Showing papers on "Terrane published in 1974"

Geologic Evolution of the Sierra Nevada de Santa Marta, Northeastern Colombia

Abstract: New geologic, petrographic, and radiometric evidence (52 ages) from the Sierra Nevada suggest that plate tectonics controlled the complex Mesozoic evolution of the Caribbean continental margin. The triangular Sierra Nevada massif is bounded by the Oca fault, Santa Marta–Bucaramanga fault, and Cesar lineament. During the Tertiary, dextral and sinistral movement of 65 and 110 km, respectively, occurred along the Oca and Santa Marta–Bucaramanga faults; subsequently, several thousand meters of uplift produced the present geomorphic setting. Three metamorphic terranes are present; they differ petrographically and geochronologically and are separated by the Sevilla and Cesar lineaments (geosutures). The youngest terrane consists of three northeast-trending regional metamorphic; belts (Permian-Triassic gneiss, Jurassic schist, and Cretaceous-Paleocene green schist) that formed in successive subduction zones northwest of the Sevilla lineament. Tertiary plutons intrude this terrane. Most of the Sierra Nevada massif consists; of l,300-m.y.-old granulite terrane overlair by unmetamorphosed Paleozoic and Permian(?)-Triassic rocks and intruded by four northeast-trending belts of plutons that filled successive dilational rifts. These plutonic belts become younger, shallower, and more potassic in a southeastward direction. Extensional disruption, with transform separations up to 46 km, culminated with Middle Jurassic emplacement of two belts of composite batholiths and extensive ignimbritic eruptions. These events are related to the same southeast-dipping subduction zone that produced the Jurassic schist in the youngest metamorphic terrane. The third metamorphic terrane consists of younger(?) Precambrian amphibolite-grade rocks overlain by Silurian phyllites and unmetamorphosed Paleozoic and Mesozoic rocks that are typical of the Cordillera Oriental.

Deformation and Metamorphism of the Franciscan Subduction Zone Complex Northwest of Pacheco Pass, California

Abstract: The Franciscan Complex northwest of Pacheco Pass, California, includes three fault-bounded units, each characterized by a different deformational style and suite of metamorphic mineral assemblages. Structurally highest is jadeitic pyroxene-bearing metagraywacke semischist. The areally extensive Garzas tectonic melange separates the semischist from the structurally lowest pumpellyite-bearing Orestimba metagraywacke. The Garzas melange is representative of Franciscan melanges in general. These mappable bodies have an internal fabric dominated by penetrative, mesoscopic shear fractures and contain tectonic inclusions of all sizes immersed in a pervasively sheared, generally fine-grained matrix. The shear fractures record brittle deformation of consolidated rock bodies. Many melanges contain exotic inclusions, clearly not derived from adjacent units, and metamorphic mineral assemblages and textures indicate that they were metamorphosed before being tectonically mixed with more voluminous, generally lower grade, metagraywacke inclusions. The structural units are grossly sheetlike in external form and are separated from one another by gently to steeply dipping major faults. Unlike low-angle thrusts in imbricated Cordilleran terranes, the faults do not systematically repeat or offset a normal stratigraphic sequence but rather juxtapose rock units that bear no apparent stratigraphic, deformational, or metamorphic relation to one another. The structural units were separately deformed and metamorphosed under a variety of conditions prior to their tectonic juxtaposition during late Mesozoic continental margin subduction. Field and petrographic evidence permit, but do not prove, the hypothesis that both the semischist and exotic, high-grade melange inclusions once were more deeply buried and have been emplaced upward into their present anomalously shallow structural positions.

Oceanic Crust Forms Basement of Eastern Panamá

Abstract: Basement rocks of parts of eastern Panama include tholeiitic pillow basalt and diabase overlain by sedimentary rocks typical of deep oceanic environments. Both paleontologic and stratigraphic evidence indicate that some of these rocks are of Late Cretaceous age or older. Regional Bouguer anomalies over the basement terrane exceed +120 mgal, indicating that eastern Panama is a raised block of oceanic crust. Age relations in the Caribbean region apparently preclude an “Atlantic” or single intra-Caribbean origin for eastern Panama and the southern Caribbean basin, but multiple intra-Caribbean origins of the basaltic basement rocks are permitted by the age data. An in situ origin of the oceanic basement of Panama at a position which later became a Cenozoic island arc is likewise consistent with the available geologic and geophysical data. Seismic horizon B″ in the Caribbean is correlative with or overlain by deep-sea sedimentary rocks of Coniacian to Campanian age. This horizon forms the top of the apparent basement of eastern Panama and, thus, the eastern isthmus is a horstlike block that has been elevated or obducted a minimum of 6 km since Coniacian-Maastrichtian time, partly caused by northeastward underflow of the Pacific plate but possibly related to southwestward movement of the Caribbean plate beneath the isthmus.

