Nature and P-T-t constraints of very low-grade metamorphism in the Triassic-Jurassic basins, Coastal Range, central Chile
Triassic-Jurassic volcano-sedimentary sequences in the Coastal Range of central Chile (34° 45/35°20'S) from the Vichuquén-Tilicura and Hualañé-Gualleco basins display metamorphic assemblages indicative of very low-grade conditions. Triassic and Lower Jurassic metapelites achieved anchizonal con...
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| Autores principales: | , |
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| Lenguaje: | English |
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Servicio Nacional de Geología y Minería (SERNAGEOMIN)
2005
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| Acceso en línea: | http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082005000200002 |
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| Sumario: | Triassic-Jurassic volcano-sedimentary sequences in the Coastal Range of central Chile (34° 45/35°20'S) from the Vichuquén-Tilicura and Hualañé-Gualleco basins display metamorphic assemblages indicative of very low-grade conditions. Triassic and Lower Jurassic metapelites achieved anchizonal conditions (IC, b o, coal-rank and fluid inclusions data: P »1.3, T»190) at 181-184 Ma, under geothermal gradient of »35°Ckm-1 during extensional geodynamic conditions. Nevertheless, in stratigraphically higher mafic volcanic sequences, of Middle to Late Jurassic age, the presence of chlorite (Xc =0.98-0.99), three types of epidote (XFe3+ = 41.14±0.90, 30.08±1.53 and 18.05±1.75), titanite, Fe-rich and Fe-poor pumpellyite and hydrogarnet (+albite and quartz) are indicative of re-equilibration under prehnite-pumpellyite facies conditions (P »3 kbar, T »300°C) and variable oxygen fugacity. A change from an extensional setting (with maximum basin subsidence and development of burial very low-grade metamorphism in the Triassic-Lower Jurassic metapelitic sequences) to a compressional setting (with local overthrusting of Triassic and Lower Jurassic sequences over Middle to Late Jurassic volcano-sedimentary sequences) is proposed to explain the contrasting metamorphic conditions between Triassic-Lower Jurassic metapelites and Middle-Late Jurassic metabasites |
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