Mesozoic-Cenozoic evolution of the North Patagonian Batholith in Aysen, southern Chile

• Published in: Journal of the Geological Society Vol. 156; no. 4; pp. 673 - 694
• Main Authors: Pankhurst, Robert J, Weaver, S. D, Hervé, F, Larrondo, P
• Format: Journal Article Conference Proceeding
• Language: English
• Published: London Geological Society of London 01-07-1999; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: absolute age; Aisen Chile; Aisen del General Carlos Ibanez del Campo Chile; alkaline earth metals; calc-alkalic composition; Cenozoic; Chile; Crystalline rocks; dates; Earth sciences; Earth, ocean, space; Exact sciences and technology; genesis; geochemistry; Geochronology; Geology; granites; igneous and metamorphic rocks; Igneous and metamorphic rocks petrology, volcanic processes, magmas; igneous rocks; intrusions; Isotope geochemistry. Geochronology; isotope ratios; isotopes; lithofacies; magmatism; melting; Mesozoic; metals; metaluminous composition; Nd-144/Nd-143; neodymium; Patagonian Batholith; petrography; Petrology; Plate tectonics; plutonic rocks; plutons; rare earths; Rb/Sr; South America; Sr-87/Sr-86; stable isotopes; Stone; strontium; subduction; tectonics; Patagonian Andes; Patagonian Batholith; Andes; Southern Andes; Chile; Patagonia; absolute age; petrogenesis; tectonics; granites; isotopes; South America; Mesozoic; Nd-144/Nd-143; underplating; tonalite; calc-alkalic composition; gabbros; orogenic magmatism; rare earths; zircon; silicates; dating; Cenozoic; Sr-87/Sr-86; nesosilicates; granodiorites; granitoids; Tertiary; igneous rocks; lower crust; U/Pb; Cretaceous; partial melting; chemical analysis; Rb/Sr; leucogranite; subduction; plutonic rocks; Phanerozoic
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/gsjgs.156.4.0673

A detailed Rb-Sr geochronological and geochemical study has been carried out on granitoids of the North Patagonian batholith in Aysen. The results for 25 plutonic bodies reveal a complex age pattern. The principal zones defined are, from west to east: Late Cretaceous (a single 76 Ma pluton), Early Cretaceous (c. 135 Ma), Eocene (c. 45 Ma), and Early Miocene (25-15 Ma), reverting to mid-Cretaceous (120-90 Ma) in the Main Cordillera. The igneous suite is typically metaluminous and calc-alkaline, with hornblende-biotite granodiorite and tonalite dominant, although small bodies of Late Miocene/Pliocene (c. 10-5 Ma) peraluminous leucogranite occur sporadically. Tertiary plutonism extends to gabbroic compositions and is concentrated in the vicinity of the dextral strike-slip Liquine-Ofqui fault zone. The highest initial 87Sr/86Sr ratios (c. 0.7050) occur in the Early Cretaceous group, with a sharp decrease to 0.7034-0.7045 that persists until a Late Miocene reversal to higher values (0.7040-0.7048). These variations are reflected by Nd isotopes, but trends in the εSrt v. εNdt diagram show that this is not due to contamination from the accretionary complex into which the batholith was emplaced. An origin by melting of mafic crustal underplate and lower crust is suggested for the main magma suite. The discrete episodes of magmatism correlate with significant changes in subduction kinematics.