George W. Moore

Deposit from a Giant Wave on the Island of Lanai, Hawaii

Limestone-bearing gravel, the newly named Hulopoe Gravel, blankets the coastal slopes on Lanai. The deposit, which reaches a maximum altitude of 326 meters, formerly was believed to have been deposited along several different ancient marine strandlines, but dated submerged coral reefs and tide-gauge measurements indicate that the southeastern Hawaiian Islands sink so fast that former worldwide high stands of the sea now lie beneath local sea level. Evidence indicates that the Hulopoe Gravel and similar deposits on nearby islands were deposited during the Pleistocene by a giant wave generated by a submarine landslide on a sea scarp south of Lanai.

Westward Tidal Lag as the Driving Force of Plate Tectonics

As spreading at known interarc basins occurs to the west of westward-dipping subduction zones, and movement of the lower plates is also to the west, it is suggested that all plates move chiefly westward. Rates of motion are equal to a net difference between eastward and westward transport on semidiurnal tidal bulges. Eastward-dipping subduction zones at the leading edges of plates that are primarily continental are overridden by less dense material and are forced to step westward. Yet lines of downbending of westward-dipping subduction zones are fixed with respect to the lower mantle, and interarc basins result from westward movement of their adjacent plates. These fixed subduction zones can be used to calibrate previously measured movement between plates; they suggest that the westward transport imparted during each tidal cycle is as much as 0.3 mm.

Tectonic Evolution of the Southern Gulf of Mexico

A detailed magnetic survey in the southern Gulf of Mexico shows subdued irregular magnetic anomalies that are similar in wave length to those attributed to sea-floor spreading on present-day oceanic rises. The small amplitude of these anomalies, about 75γ, would be compatible with an oceanic basalt source at a depth of 10 km, and previous seismic refraction studies in this area have shown that layer 2 of the oceanic crust (presumed to be basalt) does indeed lie at approximately that depth. Palynomorphs in Deep Sea Drilling Project samples of cap-rock material from the Sigsbee Knolls have shown the associated salt to be Jurassic. A crustal model, based on seismic refraction evidence and on new gravity data, suggests that, whereas the salt-dome belt of the southern gulf is underlain by a thick layer with a density of 2.2 g per cm 3 (presumed to be halite rock), adjacent deeper areas of the basin seem to lack this low density layer. In northeastern Mexico, Triassic red beds fill grabens that are correlative with the Newark Group of the Atlantic Coast and suggest that the Gulf of Mexico originated at the time of the initial rifting of the North Atlantic. When the gulf was about half-opened during the Jurassic, oceanic circulation was restricted; and thick deep-basin evaporite deposits, analogous to those found in the Mediterranean Sea by the Deep Sea Drilling Project, were laid down. Further opening established normal salinity and led to the development of salt-free areas of oceanic crust that separated the Sigsbee Escarpment (together with adjacent ridges of offshore Mexico) from the Sigsbee Knolls and salt domes of Cuba. The subsequent structural evolution of the Gulf of Mexico basin is believed to have been mainly a result of interaction between it and tectonic plates of the Pacific area. After opening of the gulf, subduction began along the Cuban arc, where Atlantic rifting had created a nearly uninterrupted tract of oceanic crust extending from the Pacific between Yucatan and Colombia. Then, folding and gravity sliding associated with Laramide deformation on the west side of the gulf led to salt anticlines that underlie the ridges offshore from Mexico. Except for continued diapirism and subsidence associated with sediment loading, present tectonic activity is confined to the southwestern corner of the gulf, where volcanism and intermediate-focus earthquakes are a distant manifestation of subduction along the Middle America Trench on the Pacific side of Mexico.

Sea-Floor Spreading at the Junction between Gorda Rise and Mendocino Ridge

A Quaternary deformation pattern revealed by new sub-bottom acoustic profiles supplements previous knowledge derived chiefly from magnetic and seismic evidence on the contemporary tectonics off northern California. An inferred age for the sedimentary cover along the axis of the southern part of Gorda Rise suggests that no volcanism has occurred along that part of the rise for more than 100,000 years. Sea-floor spreading at the rise crest has been accommodated by sinking of a keystone block that forms the floor of Escanaba Trough, the median valley of the rise. Differential movement between Pacific and American tectonic plates could have caused the deformation pattern, and during this movement, the displacement offshore beyond the northwest end of the San Andreas fault is inferred to have divided at Cape Mendocino between a fault along Mendocino Ridge and a fault segment that connects with the Blanco fault farther northwest.

Handbook of Marine Mineral Deposits

Handbook of Marine Mineral Deposits delves into marine mineral exploration and mining, covering both the fields economics and the state of the art of its science. The 1982 Law of the Sea Convention had a chilling effect on the deep-sea mining industry Later in the 1980s, most nations adopted the 370-km exclusive economic zone, which rekindled interest in the industry. Amendments made to the law in 1994 have also improved the outlook since then. India has agreed to abide by the Law of the Sea Convention by setting aside reserves of manganese nodules in the Central Indian Basin for international use that equal those it has claimed for itself.

Growth of the Andes by Rejuvenated Subduction

Subduction-zone magmatism became extensive along the west coast of South America during the Ordovician, soon after Gondwana was assembled. During the remainder of the Paleozoic and the early Mesozoic, eastward subduction of the Farallon plate led to emplacement of a succession of granitic and volcanic rocks. During the Cretaceous, when South America broke away from Africa and began moving independently toward the Pacific Basin, the resulting opposite motions of the South American and Farallon plates toward the subduction zone caused vigorous tectonic mountain building. But by the Oligocene, South America had advanced more than 2000 km beyond the position of the Cretaceous subduction zones root in the lower mantle. The South American plate, moving westward over the subducting plate, pushed down and flattened the curved top of the subducting slab, as indicated by todays flattened earthquake zone under South America. I hypothesize that this flattening increased the subducting slabs resistance with the und...

Theories of the Earth and Universe—A History of Dogma in the Earth Sciences

S. Warren Carey rejects the concept of subduction. In this book he links together four subequal themes, with a few autobiographical notes sprinkled throughout, listed as follows in order of decreasing length: a history of science, a lucid review of tectonics and structural geology, an updating of his hypothesis that the Earth is expanding, and a review of the frontiers of cosmology, leading finally to a suggested mechanism for the expansion. Tectonics and structural geology have served as the hub of Careys long and wide-ranging career, and the history of science section of this book emphasizes geology and geophysics, with special reference to the tribulations of scientists like Sam Carey himself, who marched to a different drummer and bucked the establishment. Carey began his career, his dissertation work, in New Guinea, site of the worlds most vigorous shearing (some would say transpression) between the Australia-India and the Pacific “polygons” (Carey uses that term to distinguish his 2900-km-thick tectonic blocks that move on the liquid outer core of the Earth from the 100-km-thick plates of plate tectonic theory). He immediately became a mobilist, and for the next 20 years, along with a few other geologists of vision, had to grapple with a fixist establishment.