TY - JOUR
T1 - Deformation sequence of Baltimore gneiss domes, USA, assessed from porphyroblast Foliation Intersection Axes
AU - Yeh, Meng Wan
N1 - Funding Information:
The earlier version of the manuscript has benefited greatly from a through and constructive review by Domingo Aerden, Tim Bell, and Gary Solar that I wish to fully acknowledge. I also thank S.C. Fang and Ken Hickey for providing valuable suggestions on statistical analyses. The final English polishing from Charles Hutchison is greatly appreciated. This work was part of a PhD dissertation and was supported by the Earth Science Department, James Cook University, Australia.
PY - 2007/5
Y1 - 2007/5
N2 - The NE-SW trending gneiss domes around Baltimore, Maryland, USA, have been cited as classic examples of mantled gneiss domes formed by diapiric rise of migmatitic gneisses [Eskola, P., 1949. The problem of mantled gneiss domes. Quarterly Journal of Geological Society of London 104/416, 461-476]. However, 3-D analysis of porphyroblast-matrix foliation relations and porphyroblast inclusion trail geometries suggests that they are the result of interference between multiple refolding of an early-formed nappe. A succession of six FIA (Foliation Intersection Axes) sets, based upon relative timing of inclusion texture in garnet and staurolite porphyroblasts, revealed 6 superposed deformation phases. The successions of inclusion trail asymmetries, formed around these FIAs, document the geometry of deformation associated with folding and fabric development during discrete episodes of bulk shortening. Exclusive top to NW shear asymmetries of curvature were recorded by inclusion trails associated with the vertical collapsing event within the oldest FIA set (NE-SW trend). This strongly indicates a large NE-SW-striking, NW-verging nappe had formed early during this deformation sequence. This nappe was later folded into NE-SW-trending up-right folds by coaxial shortening indicated by an almost equal proportion of both inclusion trail asymmetries documented by the second N-S-trending FIA set. These folds were then amplified by later deformation, as the following FIA sets showed an almost equal proportion of both inclusion trail asymmetries.
AB - The NE-SW trending gneiss domes around Baltimore, Maryland, USA, have been cited as classic examples of mantled gneiss domes formed by diapiric rise of migmatitic gneisses [Eskola, P., 1949. The problem of mantled gneiss domes. Quarterly Journal of Geological Society of London 104/416, 461-476]. However, 3-D analysis of porphyroblast-matrix foliation relations and porphyroblast inclusion trail geometries suggests that they are the result of interference between multiple refolding of an early-formed nappe. A succession of six FIA (Foliation Intersection Axes) sets, based upon relative timing of inclusion texture in garnet and staurolite porphyroblasts, revealed 6 superposed deformation phases. The successions of inclusion trail asymmetries, formed around these FIAs, document the geometry of deformation associated with folding and fabric development during discrete episodes of bulk shortening. Exclusive top to NW shear asymmetries of curvature were recorded by inclusion trails associated with the vertical collapsing event within the oldest FIA set (NE-SW trend). This strongly indicates a large NE-SW-striking, NW-verging nappe had formed early during this deformation sequence. This nappe was later folded into NE-SW-trending up-right folds by coaxial shortening indicated by an almost equal proportion of both inclusion trail asymmetries documented by the second N-S-trending FIA set. These folds were then amplified by later deformation, as the following FIA sets showed an almost equal proportion of both inclusion trail asymmetries.
KW - Foliation Intersection Axes
KW - Gneiss domes
KW - Nappe
KW - Porphyroblasts
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U2 - 10.1016/j.jsg.2006.12.003
DO - 10.1016/j.jsg.2006.12.003
M3 - Article
AN - SCOPUS:34247477331
SN - 0191-8141
VL - 29
SP - 881
EP - 897
JO - Journal of Structural Geology
JF - Journal of Structural Geology
IS - 5
ER -