Record Details

Contrasting responses of Rb-Sr systematics to regional and contact metamorphism, Laramie Mountains, Wyoming, USA

DSpace at IIT Bombay

View Archive Info
 
 
Field Value
 
Title Contrasting responses of Rb-Sr systematics to regional and contact metamorphism, Laramie Mountains, Wyoming, USA
 
Creator PATEL, SC
FROST, CD
FROST, BR
 
Subject anorthosite complex
shear zones
oxygen-isotope
sphene growth
morton pass
deformation
strontium
geochronology
province
range
contact metamorphism
laramie mountains
rb-sr and sm-nd isotopes
regional metamorphism
 
Description Archean supracrustal sequences of pelitic, quartzitic, calcareous and mafic compositions in the central Laramie Mountains, Wyoming, have been affected by two metamorphic events: a 1.78 Ga amphibolite-grade regional metamorphism, and a 1.43 Ga contact metamorphism resulting from the intrusion of the Laramie Anorthosite Complex (LAC). Rb-Sr whole-rock isotopic data from both outside and within the LAC contact aureole define a linear array that lies along a 1.78 Ga isochron. This date has been independently established as the time of amphibolite facies regional metamorphism associated with collision of the Archean Wyoming province and the Proterozoic Colorado province along the Cheyenne belt. The Rb-Sr isotopic data require that Sr was redistributed during regional metamorphism on a scale of at least tens of metres. Although within the 2 km-wide aureole of LAC the pelitic rocks were thermally metamorphosed at temperatures greater than 800 degrees C, none of the whole-rock Rb-Sr data from samples within the LAC aureole show evidence of resetting at 1.43 Ga. It is interpreted that the regional metamorphism involved fluid transport which facilitated Sr isotopic resetting, whereas the contact metamorphism occurred in a relatively dry environment in which isotopic mobility was restricted to centimetre-scale or less. Rb-Sr data for biotite, feldspar and whole rock from a regional metamorphosed pelitic schist give an isochron age of 1450 +/- 40 Ma, which is interpreted as a cooling age resulting from crustal uplift. Rb-Sr data for biotite, quartz + feldspar and whole rock from a pelitic schist affected by contact metamorphism give an isochron age of 1420 +/- 43 Ma, the time of isotopic re-equilibration in response either to crustal uplift or to both contact metamorphism and crustal uplift. This study demonstrates that although the response of isotopic systems to metamorphism is complex, isotopic data provide insight into metamorphic processes that is difficult to obtain by other means.
 
Publisher BLACKWELL SCIENCE INC
 
Date 2011-07-19T05:48:30Z
2011-12-26T12:51:01Z
2011-12-27T05:37:20Z
2011-07-19T05:48:30Z
2011-12-26T12:51:01Z
2011-12-27T05:37:20Z
1999
 
Type Article
 
Identifier JOURNAL OF METAMORPHIC GEOLOGY, 17(3), 259-269
0263-4929
http://dspace.library.iitb.ac.in/xmlui/handle/10054/5190
http://hdl.handle.net/10054/5190
 
Language en