Clockwise rotations recorded in redbeds from the Jinggu Basin of northwestern Indochina

Abstract

Paleomagnetic data have been used to infer clockwise rotations and significant southward motion of the Indochina block during Cenozoic extrusion from the India-Asia collision zone. Because the Cenozoic of the Indochina block has been sparsely sampled to date and is key to determining the timing of this tectonic motion, we performed an extensive paleomagnetic study on Paleocene to Oligocene redbeds and middle Miocene sandy silts from the Jinggu Basin (23.5°N, 100.7°E), in northern Indochina. Paleomagnetic results from the redbeds pass fold tests, but they show exclusively normal polarity. There is controversy, however, on the age assignment to the lower part of the succession. If the age of the redbeds is indeed Paleogene, this indicates a prefolding remagnetization associated with Oligocene deformation of the Indochina block. If the age of the redbeds would be Late Cretaceous, their magnetization may be primary, and deposition could have taken place during the Cretaceous normal superchron. However, the abundance of secondary hematite in the redbeds in combination with the biostratigraphy, which indicates a Paleogene age for at least the upper two formations of the redbeds in the Jinggu Basin, implies a pervasive remagnetization. The middle Miocene sediments pass both the fold test and the reversals test and contain magnetite as well as hematite as carriers, suggesting a primary magnetization. Our large data set from the redbeds (>2000 paleomagnetic directions) demonstrates an ~30°-35° clockwise rotation of the Jinggu Basin with respect to Eurasia, for both scenarios, i.e., when compared to a ca. 100 Ma pole (if the redbeds carry a primary natural remanent magnetization) or to a ca. 30 Ma pole (if the sequence is remagnetized). The middle Miocene results, however, indicate that the Jinggu Basin experienced no significant (2° ± 5.6°) rotation with respect to Eurasia. Since no major deformation has occurred within northern Indochina during Late Cretaceous to Eocene times, our results reflect a major clockwise rotation of the Indochina block during its Oligocene to early Miocene extrusion from the India-Asia collision zone.

Paleomagnetic Evidence for 25–15 Ma Crust Fragmentation of North Indochina (23–26°N): Consequence of Collision With Greater India NE Corner?

“…Considering the evidence in the literature, Jurassic‐Oligocene rocks from both the Simao and the Chuandian domain often show significant CW rotations, and remnants of Neogene sediments unconformably covering the older strata are essentially not rotated (Table S1 and Figure ). Li, Yang, et al () reported data from Oligocene and mid‐Miocene sedimentary rocks from the Jinggu area, about 100 km SW of our Simao study area (Figure ). The Oligocene red beds were found to be remagnetized before tilting, then variably CW rotated in the 20–90° range, while gently dipping mid Miocene (ca.…”

“…The Chuandian domain yields a rather clear pattern of 15–20° CW rotations for Cretaceous‐Oligocene red beds (Funahara et al, ; Gao et al, ; Li et al, , ; Otofuji et al, ; Tong et al, ; Wang, Yang, et al, ; Yang, Sun, et al, ; Yoshioka et al, ; Zhu et al, ). Jurassic‐Oligocene red beds from the Baoshan, Lanping, and northern Simao domains provide highly variable CW rotations, in few cases exceeding 90° (Chen et al, ; Funahara et al, ; Gao et al, ; Huang & Opdyke, , ; Kondo et al, ; Li, Yang, et al, ; Li et al, ; Sato et al, , , ; Tanaka et al, ; Tong et al, , ; Yang, Yin, et al, ; Yang, Sun, et al, ). In the Tengchong domain, both CW and counterclockwise (CCW) rotations have been documented (Kornfeld et al, , ).…”

Relationship Between Orogenic Gold Mineralization and Crustal Shearing Along Ailaoshan‐Red River Belt, Southeastern Tibetan Plateau: New Constraint From Paleomagnetism

“…The paleolatitude 19.9° ± 3.6°N for the Zhenyuan deposit and 16.2° ± 2.9°N for the Chang'an deposit are generally comparable to the value of 19.0° ± 3.6°N for the ca. 20.0 Ma strata at Jinggu in Indochina block (Figures a and d; Chen et al, ; Cogné et al, ; Gao et al, ; Li et al, ). However, the paleolatitudes of these deposits are strikingly different from those obtained from strata of ca.…”

High‐Resolution Eocene Magnetostratigraphy of the Xijigou Section: Implications for the Infilling Process of Xining Basin, Northeastern Tibetan Plateau

“…However, there is an increasing availability of terrestrial sedimentary archives of the Eocene. These sites are located on the northeastern margin of the Tibetan Plateau (Bosboom et al, ; Chi et al, ; Dai et al, ; Horton et al, ; Long et al, ; Miao et al, ; Sun et al, ; Yue et al, ), in central China (Bowen et al, ; Ting et al, ; Zhu et al, ), northeastern China (Chen et al, ), southwestern China (Li et al, ; Su et al, ), North and South America (Hyland et al, ; Hyland et al, ; Hyland & Sheldon, ; Koch et al, ; Krause et al, ), and Europe (Egger et al, ). Research on these Eocene sections has focused mainly on chronology and specific climatic events, whereas few studies have drawn stratigraphic comparisons between different sections (Fang et al, ; Smith et al, ).…”