No. Registros Solicitud 1 5614 colombia
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CC - CATEGORY CODES: 24-Quaternary-geology DT - DOCUMENT TYPE: Serial; Conference-Document BL - BIB LEVEL: Analytic NN - ANNOTATION: IGCP Project No. 281. IL - ILLUSTRATION: Refs: 24; illus. incl. 1 table, strat. cols., sketch map. RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. IS - ISSN: 0168-6305 CO - CODEN: #02325 AN - ACCESSION NUMBER: 1998-010565 UD - UPDATE CODE: 199804 Registro 5162 de 5614 - GeoRef Disc 4: 1993-1996 TI - TITLE: Cretaceous black shales in the Eastern Cordillera/ Colombia. AU - AUTHORS: Mann-U; Stein-R AF - AUTHOR AFFILIATION: Alfred-Wagener-Institut for Polar and Marine Research, Bremerhaven, Federal Republic of Germany BK - BOOK TITLE: In: Seventh meeting of the European Union of Geosciences; abstract supplement. BA - BOOK AUTHORS: Anonymous SO - SOURCE: Terra Abstracts. 5, Suppl. 1; Pages 702. 1993. PB - PUBLISHER: Blackwell Scientific Publications. Oxford, International. 1993. CP - COUNTRY OF PUBLICATION: International PY - PUBLICATION YEAR: 1993 CN - CONFERENCE INFORMATION: Seventh meeting of the European Union of Geosciences. Strasbourg, France. April 4-8, 1993. LA - LANGUAGE: English DE - DESCRIPTORS: Andes-; black-shale; carbon-; clastic-rocks; claystone-; Colombia-; Cretaceous-; Eastern-Cordillera; macerals-; Magdalena-Colombia; Mesozoic-; organic-carbon; Rock-Eval; sedimentary-rocks; South-America; thermal-maturity; vitrinite- CC - CATEGORY CODES: 06A-Sedimentary-petrology DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document BL - BIB LEVEL: Analytic RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. IS - ISSN: 0954-4887 AN - ACCESSION NUMBER: 1998-069397 UD - UPDATE CODE: 199824 Registro 5163 de 5614 - GeoRef Disc 4: 1993-1996 TI - TITLE: Beryl, variety emerald, Chivor Mine, Chivor, Colombia. AU - AUTHORS: Cook-Robert-B AF - AUTHOR AFFILIATION: Auburn University, Department of Geology, Auburn, AL, United States SO - SOURCE: Rocks and Minerals. 68; 5, Pages 332-334. 1993. PB - PUBLISHER: Heldref Publications. Washington, DC, United States. 1993. CP - COUNTRY OF PUBLICATION: United-States PY - PUBLICATION YEAR: 1993 LA - LANGUAGE: English DE - DESCRIPTORS: Andes-; beryl-; Chivor-Colombia; Chivor-Mine; Colombia-; emerald-; gems-; mineral-resources; Northern-Andes; physical-properties; popular-geology; ring-silicates; silicates-; South-America; spatial-distribution; variations- CC - CATEGORY CODES: 28A-Economic-geology,-geology-of-nonmetal-deposits DT - DOCUMENT TYPE: Serial BL - BIB LEVEL: Analytic IL - ILLUSTRATION: Refs: 3; illus. RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. IS - ISSN: 0035-7529 CO - CODEN: ROCMAR AN - ACCESSION NUMBER: 1999-003817 UD - UPDATE CODE: 199902 Registro 5164 de 5614 - GeoRef 1997-2001 TI - TITLE: Seasonality in ENSO-related precipitation, river discharges, soil moisture, and vegetation index in Colombia. AU - AUTHORS: Poveda-German; Jaramillo-Alvaro; Gil-Marta-Maria; Queceno-Natalia; Mantilla-Ricardo-I AF - AUTHOR AFFILIATION: Universidad Nacional de Colombia, Prosgrado en Aprovechamiento de Recursos Hidraulicos, Medellin, Colombia SO - SOURCE: Water Resources Research. 37; 8, Pages 2169-2178. 2001. PB - PUBLISHER: American Geophysical Union. Washington, DC, United States. 2001. CP - COUNTRY OF PUBLICATION: United-States PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English DE - DESCRIPTORS: Amazon-Basin; atmospheric-precipitation; climate-; Colombia-; discharge-; El-Nino; El-Nino-Southern-Oscillation; fluid-dynamics; fluvial-features; hydrologic-cycle; hydrology-; La-Nina; moisture-; normalized-difference-vegetation-index; Pacific-Ocean; rivers-; seasonal-variations; soils-; South-America; streamflow-; vegetation- CC - CATEGORY CODES: 21-Hydrogeology DT - DOCUMENT TYPE: Serial BL - BIB LEVEL: Analytic IL - ILLUSTRATION: Refs: 32; illus. incl. 3 tables. