TY - JOUR
T1 - Partial convective overturn of Archaean crust in the east Pilbara Craton, Western Australia
T2 - Driving mechanisms and tectonic implications
AU - Collins, W. J.
AU - Van Kranendonk, M. J.
AU - Teyssier, C.
PY - 1998/1/1
Y1 - 1998/1/1
N2 - Strain varies systematically from weakly-developed, outward-dipping, S-tectonites in the ∼33203310 ± 10 Ma Mount Edgar Batholith to intensely deformed, subvertical, L-tectonites in greenstones of the Warrawoona syncline. A consistent 'greenstone-down/batholith-up' sense of shear is recorded in batholithic domal margins and adjacent high-grade supracrustal rims: lineations converge to a central zone of subvertical extension (zone of sinking) along the synclinal axis. At domal margins, early kinematic granitoid sheets and 'intrusive diatexites' are subconcordant to a well-developed, dome-parallel schistosity, but late- to post-kinematic intrusives are discordant, high-level plutons. All granitoids are the same age, within analytical error. These syn-doming features conform with structural tests for diapirs, and differ from those expected during metamorphic core complex formation and cross-folding. Diapirism is part of a larger process involving partial convective overturn of the crust. Based on strain patterns and kinematic criteria, we argue that deformation was initiated by sinking of greenstones, which rapidly subsided; the domes then rose passively as accommodation structures. Ongoing doming (D4) partitioned strain to the southern rim of the batholith and uplifted a wedge of the Warrawoona Syncline keel. We consider that crustal overturn occurred in response to mantle plume activity: Eruption of a 5-10 km thick, ∼3325 Ma, mafic-ultramafic greenstone pile onto an older granite-greenstone terrain created a negatively buoyant crust, but convective overturn occurred some 5-20 Ma later, triggered by widespread anatexis (thermal softening). Convective overturn may have been a common Archaean process, occurring in response to a hotter mantle, and represents an end-member deformation mechanism that includes thrust-accretion of lithotectonic assemblages in other Archaean terranes, such as the Superior Province of Canada.
AB - Strain varies systematically from weakly-developed, outward-dipping, S-tectonites in the ∼33203310 ± 10 Ma Mount Edgar Batholith to intensely deformed, subvertical, L-tectonites in greenstones of the Warrawoona syncline. A consistent 'greenstone-down/batholith-up' sense of shear is recorded in batholithic domal margins and adjacent high-grade supracrustal rims: lineations converge to a central zone of subvertical extension (zone of sinking) along the synclinal axis. At domal margins, early kinematic granitoid sheets and 'intrusive diatexites' are subconcordant to a well-developed, dome-parallel schistosity, but late- to post-kinematic intrusives are discordant, high-level plutons. All granitoids are the same age, within analytical error. These syn-doming features conform with structural tests for diapirs, and differ from those expected during metamorphic core complex formation and cross-folding. Diapirism is part of a larger process involving partial convective overturn of the crust. Based on strain patterns and kinematic criteria, we argue that deformation was initiated by sinking of greenstones, which rapidly subsided; the domes then rose passively as accommodation structures. Ongoing doming (D4) partitioned strain to the southern rim of the batholith and uplifted a wedge of the Warrawoona Syncline keel. We consider that crustal overturn occurred in response to mantle plume activity: Eruption of a 5-10 km thick, ∼3325 Ma, mafic-ultramafic greenstone pile onto an older granite-greenstone terrain created a negatively buoyant crust, but convective overturn occurred some 5-20 Ma later, triggered by widespread anatexis (thermal softening). Convective overturn may have been a common Archaean process, occurring in response to a hotter mantle, and represents an end-member deformation mechanism that includes thrust-accretion of lithotectonic assemblages in other Archaean terranes, such as the Superior Province of Canada.
UR - http://www.scopus.com/inward/record.url?scp=0032155037&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0032155037&partnerID=8YFLogxK
U2 - 10.1016/S0191-8141(98)00073-X
DO - 10.1016/S0191-8141(98)00073-X
M3 - Article
AN - SCOPUS:0032155037
SN - 0191-8141
VL - 20
SP - 1405
EP - 1424
JO - Journal of Structural Geology
JF - Journal of Structural Geology
IS - 9-10
ER -