Search results for "Closure temperature"
showing 6 items of 6 documents
Timing of deformational events in the Río San Juan complex: implications for the tectonic controls on the exhumation of high-P rocks in the northern …
2013
An integrated structural, petrological and geochronological study was undertaken to constrain the tectonic history and controls on the exhumation of the high-P rocks of the Río San Juan complex in the northern Caribbean subduction–accretionary wedge. In the main structural units of the complex, microtextural analyses were performed to identify the fabrics formed at peak ofmetamorphismin eclogite-facies conditions and during the main retrogressive event toward the low-P amphibolite or blueschist/greenschist-facies conditions. U–Pb SHRIMP dating on zircon rims (71.3 ± 0.7 Ma) coupled with 40Ar–39Ar analyses on phengite (~70– 69 Ma) in felsic sills placed temporal constraints on the exhumation…
Diffusion versus recrystallization processes in Rb–Sr geochronology: Isotopic relics in eclogite facies rocks, Western Gneiss Region, Norway
2008
Abstract Rb–Sr and U–Pb isotopic data for granulite facies rocks, forming textural relics with respect to eclogite facies metamorphism in the Western Gneiss Region (WGR) of Norway, highlight the importance of textures and mineral reaction kinetics for the interpretation of geochronological data. Studied rocks from Bardsholmen, southern WGR, were subjected to granulite facies metamorphism at 955 ± 3 Ma (U–Pb, zircon). Later on, they experienced a subduction-related, kinetically stranded eclogitization ( T > 650 °C at ∼20 kbar) at 404 ± 2 Ma (Rb–Sr multimineral internal isochron data), followed by exhumation through amphibolite facies conditions. Full conversion of granulite to eclogite was …
Further evidence for an early Carboniferous (∼340 Ma) age of high-grade metamorphism in the Saxonian granulite complex
1998
U–Pb and Pb–Pb zircon ages for metamorphic zircons from granulites in the Saxonian granulite complex are reported, using the SHRIMP ion microprobe, conventional multigrain and single-gain techniques and the evaporation method. This is complemented by a Pb–Pb evaporation age for a post-granulite granite emplaced into the schist mantle around the granulites during uplift of the complex. We also demonstrate that zircon ages are not reset during high-grade metamorphism, as commonly argued, but have a very high closure temperature and usually preserve the isotopic composition reflecting the time of their formation. Multifaceted zircons from four granulite samples that probably grew close to the …
Four- and five-phase peridotites from a continental rift system: evidence for upper mantle uplift and cooling at the Ross Sea margin (Antarctica)
1992
Upper mantle plagioclase+spinel- and spinel-peridotite xenoliths occur in basanitic and tephritic lavas of the 2.7 my to Recent Mt. Melbourne Volcanic Field (Antarctica). This field belongs to the Cenozoic McMurdo volcanic group which is located between the deep western trough of the Ross Sea rift system and the uplifted rift shoulder of the Transantarctic Mountains. Our samples cover the transition zone between rift and shoulder. We examined texture and composition of plagioclase+spinel and normal spinel peridotites and determined temperatures and pressures of formation using the internally consistent Ca-ol/cpx and 2px-thermobarometer of Kohler and Brey (1990) and Brey and Kohler (1990). D…
Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry
2020
International audience; Magnetite is a ubiquitous oxide in ultramafic and mafic rocks, which is present in a large range of geological and tectonic settings. In the case of high-pressure ultramafic rocks, exhumation timing is commonly constrained by geochronometers in nearby lithologies. The development of the magnetite (U-Th-Sm)/He method (MgHe) has opened new perspectives to refine the exhumation history of such rocks. However no thermal history has been deduced using MgHe data so far. Here we applied MgHe dating to magnetite from an HP-LT alpine ophiolite body (Rocher Blanc) from the Schistes lustres units (Western Alps, France) where part the P-T-t history is constrained to further refi…
A ∼700 Ma Sm–Nd garnet–whole rock age from the granulite facies Central Kaoko Zone (Namibia): Evidence for a cryptic high-grade polymetamorphic histo…
2007
Continental collision of the Kalahari and the Congo craton in Africa and the Rio de la Plata Craton in South America resulted in a structurally complex Neoproterozoic belt system, the Kaoko–Dom Feliciano–Ribeira belt. It is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at ∼580–550 Ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events. The Kaoko Belt (NW Nambia), representing the belt system between the southern Congo Craton and the Rio de la Plata Craton, is an ideal object to study these complexities. Within this belt, high-grade meta-igneous and metasedimentary rocks of t…