No. Registros Solicitud 1 5614 colombia



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Registro 619 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Palinologia del Santoniano Tardio al Maastrichtiano del piedemonte llanero Colombiano; correlacion con el paleocinturon tropical

Translated Title: Upper Santonian to Maestrichtian palynology of the Colombian Llanero piedmont; correlation with the tropical paleobelt.

AU - AUTHORS: Sarmiento-Gustavo; Guerrero-Javier

AF - AUTHOR AFFILIATION: Universidad Nacional de Colombia, Departamento de Geociencias, Bogota, Colombia

SO - SOURCE: Geologia Colombiana. 25; Pages 111-147. 2001.

PB - PUBLISHER: Universidad Nacional de Colombia, Facultad de Ciencias, Departamento de Geociencias. Bogota, Colombia. 2001.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: Spanish



LS - LANGUAGE OF SUMMARY: English

AB - ABSTRACT: The palynological analysis of outcrop samples from the E foothills of the Eastern Cordillera, corresponding to the top of the Chipaque Formation, Guadalupe Group and Guaduas Formation, establishes the presence of dinoflagellates, pollen and spores of appreciable biostratigraphic value. The potential of correlation of these elements is compared with data from other parts of the world in the tropical belt, for the interval Late Santonian-Late Maastrichtian. The Late Santonian is represented in the mudstones of the Chipaque Formation, by the common occurrence of the genus Dinogymnium, specifically by the first appearance of D. digitus and D. Vozzhennikovae, and the last appearance of D. longicornis. Additionally, the last appearance of Xenascus ceratioides is registered in the upper part of the Chipaque Formation. The Early Campanian Arenitas de San Antonio Formation of the Lower Guadalupe Alloformation, is characterized by the first appearance of Trichodinium castanea, Cerodinium granulostriatum and Andalusiella mauthei punctata, as well as the last appearance of Areoligera senonensis, Palaeohystrichophora infusorioides, Dinogymnium westralium, D. undulosum, D. vozzhennicovae and Odontochitina operculata. The association that differentiates palynologically the Late Campanian, is present in the Lodolitas de Aguacaliente Formation of the Middle Guadalupe Alloformation and exhibits the following characteristics: First occurrence of Senegalinium bicavatum, Andalusiella mauthei aegyptiaca, A. gabonenesis, Cerodinium diebellii and Anphigymnium mitratum, and last presence of Trichodinium castanea, A. mauthei punctata, Cerodinium granulostriatum and Alisogymnium euclaensis. The Early Maastrichtian Arenitas de San Luis de Gaceno Formation of the Upper Guadalupe Alloformation is characterized by the last occurrence of Senegalinium bicavatum, Cerodinium diebellii, Cerodinium granulostriatum and Andalusiella mauthei. The upper boundary of the Late Maastrichtian Guaduas Formation corresponds to the unconformity at the base of the (Late Paleocene) Socha Inferior Formation. The palynological association is comparable with the one found in the lower part of the same unit in the locality of Sutatausa. The last occurrence of Andalusiella gabonensis, Dinogymnium acuminatum and Buttinia andreevii defines the Late Maastrichtian. Biostratigraphic studies from other parts of the world have demonstrated the provinciality of Late Cretaceous dinoflagellates. The association that characterizes the Campanian corresponds to the province of the "paleocinturon tropical" and contains species of the genus Andalusiella, Trichodinium, Cerodinium and Senegalinium, in several localities of Northern South America and Africa. However, some of these groups display a dispersion that extends to the North Hemisphere, like the first appearance of Andalusiella in the upper part of the Early Campanian, and the first appearance of Senegalinium, in the lower part of the Late Campanian. During the Maastrichtian, provincialism continues characterizing N South America and Africa; the palynomorphs that have their last appearance are: Senegalinium bicavatum, Cerodinium granulostriatum, Andalusiella mauthei, Andalusiella gabonensis and Dinogymnium acuminatum. The ratio of palynomorphs of marine origin POM (dinoflagellates, foraminiferal lining and acritarchs), to palynomorphs of continental origin POC (pollen, spores and fungis) reflects the changing position of the shoreline. The group of dinoflagellates is important in the mudstone units representing relatively high sea levels. The palynomorphs derived from fungis, pollen and spores, increase their contents in the sandy units representing relatively low sea levels. The almost total disappearance of dinoflagellates starts from the upper part of the Arenitas de San Luis de Gaceno Formation.

