Portal de Periódicos da CAPES

Crustal Evolution and Global Tectonics: A Petrogenic View

1974; Geological Society of America; Volume: 85; Issue: 6 Linguagem: Inglês

10.1130/0016-7606(1974)85 2.0.co;2

1943-2674

A. E. J. Engel, SONJA P. ITSON, Celeste G. Engel, DALE M. STICKNEY, EDWARD J. CRAY,

Geomagnetism and Paleomagnetism Studies

Research Article| June 01, 1974 Crustal Evolution and Global Tectonics: A Petrogenic View ALBERT E. J. ENGEL; ALBERT E. J. ENGEL 1Scripps Institution of Oceanography, Geologic Research Division, P. O. Box 1529, La Jolla, California 92037 Search for other works by this author on: GSW Google Scholar SONJA P. ITSON; SONJA P. ITSON 1Scripps Institution of Oceanography, Geologic Research Division, P. O. Box 1529, La Jolla, California 92037 Search for other works by this author on: GSW Google Scholar CELESTE G. ENGEL; CELESTE G. ENGEL 1Scripps Institution of Oceanography, Geologic Research Division, P. O. Box 1529, La Jolla, California 92037 Search for other works by this author on: GSW Google Scholar DALE M. STICKNEY; DALE M. STICKNEY 2Department of Geology, California State University, San Diego, California 92115 Search for other works by this author on: GSW Google Scholar EDWARD J. CRAY, JR. EDWARD J. CRAY, JR. 3Departmentof Geology, University of California, Davis, Davis, California 95616 Search for other works by this author on: GSW Google Scholar Author and Article Information ALBERT E. J. ENGEL 1Scripps Institution of Oceanography, Geologic Research Division, P. O. Box 1529, La Jolla, California 92037 SONJA P. ITSON 1Scripps Institution of Oceanography, Geologic Research Division, P. O. Box 1529, La Jolla, California 92037 CELESTE G. ENGEL 1Scripps Institution of Oceanography, Geologic Research Division, P. O. Box 1529, La Jolla, California 92037 DALE M. STICKNEY 2Department of Geology, California State University, San Diego, California 92115 EDWARD J. CRAY, JR. 3Departmentof Geology, University of California, Davis, Davis, California 95616 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (6): 843–858. https://doi.org/10.1130/0016-7606(1974)85 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 MailTo Tools Icon Tools Get Permissions Search Site Citation ALBERT E. J. ENGEL, SONJA P. ITSON, CELESTE G. ENGEL, DALE M. STICKNEY, EDWARD J. CRAY; Crustal Evolution and Global Tectonics: A Petrogenic View. GSA Bulletin 1974;; 85 (6): 843–858. doi: https://doi.org/10.1130/0016-7606(1974)85 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 Studies of the relative abundances and characteristics of rock types, series, and complexes through time reflect both general and subtle features of crustal and upper-mantle environments. These studies also suggest salient aspects of the dynamothermal and global tectonic history of the last 3,500 m.y.Among the many petrochemical indices, the ratio K2O/Na2O reflects both the degree of differentiation (fractionation) of igneous rocks and the more or less mature (residuate) nature of clastic sediments. Accordingly, this ratio is a guide to the thickness, composition, and stability of source and crusial site of rock emplacement. Average K2O/Na2O of rocks, rock complexes, and terranes decreasing from 1 are typical of rock series formed in primitive borderland and arc-to–oceanic-crustal sites. Average values of K2O/Na2O increasing from 1 characterize rock series evolving in and on more mature arc-to-continental sites.Relative abundances of the most common and characteristic rock assemblages of various ages and their weighted average K2O/Na2O suggest profound episodicity in crustal evolution and global tectonics. At least three macro-episodes of major significance are defined: the Archean, >2,500 m.y. B.P.; the Proterozoic-Paleozoic, 250 m.y. B.P.; and the Mesozoic-Cenozoic, ∼250 m.y. B.P. to present. Within these macro-episodes, there are innumerable subordinate episodes and variously developed rock cycles.Most major Archean rocks, rock complexes, and terranes have a K2O/Na2O of <1, some <0.7. They are components of emerging proto-cratons and interspersed, subparallel, relatively simatic orogenic belts, presumably involving oceanic spreading centers, arcs, interarc basins, and subduction zones. By 2,500 m.y. B.P., however, the more "granitic" proto-cratons converged, telescoping many oceanic, arc-interarc, and borderland environments into subparallel series of synclinoid "greenstone" belts. The aggregate formed perhaps one, at most two, major protocontinents.Archean thermal gradients varied abruptly both vertically and laterally from very steep to moderate and created highly unstable, thin to thick, labile lithosphere and protocrusts commonly inhospitable to the evolution of widespread, highly fractionated calc-alkaline series or mature sediments. Heat transfer was largely via convection and advection. The advective loss was undoubtedly large, associated especially with the extrusion of floods of ultramafic to felsic magmas and related upward streaming of volatiles. Culmination of major Archean orogenies and subsequent thermal decay about 2,500 m.y. B.P. induced relative crustal quiet and resetting of most Archean Rb/Sr and K/Ar radiomentric clocks between 2,600 and 2,400 m.y. B.P.In the early Proterozoic (∼1,700 to 2,300 m.y. B.P.), many segments of the megacontinent(s) were sufficiently cool, thickened, and fractionated to remain quasi-coherent, deforming and cracking internally as well as marginally above convecting mantle forces. Widespread, relatively ensialic orogenic regions evolved above many thinner sialic zones. These were repeatedly refractionated and redated as they became populated by igneous series with K2O/Na2O commonly 1.2 and, in sedimentary sequences, often > 2. Nevertheless, the occurrences of lower Paleozoic ophiolite, blueschist, and less fractionated rock complexes in many Phanerozoic orogens suggest the onset of the large-scale continental rifting and global drift characteristic of post-Permian time. These events are reflected in variously depressed lower Paleozoic K2O/Na2O and, subsequently, in the plunge of average K2O/Na2O of major Mesozoic rock complexes to near Archean lows of ∼0.5 to 0.9, especially in the circum-Pacific.The petrochemical and structural data indicate the significant differences as well as similarities between the Archean and post-Permian. The Archean was dominated by the evolution and aggregation of protocontinents, arcs, and intervening oceanic crusts. The post-Permian was dominated by the unique fragmentation and widespread drift (>1,500 km) of large, thick, cool, fractionated, continental fragments and by the birth of new large ocean basins and island-arc chains. 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.