The Imataca Complex, NW Amazonian Craton,Venezuela: Crustal evolution and integration of geochronological and petrological coolinghistories |
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作者单位: | [1]CentrodePesquisas,Geocronol6gicasInstitutodeGeociencias,UniversidadedeSaeoPaulo,RuadoLago562,CidadeUniversitaria,Butanta,SaoPaulo,Brasil.CEP05588-900 [2]Centro/Dept.Geologia,EdificioC2,5°piso,FaculdadeCiencias,UniversidadedeLisboa,CampoGrande,1749-016Lisboa,Portugal. [3]ResearchSchoolofEarthSciences,AustralianNationalUniversity. [4]MinisteriodeMinasdeVenezuela,CiudadBolivar. [5]Cia.MineraSOPEVEN,Venezuela. |
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摘 要: | 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/Ma.After 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.
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关 键 词: | 亚马逊河 钕 地质年代学 太古代 |
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