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... Flood Geology Explain the Fossil Record? Creation Ex Nihilo Technical Journal, 10 (1996): 1: 32 - 69). All creationists, however, seem to agree that many Achaean and Proterozoic formations are of pre-flood age, and that at least Paleozoic strata represent flood deposits. ] The Precambrian craton's of all continents are composed of numerous distinct terrane's of different isotopic ages, structural trends, lithotomies, and paleo magnetic and tectonic histories.
These terrane's are typically bounded by collisional origins. Stratigraphic relationships can be used to show that North America (and the rest of Laurentia), for example, underwent an extensive tectonic evolution well before the Cambrian seas transgressed over the North American craton in the early Phanerozoic. The North American craton is separated into seven such provinces. Examples of well studied Proterozoic orogenic fold belts in North America include the Woman belt or oregon and the Trans-Hudson belt between the Wyoming and Superior crystal provinces in the northern US. Condie (1989) states: Field and geophysical data from the Canadian Shield, as well as results from boreholes in in platform sediment, indicate that North America is an amalgamation of plates, recently referred to as the United Plates of America (Hoffman, 1988).
The Archaean crust is composed of at least six separate provinces joined by early Proterozoic fold belts. The systematic asymmetry of stratigraphic sections, structure, metamorphic ism, and igneous rocks is consistent with an origin by subduction and collision. Such asymmetry is particularly well-displayed along the Trans Hudson, Labrador, and Penokean orogenic belts. In these belts, zones of foreland deformation are dominated by thrusts and recumbent folds, whereas hinterlands typically show transcurrent faults. Both features are characteristic of subduction zones. Some Proterozoic origins have large accretionary prisms (p. 354).
Craton's, often thought of as the stable basement, have Archaean subcratons themselves, which are in turn surrounded by younger Proterozoic fold belts. For instance, the Yangtze craton appears to have been formed by collision / accretion processes operating during the Proterozoic (Guo et al. , 1985). It consists of a late Archaean (2. 86 U-Pb) nucleus to the northwest, flanked by progressively younger Proterozoic rock to the south. Tectonically employed ophiolite's are found at least as far back as the mid-Proterozoic, and disputed ophiolite's or oph iolite analogs are found in much older Archean crustal provinces.
These demonstrate the existence of spreading boundaries and plate collisions, and hence tectonic plate motion, since at least early Proterozoic (the YEC pre-flood) time. Ophiolite's occur in several Proterozoic orogenic belts and provide strong evidence of the existence of oceanic plates like those of today. The oldest is an oph iolite in the Cape Smith belt on the south side of Hudson Bay in Canada whose age has been firmly established at 1. 999 billion years. There is a 1. 8 -billion-year-old oph iolite in the Svecofennian belt of southern Finland, but most Proterozoic ophiolite's are 1 billion to 570 million years old and occur in the Pan-African belts of Saudi Arabia, Egypt, and The Sudan, where they occur in sutures between a variety of island arcs (Britannica. com article Precambrian Time) Another line of evidence which shows that plate tectonic processes were active during the Proterozoic is based on paleo magnetic data. While much less complete than Phanerozoic data, paleo magnetic data from Proterozoic formations (such as the massive Kaweenawan basalts [Halls et al. , 1982 ] and the Grand Canyon Supergroup [Elston et al. , 1973 ], etc. ) show the pre-flood continents moving with respect to latitude over time during the Proterozoic, at rates comparable to, though slightly faster than, those measured today (< 20 cm / yr ).
Condie states that rates of Proterozoic plate motions can be obtained from APW paths... results indicate that Proterozoic continental plate velocities (3 - 10 cm / y ) often exceeded those of present-day continental plates (which average about 5 cm / y ) and were equivalent to those of present day oceanic plates (p. 219). Such gradual slowing is expected due to gradual reduction in the amount of heat generated within the earth by decaying radionuclide. A characteristic feature of Phanerozoic and Proterozoic APW paths is the presence of loops with an average periodicity of roughly 200 my. In Phanerozoic APW paths, these loops can often be correlated with orogenic episodes. Several loops in Proterozoic APW paths also appear to be correlated with major orogenic episodes (1150, 1750, and 1850 in North America; 1100 and 2150 in Africa; Condie, 1989, p. 333).
For instance, the portion of the mid to late Proterozoic APWP for the North American craton constructed from the Kaweenawan basalts and the Grand Canyon Supergroup has yielded the temporally longest, stratigraphic ally controlled polar path yet developed for North America (~ 1250) to 800 Ma), and describes a prominent loop. P. K. Link et al. note: The polar path for the Unkar Group, beginning at the level of the Shinumo Quartzite and extending to the lower member of the Nankoweap Formation, overlaps and coincides with the polar path reported from lower, middle, and upper Kaweenawan rocks of the Lake Superior region (p. 479).
The composite polar path... from the Unkar-Nankoweap and Kaweenawan-Chequamegon poles, shows an overlapping, concordant, nonconflicting progression of poles, and a single polar path for the two regions. The concordant north- and then south-trending paths form a single loop that is here called the Unkar- Kaweenawan loop (p. 480). The apex of the Unkar-Kaweenawan loop appears to coincide with the end of the Grenville orogeny and the cessation of Kaweenawan rifting.
