P–T–time evolution of the Mejillones Metamorphic Complex: Insights into Late Triassic to Early Jurassic orogenic processes in northern Chile

M. Calderón, H. J. Massonne, F. Hervé, T. Theye

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Better constrained pressure-temperature (P-T) histories of metamorphic complexes along the Andean continental margin are important for understanding the late Paleozoic and Mesozoic tectonic evolution of the southwestern margin of Gondwana. The Mejillones Metamorphic Complex of the northern Chilean Coastal Cordillera is composed of two tectonic units, the Morro Mejillones and Morro Jorgiño blocks. These units are bound by the NW-trending Caleta Herradura fault and show distinctly metamorphic ages and thermal evolution. The Morro Mejillones block was metamorphosed at low pressure conditions (andalusite-sillimanite series) during the intrusion of tonalitic plutons at ca. 208 Ma, as indicated by available geochronological data. In contrast, the Morro Jorgiño block comprises amphibolite-facies schists, gneisses and foliated metabasites with characteristic garnet–bearing mineral assemblages. For garnet–bearing pelitic gneisses, a clockwise P-T path has been determined from pseudosection modelling in the MnNCKFMASHTO system. The proposed evolution is characterized by a pressure increase from 7.5 to 8.5 kbar at increasing temperatures from 585 to 615 °C. Decompression to 6 kbar followed, accompanied by heating to 630–640 °C. Electron microprobe Th-U-Pb in-situ dating of high-Y monazite grains yielded a weighted average age of ca. 190 ± 4 Ma, which is interpreted as the age of tectonic burial of metamorphic rocks of the Morro Jorgiño tectonic unit. We infer that the block was buried to ~ 25 km depth through contractional deformation of the continental edge in a subduction zone, likely linked to the docking of the Mejillonia terrane. Rapid exhumation followed and the ensuing juxtaposition of both tectonic units was controlled by Jurassic transtensional activity of the Atacama Fault System.

Original languageEnglish
Pages (from-to)383-398
Number of pages16
JournalTectonophysics
Volume717
DOIs
Publication statusPublished - 16 Oct 2017

Keywords

  • Barrovian-type metamorphism
  • Morro Jorgiño tectonic unit
  • P-T pseudosections
  • Th–U–Pb monazite geochronology

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes

Fingerprint

Dive into the research topics of 'P–T–time evolution of the Mejillones Metamorphic Complex: Insights into Late Triassic to Early Jurassic orogenic processes in northern Chile'. Together they form a unique fingerprint.

Cite this