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. IS - ISSN: 0043-1397 CO - CODEN: WRERAQ AN - ACCESSION NUMBER: 2001-080075 UD - UPDATE CODE: 200124 Registro 5165 de 5614 - GeoRef 1997-2001 TI - TITLE: Late Holocene environmental history of southern Choco region, Pacific Colombia; sediment, diatom and pollen analysis of core El Caimito. AU - AUTHORS: Velez-M-I; Wille-M; Hooghiemstra-H; Metcalfe-S; Vandenberghe-J; van-der-Borg-K AF - AUTHOR AFFILIATION: University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics (IBED), Amsterdam, Netherlands SO - SOURCE: Palaeogeography, Palaeoclimatology, Palaeoecology. 173; 3-4, Pages 197-214. 2001. PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 2001. CP - COUNTRY OF PUBLICATION: Netherlands PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English AB - ABSTRACT: We present a multi-proxy study of pollen, diatoms, sediment characteristics and major elements of a 610-cm sediment core from lake El Caimito, located in the humid rain forest of southern Choco, Pacific Colombia. We propose an integrated reconstruction of the local basin development and of the regional vegetation which is possibly related to the tectonic activity of an unstable coastal area. Time control is based on 7 AMS (super 14) C dates that show that the record represents the last 3850 cal yr BP. From 3850 to 2700 cal yr BP sandy deposits, low carbon content, absence of diatoms, and low diversity of the pollen spectra indicate that the site was under the influence of the fluvial system. Erosive event(s) removed part of the sediment record and we observed a hiatus representing 700 years. After that, the basin became more isolated from the river drainage system. From 2010 to 1430 cal yr BP mainly clay was deposited and repeatedly interrupted by river pulses that left sandy and silty horizons in the record. Benthic and littoral-benthic diatom species indicate a shallow water body and a stable water chemistry. Mangrove forest was close to the lake, apparently growing along the close-by inlets. Regionally, the main vegetation elements were palms, and taxa in the families of Moraceae-Urticaceae, Melastomataceae, Fabaceae and from a number of other families and genera, characteristic of tropical lowland rain forest. From 1430 to 810 cal yr BP the river impact gradually diminished. Each fluvial event that affected the local forest is shown in the pollen record by an expansion of Cecropia dominated pioneer forest. Decreasing intensity of forest disturbance coincides with an increase in the diversity of fossil pollen taxa, possibly reflecting an increasing plant diversity of the forest. Mangrove pollen declined, indicating that the coastline moved seaward and suggesting tectonic uplift of the coastal area. Between 810 and 580 cal yr BP mangrove forest was closer to the lake again, reflecting an inland migration of the coastline, suggesting tectonic subsidence. From 580 to 300 cal yr BP the last fluvial events were recorded. Diatom associations indicate oligotrophic and acidic water. The mangrove belt moved seaward again, suggesting tectonic uplift. Palms and Cecropia became more abundant, suggesting increased human impact in the near shore lowland forest. During the last 300 years, stable lacustrine conditions and lowland rain forest with the highest floral diversity is registered. DE - DESCRIPTORS: absolute-age; algae-; biogeography-; C-14; carbon-; Cenozoic-; Choco-Colombia; Colombia-; cores-; dates-; diatoms-; El-Caimito-Colombia; forests-; Holocene-; humid-environment; isotopes-; lacustrine-environment; lake-sediments; major-elements; microfossils-; miospores-; paleoclimatology-; paleoecology-; paleoenvironment-; paleogeography-; palynomorphs-; Plantae-; pollen-; pollen-analysis; pollen-diagrams; Quaternary-; radioactive-isotopes; rain-forests; savannas-; sediments-; South-America; terrestrial-environment; upper-Holocene; vegetation- CC - CATEGORY CODES: 24-Quaternary-geology DT - DOCUMENT TYPE: Serial BL - BIB LEVEL: Analytic MC - MAP COORDINATES: LAT: N023200; N023200; LONG: W0773600; W0773600. IL - ILLUSTRATION: Refs: 59; illus. incl. charts, 2 tables, sketch map. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands IS - ISSN: 0031-0182 CO - CODEN: PPPYAB AN - ACCESSION NUMBER: 2001-075672 UD - UPDATE CODE: 200123 Registro 5166 de 5614 - GeoRef 1997-2001 TI - TITLE: Effective use of non-seismic methods for petroleum exploration. AU - AUTHORS: Ceron-John; Lombo-C; Williams-Stephen; Bain-John AF - AUTHOR AFFILIATION: Ecopetrol, Bogota, Colombia BK - BOOK TITLE: In: Non-seismic technology. BA - BOOK AUTHORS: Anonymous SO - SOURCE: First Break. 19; 9, Pages 523-528. 2001. PB - PUBLISHER: Blackwell Science, on behalf of the European Association of Geoscientists & Engineers (EAGE). Oxford, United Kingdom. 2001. CP - COUNTRY OF PUBLICATION: United-Kingdom PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English DE - DESCRIPTORS: basement-; Bouguer-anomalies; Colombia-; Florencia-Colombia; geophysical-methods; gravity-anomalies; gravity-methods; magnetic-methods; magnetotelluric-methods; outcrops-; petroleum-; petroleum-exploration; South-America CC - CATEGORY CODES: 20-Applied-geophysics; 29A-Economic-geology,-geology-of-energy-sources DT - DOCUMENT TYPE: Serial BL - BIB LEVEL: Analytic MC - MAP COORDINATES: LAT: S040000; N121500; LONG: W0670000; W0790000. IL - ILLUSTRATION: Refs: 7; illus. incl. sect., geol. sketch maps. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. IS - ISSN: 0263-5046 CO - CODEN: #51516 AN - ACCESSION NUMBER: 2001-073993 UD - UPDATE CODE: 200123 Registro 5167 de 5614 - GeoRef 1997-2001 TI - TITLE: Trends in long-period seismicity related to magmatic fluid compositions. AU - AUTHORS: Morrissey-M-M; Chouet-B-A AF - AUTHOR AFFILIATION: Colorado School of Mines, Department of Geology and Geological Engineering, Golden, CO, United States BK - BOOK TITLE: In: Magma degassing through volcanoes; a tribute to Werner F. Giggenbach; selected papers presented at IAVCEI general assembly; Symposium 4, Volcanic gases. BA - BOOK AUTHORS: Allard-Patrick (editor); Shinohara-Hiroshi (editor); Wallace-Paul-J (editor) SO - SOURCE: Journal of Volcanology and Geothermal Research. 108; 1-4, Pages 265-281. 2001. PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 2001. RP - RESEARCH PROGRAM: USGSOP (Non-USGS publications with USGS authors) CP - COUNTRY OF PUBLICATION: Netherlands PY - PUBLICATION YEAR: 2001 CN - CONFERENCE INFORMATION: IAVCEI general assembly; Symposium 4, Volcanic gases. Puerto Vallarta, Mexico. January 19-24, 1997. LA - LANGUAGE: English AB - ABSTRACT: Sound speeds and densities are calculated for three different types of fluids: gas-gas mixture; ash-gas mixture; and bubbly liquid. These fluid properties are used to calculate the impedance contrast (Z) and crack stiffness (C) in the fluid-driven crack model (Chouet: J. Geophys. Res., 91 (1986) 13,967; 101 (1988) 4375; A seismic model for the source of long-period