Trace element mobility in cold desert alteration systems

Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online's data policy on reuse of materials please consult the policies page. Introduction: Alteration of rocks is a fundamental process that occurs in all environments across the solar system in different forms. Understanding the patterns of alteration, the formation of different products, the liberation of certain elements from minerals can inform us about environments billions of years old [e.g. 1, 2, 3]. They can give us information about quantities of water, temperatures, atmospheres and biology. This study focuses on cold desert environments and the geo-chemical fingerprints processes leave in some of the most abundant minerals in the solar system. Specifically, this study looks at how trace elements move in cold weathering systems, using Antarctic ordinary chondrites as an analogue, and how weathering features of cold environments combine with little water to interact with rocks. Samples: Four L6 chondrites collected from Ant-arctica were used in the study: QUE 94214, QUE 99022, ALH 78130 and ALH 85017. The meteorites used cover the range of weathering and fracture grades A-C (A being least, C being most) as set out in the Antarctic Newsletter [4]. Thin and thick sections of the rims and interiors of QUE 94214 and ALH 78130, rim sections from ALH 85017 and interior sections of QUE 99022 were used for petrological studies. All rim sections contain fusion crust. Methods: Reflectance and transmitted light mi-croscopy was performed to get an overview of the sample texturally and mineralogically. A FEI Quanta 3D dual beam scanning electron microscope fitted with an Oxford Instruments 80 mm X-MAX energy disper-sive X-ray detector was used at The Open University to obtain images and element maps. From these, modal counts of mineral types were obtained. Also quantified were the amounts of Fe-Ni metals and sulphides converted to alteration products, as well as a general % of sample covered with rust, using the imaging software package imageJ. Trace element analysis was carried out using LA-ICP-MS on an Agilent 7500 s quadrupole mass spectrometer coupled to a New Wave 213 nm Nd–YAG laser system using a 60 μm spot size. Petrology: The most obvious evidence of alteration in meteorites is macroscopically visible red rust. As such, it is used as the basis for most weathering grades [4, 5]. The rust originates from the …