Paleodrainage Pattern and Late-Orogenic Basins of the Canadian Cordillera

Abstract: Recent models for the tectonic evolution of the Canadian Cordillera can be tested by relating uplift of the orogenic core zones to the depositional record of the foreland and successor basins but this requires a comprehensive understanding of paleodrainage The Canadian Cordillera is made up of two orogens the Columbian Orogen on the east and the Pacific Orogen on the west Most of the late orogenic molasse deposits are related to the Columbian Orogen Omineca Crystalline Belt and Rocky Mountain Belt In the Columbian Orogen three structural elements placed controlling restraints on late orogenic drainage uplifts re entrants and salients and longitudinal intramontane fault zones The uplift boundary can be defined as a zone of great vertical displacement of pre orogenic sedimentary and volcanic rocks and probable involvement of terrane intruded or metamorphosed in Precambrian time The uplift boundary separated the aggradational molasse basins from the erosional domain of the drainage system Most of the clastic sediment derived from the uplifted core zone was trans ported by rivers flowing in longitudinal intramontane valleys These rivers merged near re entrants of the uplift boundary and discharged their load into elongate molasse basins During growth of folds and thrust faults within the orogen valleys near the structural re entrants constituted the shortest dispersal paths be tween the rising core zones and the subsiding foreland awl succes or hasins The area in front of the regional re entrants Crowsnest Peace Liard and Peel on the east side Chukachida and Thompson on the west side therefore display the best developed molasse deposits in foreland basins to the east and successor basins to the west From the structural salients only short though locally vigorous streams issued directly into the late orogenic basins The molasse of the Columbian foreland basin displays two upward coarsening megacycles an uppermost Jurassic through Lower Cretaceous cycle Kootenay Blairmore Assemblage and an Upper Cretaceous through Oligocene cycle Belly River Paskapoo Assemblage Regional drainage during deposition of the first cycle was directed to the north whereas during the seccnd cycle streams flowed predominantly to the southeast Straight drainage lines connecting the re entrants with the depositional basins are probably valid concepts for the earliest stages of uplift only Progressive growth of folds and thrust faults in the Rocky Mountain Belt and faulting near intramontane valleys produced curved and even U shaped river systems which merged near re entrants and effected thorough mixing of compositionally diverse sediment loads The molasse of the successor basins reflects progressive unroofing of the crystalline core zone The two cycles of the Columbian foreland are similar to molasse sequences in the Alps and seem to reflect two phases of isostatic uplift related to repeated intervals of tectonic crustal thickening

Seismicity of the Middle America arc-trench system near Managua, Nicaragua

Abstract: Hypocenters of earthquakes occurring during the period 1950 through 1972 in the Middle America arc-trench system near Managua, Nicaragua, have been relocated by the method of joint hypocenter determination (JHD) or the master event method with the Managua earthquake of December 23, 1972 as the calibration event. The relocated hypocenters show a considerably narrower Benioff zone than previous hypocenters of the same earthquakes and clearly separate shallow-focus volcanic terrane earthquakes of the type which struck Managua from the Benioff zone earthquakes. The shallow-focus volcanic terrane earthquakes are probably caused by tectonic conditions associated with the formation of the Nicaraguan depression or the principal chain of Quaternary volcanoes. The Managua earthquake of December 23, 1972 may have occurred as a consequence of slippage along a transform fault zone which connects offset segments of the chain of Quaternary volcanoes; the volcanic chain is then taken to be the surface expression of a secondary spreading zone which lies above the Benioff zone of the Middle America arc-trench system. Alternatively, the recent Managua earthquake may have occurred as a consequence of regional east-west tension in the Nicaraguan depression.

A Comparison of Some Triassic Rocks in the Hokonui and Alpine Belts of South Island, New Zealand

Abstract: Kaihikuan (upper Middle Triassic) clastics of the Hokonui belt fine from west to east, and hence were derived from the west. Deep erosion of a volcanic terrane and associated shallow intrusives contributed most of the sediment, but reworking of contemporaneous pyroclastic debris was also an important process. In the Alpine belt, the source of Kaihikuan sediments was a deep-seated acidic plutonio terrane. At least some of the deposits formed in nearshore, shallow-marine environments. The Alpine belt sequences do not fit lateral extrapolations of sedimentologic or petrologie trends of the Hokonui belt, and thus cannot be explained as distal facies of the same sedimentary basin. The two belts probably were juxtaposed by faulting.

