Garnet composition in the Indus Fan core sediments from IODP Expedition 355 (Arabian Sea)

2 2. Introduction The study of heavy minerals, and in particular the study of garnets using Raman spectroscopy, is an appropriate technique for provenance studies and palaeoenvironmental investigations in natural climate-tectonic sedimentary archives. The thesis is born in the world of sedimentary petrology, and it has, first, the aim to valorise the Raman spectroscopy for the study of sediments and garnets as the best way to represent the source rocks and as an established method for provenance studies (Morton, 1985). This modern tool has shown to be very practical thanks to its velocity to get data back, as there is no need to prepare the sample before its use. It is very important to specify that this tool does not want to replace the use of the optical microscope, which is always the best way where to start every study from, but it has to be considered as an implemented device to identify the chemistry of these common detrital minerals. For this reason, it is very helpful to combine all the available techniques in a such complex orogenic setting and study. There is not any well-done study with the use of just one tool: Raman spectroscopy is very efficient for a quantitative approach and it has the power to identify more clearly some minerals with similar optical properties that sometimes could result difficult to recognise and could be easily confused with the only use of an optical microscope. It is also used in the case of minerals which present solid solutions: this is the studied case, which uses garnets due to this mineral is a solid solution which consists of six main end members. Garnet is selected for this study for different reasons. It is very easy to be recognized thanks to its isometric property. Also, it is a very common mineral and one of the more known: from igneous and metamorphic rock to sedimentary, from the mantle to the crust. Garnet has high diagenesis resistance (Morton & Hallsworth, 1999; Morton & Hallsworth, 2007) and its potential to reflect the chemical composition of the source rock, even after being transported for thousands of kilometres, is a unique characteristic which makes it more and more interesting and object of study. All these instruments and knowledge are then applied to the Laxmi Basin, where the Indus Fan is located. Its sediments had been sampled during the International Ocean Discovery Program Expedition 355 because this area is an important geological place to understand palaeoenvironmental changes. Marine sediments in the Arabic Sea are the best way to understand climate and tectonic evolutions during geological time. Garnet is here employed