U-Pb zircon model ages for eleven major units from the Halaban-Al Amar region of the eastern Arabian Shield indicate three stages of evolution: (1) plate convergence, (2) plate collision, and (3) post-orogenic intracratonic activity. Convergence occurred between the western Afif and eastern Ar Rayn plates that were separated by oceanic crust. Remnants of oceanic crust now comprise the ophiolitic complexes of the Urd group. The oldest plutonic unit in the study is from one of these complexes and gave an age of 694 ± 8 Ma. Detrital zircons from the sedimentary Abt formation of the Urd group, which is intercalated with the ophiolitic rocks, were derived from source rocks with a mean age of 710 Ma. The Abt formation may be an accretionary wedge on the western margin of the Ar Rayn plate. Plate convergence was terminated by collision of the Afif and Ar Rayn plates during the Al Amar orogeny which began about 670 Ma. During collision, the Urd group rocks were deformed and in part obducted on to one or both plates. Synorogenic leucogranitoid rocks were intruded from 670 to 640 Ma. From about 640 to 630 Ma, widespread unfoliated dioritic plutons were emplaced in the Ar Rayn block, and represent the end of orogenesis related to collision. There is no definitive evidence for a significantly older basement beneath the study region.
On the basis of 13 new U/Pb ages for plutonic rocks from the southernmost portion of the Saudi Arabian Shield, the Nabitah mobile belt and orogeny are defined.The Nabitah mobile belt is a 100-to 200-km-wide, 1000-km-long, northstriking belt of intensely deformed rocks that include ophiolitic and synorogenic plutonic complexes.The age data for all but one sample are highly concordant, and it is confirmed that U/Pb systems in zircons from the region remained undisturbed until the late Tertiary.island arc formed over a west-dipping subduction zone; (2) collision between the Hijaz-Asir and Afif plates (680-640 Ma); and (3) neocratonic intraplate activity after suturing (<640 Ma).The evolution of the shield is interpreted in terms of a microplate accretion model in which the Nabitah suturing episode is only one of a number of such suturing events that occurred in the Arabian Shield.On this basis, three main stages of evolution are proposed for the shield: (1) preaccretion, during which the Hijaz-Asir island-arc assemblage was formed by plate-tectonic processes from >950 to 690 Ma;(2) plate accretion during 690-630 Ma to form the Arabian-Nubian neocraton; and (3) intraplate activity from 630 to <550 Ma, during which the Murdama molasse, Pan-African posttectonic granites, and Najd fault zone formed.The Arabian erogenic belts are discussed relative to the Pan-African Mozambique and Dahomeyan-Pharusian mobile belts of Africa.Base metals are preferentially associated with the island-arc domains, gold with the Nabitah suture zone, and tin, tungsten, lead, and silver with the Afif province of the eastern shield.
Research Article| January 01, 1976 Geochronology of the Arabian Shield, western Saudi Arabia: K-Ar results ROBERT J. FLECK; ROBERT J. FLECK 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar R. G. COLEMAN; R. G. COLEMAN 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar H. R. CORNWALL; H. R. CORNWALL 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar W. R. GREENWOOD; W. R. GREENWOOD 2U.S. Geological Survey, Jeddah, Saudi Arabia Search for other works by this author on: GSW Google Scholar D. G. HADLEY; D. G. HADLEY 2U.S. Geological Survey, Jeddah, Saudi Arabia Search for other works by this author on: GSW Google Scholar D. L. SCHMIDT; D. L. SCHMIDT 2U.S. Geological Survey, Jeddah, Saudi Arabia Search for other works by this author on: GSW Google Scholar W. C. PRINZ; W. C. PRINZ 3U.S. Geological Survey, Washington, D.C. 20244 Search for other works by this author on: GSW Google Scholar J. C. RATTÉ J. C. RATTÉ 4U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT J. FLECK 1U.S. Geological Survey, Menlo Park, California 94025 R. G. COLEMAN 1U.S. Geological Survey, Menlo Park, California 94025 H. R. CORNWALL 1U.S. Geological Survey, Menlo Park, California 94025 W. R. GREENWOOD 2U.S. Geological Survey, Jeddah, Saudi Arabia D. G. HADLEY 2U.S. Geological Survey, Jeddah, Saudi Arabia D. L. SCHMIDT 2U.S. Geological Survey, Jeddah, Saudi Arabia W. C. PRINZ 3U.S. Geological Survey, Washington, D.C. 20244 J. C. RATTÉ 4U.S. Geological Survey, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (1): 