Late Jurassic to Early Cretaceous red beds of the Phuquoc Formation were sampled at 33 sites from the Sihanoukville and Koah Kong areas of the Phuquoc-Kampot Som Basin, southwestern Cambodia. Two high-temperature remanent components with unblocking temperature ranging 650°-670 °C and 670-690 °C were identified. The magnetization direction for the former component (D=5.2°, I=18.5° with α95=3.1° in situ) reveals a negative fold test that indicates a post-folding secondary nature. However, the latter component, carried by specular hematite, is recognized as a primary remanent magnetization. A tilt-corrected mean direction of D=43.4°, I=31.9° (α95=3.6°) was calculated for the primary component at 11 sites, corresponding to a paleopole of 47.7°N, 178.9°E (A95=3.6°). When compared with the 130 Ma East Asian pole, a southward displacement of 6.0°±3.5° and a clockwise rotation of 33.1°±4.0° of the Phuquoc-Kampot Som Basin (as a part of the Indochina Block) with respect to East Asia were estimated. This estimate of the clockwise rotation is ~15° larger than that of the Khorat Basin, which we attribute to dextral motion along the Wang Chao Fault since the mid-Oligocene. The comparison of the herein estimated clockwise rotation with the counter-clockwise rotation reported from the Da Lat area in Vietnam suggests the occurrence of a differential tectonic rotation in the southern tip of the Indochina Block. During the southward displacement of the Indochina Block, the non-rigid lithosphere under its southern tip moved heterogeneously, while the rigid lithosphere under the Khorat Basin moved homogeneously.
- Indochina Peninsula
- Late Jurassic to Early Cretaceous
ASJC Scopus subject areas
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science