Sea-floor spreading

One of the most remarkable successes of paleomagnetism has been in the study of sea floor spreading. 

It has been established that the He/ He ratio has values characteristic of the source of the gas. Deep oceanic waters over rift zones and sea-floor spreading centres are found not only to be enriched in total He, relative to the solubility equilibrium with the atmosphere. 

Relatively recent (<1 Ga) volcanic resurfacing of Venus may have erased earlier evidence for plate tectonics, and there is some discussion on whether Mars may have experienced sea-floor spreading early in its history (e.g. Connemey et al. 1999 see also Stevenson 2001). 

Microorganisms are found in a variety of environments aquatic, marine, ground water, soil, and even in the arctic. Many are found in extreme environments from tundra to the superheated smokers at the sites of sea floor spreading. The adaptability of microorganisms extends to the degradation of many types of xenobiotics. 

LIPs are sites of extensive basaltic volcan-ism, which originate in a manner which is separate from the processes of sea-floor spreading. 

Helmstedt, H., Padgham, W.A., and Brophy, J.A., 1986. Multiple dykes in the Lower Kam Group, Yellowknife greenstone belt evidence for Archaean sea-floor spreading. Geology, 14, 562-6. 

Masson, D.G. Miles, P.R. (1984) Mesozoic sea-floor spreading between Iberia, Europe and North America. Mar. Geol., 56, 279-287. 

J. A. Welhan, H. Craig. Methane, hydrogen and helium in hydrothermal fluids at 21° N on the East Pacific Rise, Hydrothermal Processes at Sea Floor Spreading Centers, P. Rona et al. (Ed.), 391-409,1983. 

Holser WT, Schidlowski M, Mackenzie FT, Maynard JB (1988) Geochemical cycles of carbon and sulfur. In Gregor CB, Garrels RM, Mackenzie FT and Maynard JB (eds) Chemical Cycles in the Evolution of the Earth. John Wiley Sons, New York, p 105-173 Hunt JM (1972) Distribution of carbon in crast of earth. Am Assoc Petrol Geol Bull 56 2273-2277 Hunt JM (1979) Petroleum Geochemistry and Geology. W. H. Freeman, San Francisco Jannasch HW, Wirsen CO (1979) Chemosynthetic primary production at East Pacific sea floor spreading centers. BioSci 29 592-598... 

The Red Sea was opened by sea-floor spreading. Part of the motion of the Arabian Plate was turned into the Gulf of Aqaba along the Dead Sea transform. About 70 km of the slip occurred only 4-5 Ma ago (Ben-Avraham et al, 1979a,b). An age of 20-30 Ma BP is derived for the initial continental breakup of the Gulf of Aqaba. The lands bordering the Gulf in the area of... 

A constructive (or divergent) plate margin occurs when two plates move away from each other. It is marked by a mid-oceanic ridge where basaltic material wells up from the mantle to form new oceanic crust, in a process known as sea-floor spreading. The production of new crust at constructive plate... 

Schopf JM (1969) Ellsworth Mountains Position in West Antarctica due to sea-floor spreading. Science 164 63-66 Shackleton RM (1996) Precambrian collision tectonics in Africa. In Coward MP, Ries AC (eds) Collision tectonics. Special Publication, vol. 76. Geological Society London, London, pp 345-362... 

Continental drift was eventually taken seriously after it became possible in the 1950s to track the past movement of the continents by measuring the declination and the inclination of the magnetic field that was embedded in basalt flows at the time they crystallized (van Andel 1992 Smith 1992). The pattern of magnetic anomalies of the ocean floor that was revealed by Vine and Matthews (1963), combined with the recognition of island arcs by Wilson (1963a, 1965, 1973), supported the concept of sea-floor spreading... 

Schopf JM (1969) Ellsworth Mountains Position in West Antarctica due to sea-floor spreading. Science 164 63-66... 

Fig. 16.39 The Balleny Islands are located about 250 km north of the Pennell Coast of northern Victoria Land. They are the summits of volcanoes on a submarine ridge that is aligned with the Tasman Fracture Zone located north of the Pacific-Antarctic sea-floor spreading ridge. Volcanic eruptions on Buckle Island were reported in 1839 and 1899. However, an infrared survey published in 1969 did not detect any thermal anomalies (Burge tuid Parker 1969) (Adapted from Wright and Kyle (1990a) in LeMasurier and Thomson (1990))...

As well as around the K/T Boundary, there were earlier ones, for instance at the Permian/ Triassic (P/T) Boundary about 248 million years ago. When the former took place, there may have been an alteration in sea-floor spreading rates and a drop in the carbonate compensation depth (CCD) in the Atlantic, succeeded by a rise. Another such drop occurred in the Early Tertiary and may have been the result of a supernova. Four episodes were recognized in the... 

Right now, the best vehicle for finding new life forms isn t a starship, but a submarine. The Juan de Fuca ridge off the Pacific Northwest coast is a different kind of vent system from that of Clue 3. Here the sea floor spreads faster and the spires are more recent, with more sulfur, more acid, and much hotter temperatures. These temperatures both form and break bonds with alacrity. 

Yeats, R. S. Southern California structure, sea-floor spreading, and history of the Pacific Basin. Geol. Soc. Am. Bull. 79, 1693—1702 (1968). 

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