Geology and petrochemistry of weakly metamorphosed rocks in the upper Wakatipu district, southern New Zealand

Abstract: The area near the head of Lake Wakatipu lies between the Livingstone Fault to the west, and the Otago Schist terrane to the east. The area is divided into three major tectonic slices or subareas by north-striking faults. A eastward-younging sequence of Caples Group strata in the western-subarea is subdivided into four informal units consisting predominantly of volcanogenic sediments, feldspathic sandstone, tuff and tuffaceous sandstone, and grey sandstone and slate respectively. The Greenstone Ultramafite Belt, which separates the western subarea from the middle subarea, is interpreted as a tectonic melange of serpentinite, metagabbro, mafic volcanic and meta-sedimentary rocks. The synclinal Bold Peak unit, predominantly rhythmically alternating green sandstone and slate, occupies the middle subarea and is separated by an important inferred fault, the West Wakatipu Fault, from the eastern subarea which represents the western limit of the Haast Schist of Central Otago. Five metamorphic zones are r...

Active Continental Margins: Contrasts Between California and New Zealand

Abstract: The margins of the Pacific Ocean in both California and New Zealand each contains two parallel terranes similar in age but very different in lithology, structure, and metamorphic mineral assemblages. In California, the structurally lower terrane is the Franciscan assemblage, deposited in deep marine environments and made up of rarely fossiliferous graywacke and shale with minor amounts of submarine volcanic rocks, radiolarian chert, and foraminiferal limestone. The Franciscan is separated from coeval fossiliferous sedimentary rocks of the Great Valley sequence to the east by a major fault zone along which ultramafic rocks are abundant. In New Zealand, the poorly fossiliferous Alpine assemblage, composed of graywacke with minor submarine volcanics and chert, is separated from coeval sedimentary rocks of the Hokonui assemblage by an ultramafic belt. In both California and New Zealand, these parallel sedimentary belts are adjacent to older crystalline terranes (Sierra Nevada and Tasman or Fiordland belts). These similarities, plus many other features common to both areas, including similar structure, metamorphism, and geophysical anomalies, have led many earlier workers to conclude that they formed under the same conditions, but at different times.

Talc-garnet-kyanite-quartz schist from an eclogite-bearing terrane, Western Tasmania

Abstract: Talc-garnet-kyanite-quartz schist occurs in an eclogite-bearing terrane in the Precambrian of Western Tasmania. It is argued that this rock was formed at a pressure of ⪚ 10 kb and a temperature of 600°±20° C.

Operation Basement: Buried Precambrian Rocks of Missouri--their Petrography and Structure

Abstract: The buried Precambrian basement of Missouri is described on the basis of data from 550 drillholes, petrographic analyses of more than 1,000 samples, and geophysical and structural data. Prominent topographic and probable structural highs are identified as (1) the Central Missouri high, (2) the Southeast Missouri high, (3) the Southwest Missouri high, and (4) the Northeast Missouri high. The first two of these underlie the Ozark dome. Basement rocks associated with the Central Missouri high and locally found elsewhere are gneissic granite, gneiss, and schist. These rocks formed at deeper crustal levels, subsequently have been upwarped to the basement surface, and may be part of an earlier orogenic period. They include lenses of infolded metamorphosed sediments, as well as intrusive granite and basic plutonic rocks. It is assumed that the crustal complex is older than late Precambrian igneous rocks exposed in southeast Missouri, and that regionally persistent prominent northwest trends observed on geophysical maps and in Paleozoic structures are related to structural belts of the crustal complex. In western Missouri a northwest-trending basement fault is defined and interpreted as the northern fault of a graben wher supracrustal Precambrian and possibly younger rocks locally are preserved and brought into contact with metamorphic rocks. The association of late Precambrian rhyolitic volcanic and related shallow intrusive rocks is referred to as the St. Francois terrane. These rocks are exposed in southeast Missouri and extend in the subsurface northwestward. They are associated with the Southwest Missouri high and the Northeast Missouri high. Volcanic rocks identified from southwest Missouri may be part of a volcanic terrane extending into southeast Kansas and northeast Oklahoma; rhyolite in northeast Missouri may extend into Illinois. The granitic rocks of the St. Francois terrane are interpreted as postorogenic subvolcanic massifs that are exposed at the basement surface where pre-Paleozoic uplift and erosion removed their supracrustal cover. Northeast-southwest structural trends are believed to be related in part t the evolution of the St. Francois terrane and are superimposed on the older trends. The youngest igneous rocks of the basement complex are dikes and sills of tholeiitic diabase intruded along both sets of pre-existing structural zones. Local accumulations of unmetamorphosed clastic sediments on the basement surface may be Precambrian or younger.

