Extensional Tectonics and Basement Uplift of the Fansipan and Tule Mountain Ranges in Northern Vietnam

Yu-Chang Chan,Thi-Hue Dinh,Chih-Tung Chen

doi:10.3389/feart.2021.741670

Abstract

The Fansipan and Tule mountain ranges, northern Vietnam, are regions with high elevations and are adjacent to the Red River Fault, which is an important structure that is related to the India-Eurasia collision. How mountain elevations are maintained today under a humid subtropical climate is important for improving the knowledge of the tectonic deformations in northern Vietnam and may have broader implications for the crustal dynamics of circum-Tibetan regions. We therefore utilized observations from field and digital elevation model (DEM) data and geomorphic analyses to constrain the active fault systems that have likely contributed to the uplift of mountain ranges. Our observations from DEM and field data indicate potential active normal and strike-slip faults such as the Phong Tho-Nam Pia Fault, Tule Fault, and Nghia Lo Fault. In addition to these observations, the results from geomorphic indices, which include both the stream-length gradient index (SL) and normalized steepness index (ksn), present high values for the footwalls of the inferred normal faults and low values for the hanging walls. Most of the identified knickpoints are related to the locations of mapped faults. Correlations of these data indicate that recent movements of the Fansipan and Tule mountain ranges are dominated by strike-slip and normal faulting under a NE-SW minimum extensional regime. We therefore propose that extensional tectonics associated with isostatic rebound likely plays a role in maintaining mountain elevations over long periods despite the continuous weathering and erosion present in monsoon-affected areas.

Highlights

Over the last few decades, there has been increasing interest in how the Earth’s crust deforms on the Tibetan Plateau and its surrounding regions as a result of the collision between the Indian and Eurasian plates (e.g., Burchfiel, 2004; Kirby and Ouimet, 2011; Molnar and Tapponnier, 1975; Shen et al, 2005; Tapponnier et al, 1982)
It is possible that the pattern of steep triangular facets on the southeastern sides of the Fansipan and Tule mountain range is associated with active normal faulting
We propose that the recent uplift of the Fansipan and Tule mountain ranges is controlled by extensional tectonics (Figure 14) with alternations of normal and strike-slip faulting as a consequence of the interactions between the tectonics induced by movements of the southeastern regions of the Tibetan Plateau and erosional processes

Summary

Introduction

Over the last few decades, there has been increasing interest in how the Earth’s crust deforms on the Tibetan Plateau and its surrounding regions as a result of the collision between the Indian and Eurasian plates (e.g., Burchfiel, 2004; Kirby and Ouimet, 2011; Molnar and Tapponnier, 1975; Shen et al, 2005; Tapponnier et al, 1982). Many studies have been carried out in mountainous areas within and surrounding major strike-slip faults, which are some of the most important structures related to the India-Eurasia collision (e.g., Schoenbohm et al, 2004; Wang et al, 2016, 2017) Most of these studies focused on analyzing the tectonic deformations in the central and eastern Tibetan Plateau to the Chinese Yunnan regions. In northern Vietnam, the abrupt high elevations of the Fansipan and Tule mountain ranges, which comprise mountain peaks that are more than 3,000 m above sea level, are present adjacent to the RRF, which is a strike-slip dominated fault How such high elevations formed and were maintained under a humid subtropical monsoon climate is central to understanding the tectonic deformation in this area and may have implications for crustal dynamics in the circum-Tibetan region

Methods

Results

Conclusion