Development of an intra-carbonate detachment during thrusting; the variable influence of pressure solution on deformation style, Khao Khwang fold and thrust belt, Thailand

Classic detachment zones in fold and thrust belts are generally defined by a weak lithology (typically salt or shale), often accompanied by high over-pressures. This study describes an atypical detachment that occurs entirely within a relatively strong Permian carbonate lithology, deformed during th...

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Bibliographic Details
Published in:Geosphere (Boulder, Colo.) Colo.), 2021-04, Vol.17 (2), p.602-625
Main Authors: Morley, C. K, Jitmahantakul, S, von Hagke, C, Warren, J, Linares, F
Format: Article
Language:English
Subjects:
Asia
bedding
carbonate rocks
chemically precipitated rocks
clastic rocks
cleavage
deformation
detachment faults
evaporites
Far East
faults
fold and thrust belts
folds
foliation
Indosinian Orogeny
Khao Khwang Belt
Khao Yai Member
limestone
lithofacies
Mesozoic
Na Phra Lan Member
overpressure
Paleozoic
Permian
planar bedding structures
pressure solution
recrystallization
salt
sedimentary rocks
sedimentary structures
shale
stratigraphic units
structural analysis
Structural geology
style
Thailand
thrust faults
Triassic
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Summary:Classic detachment zones in fold and thrust belts are generally defined by a weak lithology (typically salt or shale), often accompanied by high over-pressures. This study describes an atypical detachment that occurs entirely within a relatively strong Permian carbonate lithology, deformed during the Triassic Indosinian orogeny in Thailand under late diagenetic-anchimetamorphic conditions. The key differences between stratigraphic members that led to development of a detachment zone are bedding spacing and clay content. The lower, older, unit is the Khao Yai Member (KYM), which is a dark-gray to black, well-bedded, clay-rich limestone. The upper unit, the Na Phra Lan Member (NPM), comprises more massive, medium- to light-gray, commonly recrystallized limestones and marble. The KYM displays much tighter to even isoclinal, shorter-wavelength folds than the NPM. Pressure solution played a dominant role throughout the structural development-first forming early diagenetic bedding; later tectonic pressure solution preferentially followed this bedding instead of forming axial planar cleavage. The detachment zone between the two members is transitional over tens of meters. Moving up-section, tight to isoclinal folds with steeply inclined axial surfaces are replaced by folds with low-angle axial planes, thrusts, and thrust wedging, bed-parallel shearing, and by pressure solution along bedding-parallel seams (that reduce fold amplitude). In outcrops 100-300 m long, reduction of line-length shortening on folds from >50% to
ISSN:1553-040X
1553-040X
DOI:10.1130/GES02267.1