Petrology of the origin of the Permian - Triassic volcanic complexes of the Hien River- An Chau rift system

08/07/2023

A detailed study on the material composition of the Permian - Triassic volcanic formations of the Hien River - An Chau rift system has scientific and practical significance and is an urgent issue to aim at determining prospects of the accompanying endogenous minerals. Dr. Tran Viet Anh and the research team of the Institute of Geology in collaboration with the Institute of Geology and Minerals, Siberian Sub-Institute, the Russian Academy of Sciences, conducted the task: "Study on the petrology of the origin of the Permian - Triassic volcanic complexes of the Hien River - An Chau rift system, Northeast Vietnam” (Code: QTRU01.09/20-21). The task was graded excellent by the Acceptance Council at the Vietnam Academy of Science and Technology.

Dr. Tran Viet Anh and members of the research team

The previous view that the Permi-Trias volcanic formations developed in the geologic structure of Southeast Asia, particularly as products of magmatic activity associated with the Emeishan plume mantle (ELIP), was interested in detailed research by the world geologists. (Wang et al., 2007, 2011; Chung et al., 1995;). Related to them is the prospect of these rare metals in plume mantle-related mafic–ultramafic activities (Borisenko et al., 2006; Zhong et al., 2006). This petrographic province (magmatic eruption activity on a huge area) occupies an area of up to 250,000km2, including most of the Yangtze River bed and a part of the territory of Vietnam (Da River rift) as well as Thailand, with an average thickness of about 2km, volume to 0.5,106km3.

The high-titanium and low-titanium basalt rocks are the main components of the Emeishan trap, and according to the researchers, they were mainly formed over a period of 260-250 million years. In addition, as a result of the mantle-shell interaction, felsic rocks are commonly distributed in the territory of Vietnam (Shellnut et al, 2020).

Basalt and Hien River acid eruption rocks, the research object of this mission, were formed during that time. In order to understand the origin of basalt as well as rhyolite in the eruptive mantles of LIP, isotope studies are often carried out, most commonly Rb-Sr, Nd-Sm and U-Pb isotopes. Based on the synthesis of geological, geochemical and isotopic data of volcanic rocks, people proceed to build a model of the origin of magma formation (associated with the tectonic context) as well as related mineralogy. In the process of implementing the Task, the research team also used the method of synthesis and maximum analysis of published documents, including sample collection collected from previous studies.

In addition to traditional research methods, modern research methods have been applied in, including: X-ray fluorescence spectroscopy: analysis of major elements; Plasma spectroscopy (ICP-MS) – determination of the composition of rare elements and the isotopic composition of Rb-Sr, Nd-Sm; research on morphological characteristics and composition of zircon separated from bedrock or from weathering zone on bedrock to determine the origin of zircon (magma, metamorphic, remnant); U-Pb isotope analysis in zircon by LA-ICP-MS method to determine the age of formation of zircon in studied samples. The task analyzed hundreds of zircon grains on more than 20 old samples at the Institute of Geology and Minerals, Siberian Sub-Institute, Russian Academy of Sciences.

Sections have conducted field survey

The task conducted a new and systematic analysis of isotopic composition, chemical composition of rare trace elements, and geo-mineralogical composition of most of the magma formations in the Hien River zone. The following remarkable results have been achieved:

• Firstly, within the Song Hien zone, it is possible to divide three magmatic activities based on chemical composition, rare element composition and isotope ratio: Mafic-ultramafic, neutral magma and felsic activities in Cao Bang area with potential related to Cu-Ni and PGE minerals; Magma mafic activities of the basalt bridging type along the Cao Bang-Tien Yen fault have a characteristic composition for the ancient oceanic crust; Contrasting eruption formations in Lang Son area are typical for the context of intra-plate rifting.

• Second, the age of the magmatic formations in the Hien River zone is the Late Permian-Early Triassic age which has been confirmed in the study of the task. It coincides with the closing of the Paleo Tethys Sea.

• Third, the evolution of magma in the Hien River zone is very complicated with different magma source characteristics of each activity.

• Fourth, these magmatic activities can be formed by the rapid spreading mechanism of the South China continental margin due to the closing process of the Paleo Tethys Sea.

The important result obtained by the task is to analyze and publish a series of formation ages of many magmatic rocks of the Hien River structure. This age data is an important premise for further studies and publications on magma as well as related mineralogy activities in the Northeast of Vietnam. The task completed a very large amount of chemical and isotopic analysis of the Permian-Triassic magma formations in Northeast Vietnam. The task has published 01 article in the list of SCI that has high scientific value and is a product with a high number of citations. In addition to the scientific significance of the published works, the mission has oriented further studies on minerals, for example: the study of rare earth compositions in minerals, and the study of crystal structures using equipment suffer from EPMA.

Translated by Phuong Huyen

Link to Vietnamese version

Tags: