Open AccessSeismic structure and lithospheric rheology from deep crustal xenoliths, central Montana, USA
Author(s) -
Mahan K. H.,
SchultePelkum V.,
Blackburn T. J.,
Bowring S. A.,
Dudas F. O.
Publication year - 2012
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2012gc004332
Subject(s) - geology , xenolith , crust , lithosphere , peridotite , mantle (geology) , crustal recycling , geochemistry , petrology , volcano , continental crust , tectonics , seismology
Improved resolution of lower crustal structure, composition, and physical properties enhances our understanding and ability to model tectonic processes. The cratonic core of Montana and Wyoming, USA, contains some of the most enigmatic lower crust known in North America, with a high seismic velocity layer contributing to as much as half of the crustal column. Petrological and physical property data for xenoliths in Eocene volcanic rocks from central Montana provide new insight into the nature of the lower crust in this region. Inherent heterogeneity in xenoliths derived from depths below ∼30 km support a composite origin for the deep layer. Possible intralayer velocity steps may complicate the seismic definition of the crust/mantle boundary and interpretations of crustal thickness, particularly when metasomatized upper mantle is considered. Mafic mineral‐dominant crustal xenoliths and published descriptions of mica‐bearing peridotite and pyroxenite xenoliths suggest a strong lower crust overlying a potentially weaker upper mantle.