9–21. https://doi.org/10.1130/0016-7606(1976)87<9:GOTASW>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation ROBERT J. FLECK, R. G. COLEMAN, H. R. CORNWALL, W. R. GREENWOOD, D. G. HADLEY, D. L. SCHMIDT, W. C. PRINZ, J. C. RATTÉ; Geochronology of the Arabian Shield, western Saudi Arabia: K-Ar results. GSA Bulletin 1976;; 87 (1): 9–21. doi: https://doi.org/10.1130/0016-7606(1976)87<9:GOTASW>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract An orogenic event, correlated with the Pan-African event in eastern Africa, affected the Arabian Peninsula between 510 and 610 m.y. ago and is well-recorded geochronologically. The event probably included two thermal pulses or maxima, the first occurring between 560 and 610 m.y. ago and the second between 510 and 540 m.y. ago. The earlier pulse, the more severe one, included the majority of the igneous activity and metamorphism. During the last part of the 510- to 610-m.y. period, left-lateral strike-slip faulting occurred along a set of northwest-trending en echelon fracture zones, whose composite displacement may be as large as 240 km. At least one and probably more orogenic events affected the Arabian Peninsula before the Pan-African event, but only minimum ages can be assigned to these, because thermal effects of the 510- to 610-m.y. event have reset K-Ar ages. Major diorite-granite batholiths, however, formed before 760 m.y. ago. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Nine polishled thin sectionis have been exposed to nulclear track plates, three have been counted by alplia-particle spectrometry, and one has been examined by electron mocroprobe. Interpretation of the results is in a preliminary stage. Alpha track distribiutioni in the autoradiograph of a breccia forms a network that appears related to the rims of accretionary lapilli comiiposinig the breccia. Thorium in a coarse-grained crystalline rock is concenitrated in micron-sized, zirconium-rich crystals. Alplia count rates agree with what would be predicted from previously reported thorium and uranium contents of the same rocks, suggesting secular equilibriunm for the thorium and uranium decay series.
The radiocarbon content of contemporary pre-bomb marine shells from the region of upwelling of the Pacific coast of South America has been determined and found to be somewhat similar to the content of shells from the coast of California and the west coast of Mexico. Deviations of up to -8.5 percent with reference to the contemporary biospheric carbon-14 standard have been observed for the Peruvian coast. Values of from -0.35 to -4.04 percent have been obtained for marine shells from the Galopagos group. Problems associated with radiocarbon dates based on shells are discussed.
Research Article| March 01, 1970 Precambrian Metamorphism of the Belt Supergroup in Idaho R. R REID; R. R REID Unirersitv of Idaho, College of Mines, Moscow, Idaho 83843 Search for other works by this author on: GSW Google Scholar W. R GREENWOOD; W. R GREENWOOD National Aeronautics and Space Administration, Manned Spacecraft Center, Houston, Texas 77058 Search for other works by this author on: GSW Google Scholar D. A MORRISON D. A MORRISON National Aeronautics and Space Administration, Manned Spacecraft Center, Houston, Texas 77058 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (3): 915–918. https://doi.org/10.1130/0016-7606(1970)81[915:PMOTBS]2.0.CO;2 Article history received: 31 Oct 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. R REID, W. R GREENWOOD, D. A MORRISON; Precambrian Metamorphism of the Belt Supergroup in Idaho. GSA Bulletin 1970;; 81 (3): 915–918. doi: https://doi.org/10.1130/0016-7606(1970)81[915:PMOTBS]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Radiometric dating of zircon indicates a 1525± 82 m.y. age of crystallization for augen gneiss that intrudes metasedimentary rocks (near Elk City, Idaho) correlated with the Prichard Formation of the Belt Supergroup. The augen gneiss appears to be late synkinematic with the first deformation and metamorphic event in the metasedimentary rocks. Therefore, the first deformation and metamorphism are also Precambrian in age. Diopside-gneiss-bearing rocks on the Lochsa River, Idaho, correlated to the Wallace Formation of the Belt Supergroup, have a structural history similar to the rocks intruded by augen gneiss. Therefore, the diopside-gneiss-bearing rocks also were metamorphosed at 1525 m.y. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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