DE - DESCRIPTORS: Arenitas-de-San-Antonio-Formation; biostratigraphy-; Boyaca-Colombia; Campanian-; Chipaque-Formation; clastic-rocks; Colombia-; correlation-; Cretaceous-; Dinoflagellata-; Guadalupe-Group; Guadauas-Formation; Llanos-; Lodolitas-de-Aguascaliente-Formation; Maestrichtian-; Mesozoic-; microfossils-; miospores-; palynomorphs-; piedmonts-; pollen-; pollen-analysis; Santonian-; sedimentary-rocks; Senonian-; siltstone-; Socha-Formation; South-America; Upper-Cretaceous

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: N040000; N050000; LONG: W0730000; W0740000.

IL - ILLUSTRATION: Refs: 82; illus. incl. strat. col., geol. sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute.

IS - ISSN: 0072-0992

CO - CODEN: GECBA7

AN - ACCESSION NUMBER: 2002-016222

UD - UPDATE CODE: 200206

Registro 620 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: The stratigraphy of the W side of the Cretaceous Colombian basin in the upper Magdalena Valley; reevaluation of selected areas and type localities including Aipe, Guaduas, Ortega, and Piedras.

AU - AUTHORS: Guerrero-Javier; Sarmiento-Gustavo; Navarrete-Rosa-Esther

AF - AUTHOR AFFILIATION: Universidad Nacional de Colombia, Departamento de Geociencias, Bogota, Colombia

SO - SOURCE: Geologia Colombiana. 25; Pages 45-110. 2001.

PB - PUBLISHER: Universidad Nacional de Colombia, Facultad de Ciencias, Departamento de Geociencias. Bogota, Colombia. 2001.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: English

AB - ABSTRACT: Marine strata composed of mixtures of calcareous and terrigenous particles dominate the. Cretaceous succession of the Upper Magdalena Valley (UMV). These include mainly biomicrites, biosparites, mudstones, sandstones and mixed calcareous/terrigenous rocks of a litharenitic affinity. Sedimentary rocks deposited in fluvial environments, and including granule and pebble conglomerates, are present only in the lowermost and uppermost parts of the section. The succession was deposited in a ramp, which had an inclination of about 0.06 degrees toward the E and reached marine depths of 200 to 250 m on the axis of the basin. The whole Cretaceous section of the UMV was sourced from the W by the ancestral Central Cordillera metamorphic/volcanic arc, as indicated by the abundant content of metamorphic and volcanic rock fragments. The new term CRETACEOUS COLOMBIAN BASIN is proposed to make emphasis in a single elongated back-arc basin which opened N to the Caribbean and connected intermittently to the S with other back-arc and foreland basins E of the volcanic arc, along Ecuador, Peru, Bolivia, Chile, and Argentina. The basin reached a width of 400 to 500 km during times of high sea levels and had two sources of sediment, one W in the Central Cordillera and another E in the Guyana Shield. The strata in the W side of the basin have a calcareous/litharenitic nature, in contrast with the ones in the opposite E side that have a quartzarenitic nature, because the last ones were sourced mainly by the Precambrian and Paleozoic sedimentary rocks of the Guyana Shield. Sedimentary environments in the UMV were controlled mainly by eustatic sea level changes that affected the whole intracratonic basin, so that sea level pulses are synchronous in both, E and W sides of the basin. Since the sequence stratigraphy of sea level changes in the UMV is synchronous with the one in the Eastern Cordillera and Llanos Foothills, a framework of allostratigraphic units is formally proposed for the whole basin. Type localities and selected areas from the UMV including Aipe, Guaduas, Ortega, and Piedras were sampled for analyses of sedimentary petrography and micropaleontology of foraminifers and palynomorphs, allowing precise characterization of the units and appropriate dating. The oldest known ages of the Cretaceous sedimentary succession in this part of the basin are Aptian; however, the ancestral Central Cordillera also sourced older Cretaceous strata of known Berriasian to Barremian age in adjacent areas.

DE - DESCRIPTORS: Aipe-Colombia; allostratigraphy-; Andes-; arenite-; back-arc-basins; Barremian-; basins-; Berriasian-; biomicrite-; biosparite-; biostratigraphy-; Buscavida-Formation; Caballos-Formation; calcareous-composition; carbonate-rocks; Central-Cordillera; clastic-rocks; Colombia-; Cretaceous-; depositional-environment; Eastern-Cordillera; El-Cobre-Formation; eustacy-; Foraminifera-; Guaduas-Colombia; Guyana-Shield; Hondita-Formation; hydrocarbons-; Invertebrata-; La-Tabla-Formation; limestone-; litharenite-; lithostratigraphy-; Lomagorda-Formation; Lower-Cretaceous; Magdalena-Valley; Mesozoic-; microfossils-; mudstone-; Olini-Group; organic-compounds; Ortega-Colombia; paleogeography-; palynomorphs-; petrography-; petroleum-; Piedras-Colombia; Protista-; sandstone-; Seca-Formation; sedimentary-rocks; sequence-stratigraphy; South-America; Tetuan-Formation; Yavi-Formation

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: N030000; N050000; LONG: W0740000; W0760000.

IL - ILLUSTRATION: Refs: 56; illus. incl. 5 tables, sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute.

IS - ISSN: 0072-0992

CO - CODEN: GECBA7

AN - ACCESSION NUMBER: 2002-016221

UD - UPDATE CODE: 200206

Registro 621 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Edad de la Formacion Vijes en el pozo V3A, Oligoceno del piedemonte oriental de la Cordillera Occidental, Departamento del Valle del Cauca, Colombia

Translated Title: Age of the Vijes Formation in the V3A Well, Oligocene of the eastern piedmont of the Western Cordillera, Department of Valle del Cauca, Colombia.

AU - AUTHORS: Duenas-Hernando; Navarrete-Rosa-Esther; Mojica-Jairo; Pardo-Mauricio; Camargo-Roger

AF - AUTHOR AFFILIATION: Bioss, Bogota, Colombia

SO - SOURCE: Geologia Colombiana. 25; Pages 25-43. 2001.

PB - PUBLISHER: Universidad Nacional de Colombia, Facultad de Ciencias, Departamento de Geociencias. Bogota, Colombia. 2001.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: Spanish

LS - LANGUAGE OF SUMMARY: English

AB - ABSTRACT: Outcrops of the Vijes Formation are restricted to the Vijes and Mulalo areas, which are located in the northwestern part of the Valle del Cauca Basin. Based on its micro-paleontological content (palynomorphs and forams) an Oligocene age has been assigned for this Marine Unit for long time considered as an Eocene to Miocene Formation. The Vijes Formation, has a thickness close to 180 m. It is made up of limestones, dirty sandstones and calcareous siltstones, that allow to sub-divide it in four Units which from bottom to top are: 1-) Polimictic conglomerates with local intercalation of plant bearing siltstones (0 and 20 m). 2-) Reef limestones, with abundant bivalve-remains, calcareous algae, strong foraminifers, gastropods, colonial and solitary corals. 3-) Dark siltstones and fine-grained sandstones that have yielded abundant microfossils assemblages which include some crustacean remains. 4-) Quartz-sandstones, with plant remains. Twelve core samples from the Vijes Formation, in the V3-A borehole were analyzed using palynological and foram methods. These samples provided good microfossil assemblages, which belong to the Cicatricosisporites dorogensis pollen zone and to the planktonic foram biozones Cassigerinella chipolensis/Pseudohastigerina micra, Globigerina ampliapertura and Globorotalia opima opima. The boundary between these biozons corresponds to the limit between the Rupelian and Chattian (30 Ma), and is related to the principal sea level drop during the Tertiary. The Vijes Formation is resting unconformable on the Diabasic Group of Turonian-Santonian age and underlies Quaternary sediments. This hiatus indicates that in the Valle del Cauca Basin the Western Cordillera has undergone deformation, emersion and erosion periods between the Late Cretaceous and the Late Eocene. The area where strata from the Vijes Formation were deposited, can be considered as a sea gate that allowed the entrance of Oligocene waters coming from the West to the present Cauca Valley area. This fact could explain the presence of marine horizons within Guachinte (La Leona Horizon) and Ferreira Formations (San Francisco Horizon).