events and harmonic tremor. In: Gasparini, P., Scarpa, R., Aki, K. (Eds.), Volcanic Seismology, IAVCEI Proceedings in Volcanology, Springer, Berlin, 3133). The fluid-driven crack model describes the far-field spectra of long-period (LP) events as modes of resonance of the crack. Results from our calculations demonstrate that ash-laden gas mixtures have fluid to solid density ratios comparable to, and fluid to solid velocity ratios lower than bubbly liquids (gas-volume fractions <10%). This difference results in synthetic far-field spectra with higher impedance contrasts and narrower spectral bandwidths for ash-laden gas mixture than spectra for bubbly liquids. Spectral characteristics are described in terms of the quality factor Q (super -1) . Q (super -1) is measured by the ratio of the frequency of the dominant spectral peak to the bandwidth of the peak measured at one half of its amplitude. This factor expresses the losses of energy due to elastic radiation Q (sub r) (super -1) and other dissipative mechanisms Q (sub i) (super -1) at the source, Q (super -1) = Q (sub r) (super -1) +Q (sub i) (super -1) . Spectra for LP events recorded at active volcanoes such as Galeras in Colombia and Kilauea in Hawaii, have Q (super -1) factors in the range of 0.1-0.002. The Q (sub r) (super -1) factors due to radiation loss calculated for a sphere filled with a H (sub 2) O-CO (sub 2) or H (sub 2) O-SO (sub 2) gas mixture, vary between 0.0015 and 0.0040 with a change in wt% H (sub 2) O at 800-1600 K and 10-50 MPa. For gas-rich mixtures, Q (sub r) (super -1) has a strong dependence on resonator geometry (spherical versus rectangular). The spectra from a resonating sphere filled with gas-rich mixture yields values of Q (sub r) (super -1) an order of magnitude smaller than those from a rectangular crack. For a resonating crack filled with an ash-gas mixture (or pseudogas), Q (sub r) (super -1) varies parabolically from approximately 0.006 for an ash-rich mixture, to 0.0015 or 0.0023 for a H (sub 2) O-rich or CO (sub 2) -rich mixture at 800 K and 25 MPa. For low (<20%) gas-volume fraction fluids (foams, bubbly fluids and ash-rich pseudogases), the magnitudes for Q (sub r) (super -1) are independent of crack geometry. Spectra associated with a foam (gas-volume fractions 10-90%) or bubbly basalt (gas-volume fractions <10%) may have a dominant spectral peak with values of Q (sub r) (super -1) on the order of 0.01 and 0.1, respectively. The spectra from a resonating sphere filled with a foam containing >20% gas-volume fraction yields values of Q (sub r) (super -1) similar to those for a rectangular crack. As with gas-gas and ash-gas mixtures, an increase in mass fraction narrows the bandwidth of the dominant mode and shifts the spectra to lower frequencies. Including energy losses due to dissipative processes in a bubbly liquid increases attenuation. Attenuation may also be higher in ash-gas mixtures and foams if the effects of momentum and mass transfer between the phases were considered in the calculations. DE - DESCRIPTORS: attenuation-; carbon-dioxide; cracks-; eruptions-; fluid-inclusions; gases-; high-pressure; inclusions-; lava-flows; magmas-; mathematical-methods; prediction-; pressure-; seismicity-; sulfur-dioxide; velocity-; volcanic-ash; volcanism-; volume- CC - CATEGORY CODES: 24-Quaternary-geology DT - DOCUMENT TYPE: Serial; Conference-Document BL - BIB LEVEL: Analytic IL - ILLUSTRATION: Refs: 32; illus. incl. 1 table. