Author:
WILLNER ARNE P.,MASSONNE HANS-JOACHIM,RING UWE,SUDO MASAFUMI,THOMSON STUART N.
Abstract
AbstractIn the late Palaeozoic fore-arc system of north-central Chile at latitudes 31–32°S (from the west to the east) three lithotectonic units are telescoped within a short distance by a Mesozoic strike-slip event (derived peakP–Tconditions in brackets): (1) the basally accreted Choapa Metamorphic Complex (CMC; 350–430°C, 6–9 kbar), (2) the frontally accreted Arrayán Formation (AF; 280–320°C, 4–6 kbar) and (3) the retrowedge basin of the Huentelauquén Formation (HF; 280–320°C, 3–4 kbar). In the CMC, Ar–Ar spot ages locally date white-mica formation at peakP–Tconditions and during early exhumation at 279–242 Ma. In a local garnet mica-schist intercalation (570–585°C, 11–13 kbar) Ar–Ar spot ages refer to the ascent from the subduction channel at 307–274 Ma. Portions of the CMC were isobarically heated to 510–580°C at 6.6–8.5 kbar. The age of peakP–Tconditions in the AF can only vaguely be approximated at ≥ 310 Ma by relict fission-track ages consistent with the observation that frontal accretion occurred prior to basal accretion. Zircon fission-track dating indicates cooling below ~ 280°C at ~ 248 Ma in the CMC and the AF, when a regional unconformity also formed. Ar–Ar white-mica spot ages in parts of the CMC and within the entire AF and HF point to heterogeneous resetting during Mesozoic extensional and shortening events at ~ 245–240 Ma, ~ 210–200 Ma, ~ 174–159 Ma and ~ 142–127 Ma. The zircon fission-track ages are locally reset at 109–96 Ma. All resetting of Ar–Ar white-mica ages is proposed to have occurred byin situdissolution/precipitation at low temperature in the presence of locally penetrating hydrous fluids. Hence syn- and postaccretionary events in the fore-arc system can still be distinguished and dated in spite of its complex heterogeneous postaccretional overprint.
Publisher
Cambridge University Press (CUP)
Reference62 articles.
1. Godoy E. & Charrier R. 1991. Antecedentes mineralogicos para el origen de las metabasitas y metacherts del Complejo Metamórfico del Choapa (Región de Coquimbo, Chile): un prisma de acreción Palaeozoico Inferior. Actas 6. Congreso Geológico Chileno, 410–14.
2. Hallazgo de foraminíferos del Carbonífero Superior en la Formación Huentelauquén;Rivano;Revista Geológica de Chile,1983
3. Activity?composition relations for phases in petrological calculations: an asymmetric multicomponent formulation
4. Mid-cretaceous crustal shortening: evidence from a regional-scale ductile shear zone in the Coastal Range of central Chile (32° S)
5. Massonne H.-J. 1997. An improved thermodynamic solid solution model for natural white-micas and its application to the geothermobarometry of metamorphic rocks. Geological Survey of Finland, Guide 46, Mineral equilibria and databases, Abstracts, 49.
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