DE - DESCRIPTORS: Andes-; biostratigraphy-; biozones-; calcareous-composition; carbonate-rocks; Cenozoic-; clastic-rocks; Colombia-; correlation-; Foraminifera-; Invertebrata-; limestone-; microfossils-; miospores-; Oligocene-; paleoenvironment-; Paleogene-; palynomorphs-; piedmonts-; planktonic-taxa; pollen-; Protista-; reefs-; sandstone-; sea-level-changes; sedimentary-rocks; South-America; Tertiary-; transgression-; Valle-del-Cauca-Basin; Valle-del-Cauca-Colombia; Vijes-Formation; Western-Cordillera

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: N030000; N050000; LONG: W0760000; W0773000.

IL - ILLUSTRATION: Refs: 46; illus. incl. 3 tables, sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute.

IS - ISSN: 0072-0992

CO - CODEN: GECBA7

AN - ACCESSION NUMBER: 2002-016220

UD - UPDATE CODE: 200206

Registro 622 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: La fauna de Amonitas del Triasico Tardio en el Miembro Chicala (= parte baja de la Formacion Saldana) en Payande, Tolima, Colombia

Translated Title: Upper Triassic ammonite fauna of the Chicala Member (lower Saldana Formation) in Payande, Tolima, Colombia.

AU - AUTHORS: Mojica-Jairo; Prinz-Grimm-Peter

AF - AUTHOR AFFILIATION: Universidad Nacional de Colombia, Departamento de Geociencias, Bogota, Colombia

SO - SOURCE: Geologia Colombiana. 25; Pages 13-23. 2001.

PB - PUBLISHER: Universidad Nacional de Colombia, Facultad de Ciencias, Departamento de Geociencias. Bogota, Colombia. 2001.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: Spanish

LS - LANGUAGE OF SUMMARY: English; German

AB - ABSTRACT: Five Late Triassic ammonite species from the Chicala Member of the Saldana Formation are described. The fossil bearing outcrops are located 3 km south-western of the Payande town, Tolima District. The identified forms belong to Rhabdoceras suessi Hauer 1860, Lissonites canadensis Tozer 1979, Peripleurites roemeri Mojsisovics 1893, Peripleurites boeckhi Mojsisovics 1893 and Cycloceltites cowichanensis Tozer 1994a. This association is representative of almost all the Raethian stage (in European sense) or of the Upper Norian (in north-American sense). However, no elements of most Upper Raethian have been found, that is the Choristoceras marshi Zone, well known in northern Chile and western Canada. The results obtained for the Chicala Member restrict the age of the underlying Payande Formation to the European Norian or the north-American Middle Norian. The described ammonites present faunistic affinity with those typical of the tethyan, alpine and central Andean realms.

DE - DESCRIPTORS: Ammonites-; Ammonoidea-; Andes-; biostratigraphy-; biozones-; Central-Andes; Cephalopoda-; Chicala-Member; Colombia-; correlation-; Invertebrata-; lithostratigraphy-; Mesozoic-; Mollusca-; Norian-; Payande-Colombia; Rhaetian-; Saldana-Formation; South-America; Tetrabranchiata-; Tolima-Colombia; Triassic-; Upper-Triassic

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: N034500; N043000; LONG: W0744500; W0754500.