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands IS - ISSN: 0377-0273 CO - CODEN: JVGRDQ AN - ACCESSION NUMBER: 2001-071990 UD - UPDATE CODE: 200122 Registro 5168 de 5614 - GeoRef 1997-2001 TI - TITLE: Toward the next stage of the Global Mapping Project; successful completion of phase 1 with release of Global Map Version 1.0. AU - AUTHORS: Une-Hiroshi AF - AUTHOR AFFILIATION: Geographic Survey Institute, Ibaraki, Japan SO - SOURCE: Bulletin of the Geographical Survey Institute. 47; Pages 13-19. 2001. PB - PUBLISHER: Ministry of Land, Infrastructure, Geographical Survey Institute. Ibaraki-Ken, Japan. 2001. CP - COUNTRY OF PUBLICATION: Japan PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English AB - ABSTRACT: The Global Mapping Project has successfully completed its first phase celebrated with the great number of participating countries and the release of Global Map Version 1.0 in November 2000. In November 2000, "Global Mapping Forum 2000" was held in Hiroshima, Japan. The highlight of the Forum was a declaration of the release of the Global Map Version 1.0. As of the end of 2000, Global Map Version 1.0 for six countries was available for non-commercial users via the Internet. In addition, the data for more than ten other countries that are nearly completing the production of their Global Map will become available soon. Not only within a global environmental context, the Global Map has also recently been attracting attention as a realistic framework dataset of various global geospatial initiatives such as the Global Spatial Data Infrastructure, Digital Earth Project and UN Geographic Information Working Group. In May 2001, the Eighth Meeting of International Steering Committee for Global Mapping will be held in Cartagena, Colombia. One of the most important issues to be discussed at the meeting will be the target, strategy and action plans for the second phase of the Global Mapping Project. DE - DESCRIPTORS: cartography-; data-processing; digital-cartography; global-; Global-Mapping-Project; information-systems; mapping-; methods- CC - CATEGORY CODES: 15-Miscellaneous DT - DOCUMENT TYPE: Serial BL - BIB LEVEL: Analytic IL - ILLUSTRATION: Refs: 7; illus. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. IS - ISSN: 0373-7160 CO - CODEN: BGGIA7 AN - ACCESSION NUMBER: 2001-071487 UD - UPDATE CODE: 200122 Registro 5169 de 5614 - GeoRef 1997-2001 TI - TITLE: High altitude C (sub 4) grasslands in the Northern Andes; relicts from glacial conditions?. AU - AUTHORS: Boom-A; Mora-G; Cleef-A-M; Hooghiemstra-H AF - AUTHOR AFFILIATION: University of Amsterdam, Hugo de Vries-Laboratory, Amsterdam, Netherlands SO - SOURCE: Review of Palaeobotany and Palynology. 115; 3-4, Pages 147-160. 2001. PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 2001. CP - COUNTRY OF PUBLICATION: Netherlands PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English AB - ABSTRACT: The altitudinal vegetation distribution in the northern Andes during glacial time differed from the present-day conditions as a result of temperature and precipitation change. New evidence indicate that as a response to a reduced atmospheric partial CO (sub 2) pressure (pCO (sub 2) ), the competitive balance between C (sub 3) and C (sub 4) plants have changed. Effects may have remained virtually undetected in pollen records, but can be observed using a stable carbon isotope analysis. Vegetation dominated by C (sub 4) taxa, belonging to the families Cyperaceae (e.g. Bulbostylis and Cyperus) and Poaceae (e.g. Muhlenbergia, Paspalum and Sporobolus), may have been able to replace for a significant part the modern type C (sub 3) taxa (e.g. species belonging to Carex, Rhynchospora, Aciachne, Agrostis, Calamagrostis, and Chusquea). Impact of reduced glacial