XII. Discussion

1965 ◽  
Vol 258 (1088) ◽  
pp. 137-144 ◽  
Keyword(s):  
West Coast ◽  
Continental Drift ◽  
The United States ◽  
The Body ◽  
Lateral Movement ◽  
The West ◽  
Geological Evidence ◽  
The Earth ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

We have heard today about the palaeomagnetic evidence which requires the magnetic pole to wander through the body of the Earth and at the same time the continents to wander over the surface of the Earth, since Mesozoic times. We have heard the geological evidence reiterated as evidence of continental drift. Others in the past have equally ably demonstrated that this does not need to be considered evidence of continental drift. We have seen the continents authoritatively reconstructed by a computer. This seems most convincing except of course it seems necessary to discard Central America, Mexico, the Gulf of Mexico, the Caribbean Sea and the West Indies, along with their pre-Mesozoic rocks! On the other hand we have seen evidence that the ocean crust too breaks into blocks which shift relative to each other by distances up to 1400 km. A series of transcurrent faults occur along the west coast of the United States. Unmentioned is the similar fault along the east coast which extends across 600 km of the continent and out into the sea, continuing, some think, across the Atlantic to the mid-ocean ridge. On land this fault has been dated as pre-Mesozoic. It is at the same latitude as the Mendocino Escarpment off the west coast but shows right lateral movement while the latter shows predominantly left lateral movement.

scholarly journals A Climatology of 500-hPa Closed Lows in the Northeastern Pacific Ocean, 1948–2011

2014 ◽  
Vol 53 (6) ◽  
pp. 1578-1592 ◽  
Author(s):  
Nina S. Oakley ◽  
Kelly T. Redmond
Keyword(s):  
United States ◽  
Pacific Ocean ◽  
Interannual Variability ◽  
West Coast ◽  
The United States ◽  
Western United States ◽  
The West ◽  
Reanalysis Dataset ◽  
The Pacific ◽  
Northeastern Pacific

AbstractThe northeastern Pacific Ocean is a preferential location for the formation of closed low pressure systems. These slow-moving, quasi-barotropic systems influence vertical stability and sustain a moist environment, giving them the potential to produce or affect sustained precipitation episodes along the west coast of the United States. They can remain motionless or change direction and speed more than once and thus often pose difficult forecast challenges. This study creates an objective climatological description of 500-hPa closed lows to assess their impacts on precipitation in the western United States and to explore interannual variability and preferred tracks. Geopotential height at 500 hPa from the NCEP–NCAR global reanalysis dataset was used at 6-h and 2.5° × 2.5° resolution for the period 1948–2011. Closed lows displayed seasonality and preferential durations. Time series for seasonal and annual event counts were found to exhibit strong interannual variability. Composites of the tracks of landfalling closed lows revealed preferential tracks as the features move inland over the western United States. Correlations of seasonal event totals for closed lows with ENSO indices, the Pacific decadal oscillation (PDO), and the Pacific–North American (PNA) pattern suggested an above-average number of events during the warm phase of ENSO and positive PDO and PNA phases. Precipitation at 30 U.S. Cooperative Observer stations was attributed to closed-low events, suggesting 20%–60% of annual precipitation along the West Coast may be associated with closed lows.

Convection tectonics: some possible effects upon the Earth's surface of flow from the deep mantle

1988 ◽  
Vol 25 (8) ◽  
pp. 1199-1208 ◽  
Author(s):  
J. Tuzo Wilson
Keyword(s):  
Land Surface ◽  
Angle Of Incidence ◽  
Gulf Of Aden ◽  
Upward Flow ◽  
New Techniques ◽  
Ocean Ridges ◽  
The Earth ◽  
Mid Ocean Ridge ◽  
The Subject ◽  
Ocean Ridge

