Review of Subduction Slabs Study: From a variety of observations
Prepared by: Yang Yang
September 25, 2014
Abstract
Subduction zones are sites of convective downwelling of Earth’s lithosphere, which provides the dominate force of the driving force for mantle convection. It is through subducted slabs that oceanic crust and sediments, including volatile compounds are recycled back into mantle. Studying subduction slab is one of the most important parts of studying lithosphere dynamics. There have been a number of recent reviews of subduction zones with some specifically focusing on seismology, the mantle wedge, phase changes, the fate of slabs and water in mantle. However, in this review, I attempt to provide a broad summary that emerges from recent observations and model of subduction. Our understanding of the geometry and composition of subducted slabs, as well as the physical process of subduction, comes from indirect observation including earthquake seismology, gravity, topography, geochemistry, and petrology of island arc lavas. Also, numerical calculations of the dynamics of subducted slabs and slab thermal models also play an important role to test the model we build based on our observations. This review will include most of recent studies on these aspects. Finally, I will try to sum up the challenges on our future study of subduction slabs.
Slab Geometry Study from seismology
In history, the geometry of subducted slab is studied by earthquake hypocenter and
This lab uses earthquake data to construct profiles of two convergent boundaries: the Tonga Trench and the Peru-Chile Trench. Where two tectonic plates converge, if one or both of the plates is an oceanic lithosphere, a subduction zone will form. When crust is formed at a mid-ocean ridge, it is hot and buoyant meaning it has a low density. As it spreads away from the ridge and cools and contracts, or becomes denser, it is able to sink into the hotter underlying mantle. 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. The density of the
As a tectonic plate slides into the mantle, the heat releases fluids trapped in the plate. Seawater and carbon dioxide, rise into the upper plate and can partially melt the overlying crust, forming magma. And magma most likely means volcanoes are around.
The theory of plate tectonics states that the Earth’s lithosphere (top layer of the Earth’s crust) is split up into rigid sections called plates that are moving relative to one another as they move on top of the underlying semi-molten mantle. These plates are either continental, The North American Plate, or oceanic, The Nazca Plate.
The gravitational stress on the volcano flanks develops large-scale on-shore and off-shore sliding, related to the activity of the rift zones. The M=7.2 earthquake at Kilauea on 1975 was probably related to strain accumulated throughout the south flank from dikes intruded in the rift zone (Swanson et al., 1976). However, the earthquake itself resulted from abrupt southward movement of the south flank across the underlying oceanic crust, activating the Hilina-Pali fault system. Such faulting not only provides a means for the flanks to adjust continuously to intrusions, but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis. Therefore, rift intrusion and lateral spreading are major contributors
The new volcanic material welling up into the void, which forms a ribbon of new materials and breaks down its center gradually, when the plates move apart from the axis of the mid-oceanic ridge system. Therefore, every separating plate accretes one half a ribbon of new lithosphere, and, thus, a new surface is added (Pitman, W.C, 2007). The process is continuous, and separation is always happening at the
Pushing forces generated in the lithosphere above the adjacent downgoing portion of the convection cell result in the formation of a deep-sea trench that eventually develops into what type of plate
A period of volcanism resulted in igneous intrusions within the Raton Basin-Sierra Grande Uplift Province that was sourced from the upper mantle about 26. 6 billion years ago and is associated with parallel dikes and sills (Higley, 2007). Igneous rocks are common within the Raton Basin and include Tertiary dikes and sills that range in age from 6.7 to 29 5 million years ago (Flores and Bader, 1999). One of the main differences between dikes and sills is that dikes are longer lived magma conduits and sills are features that form when magma is in neutral buoyancy with the surrounding rock (Rooper et al., 2006). These volcanic events are associated with hydrothermal alteration of coal within the basin (Higley, 2007).
Initially, earthquakes shape the Earth’s surface by creating mountains and geysers. In the article “Historic Earthquakes,” it reads, “High intensities were observed in the northwest section of Yellowstone National Park. Here, new geysers erupted, and massive slumping caused large cracks in the ground from which steam emitted” (Stover 3). Consequently, when the geo-process of earthquakes occurs, it molds and changes the earth by creating new geothermal
It is minimal realized that lying underneath one of The United States biggest and most beautiful National Parks - Yellowstone Park - is one of the biggest "super volcanoes" on the planet. Every year, a huge number of guests come to respect the hot springs and fountains of Yellowstone, the Nation's first national park. Few are mindful that these miracles are powered by hotness from a vast repository of incompletely liquid rock (magma), simply a couple of miles underneath their feet. As this magma-which drives one of the world's biggest volcanic frameworks climbs, it pushes up the Earth's hull underneath the Yellowstone Plateau.
On Friday March 11th, 2011 at 2:46 pm, the fifth largest earthquake recorded since 1900 with a magnitude of 9.0, 1.7 Richter scale points greater than the devastating Vancouver Island earthquake of 1946, struck the coast of Japan, 231 miles northeast of Tokyo1, causing a devastating regional and global catastrophe.
Annotated Bibliography Capra, L. (2006). Abrupt climatic changes as triggering mechanisms of massive volcanic collapses. Journal of Volcanology and Geothermal Research, 155(3), 329-333. This article explains how volcanic collapse can affect the climate.
The different tectonic plates rest on the mantle, a very hot layer of earth that is directly beneath the crust. There are seven major tectonic plates, their names are The Pacific Plate, The North American Plate, The Eurasian Plate, The African Plate, The Antarctic Plate, The Australian Plate, and The South American Plate. In addition to these major plates there are also many smaller tectonic plates that make up parts of the Earth's crust. When the boundaries between plates shift, this causes earthquakes. There are three types of movements that cause earthquakes. Divergent is when the plates move away from each other, Subduction is when one plate moves underneath another, and Transform is when the plates grind against each other. The lithosphere is another name for earth's crust and mantle, it is made up of all the tectonic
Subduction zone magmas are formed by convergent plate boundaries between oceanic-continental plates or oceanic-oceanic plates (at least one tectonic plate has to be oceanic) (see Fig.1). According to Grotzinger and Jordan (2010), when the oceanic lithosphere gets subducted, there is fluid induced melting occurring to the mantle wedge. Therefore, this generates magmas of varying composition.
The Aleutian Trench is part of the Pacific Ring of Fire and is located along a convergent plate boundary. At this plate boundary, two plates are colliding. More specifically, this oceanic trench is a subduction zone in which the Pacific Plate is being subducted under the North American Plate. This occurs because the Pacific Plate, an oceanic plate, is denser than the North American plate, a continental plate and thus gets swallowed into the Earth’s mantle. As the denser plate is subducted under the other, the trench is formed. In addition to the formation of the trench, a subduction zone also forms a volcanic arc which occurs because as the Pacific plate is descending into the mantle, it begins to melt. The melted rock consequently rises to
Heat emission from subduction zones can take many forms, such as volcanoes, geysers and hot springs. When lateral plate movement induced gaps occur between plates, collisions occur between other plates. This results in partial plate destruction. This causes mass amounts of heat to be produced due to frictional forces and the rise of magma from the mantle through propagating lithosphere fractures and thermal plumes sometimes resulting in volcanism. During plate movement, continental plates are constantly being consumed and produced changing plate boundaries.