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Early Cretaceous subduction of continental crust at the Diego de Almagro archipelago, southern Chile

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Episodes 2003年第4期26卷 285-289页

作者： FranciscoHervé C.MarkFanning DepartamentodeGeologia UniversidaddeChileCasilla13518Correo21SantiagoChile researchschoolofearthsciences TheAustralianNationalUniversityCanberraACT0200Australia

In the Diego de Almagro archipelago of southern Chile, a quartz rich mica schist and a mylonitized granite contain Late Jurassic zircons of ca 166 and 170 Ma respectively. These rocks were metamorphosed during the Cretaceous in a subduction zone environment, which developed blueschist assemblages in metabasalts interleaved with the mica schist. The dated rocks were probably part of the acid large igneous province developed in southwestern Gondwanaland during the extensional phase which preceded the dismembering of the supercontinent. They constitute evidence that tectonic erosion of the margin occurred, as these siliceous igneous rocks, formed in the South American upper plate, were transported in the subduction zone to some 20 km depth prior to their exhumation. These rocks are in tectonic contact through the Seno Arcabuz shear zone, with late Permian turbidites of the Duque de York complex, which did not undergo blueschist metamorphism.

关键词：早白垩纪石英富集片岩群岛智利南部

Proposal to redefine the Quaternary

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Episodes 2004年第2期27卷 127-127页

作者： BradPillans President INQUAStratigraphy＆ChronologyCommissionResearchSchoolofEarthSciencesTheAustralianNationalUniversityCanberra.ACT0200Australia

The following proposal has been circulated, via the Executive of the International Union for Quaternary Research (INQUA), to all INQUA members for discussion. It also appears on the ICS web site (***). Comments may be... 详细信息

关键词：子系统时间量程计算机网络晚第三纪地层学

The Imataca Complex, NW Amazonian Craton,Venezuela： Crustal evolution and integration of geochronological and petrological coolinghistories

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Episodes 2004年第1期27卷 3-12页

作者： ColomboC.G.Tassinari JoseM.U.Munha WilsonTeixeira TeresaPalacios AllenP.Nutman CesarSosaS. AdjairP.Santos BrunoO.Calado CentrodePesquisas Geocronol6gicasInstitutodeGeocienciasUniversidadedeSaeoPauloRuadoLago562CidadeUniversitariaButantaSaoPauloBrasil.CEP05588-900 Centro／Dept.Geologia EdificioC25°pisoFaculdadeCienciasUniversidadedeLisboaCampoGrande1749-016LisboaPortugal. researchschoolofearthsciences AustralianNationalUniversity. MinisteriodeMinasdeVenezuela CiudadBolivar. Cia.MineraSOPEVEN Venezuela.

SHRIMP U/Pb-zircon data and Nd mean crustal residence ages indicate that the lmataca Complex developed from an Archean (≥3.2Ga) continental protolith which has undergone considerable isotopic disturbance plus and juvenile accretion during late-Archean (-2.8Ga) times. Transamazonian granulites experienced peak metamorphic conditions of 750-800℃, 6-8kbar with associated transpressive thrusting and tectonic imbrication. Geochronology on zircon, pyroxene and garnet constrains the timing of peak metamorphism at 1.98-2.05Ga. Diffusion modeling of Fe-Mg exchange between biotite inclusions and host garnet yields (near metamorphic peak) cooling rates of 50-100℃/Ma, with petrological cooling rates being generally consistent with cooling rates determined from geochronology. Combining the retrograde P-T path with cooling rates suggests that after the metamorphic peak, large portions of the lmataca Complex were exhumed from 30 to 17km at a rate of 7-2km/*** this, exhumation rates progressively decreased as the rocks approached the surface. Rapid overall upliftlerosion had ceased when the rocks passed below 600-550℃ at 2.01-1.96 Ga ago. Observed variations in mineral cooling ages are interpreted as to reflect episodic differential tectonic exhumation within major fault systems. Inferred (maximum) ages of fault re-activation generally coincide with major continental accretion events in the Amazonian Craton and reflect long-term thermal evolution of the lmataca terrane, as conditioned by variable response to continued continental convergence during the Proterozoic.

关键词：亚马逊河钕地质年代学太古代

Quaternary： status, rank, definition, survival

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Episodes 2005年第2期28卷 118-120页

作者： Marie-PierreAubry WilliamA.Berggren JohnVanCouvering BrianMcGowran BradPillans FritsHilgen DepartmentofGeologicalSciences RutgersUniversity610TaylorRoadPiscatawayNJ08854-8066USA DepartmentofGeologicalSciences RutgersUniversity610TaylorRoadPiscatawayNJ08854-8066USA／／DepartmentofGeologyandGeophysicsWoodsHoleOceanographicInstitutionWoodsHoleMa02543USA TheMicropaleontologyProject 256FifthAvenueNewYorkCityNYUSA SchoolofEarth＆EnvironmentalSciences TheUniversityofAdelaideDP313AdelaideSA5005Australia researchschoolofearthsciences TheAustralianNationalUniversityCanberraACT0200Australia

The long controversy over the term ‘Quaternary' as a chronostratigraphic unit may be reaching an apotheosis, judging from recent papers (Pillans and Naish, 2004; Gibbard et al., 2005; and referencest herein). The debate is no longer centered on whether there should be a place in the geological time scale for a unit termed ‘Quaternary'-despite its dubious past, it cannot be denied that a large body of earth-historical research is strongly identified with this term. The challenge now concerns an appropriate rank and definition of Quaternary with regard to other chronostratigraphic units. Several options have been proposed (Pillans and Naish, 2004), and Gibbard et al. (2005) encourage a debate on these before decision is reached. In this brief note, we describe an arrangement not previously considered that seems advantageous. It is instructive, however, to first review the Pleistocene Series and Neogene System, the two units that are directly affected by introduction of the Quaternary into the chronostratigraphic hierarchy.

关键词：第四纪冰川地形特征沉积作用识别方法