atmospheric pCO (sub 2) levels and lower glacial temperatures on the composition and the elevational distribution of the vegetation types is discussed. The present high Andean vegetation communities may differ from the glacial equivalents (non-modern analogue situation). We identified dry Sporobolus lasiophyllus tussock grassland and Arcytophyllum nitidum dwarfshrub paramo as the possible relict communities from glacial time. The effect on previous estimates of paleo-temperatures is estimated to be small. DE - DESCRIPTORS: Andes-; Angiospermae-; atmosphere-; Bogota-Colombia; C-13-C-12; carbon-; carbon-dioxide; Cenozoic-; climate-change; cold-environment; Colombia-; communities-; Cyperaceae-; Eastern-Cordillera; ecosystems-; glacial-environment; grasses-; grasslands-; isotope-ratios; isotopes-; Monocotyledoneae-; Northern-Andes; paleoclimatology-; paleoecology-; paramo-environment; Plantae-; Poaceae-; Quaternary-; relict-materials; South-America; Spermatophyta-; stable-isotopes; subalpine-environment; terrestrial-environment; upper-Quaternary; vegetation- CC - CATEGORY CODES: 24-Quaternary-geology DT - DOCUMENT TYPE: Serial BL - BIB LEVEL: Analytic MC - MAP COORDINATES: LAT: N043000; N045000; LONG: W0740000; W0741500. NN - ANNOTATION: Neth. Inst. Sea Res. (NIOZ), Contrib. No. 3391. IL - ILLUSTRATION: Refs: 63; illus. incl. 1 table. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands IS - ISSN: 0034-6667 CO - CODEN: RPPYAX AN - ACCESSION NUMBER: 2001-069349 UD - UPDATE CODE: 200122 Registro 5170 de 5614 - GeoRef 1997-2001 BK - BOOK TITLE: Surviving Galeras. BA - BOOK AUTHORS: Williams-Stanley; Montaigne-Fen BF - BOOK AUTHOR AFFILIATION: Arizona State University, Department of Geology, Tempe, AZ, United States PB - PUBLISHER: Houghton Mifflin Company. Boston, MA, United States. Pages: 270. 2001. CP - COUNTRY OF PUBLICATION: United-States PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English DE - DESCRIPTORS: Andes-; Colombia-; eruptions-; Galeras-; Galeras-eruption-1993; geologic-hazards; popular-geology; South-America; volcanic-risk; volcanoes- CC - CATEGORY CODES: 24-Quaternary-geology DT - DOCUMENT TYPE: Book BL - BIB LEVEL: Monograph MC - MAP COORDINATES: LAT: N011300; N011300; LONG: W0772200; W0772200. IL - ILLUSTRATION: Refs: 124; illus. incl. sketch map. RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute. IB - ISBN: 0-618-03168-5 AN - ACCESSION NUMBER: 2001-067317 UD - UPDATE CODE: 200121 Registro 5171 de 5614 - GeoRef 1997-2001 TI - TITLE: Carboniferous to Cretaceous assembly and fragmentation of Mexico. AU - AUTHORS: Dickinson-William-R; Lawton-Timothy-F AF - AUTHOR AFFILIATION: University of Arizona, Department of Geosciences, Tucson, AZ, United States SO - SOURCE: Geological Society of America Bulletin. 113; 9, Pages 1142-1160. 2001. PB - PUBLISHER: Geological Society of America (GSA). Boulder, CO, United States. 2001. CP - COUNTRY OF PUBLICATION: United-States PY - PUBLICATION YEAR: 2001 LA - LANGUAGE: English AB - ABSTRACT: The geologic framework of Mexico evolved through the Phanerozoic assembly and fragmentation of crustal elements derived from Laurentia, Gondwana, and an intra-Pacific volcanogenic terrane. In middle Paleozoic time, an inactive south-facing Laurentian continental margin of transform origin passed through northern Mexico to connect the miogeoclinal Cordilleran margin with the passive continental margin formed by Cambrian rifting in Texas. Gondwanan blocks of eastern Mexico were accreted to Laurentia by juxtaposition along the Ouachita-Marathon suture belt in earliest Permian time. Subsequent Jurassic opening of the Gulf of