LSU High Resolution Provenance Studies of Clastic Sedimentary Material

Determining the source of detritus of clastic material in sedimentary and metasedimentary rocks has undergone tremendous changes in the last few years. A particular thrust of recent provenance studies has been its relation to tectonics and tectonic reconstruction. In addition to the more traditional methods of point counting various detrital components, geologists now use the mineral chemistry and the geochronology of detrital constituents, the isotopic character of the rocks and minerals, and the trace element chemistry of the rocks to establish more details about the provenance of clastic material.

Dr. Darrell Henry has been taking his expertise in mineralogy-petrology and has applied it to provenance investigations of clastic material in sediments, sedimentary rocks and metasedimentary rocks. There are many possible detrital materials that may retain mineral chemistry and textures of the rock from which it was derived. One of the critical factors is the preservation of these detrital material in the weathering and/or diagenetic environment. If clastic materials are buried rapidly or under cool conditions, most minerals will survive with their provenance information (unless they undergo diagenetic or metamorphic modification). Three minerals are particularly refractory in clastic sedimentary and diagenetic environments: zircon, rutile and tourmaline. Zircon is most commonly used for geochronologic information of the source material. Rutile is beginning to be used to establish the source rock identity. However, tourmaline has the most chemical flexibility and is highly sensitive to the environment (rock) in which it was formed.

Tourmaline is one of the chief seats for boron in the Earth's crust. It is stable from essentially Earth surface conditions to well over 800ºC and 60 kbar. It is complex structure with many possible substituents that will reflect the environment of formation of the tourmaline. It is also extremely refractory in clastic sedimentary environments - being one of the most prominent heavy minerals. Consequently, it is an exceptionally good indicator of provenance of the detritus found in sedimentary and metasedimentary rocks. The ternary diagram above is an example of the application of tourmaline chemistry to provenance studies. This represents the data from a single thin section of a chlorite zone metagraywacke in which 10 source rock types were identified. For more information on tourmaline provenance studies refer to : http://www.geol.lsu.edu/dhenry/Geology7900/Tourmaline/Tourmaline.htm . For more information on tourmaline: http://www.geol.lsu.edu/dhenry/Research/tourmaline/TourmalineToday.htm

LSU has a trial course entitled "High Resolution Provenance" that has explored a wide variety of different aspects of provenance indicator possibilities:  http://www.geol.lsu.edu/dhenry/Geology7900/7900syllabus.htm