Tectonic spreading

Sediment-free, on-axis systems at tectonic spreading centres, which have high temperature gradients (as they lie directly above magma chambers). The mean temperature of the ejected water is 620-640 K, the throughput 24 km3/year. 

Some trace metals are transported into the ocean as a component of hydrothermal fluids. This process is discussed further in Chapter 19- To briefly summarize, hydrothermal fluids are produced when seawater penetrates into cracks in the crust near tectonic spreading centers. The seawater is heated as it comes into contact with magma. The hot seawater leaches a number of trace metals from the magma. The resulting hydrothermal fluids are acidic and do not contain O2, so most of the metals are present in reduced form. Because of their high temperatures, the hydrothermal fluids have a lower density than cold seawater. Their increased buoyancy causes them to rise until they are emitted into the deep sea. Admixture with cold, oxic, alkaline seawater causes the hydrothermal metals to undergo various redox and precipitation reactions. 

The present-day best estimates are that l riv/l hydro is about 300. As l hydro increases, e.g. faster spreading of ocean crust at ridges, Csw responds. The dominant control is tectonics. 

Plate tectonics The theory that posits crustal plate movement is caused by seafloor spreading and subduction. 

The fold is complicated by trust fault as a result Neogene sediments impend from the north onto Paleological sediments of the Ninotsminda dome. That dome is believed to have a 2-storey construction. The tectonic of upper storey, which is mostly represented by Neogene sediments, does not correspond to Eocene sediments construction of lower storey. Wells under the thrust prove up cast debris, which is spread along north and south limbs of the Ninotsminda fold that configured horst construction of the whole fold. 

Divergent plate boundary Areas where adjacent tectonic plates are separating. A spreading zone. Dolomite A calcium-magnesium carbonate mineral, CaMg(C03)2-Dolostone A sedimentary carbonate rock primarily consisting of dolomite. 

Spreading zone A divergent boundary between two tectonic plates where magma from the asthenosphere rises and creates new crust on the adjacent plates. The Mid-Atlantic Ridge is an example of a spreading zone. 

Eaton GP, Wahl RR, Prostka JH, Mabey DR, Kleinkopf MD (1978) Regional gravity and tectonic patterns then-relation to late Cenozoic epeirogeny and lateral spreading in the western Cordillera. Geol Soc Am Mem 152 51-91... 

Plate tectonic activity, which is responsible on Earth for subduction zones, spreading centres and obducted ophiolites, as well as associated ore deposits of Cu, Cr and Ni described in 8.6, appears to have been less significant on other terrestrial planets. As a result, local enrichments of these and other transition elements (apart from Fe and Ti) are probably absent on the Moon, Mercury, Venus, Mars and the asteroids. Since Fe and Ti minerals are predominant on terrestrial planets, electronic spectra of Fe2+ and Fe3+ in silicates and oxides influenced by Ti4+ and Ti3+ are expected to dominate remote-sensed spectra of their surfaces. 

SeatItKir spreading, continental drift and plate tectonics have pemicaied getK hcniisiry. W e linallv understand the fate of settimenis and oceanic crust in subduclion /ones, their hurial and Iheir... 

Until the arrival of the theories of plate tectonics and seafloor spreading in the 1960s, the Earth s mantle was generally believed to consist... 

In the modern tectonic environment, melt extraction from the uppermost mantle occurs in numerous settings that include oceanic and continental spreading centers, hot-spots, and sub-duction zones, with the vast majority of melt... 

Modern oceanic mantle is defined solely by abyssal peridotites, which are samples of harzbur-gite and Iherzolite collected from fracture zones at oceanic spreading centers, and these samples are representative of shallow oceanic lithosphere that has been processed at mid-ocean ridges (see Chapter 2.04). Two types of continental mantle lithosphere are considered (i) cratonic mantle, which refers to xenoliths collected from kimberlites that sample portions of mantle beneath stable, Archean cratons and (ii) off-craton mantle, which refers to xenoliths collected from alkalic basalts that have sampled portions of the subcontinental mantle adjacent to ancient cratonic mantle (see Chapter 2.05). Also included with off-craton lithosphere are orogenic Iherzolites and ophiolites, which are slices of mantle tectonically emplaced typically at convergent margins. 

Karson J. A., Hurst S. D., and Lonsdale P. (1992) Tectonic rotations of dikes in fast-spread oceanic crust exposed near Hess Deep. Geology 20, 685-688. 

Haymon R. M., Fornari D. J., Edwards M. H., Carbotte S., Wright D., and Macdonald K. C. (1991) Hydrothermal vent distribution along the East Pacific Rise crest (9°09 -54 N) and its relationship to magmatic and tectonic processes on fast-spreading mid-ocean ridges. Earth Planet. Sci. Lett. 104, 513-534. 

Charlou J.-L., Fouquet Y., Donval J. P., Auzende J. M., Jean Baptiste P., Stievenard M., and Michel S. (1996) Mineral and gas chemistry of hydrothermal fluids on an ultrafast spreading ridge East Pacific Rise, 17° to 19°S (NAUDUR cruise, 1993) phase separation processes controlled by volcanic and tectonic activity. J. Geophys. Res. 101, 15899-15919. 

The concept of global tectonics (Dietz, 1961 Hess, 1962 Morgan, 1968 Le Pichon et al., 1973) combined the earlier proposals of continental drift and seafloor spreading into a unified theory of terrestrial dynamics. It introduced the notion of continual generation and destruction of oceanic crust and implied similar consequences for other tectonic realms. 

The above view is clearly supported by the mass/age distribution of lithologies within the same tectonic domain. For example, carbonates, chert, red clay, and terrigeneous sediments on the ocean floor (Hay et al., 1988) all have the same type of age distribution pattern that is controlled by a single variable, the rate of spreading and subduction of the ocean floor. This sedimentary mass also differs lithologically from its continental counterpart, because it is comprised of... 

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