IL - ILLUSTRATION: Refs: 30; illus. incl. strat. col., 1 table, geol. sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute.

IS - ISSN: 0072-0992

CO - CODEN: GECBA7

AN - ACCESSION NUMBER: 2002-016219

UD - UPDATE CODE: 200206

Registro 623 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: La obra geologica del profesor Otto F. Geyer en Colombia

Translated Title: The geological works of Professor Otto F. Geyer in Colombia.

AU - AUTHORS: Mojica-Jairo

AF - AUTHOR AFFILIATION: Universidad Nacional de Colombia, Departamento de Geociencias, Bogota, Colombia

SO - SOURCE: Geologia Colombiana. 25; Pages 3-12. 2001.

PB - PUBLISHER: Universidad Nacional de Colombia, Facultad de Ciencias, Departamento de Geociencias. Bogota, Colombia. 2001.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: Spanish

LS - LANGUAGE OF SUMMARY: English; German

AB - ABSTRACT: During the 60s, 70s and 80s, Professor Otto F. Geyer investigated the Triassic-Jurassic of Colombia, as well as time equivalent rocks in Ecuador and northern Peru. His work materialized in 18 contributions and represented a vigorous impulse for the knowledge of a subject, that, for a long time, was considered arid or not important. Perhaps, Geyer's most remarkable contributions are those on the Morrocoyal Formation (1969), the Pre-cretaceous Mesozoic of Colombia (1973) and the Magnafacies in the North-Andean Realm (1980a, 1980b). In his articles Geyer makes detailed descriptions of the different units investigated, reviews the stratigraphic nomenclature, discusses the fossil identifications of previous authors and proposes paleogeographic reconstructions and regional comparisons. Moreover, and as a consequence of the direct or indirect actions of Prof. Geyer, seven Colombian geologists carried out postgraduate studies at the German Universities of Stuttgart and Tubingen.

DE - DESCRIPTORS: Baden-Wurttemberg-Germany; biography-; Bohemia-; Central-Europe; Colombia-; correlation-; Czech-Republic; description-; Ecuador-; education-; Europe-; Germany-; Geyer,-Otto-F.; graduate-level-education; lithofacies-; lithostratigraphy-; Mesozoic-; Morrocoyal-Formation; nomenclature-; paleogeography-; Peru-; research-; South-America; Stuttgart-Germany; type-localities; University-of-Stuttgart

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Analytic

IL - ILLUSTRATION: Refs: 50; illus.

RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute.

IS - ISSN: 0072-0992

CO - CODEN: GECBA7

AN - ACCESSION NUMBER: 2002-016218

UD - UPDATE CODE: 200206

Registro 624 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Latitude-dependent climatic response to Milankovitch orbital forcing and its expression in Cretaceous rocks of the Northern Hemisphere.

AU - AUTHORS: Meyers-Stephen-R; Sageman-Bradley-B

AF - AUTHOR AFFILIATION: Northwestern University, Evanston, IL, United States

BK - BOOK TITLE: In: Summary of investigations 2000; Volume 1, Saskatchewan Geological Survey.

BA - BOOK AUTHORS: Christopher-J-E (editor); Gilboy-Chris-F (editor); Haidl-F-M (editor); Harper-C-T (editor); Brown-C-L (editor)

SO - SOURCE: Summary of Investigations by the Saskatchewan Geological Survey. Pages 76-81. 2000.

PB - PUBLISHER: Saskatchewan Geological Survey. Regina, SK, Canada. 2000.

CP - COUNTRY OF PUBLICATION: Canada

PY - PUBLICATION YEAR: 2000

LA - LANGUAGE: English

DE - DESCRIPTORS: biogenic-processes; Canada-; carbonate-rocks; Cenomanian-; clastic-rocks; Colombia-; Colorado-; cores-; Cretaceous-; cycles-; facies-; limestone-; lithostratigraphy-; marl-; Mesozoic-; Milankovitch-theory; North-America; paleoclimatology-; Saskatchewan-; sedimentary-rocks; South-America; Texas-; Turonian-; United-States; Upper-Cretaceous; Western-Canada; Western-Interior; Western-Interior-Seaway

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Serial; Report

BL - BIB LEVEL: Analytic

IL - ILLUSTRATION: Refs: 19; illus. incl. sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2002, American Geological Institute.

