wedge may melt due the descent of the slab, giving the main portion of the non-slab component. The slab component is derived from the subducting slab as it descends. This may consist of melting of the crustal portion of the slab, but also melting of the mantle wedge due to addition of water driven off the slab. Since the descending slab is composed of old, cold oceanic crust, there is a slight paradox in the idea of melts forming from it. However, frictional heat, as well as the heat of the underlying mantle, can drive hydrous fluids off the slab. (Machado, Chemale Jr., Conceição, Kawashita, Morata, and Van Schmus, 2003; Kimura and Yoshida, 2006).The addition of water to the mantle wedge results in the lowering of melting temperatures, allowing melts to be formed at much lower temperatures than might otherwise be expected. Also, the circulation of hot fluids allows materials dissolved in them to migrate upwards ...
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...eology. 16 (12), p1108-1111.
Paterson, S., and Tobisch, O. (1992). Rates of processes in magmatic arcs: implications for the timing and nature of pluton emplacement and wall rock deformation. Journal of Structural Geology. 14 (3), p291-300.
Schaltegger, U., Zeilinger, G., Frank, M., and Burg, J-P. (2002). Multiple mantle sources during island arc magmatism: U–Pb and Hf isotopic evidence from the Kohistan arc complex, Pakistan. Terra Nova. 14 (6), p461-468.
Smith, I. E. M., Price, R. C., Stewart, R. B., and Worthington, T. J. (2009). An assessment of the mantle and slab components in the magmas of an oceanic arc volcano: Raoul Volcano, Kermadec arc. Available: http://researchcommons.waikato.ac.nz/bitstream/10289/2685/1/Price assessment.pdf. Last accessed 10th Jul 2011.
van der Pluijm, B., and Marshak, S. (2004). Earth Structure. New York: WW Norton & Company.
Marshak, S. (2009) Essentials of Geology, 3rd ed. New York: W.W. Norton & Company, ch. 11, p. 298-320.
17. The diagram to the right illustrates what type of geologic event? Explain. (S6E5e, f)
Tarbuck E., Lutgens F., Tasa D., 2014, An Introduction to Physical Geology, 5th Ed, Pearson Education, Upper Saddle River, New Jersey.
Plummer, C.C., McGeary, D., and Carlson, D.H., 2003, Physical geology (10th Ed.): McGraw-Hill, Boston, 580 p.
Stone Mountain rises in sharp contrast to the surrounding flat, rolling landscape creating a geomorphic monadnock. Geologists appear to have consensus of the volcanic origins and underground formation of t...
One of the first people to study the xenoliths at El Joyazo was Zeck (1970); Zeck hypothesised that the xenoliths and dacitic lava of El Joyazo were derived syn-genetically from a semi-pelitic rock through anatexis. The protolith rock was thought to be separated into anatectic restites, represented by Al-rich xenoliths, and anatectic melt, represented by the dacitic lavas. The xenoliths were classified into three types: (1) almandine-biotite-sillimanite gneiss, (2) quartz-cordierite gneiss and (3) spinel-cordierite rock. Types 1 & 2 were interpreted as restite material as their structure corresponded to that of migmatitic restite, and type 3 as re-crystallised restite. It was suggested that this re-crystallisation would have taken place after that anatexis that produced types 1 & 2. Zeck described the lava, based on chemical composition, as an almandine bearing biotite-cordierite-labradorite rhyodacite. The xenoliths were described as well rounded fragments up to 40cm in diameter. The xenoliths were said to show a well developed foliation defined by biotite and sillimanite, with the exception of the spinel-cordierite rock, which exhibited a granoblastic texture. It was also noted that quartz is almost completely absent from these rocks with the exception of small, rare armoured relicts.
