TY - JOUR
T1 - Hypersolidus deformation in the lower crust of the Josephine ophiolite
T2 - Evidence for kinematic decoupling between the upper and lower oceanic crust
AU - Yoshinobu, Aaron S.
AU - Harper, Gregory D.
N1 - Funding Information:
Celeste Thomson, Nick Pincus, and Weston Yoshinobu are thanked for the their help in conducting the field work. Eric Deterding is thanked for his hospitality in the field. We thank Chris Macleod, Laurence Koogan, Dick Naslund, Benoit Ildefonse, Henry Dick, Jon Snow, and participants in the ODP Leg 176/179 Post-Cruise Meeting field trip to the Josephine ophiolite for their insightful comments on the outcrops, Greg Hirth for innumerable discussions about experimental deformation of partially molten rocks, and Scott Paterson and Keegan Schmidt for discussions on the nature of hypersolidus fabrics. Jeff Karson, Gregory Davis, and John Fletcher made valuable comments on an earlier draft of the manuscript. We thank Fletcher for comments regarding the structural restoration and for pointing out the geometric relationships between linear features in the lower crust and the poles to sheeted dikes that we originally overlooked. Rod Metcalf, Jim Evans, and an anonymous reviewer are thanked for thorough and insightful criticisms of the submitted manuscript. ASY would like to thank John McRaney at the University of Southern California for his unending support of the logistical and financial aspects of ASY's research while at the USC and Scott Paterson for his encouragement and patience. Stereonets were produced using Richard Allmendinger's Stereonet 6.2 X software. Research funded by an Amoco Fellowship and NSF Grant OCE 97-30018.
PY - 2004/1
Y1 - 2004/1
N2 - New mapping and structural observations in the lower crust of the Josephine ophiolite provide insights into the geometry and kinematics of hypersolidus flow beneath an oceanic spreading center. The lower crust, defined here as the sequence of rocks overlying mantle peridotite and beneath exposure of 100% sheeted dikes, can be divided into lower wehrlite-dunite and upper gabbroic sections. The contact between the two is mutually intrusive where exposed. Hypersolidus fabrics are the dominant structures observed. No pervasive crystal-plastic deformation is observed. Restoration of the hypersolidus foliations and igneous modal layers to their on-axis orientation indicates that they strike approximately perpendicular to the strike of the inferred paleo-spreading center as defined by the orientation of sheeted dikes and on-axis, oceanic faults. Hypersolidus lineations define a dispersed 3-D flow pattern in the lower crust, whereas extension directions in the upper crust (i.e. poles to sheeted dikes, oceanic normal faults) are unidirectional and perpendicular to the paleo-ridge axis. Collectively, these observations are consistent with partitioning of deformation between the upper and lower crust, and local ridge-parallel extension in the partially-molten lower crust due to possible subsidence of the thickened, axial upper crust. However, some component of kinematic coupling between the lower crust and mantle peridotite driven by asthenospheric flow cannot be ruled out.
AB - New mapping and structural observations in the lower crust of the Josephine ophiolite provide insights into the geometry and kinematics of hypersolidus flow beneath an oceanic spreading center. The lower crust, defined here as the sequence of rocks overlying mantle peridotite and beneath exposure of 100% sheeted dikes, can be divided into lower wehrlite-dunite and upper gabbroic sections. The contact between the two is mutually intrusive where exposed. Hypersolidus fabrics are the dominant structures observed. No pervasive crystal-plastic deformation is observed. Restoration of the hypersolidus foliations and igneous modal layers to their on-axis orientation indicates that they strike approximately perpendicular to the strike of the inferred paleo-spreading center as defined by the orientation of sheeted dikes and on-axis, oceanic faults. Hypersolidus lineations define a dispersed 3-D flow pattern in the lower crust, whereas extension directions in the upper crust (i.e. poles to sheeted dikes, oceanic normal faults) are unidirectional and perpendicular to the paleo-ridge axis. Collectively, these observations are consistent with partitioning of deformation between the upper and lower crust, and local ridge-parallel extension in the partially-molten lower crust due to possible subsidence of the thickened, axial upper crust. However, some component of kinematic coupling between the lower crust and mantle peridotite driven by asthenospheric flow cannot be ruled out.
KW - Hypersolidus foliations
KW - Klamath Mountains
KW - Lower crust
KW - Magma chamber processes
KW - Ophiolite
KW - Suprasubduction zone
UR - http://www.scopus.com/inward/record.url?scp=0347300645&partnerID=8YFLogxK
U2 - 10.1016/S0191-8141(03)00078-6
DO - 10.1016/S0191-8141(03)00078-6
M3 - Article
AN - SCOPUS:0347300645
VL - 26
SP - 163
EP - 175
JO - Journal of Structural Geology
JF - Journal of Structural Geology
SN - 0191-8141
IS - 1
ER -