Mexico by seafloor spreading displaced the Yucatan-Chiapas block southward, as it rotated anticlockwise from edge-driven shear between Colombia and Florida, along a gulf-flank transform passing through the Isthmus of Tehuantepec. The continuity of a linear north-trending Permian-Triassic arc (now represented by a granite belt) in eastern Mexico precludes strike-slip slivering of Mexico during gulf opening and implies that Colombia lay east of internally coherent Gondwanan crust of southeastern Mexico, but south of Yucatan-Chiapas, prior to Pangean breakup. During subsequent intracontinental rifting, crustal elements of eastern Mexico were displaced southeastward, along a transform between basement blocks of present northeastern and east-central Mexico, in the wake of Colombia's retreat from Laurentia. The Chortis block of nuclear Central America also lay within Pangea west of Colombia and remained attached to southern Mexico prior to its Cenozoic displacement eastward along the Cayman transform. The Caborca block of northwestern Mexico was displaced southeastward from the Cordilleran miogeocline by Permian-Triassic slip along a transform that linked the convergent Sonoma orogen with the northern end of a subduction zone in central Mexico that paralleled the Permian-Triassic magmatic arc built on Gondwanan crust of eastern Mexico. Subsequent post-Middle Triassic initiation of a west-facing continental-margin arc-trench system (i.e., with the subducting slab moving down to the east) along the structurally modified paleo-Pacific flank of Pangea produced middle Mesozoic arc assemblages extending southeastward from California and Arizona through east-central Mexico into Colombia. Beyond a compound suture belt lying outboard of the middle Mesozoic continental margin, western Mexico is underlain by Mesozoic volcanogenic crust formed beneath an east-facing intraoceanic island arc that was accreted to Laurentian and Gondwanan Mexico by arc-continent collision late in Early Cretaceous time. The accreted arc assemblage was overlapped by late Early Cretaceous-early Late Cretaceous carbonate platforms linked depositionally with comparable facies in eastern Mexico. As the offshore island arc approached the continent, progressive consumption of the intervening oceanic plate induced slab rollback beneath the Jurassic magmatic arc on the mainland, terminating arc magmatism and promoting development of associated rift troughs that extend from northeastern Mexico to southeastern California. Following arc collision and accretion, reversal of subduction polarity along the expanded western flank of Mexico created a west-facing continental-margin arc- trench system that was continuous with the Cordilleran arc and Franciscan trench of California. Subsequent subduction produced volcanic-plutonic arc assemblages on the mainland and in Baja California, which was contiguous with the mainland prior to Neogene seafloor spreading that opened the Gulf of California. A paired late Early Cretaceous subduction complex and late Mesozoic forearc basin occurred along the Pacific flank of Baja California. DE - DESCRIPTORS: accretion-; Atlantic-Ocean; block-structures; Carboniferous-; continental-drift; crust-; faults-; fragmentation-; Gondwana-; Gulf-of-Mexico; kinematics-; Laurentia-; Mesozoic-; Mexico-; North-Atlantic; paleogeography-; Paleozoic-; Pangaea-; Phanerozoic-; plate-tectonics; review-; rifting-; shear-zones; strike-slip-faults; suture-zones; systems-; tectonics-; terranes-; transform-faults; upper-Paleozoic Yüklə 20,82 Mb. Dostları ilə paylaş:
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