Dust Draws a Geochemical Signature on the Basalt Canvas
Geochemical Basalt Weathering in Deccan Trap, India.
As you know, Basalt is one of the most common volcanic rock around the world.
Basalt has a High content of Mg, Fe among volcanic rocks, so we call that the type of rock is ‘mafic’ rock. Deccan Trap, located in Westside of India, is one of the most major basaltic igneous province. Decaan Trapis also called ‘CFBPs’, which stans for ‘Continental Flood Basalt Province’. It is important that carry out the geochemical research in this area, because this area can be a large geochemical sink of major to trace element. Geochemists reveal the importance of Weathering and Alteration in Deccan Trap in terms of geochemical sinking of Elements.
And also, this area has potential importance to understanding the weathering process of continental curst because the Basalt has the opposite composition of the continental crust. The opposite composition of Deccan Trap serves as a canvas to record the effects of continental crust. Like you can see a picture on white pater better than on black paper, more explicit results can be obtained when studying things that happen in the continental crust in the opposite composition of the basalt. This study adopted these contrast chemistry between basalt and continental crust, and could effectively identify continental weathering process by dust.
HFSE and Nd Isotope fractionation With Alteration
Because of the specific mobility of the HFSE and REE, The HFSE and REE are used to study geochemical weathering patterns. HFSE, also called ‘High Field Strength Elements’, is known as immobile element. It means that HFSE composition does not change during weathering. So if the HFSE concentration of the Basaltic profile changes, it means the continental aeolian dust has been introduced the basaltic profile interior. REE means ‘Rare Earth Element’, the elements that are rarely existing in continental crust. REE has immobile mobility like HFSE, so it can be used to trace the marks of continental crust, too. Specially, Nd is one of REE and its isotope ratio are characterized by age of continental crust. For the above reason, Nd isotopic signature can be used to identify effects of weathering of aeolian dust.
In Deccan Trap, HFSE and Nd isotope signature of aeolian dust apperas at an overall depth both intermediate and high weathering basalt profile. It means aeolian dust plays a important role in the weathering. And also we can be inferred that weathering does not occur only on the surface, but also occur in the deep basalt.
Why is the HFSE and REE Weathering of Basalt in this study important?
In this study, HFSE and REE used to identify the weathering effects of aeolian dust. Actually, There are various factors that determine weathering intensity. Various chemical indexes like CIA, MIA are also used to determine weathering intensity, too. But major element chemistry can vary by various geochemical process like metasomatism, fluid rock interaction, and so on. However, with HFSE and REE, It is possible to check the inflow of dust without the influence of type of the weathering process. And also, HFSE and REE can determine various effect like secondary mineral weathering and adsorption. For the following reasons, HFSE and REE can be a powerful tool to study the crust weathering process.
Conclusion
This study showed how basalt weathering work in continental crust. It also provided high resolution of continental weathering effects by aeolian dust. This study will help us understand the development of the Ancient Earth crust and Mars crust, which are thought to be high portion of basalt. Furthermore, it may provide an opportunity to understand the Wide range of geochemical properties of Mars crust.
