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De‐bugging the ‘millipede’ porphyroblast microstructure: a serial thin‐section study and 3‐D computer animation
Author(s) -
JOHNSON S. E.,
MOORE R. R.
Publication year - 1996
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1996.00003.x
Subject(s) - geology , section (typography) , microstructure , thin section , deformation (meteorology) , foliation (geology) , geometry , mineralogy , geochemistry , metamorphic rock , materials science , computer science , composite material , mathematics , oceanography , operating system
Seventy‐five spatially orientated, serial thin sections cut from a single rock containing ‘millipede’ porphyroblast microstructure from the Robertson River Metamorphics, Australia, reveal the three‐dimensional (3‐D) geometry of oppositely concave microfolds (OCMs) that define the microstructure. Electronic animations showing progressive serial sections of the 3‐D microstructure are made available via the World Wide Web. The OCM amplitudes decrease regularly from a maximum in near‐central sections to a minimum in near‐marginal sections, whereas the OCM interlimb angles increase regularly from a minimum in near‐central sections to a maximum in near‐marginal sections. These observations illustrate that the OCMs are noncylindrical surfaces with culminations located in near‐central sections. Because the porphyroblast cores appear to have been present before significant development of the syn‐OCM foliation, all of the OCMs were formed by heterogeneous extension around these cores. The overall geometry of the OCMs described here reflects the strain state, and cannot be used to constrain deformation paths.