Mafic sills of similar age in both Unkar and Kaweenawan strata appear to have been employed at this time as well, indicating that whatever event is indicated by the apex affected a large region of the North American Craton. Accretionary continental growth continues to occur at the Pacific margins today. For instance, the Yakutat terrane and other allochthonous blocks are colliding with southern Alaska. Baha California is moving north along a transform boundary, and will probably eventually become accreted to Alaska as well. The Nazca and Juan Fernandez ridges are colliding with the western coast of South America, and the Louisville and Marcus-Never Rises are colliding with subduction zones in the western Pacific (Nur and Ben-Avraham, p. 8). India is still colliding with Eurasia, and the Himalayas continue to rise.
Numerous other terrane's of diverse types are slowly moving towards the margins of the Pacific Ocean, where they are fated to be accreted to an already massive amount of accreted allochthonous terrane's. The Ontong Java Oceanic plateau in the southwest Pacific Ocean has a crustal thickness of 36 km and may be a rifted and now submerged continental fragment. In size, it is comparable to the Yangtze continental terrain of Asia. Accreted against the south side of the Ontong Java plateau is part of the Solomon Islands volcanic arc, and numerous other volcanic arcs lie nearby.
If one imagines the closing-up of the Coral Sea, this inferred continental fragment wreathed with accreted volcanic arcs would form a major addition to the Australian continent. What might future super continents look like? Long term extrapolation based on present plate trajectories is likely to be less than perfectly accurate, since we know that plate motions can change or be reorganized over time. Nevertheless, some interesting conjectures can be made. For instance, Australia is moving north, towards Eurasia, at about 6 cm per year. Between the two continents are numerous island arcs and micro continents, such as New Guinea, Indonesia and Malaysia.
North America and Eurasia are converging with each other at a rate of about 2 cm per year. Extrapolating from current trajectories, one could easily imagine a future super continent consisting of a unified Eurasia, Australia, and North America. Joe Meet homepage has a graphic illustrating what the continents might look like in 250 my, based on current plate trajectories. West to East, the Valley and Ridge province consists of a thick sequence of relatively unmetemorphosed Paleozoic sediments that were folded and thrust to the northwest by compression from the southeast. The Blue Ridge province includes highly metamorphosed Precambrian and Cambrian crystalline rocks with the highest relief in the Appalachians. These rocks were thrust over rocks of the Valley and Ridge province to the west.
Both Shenandoah and Great Smoky Mountains National Parks are located in this province. The Piedmont province consists of metamorphosed Precambrian and Paleozoic sediments and volcanic rocks that were intruded. There is an additional province called the Appalachian Plateau, which dips gently to the west. It contains a lot of limestone units.
There are three major National Parks in the Appalachians, which all have distinct and interesting geological features. Shenandoah National Park was established in 1926 to restore a badly misused area. Dominant features in this park are shallow angle reverse faults, also known as thrust faults. The Precambrian and Cambrian rocks of the Blue Ridge province were thrust over younger sedimentary rocks of the continental margin. Movement along these faults is believed to be as large as 150 miles westward. Few good rock outcrops exist in the park due to abundant vegetation and severe weathering due to the humid environment.
The Precambrian metamorphic and igneous rocks are the dominant rock types exposed in the park. These are the Catoctin metamorphosed basalt, the Pedler gneiss and the Old Rag granite. The geology of the Great Smoky Mountains National Park is very similar to the Shenandoah National Park. The Acadia National Park, which is located along the coast of Maine, has a few major differences than the other two parks I have discussed. Glaciers covered much of this area during the past million years and glacial erosion has stripped away much of the vegetation and soil to expose abundant rock exposures. This region significantly experienced the Acadian Orogeny during the Devonian time when a suspect terrane called the Avalon terrane, lodged itself against northern North America.
A suspect terrane is defined as a province with geologic features that sharply contrast with those of nearby provinces. The Avalon terrane which docked itself next to North America during the Acadian orogeny fits this description. Its rocks are very different from those of adjacent regions. These rocks are exposed throughout the park and consist primarily of metamorphosed sedimentary and volcanic rocks. Abundant igneous activity associated with the Acadian orogeny produced large amounts of diacritic and granite igneous rock also exposed in the park. Bibliography: Howell N.
The Safeguard of the Sea. History of Cordillera. Vol. I.
London: HarperCollins, 1983. Keegan K. The Pacific Boundaries. New York: Alfred A.
Knopf, 1999. Jones W. Discovery of Pacific Ocean. New York: Basic Books, 1983. Padfield P. Proterozoic Geographical Findings.
Oxford University Press, 2 nd Edition, 1996. Dimattia W. and Oder B. Formation of the Oceanic, New York: Viking Press, 1989. Prichard, C. , Hull, R. , Chamber, M. , and Will mott, H.
Controversies of the North American Craton. Penguin Books, 2000. Borghooff K. and Pareschi O. , Structure of the Cordilleran, from Wired Magazine, issue April 1998. Coney, K. Pacific Plate Interactions.
Ontario Books, 1989. Reader and Schubert. Development of the Oceanic. Oxford University Press, 1984. Nur, V. Treasures of the Sea, from National Geographic Magazine, issue April 2000.
Hoffman H. Exploration of the Pacific, from Ontario Statesman Magazine, issue June 2001.
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