A U-Pb zircon, and Rb-Sr and U-Th-Pb whole-rock study of a polymetamorphic terrane in the central Alps, Switzerland

Abstract: U-Pb analyses of zircons from the southern paragneiss zone of the Gotthard massif in the central Alps indicate these rocks were derived from one or more source areas ≧ 1400 m.y. old and were strongly affected by both the Caledonian and Hercynian orogenies. Rb-Sr whole-rock analyses also appear to reflect the Hercynian event while Rb-Sr analyses of a metamorphic inclusion and a boudin indicate that these small-scale samples were affected by the Alpine orogeny.

Paleocurrents and composition of lower Bryneira strata (Permian) at Barrington Peak, north-west Otago

Abstract: Cross-stratification in the Annear Formation (lower Bryneira Group) in northwestern Otago indicates sediment transport from west (c. 250°) towards east (c. 70°). Petrographic and chemical data indicate that these rocks are of mixed quartzo-feldspathic-volcanic provenance and are decidedly more silicic than overlying and underlying Bryneira volcanogenic terrigenous sediments. Compositional and stratigraphic similarities with Permian sediments of the Torlesse terrane are noted, and a common source area is tentatively suggested.

40Ar/39Ar Dating of the Brighton Gabbro Complex, Lushs Bight Terrane, Newfoundland

Abstract: A hornblende sample from this complex has an apparent 40Ar/39Ar age of 495 ± 5 my. The 40Ar/39Ar data was obtained in a stepwise outgassing experiment. If, as has been suggested, the Brighton compl...

Petrography of an early Tertiary fossiliferous sandstone from the Ross Sea Area, Antarctica (Note)

Abstract: An early Tertiary sandstone from the Ross Sea area is a fossiliferous subfeldsarenite and contains numerous rounded quartz grains, many of which show abraded overgrowths. Devonian sandstones of the Beacon Supergroup, Transantarctic Mountains, comprise the most likely source terrane. The regional significance of these data is discussed.

Lineaments in Basement Terrane of the Peninsular Ranges, Southern California

Abstract: The author has identified the following significant results. ERTS and Skylab images reveal a number of prominent lineaments in the basement terrane of the Peninsular Ranges, Southern California. The major, well-known, active, northwest trending, right-slip faults are well displayed; northeast and west to west-northwest trending lineaments are also present. Study of large-scale airphotos followed by field investigations have shown that several of these lineaments represent previously unmapped faults. Pitches of striations on shear surfaces of the northeast and west trending faults indicate oblique slip movement; data are insufficient to determine the net-slip. These faults are restricted to the pre-tertiary basement terrane and are truncated by the major northwest trending faults. They may have been formed in response to an earlier stress system. All lineaments observed in the space photography are not due to faulting, and additional detailed geologic investigations are required to determine the nature of the unstudied lineaments, and the history and net-slip of fault-controlled lineaments.

Investigation of lineaments on Skylab and ERTS images of Peninsular Ranges, Southwestern California

Abstract: The author has identified the following significant results. Northwest trending faults such as the Elsinore and San Jacinto are prominently displayed on Skylab and ERTS images of the Peninsular Ranges, southern California. Northeast, north-south, and west-north-west trending lineaments and faults are also apparent on satellite imagery. Several of the lineaments represent previously unmapped faults. Other lineaments are due to erosion along foliation directions and sharp bends in basement rock contacts rather than faulting. The northeast trending Thing Valley fault appears to be offset by the south branch of the Elsinore fault near Agua Caliente Hot Springs. Larger horizontal displacement along the Elsinore fault further northwest may be distributed along several faults which branch from the Elsinore fault in the Peninsular Ranges. The northeast and west-northwest trending faults are truncated by the major northwest trending faults and appear to be restricted to basement terrane. Limited data on displacement direction suggests that the northeast and west-northwest trending faults formed in response to an earlier period of east-northeast, west-southwest crustal shortening. Such a stress system is consistent with the plate tectonic model of a subduction zone parallel to the continental margin suggested in the late Mesozoic and early Tertiary.