Until a little more than a century ago the land surface not only was the only part of the Earth accessible to humans but also was the only part for which geophysical and geochemical methods could then provide any details. Since then scientists have developed ways to study the ocean floors and some details of the interior of the Earth to ever greater depths. These discoveries have followed one another more and more rapidly, and now results have been obtained from all depths of the Earth.New methods have not contradicted or greatly disturbed either old methods or old results. Hence, it has been easy to overlook the great importance of these recent findings.Within about the last 5 years the new techniques have mapped the pattern of convection currents in the mantle and shown that these rise from great depths to the surface. Even though the results are still incomplete and are the subject of debate, enough is known to show that the convection currents take two quite different modes. One of these breaks the strong lithosphere; the other moves surface fragments and plates about.It is pointed out that if expanding mid-ocean ridges move continents and plates, geometrical considerations demand that the expanding ridges must themselves migrate. Hence, collisions between ridges and plates are likely to have occurred often during geological time.Twenty years ago it was shown that the effect of a "mid-ocean ridge in the mouth of the Gulf of Aden" was to enter and rift the continent. This paper points out some of the conditions under which such collisions occur and in particular shows that the angle of incidence between a ridge and a coastline has important consequences upon the result. Several past and present cases are used to illustrate that collisions at right angles tend to produce rifting; collisions at oblique angles appear to terminate in the lithosphere in coastal shears, creating displaced terrane, but in the mantle the upward flow may continue to uplift the lithosphere far inland and produce important surface effects; collisions between coasts and mid-ocean ridges parallel to them produce hot uplifts moving inland. For a time these upwellings push thrusts and folds ahead of them, but they appear to die down before reaching cratons.

Subduction initiation-induced rapid emplacement of garnet-bearing peridotites at a nascent forearc: Petrological and Os-Li isotopic evidence from the Purang ophiolite, Tibet

2021 ◽  
Author(s):  
Xiao-Han Gong ◽  
Ji-Feng Xu ◽  
Ren-Deng Shi ◽  
Ben-Xun Su ◽  
Qi-Shuai Huang ◽  
...  
Keyword(s):  
Oceanic Lithosphere ◽  
Garnet Peridotite ◽  
Chemical Compositions ◽  
Close Link ◽  
Geological Evidence ◽  
Subduction Initiation ◽  
Mid Ocean Ridge ◽  
Rapid Ascent ◽  
Melt Percolation ◽  
Ocean Ridge

Garnet-bearing peridotites commonly occur in the deeper parts of mature or thickened oceanic lithosphere, and are rarely exhumed and emplaced onto the seafloor. The Purang ophiolitic peridotites in south Tibet contain rare symplectite pseudomorphs after garnet, offering a unique window into the still poorly understood evolution of the deep oceanic lithosphere. Here, integrated petrologic and Os-Li isotopic data are used to constrain the evolution and dynamics of emplacement for these garnet peridotite protoliths. The Purang peridotites show wide variations of chemical compositions (spinel Cr#: 0.2−0.8) and Os model ages (up to 2.0 Ga), thus representing a piece of heterogeneous oceanic mantle lithosphere. Dunite channels show two distinctive groups of Cr# of spinels and Os-isotope compositions, with the low- to medium-Cr# (0.2−0.6) and high-Cr# (0.7−0.8) dunites reflecting the reaction of host lherzolites/harzburgites with percolating mid-ocean ridge basalt−like and boninitic melts, respectively. This confirms recent subduction initiation-related melt percolation in the Purang peridotites. Coexisting olivines and pyroxenes in the peridotites show systematic Li elemental and isotopic disequilibrium, suggesting fast cooling of the peridotites to Li closure temperature shortly after the melt percolations, likely during exhumation of the peridotites onto the seafloor. This supports a close link between subduction initiation and tectonic emplacement of the Purang peridotites. Combined with other geological evidence, we suggest the Purang peridotites may originate from the deep part of old, thick oceanic lithosphere of the Neo-Tethys. This thick oceanic lithosphere was progressively weakened and thinned likely during widespread plume-lithosphere interaction, triggering the transformation of garnet peridotite protoliths to spinel peridotites. Subsequently, initiation of a new subduction zone along the lithospheric weakness caused rapid ascent and emplacement of the Purang peridotites at a nascent forearc.

Last Years

2018 ◽  
pp. 376-386
Author(s):  
Robert E. Lerner
Keyword(s):  
United States ◽  
West Coast ◽  
The United States ◽  
Virgin Islands ◽  
Ruptured Aneurysm ◽  
Nuclear War ◽  
The West ◽  
Richard Nixon ◽  
The 1950S

This chapter details Ernst Kantorowicz's final years. Kantorowicz died of a ruptured aneurysm in September 1963. Before this, he worked on a succession of recondite articles, attended the annual meetings of the Medieval Academy and the Byzantine Institute at “Oakbarton Dumps,” vacationed on the West Coast and the Virgin Islands, and carried on earnestly with his dining and imbibing. His politics also became more leftward from the postwar years until the time of his death. For a decade and a half he was deeply worried about the possibility of nuclear war, and he held the United States responsible. During the 1950s, he was bitterly hostile to Dwight Eisenhower and Richard Nixon. On the day after Kennedy's inauguration, Kantorowicz wrote the he “couldn't be worse than Eisenhower, ” although he did change his mind.

Sign in / Sign up

Export Citation Format

Share Document