| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Journal of Petrology | Volume 41 | Number 3 | Pages 309-330 | 2000
© Oxford University Press 2000
Mineral Chemistry and Pressure–Temperature Evolution of Two Contrasting High-pressure–Low-temperature Belts in the Chonos Archipelago, Southern Chile
1INSTITUT FÜR MINERALOGIE, RUHR-UNIVERSITÄT, D-44780 BOCHUM, GERMANY
2DEPARTAMENTO DE GEOLOGIA, UNIVERSIDAD DE CHILE, CASILLA 13518, CORREO 21, SANTIAGO DE CHILE, CHILE
3INSTITUT FÜR MINERALOGIE UND KRISTALLCHEMIE, UNIVERSITÄT STUTTGART, AZENBERGSTR. 18, D-70174 STUTTGART, GERMANY
Received October 29, 1998; Revised typescript accepted September 9, 1999
 |
Abstract |
|---|
The Chonos Metamorphic Complex forms part of a belt of low-grade metamorphic rocks in the Chilean Coastal Cordillera that are interpreted as Palaeozoic–Mesozoic accretionary complexes. It comprises metapsammopelitic schists, metabasites and meta-ironstones occurring in two contrasting units. Special attention during microprobe study of key samples was given to the chemical zonation of minerals. Subsequently, conventional geothermobarometry and that using thermodynamic calculations were applied. The Eastern belt comprises rocks that are metamorphosed to pumpellyite–actinolite facies conditions and show a low degree of deformation with well-preserved sedimentary and igneous structures. Maximum P–T conditions were around 5·5 kbar and 250–280°C. The rocks of the Western belt are characterized by a transition between greenschist and albite–epidote–amphibolite facies metamorphism and show a penetrative tectonic transposition foliation S2 formed close to the pressure maximum. Maximum P–T conditions vary around 8–10 kbar and 380–500°C overstepping the stilpnomelane + phengite stability. High pressures in this belt are confirmed by regionally distributed phengites with high Si contents up to 3·5 Si per formula unit. Regional distribution of maximum temperatures is reflected by the composition of actinolitic hornblendes within the metabasites. In a garnet-bearing metabasite of the Western belt, oscillatory growth zoning of garnet was observed. The composition of corresponding mineral inclusions suggests that a prograde P–T path during garnet growth evolved from 7·5 kbar and 375°C to about 9·4 kbar and 500°C. Late garnet grew synkinematically with penetrative deformation. The retrograde P–T path in the rocks of the Western belt is constrained by the composition of mainly late strain-free minerals and involves slight cooling during decompression. Both belts are part of a subduction system. The apparent P–T gap between the belts is due to their juxtaposition during exhumation. The Eastern belt constitutes the transition towards the backstop system of the accretionary prism that is represented by the Western belt, whereas the absence of very low grade rocks west of the Western belt is attributed to tectonic erosion, which was possibly caused by subduction of a ridge.
KEY WORDS: Chonos Metamorphic Complex; accretionary complex; high-pressure–low-temperature metamorphism; oscillatory garnet zonation; phengite; P–T paths
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  A. P. Willner, F. A. Sepulveda, F. Herve, H.-J. Massonne, and M. Sudo Conditions and Timing of Pumpellyite-Actinolite-facies Metamorphism in the Early Mesozoic Frontal Accretionary Prism of the Madre de Dios Archipelago (Latitude 50{degrees}20'S; Southern Chile) J. Petrology, November 6, 2009; (2009) egp071v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. RAMIREZ-SANCHEZ, K. DECKART, and F. HERVE Significance of 40Ar-39Ar encapsulation ages of metapelites from late Palaeozoic metamorphic complexes of Aysen, Chile Geological Magazine, May 1, 2008; 145(3): 389 - 396. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. P. Richter, U. Ring, A. P. Willner, and B. Leiss Structural contacts in subduction complexes and their tectonic significance: the Late Palaeozoic coastal accretionary wedge of central Chile Journal of the Geological Society, January 1, 2007; 164(1): 203 - 214. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. AUGUSTSSON, C. MUNKER, H. BAHLBURG, and C.M. FANNING Provenance of late Palaeozoic metasediments of the SW South American Gondwana margin: a combined U-Pb and Hf-isotope study of single detrital zircons Journal of the Geological Society, December 1, 2006; 163(6): 983 - 995. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. P. WILLNER Pressure-Temperature Evolution of a Late Palaeozoic Paired Metamorphic Belt in North-Central Chile (34{degrees}-35{degrees}30'S) J. Petrology, September 1, 2005; 46(9): 1805 - 1833. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. P. WILLNER, S. N. THOMSON, A. KRONER, J.-A. WARTHO, J. R. WIJBRANS, and F. HERVE Time Markers for the Evolution and Exhumation History of a Late Palaeozoic Paired Metamorphic Belt in North-Central Chile (34{degrees}-35{degrees}30'S) J. Petrology, September 1, 2005; 46(9): 1835 - 1858. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. J. Roache, P. J. Williams, J. M. Richmond, and L. H. Chapman VEIN AND SKARN FORMATION AT THE CANNINGTON Ag Pb Zn DEPOSIT, NORTHEASTERN AUSTRALIA Can Mineral, February 1, 2005; 43(1): 241 - 262. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. BELMAR, D. MORATA, F. MUNIZAGA, C. PEREZ DE ARCE, S. MORALES, and F. J. CARRILLO Significance of K-Ar dating of very low-grade metamorphism in Triassic-Jurassic pelites from the Coastal Range of central Chile Clay Minerals, June 1, 2004; 39(2): 151 - 162. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Augustsson and H. Bahlburg Active or passive continental margin? Geochemical and Nd isotope constraints of metasediments in the backstop of a pre-Andean accretionary wedge in southernmost Chile (46{degrees}30'-48{degrees}30'S) Geological Society, London, Special Publications, January 1, 2003; 208(1): 253 - 268. [Abstract] [PDF]
|
|
|
|
 |
|
 S. N. Thomson Late Cenozoic geomorphic and tectonic evolution of the Patagonian Andes between latitudes 42{degrees}S and 46{degrees}S: An appraisal based on fission-track results from the transpressional intra-arc Liquine-Ofqui fault zone Geological Society of America Bulletin, September 1, 2002; 114(9): 1159 - 1173. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. P. Willner, S. Pawlig, H.-J. Massonne, and F. Herve METAMORPHIC EVOLUTION OF SPESSARTINE QUARTZITES (COTICULES) IN THE HIGH-PRESSURE, LOW-TEMPERATURE COMPLEX AT BAHIA MANSA, COASTAL CORDILLERA OF SOUTH-CENTRAL CHILE Can Mineral, December 1, 2001; 39(6): 1547 - 1569. [Abstract] [Full Text] [PDF]
|
|