IS - ISSN: 0228-5657

CO - CODEN: #00317

RN - REPORT NUMBER: 2000-4.1

AV - AVAILABILITY: Saskatchewan Energy and Mines, Communications Branch, Regina, SK, Canada

AN - ACCESSION NUMBER: 2002-014545

UD - UPDATE CODE: 200206

Registro 625 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Seismological constraints on the mechanism of deep earthquakes; temperature dependence of deep earthquake source properties.

AU - AUTHORS: Wiens-Douglas-A

AF - AUTHOR AFFILIATION: Washington University, Department of Earth and Planetary Sciences, Saint Louis, MO, United States

BK - BOOK TITLE: In: Processes and consequences of deep subduction.

BA - BOOK AUTHORS: Rubie-David-C (editor); van-der-Hilst-Rob-D (editor)

SO - SOURCE: Physics of the Earth and Planetary Interiors. 127; 1-4, Pages 145-163. 2001.

PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 2001.

CP - COUNTRY OF PUBLICATION: Netherlands

PY - PUBLICATION YEAR: 2001

CN - CONFERENCE INFORMATION: Alfred-Wegener workshop on Processes and consequences of deep subduction. Verbania, Italy. Sept. 1999.

LA - LANGUAGE: English

AB - ABSTRACT: Seismological observations are of vital importance for understanding the mechanism of deep earthquakes. Most of the seismological observables for earthquakes deeper than 300 km are similar to shallow earthquakes. Deep earthquakes clearly represent shear failure on a planar surface as shown by their double couple mechanisms. Deep earthquake aftershock sequences show temporal decay rates and magnitude-frequency relations (b-values) that are similar to shallow earthquakes, with the aftershocks occurring preferentially along the mainshock fault planes. In addition, deep earthquake rupture velocities are similar to those of shallow earthquakes. However, there are also some observations that are clearly distinctive relative to shallow earthquakes. Stress drops of deep earthquakes show a large variation but are larger, on average, than shallow earthquakes. Different deep seismic zones show very different b-values, in contrast to shallow earthquakes, which show similar b-values worldwide. In addition, deep earthquakes show fewer aftershocks than shallow earthquakes. A variety of observations suggest that deep earthquakes are highly sensitive to the temperature of the slab. Both deep earthquake b-values and the rate of deep earthquake aftershock occurrence are inversely correlated with the temperature of the deep slabs, suggesting that these factors are temperature-controlled to an extent much greater than with shallow earthquakes. Large deep earthquakes in warm slabs show slower rupture velocities, larger stress drops, and lower seismic efficiencies than similar earthquakes in cold slabs. The width of deep seismic zones is also probably temperature controlled, but deep earthquake rupture can propagate outside the normal limits of Benioff zone seismicity. Simple thermal models for the Tonga slab near the 1994 deep earthquake suggest that the temperature at the rupture termination point was at least 200 degrees C warmer than the temperature that limits smaller earthquakes in the slab. These observations can be used to evaluate physical models for deep earthquakes, including brittle slip along fluid-weakened faults, transformational faulting, and thermal (and perhaps melt lubricated) shear instabilities. It is difficult to explain the large fault widths of some deep earthquakes using a fluid weakening model, since hydrated materials are expected in only a narrow depth zone at the top of the slab, and the fault planes do not have the expected orientations for reactivated faults. The lateral extent of the largest deep earthquakes cast doubt on the transformational faulting model, in which events should be confined within a narrow metastable wedge. Seismological studies have also failed to find evidence for the existence of metastable olivine in slabs. The temperature dependence of deep earthquakes argues in favor of a temperature-activated phenomenon, such as thermal shear instabilities and perhaps fault zone melting.


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