and Metamorphic rocks can be found. There are also a lot of crusted plates, and violent
Mauna Loa is located on a hot spot in the Pacific Ocean. It is not near a plate boundary, in fact it is 3,200 km from the nearest plate boundary, and is situated in the middle of the Pacific tectonic plate. This is actually a rarity, as 90% of volcanoes are along a tectonic plate boundary. A hot spot occurs where long, stationary vertical pools of magma rise up and towards the plate. Movement of the tectonic plates above the hot spot created Mauna Loa, along with the other Hawaiian volcanoes. The older Hawaiian Islands were once above this stationary hot spot, but have been carried northwest by the slowly moving Pacific plate. As the plate moves, it carries the previously formed, older, volcanoes with it, creating a trail of younger, new volcanoes behind. The islands are lined up along the Hawaiian Ridge-Emperor Seamounts chain, which is 3,750 miles and includes Kauai, Maui, Oahu and Hawai’i, from north to south, respectively. There are around 80 volcanoes in this chain; most of them underwater, consequently the term seamount refer to submarine volcanoes. Three volcanoes of Hawai’i, Mauna Loa, Kilauea and Loihi seamount, are all currently sharing the Hawaiian hot spot. Although, recent evidence has shown that all three volcanoes use have separate plumbing systems to expel the lava from the pool of magma deep below them. It has also been suggested that Loihi is slowly moving Mauna Loa from the center of the island, thus shifting directly over the hot spot. The closer to the hot spot a volcano is, the more active it will be. The Hawaiian hot spot has laid down layers of lava, building up enormous islands from the ocean floor.
Riley, C.M. "Lahars." Geological and Mining Engineering Sciences. Michigan Tech. Web. 6 Feb. 2010. .
Basalt forms due to the partial melting of the layer of the mantle called the asthenosphere. The asthenosphere is the plastic zone of the mantle beneath the rigid lithosphere. Mantle plumes coming from the mesosphere can cause the asthenosphere to melt with heat or even if pressure decreases, which is called decompression melting (Richard 2011). The magma that forms from this melting is mafic magma that solidifies once it reaches the earth’s surface and cools quickly. The above process mainly occurs mainly during intraplate igneous activity which is the main explanation for volcanic activity that occurs a long distance away from a plate boundary. If the tectonic plate above the mantle plume is moving it can create a string of volcanic activity such as in Hawaii. See Fig 2.
As Kohala Volcano emerged from the sea and joined with Mahukona, a much larger Big Island began forming. With continued movement of the Pacific Plate, the center of volcanism migrated on to Mauna Kea and Hualalai, the middle-aged volcanoes, and finally on to Mauna Loa and Kilauea, which are the youngest volcanoes on the island. Over the geologically short time of several hundred thousand years, these volcanoes erupted thousands of thin flows which spread over, and built upon, older flows; each volcano growing until it finally emerged from the sea. As time went on, lava flows from one volcano began to overlap flows from other, nearby volcanoes and eventually the peaks coalesced into a single island, the Big Island. In geologically recent times, a new volcano, Loihi, began forming about 18 miles off the southeast coast of the Big Island.
Magma is a hot liquid made of melted minerals. Minerals can form crystals when they are cool. Igneous rock can form underground, where the magma cools. slowly. Or, igneous rock can form above ground, where the magma cools.
the surface it erupts as a volcano. Over time the ridge is built up by
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.
The interior structure of the earth is made up of crust, the mantle and core (inner core and outer core). Earthquakes occur on the crust. Crust forms the external layer of the earth surface. On the crust, the plate tectonics forces are in charge of causing the abrupt earth movements. Due to the existence of an immense temperature and concurrent pressure difference in the outer layer and inner layer of the earth, convection currents occur at the mantle. This energy results from overwhelming decomposition of radioactive substances contained by the rocks found at the interior of the earth. The developed convection currents lead to movement of lava; cold lava finds its way to the interior of the earth crust, while the molten lava which is generally hot, leaves the interior of the earth to the outside of the earth crust. These kinds of circulations occur at different locations of the earth surface and consequently results in segmentation of the earth due to movement in different directions.