Meso-Cenozoic deformation history of Thailand; insights from calcite
U-Pb geochronology
Abstract
U-Pb dating of calcite veins allows direct dating of brittle deformation
events. Here, we apply this method to hydrothermal calcite veins in a
fold-and-thrust belt and a large scale strike-slip fault zone in central
and western Thailand, in an attempt to shed new light on the regional
upper crustal deformation history. Calcite U-Pb dates for the Khao
Khwang Fold and Thrust Belt (KKFTB) of 221 ± 7 Ma and 216 ± 3 Ma
demonstrate that calcite precipitated during tectonic activity
associated with stage II of the Indosinian Orogeny (Late Triassic –
Early Jurassic). One additional sample from the KKFTB suggests that the
Indosinian calcite has locally been overprinted by a Cenozoic fluid
event with a different chemistry. For the Three Pagodas Fault Zone
(TPFZ), our calcite U-Pb results suggest a complex, protracted history
of Cenozoic brittle deformation. Petrographic information combined with
contrasting redox-sensitive trace elemental signatures suggest that the
vein arrays in the TPFZ precipitated during two distinct events of
brittle deformation at ∼48 and ∼23 Ma. These dates are interpreted in
the context of far-field brittle deformation related to the
India-Eurasia collision. The presented calcite U-Pb dates are in
excellent agreement with published age constraints on the deformation
history of Thailand, demonstrating the utility of the method to decipher
complex brittle deformation histories. The paper further illustrates
some of the complexities in relation to calcite U-Pb dating and provides
suggestions for untangling complex datasets that could be applied to
future studies on the deformation history of Thailand and other regions.