Geology, K-Ar geochronology and paleomagnetism of parts of the coastal cordillera of central Chile, South America

Thesis/Dissertation · Wed Jan 01 04:00:00 UTC 1986

OSTI ID:6740332

Irwin, J J

A complex composed of ultrabasic and basaltic lavas, chert-argillite, arkose and conglomerate was assembled in the coast of north central Chile prior to 220 Ma ago. Three major episodes of deformation and metamorphism have been observed in this area. The first episode of deformation and metamorphism (F/sub 1/) produced a compositional layering (S/sub 1/) and amphibolite facies metamorphism within the formations listed above. This episode of deformation and metamorphism occurred coevally with intrusion of a regionally extensive 220-200 Ma fine grained gabbro and granitic complex. The second episode of deformation and metamorphism locally formed tight, recumbent folds in S/sub 1/ and at least one low angle reverse fault. K-Ar and Rb-Sr ages on units in which F/sub 2/ folds are well developed range between 163 and 140 Ma. A third episode of deformation and low grade metamorphism (F/sub 3/) locally formed upright, open to tight folds with sharp hinges and axial planes that strike north and dip steeply east. Igneous intrusions that were affected by F/sub 3/ yield K-Ar ages between 140 Ma and 126 Ma. Undeformed cross cutting mafic dykes have been dated by K-Ar at 121 Ma. Paleomagnetic samples collected from 19 sites in radioisotopically dated (using the K-Ar and /sup 40/Ar-/sup 39/Ar techniques) Jurassic mafic dykes and plutons in the coastal cordillera of Chile yield mean paleomagnetic poles that are consistent with the average pole from coeval sequences within the South American craton. The paleomagnetic directions are consistent over the latitudinal range and variety of lithologies encompassed by this study. Paleomagnetic results presented here indicate that no major rotation or translation of crustal blocks has been taken place in this part of central Chile since middle Jurassic time.

• Research Organization: California Univ., Berkeley (USA)
• OSTI ID: 6740332
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
AGE ESTIMATION
ALKALI METALS
ALKALINE EARTH METALS
ARGON
CHILE
DEFORMATION
DEVELOPING COUNTRIES
ELEMENTS
FLUIDS
GASES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
ISOTOPE DATING
LATIN AMERICA
MAGNETISM
METALS
METAMORPHISM
NONMETALS
PALEOMAGNETISM
POTASSIUM
RARE GASES
RUBIDIUM
SOUTH AMERICA
STRONTIUM