Introduction
Four tectonic environments in which magmatism occurs: destructive plate margins, constructive plate margins/divergent plate boundaries, oceanic intraplate and continental intraplate. Arcs are magmatic products of destructive plate margins (stern, 2001) which are referred to as sites where new continental crust is created and old oceanic crust is subducted back into the mantle (Hawkesworth , Hergt, McDermott, Ellam, 1991). An island arc is a form of an arc produced by the subduction of an oceanic plate beneath another oceanic plate (Hu, 2013). Island arcs are characterised by high large ion lithophile elements and low high field strength elements ((Hawkesworth , Hergt, McDermott, Ellam, 1991). New oceanic crust is created at the mid ocean ridges and by mass balance is then destroyed (recycled back into the mantle) at the subduction zones (Jarred, 2003). As it forms it undergoes hydrothermal alteration where the composition is changed from olivine, plagioclase and glass dominated to being dominated by clay minerals i.e. low grade metamorphism (green schist facies) (Jarred, 2003) where it becomes enriched in water, carbon dioxide and incompatible trace elements such as uranium and potassium. As the crust moves away from the ridge it accumulates sediments and becomes colder, older and dense enough to subduct. As the cold slab subducts into the hot mantle, it heats up. The slab goes to greater depths faster than it’s heated therefore pressure increases therefore hydrous minerals start to break down (Aizawa, Tatsumi, Yamada, 1999). The slab undergoes metamorphic reactions from hydrous green schist facies to amphibolite facies and finally to anhydrous eclogite facies at depths of less than 100 km (Ringwood, 1977). ...
... middle of paper ...
... Leeman1, Dante Canil2, Zheng-Xue A Li ; 2005; Similar V/Sc Systematics in MORB and Arc Basalts: Implications for the Oxygen Fugacities of their Mantle Source Regions; Journal of petrology; volume 46; number 11; pages 2313-2336
Catherine A. McCammon; Mantle Oxidation State and Oxygen Fugacity: Constraints on Mantle Chemistry, Structure, and Dynamics; Bayerisches Geoinstitut
Clive R. Neal, Lawrence A. Taylor; 1989; a negative Ce anomaly in a periditite xenolith: Evidence for crustal recycling into the mantle or metasomatism?
A.E. Ringwood; 1977; Petrogenesis in island arc systems; American geophysical union
Charles R. Stern; 2011; Subduction erosion: Rates mechanisms, and its role in arc magmatism and the evolution of the continental crust and mantle; Elsevier, pages 284-308
John D. Winter; 2001; an introduction to igneous and metamorphic petrology
The area composed of the Gander, Nashoba, Avalon, and Meguma Terranes has been extensively studied for many years. However, it was only recently that the terranes were recognized as distinct geologic entities with unique tectonic histories thus there is still much debate regarding the tectonic model which brought these terranes together (Hon et al., 2007). This paper will address the geology of the peri-Gondwanan terranes and propose a potential tectonic model for the accretional orogenic events. It will also primarily focus on the juxtaposition between the Nashoba and Avalon Terranes.
The Starved Rock Member of the Saint Peter Sandstone is preserved as a northeast-southwest trending belt of strata that is ...
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
Villaros, A., Stevens, G., Moyen, J. & Buick, I.S. 2009, "The trace element compositions of S-type granites: evidence for disequilibrium melting and accessory phase entrainment in the source", Contributions to Mineralogy and Petrology, vol. 158, no. 4, pp. 543-561.
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.
They examined how much iron, molybdenum and other metals were in the environments. “These proxies seemed to indicate that oxygen concentrations in the oceans rose in several steps, approaching today's sea-surface concentrations at the start of the Cambrian, around 541 million years ago — just before more-modern animals suddenly appeared and diversified. This supported the idea of oxygen as a key trigger for the evolutionary explosion ”(Fox).
Strata, which have contained fossils in the past, are sharply defined layers that differentiate between sedimentary rocks. Although evolutionists struggle to explain why strata have such unusual characteristics, Brown’s idea of liquefaction describes why they are found in strata. The reason why fossils and strata do not form in large scale quantities today is also due to liquefaction. Liquefaction greatly sorted out all of the layers of sediments and rock, and this is why strata are organized. Without the Flood, which caused global liquefaction, strata would not be as common.
Using the topics provided in the course syllabus, I came up with three categories in total.
Convection currents deep in the mantle of the earth, begin to well up towards the surface. As the pressure increases, it sets the crustal plates in motion. There are different kinds of mountains - Volcanic, Folded, Fault-block, and Dome mountains. Volcanic mountains are formed when magma comes up through cracks in the Earth’s crust and explodes out of lava and ash. The Hawaiian volcanoes, Mt. Hood, Mt. Etna, Vesuvius, and Mt. Saint Helens is an example of volcanic mountains.
The most dramatic expression of tectonism is mountainous topography, which is either generated along continental margins by collisions between the slablike plates that make up the Earth's lithosphere or formed somewhat farther inland by rifting and faulting. Far more subtle tectonic expressions are manifested by the vast continental regions of limited relief and elevation affected by gentle uplift, subsidence, tilting, and warping. The denudational processes act upon the tectonic "stage set" and are able to modify its features in a degree that reflects which forces are dominant through time. Volcanism as a syn-tectonic phenomenon may modify any landscape by fissure-erupted flood basalts capable of creating regional lava plateaus or by vent eruptions that yield individual volcanoes.
The partition coefficient of the metals with the melt determines which element will prefer to stay in the melt or move from the melt. Therefore, this describes the Behaviour of metals during partial melting and fractionation crystallization. The partition coefficient depends on pressure, the composition of the solid, the composition of the melt and the temperature. The results that are discussed above indicate that melt of are clinopyroxene rich rocks are expected to have low Mn/Fe, Co/Fe, Ni/Co, Mn/Zn and high Zn/Fe compared to peridotite(Olivine + othopyroxene) partial melts. Throughout the process of fractional crystallization the metals (Pb, Zn and Mo) partition into crystallizing minerals or remain dissolved in the melt.
the eruptive history of Somma-Vesuvius (1). Each was preceded by a long period of stillness, which in the case of the 79 A.D. eruption lasted about 700 years. These eruptions were fed by viscous water-rich phonotitic to tephritic phonolitic magmas that appear to have differentiated in shallow crustal conditions. They are believed to have slowly filled a reservoir where differentiation was driven by compositional convection. A minimum depth of about 3 km was inferred for the top of the magmatic reservoir from
The concurrent convective circulations in the mantle leads to some segments of the mantle moving on top of the outer core which is very hot and molten in nature. This kind of movement in different segments occurs as tectonic plates. These tectonic plates are basically seven on the earth surface as major ones, although, several small ones exist also. The plates motions are characterized by varying velocities, this variance results to sub sequential collision of two plates (leading to formation of a mountain in a convergent boundary), drift of two plates (leading to formation of rifts in a divergent boundary), or parallel movement in a transform boundary(Webcache 3).