Provenance - a place of origin; specifically the area from which the constituent materials of a sedimentary rock or facies were derived (AGI Dictionary of Geological Terms - 3rd ed.)

High Resolution Provenance is meant to convey the interpretation of provenance of clastic materials to specific geologic terrains, or even rocks or rock types, through a variety of lines of evidence (through the perspective of a metamorphic petrologist).

This course is a meant to be a hybrid course drawing on

• classic sedimentary petrology

• modern mineralogy

• igneous and metamorphic petrology

• geochemistry

The promise of geologic interpretations based on clastic material has been considered for a long time.

·       James Hutton (1785) in an abstract of a dissertation read at the Royal Society of Edinburgh – Concerning the system of the Earth, its duration, and stability, 30 p. stated that  “if this part of the earth which we now inhabit had been produced, in the course of time, from materials of the former earth, we should, in the examination of our land, find data from which to reason, with regard to the nature of that world…”

• This promise has taken a long time to develop and is only now making headway

One reason we want to do this:

Clastic sediments, sedimentary and metasedimentary rocks  may preserve detrital material from orogens obscured by

• Subsequent tectonic events e.g. movement of tectonic plates or superimposed events

• Dismemberment of the orogen by faulting

• Erosion

      may be the only remaining clues, especially in ancient or metamorphosed terrains· particularly useful for tectonic reconstructions

Problem: there is general not an exact correlation between the makeup of clastic sediments and that of the source rocks

• things happen along the way.

• Clastic material may experience several stages in its history

  • Pedogenesis

  • Erosion

  • Transport

  • Deposition

  •  Burial

The makeup (composition) of sedimentary material is influenced by several processes

• physical weathering – strongly linked to chemical weathering and the relative stability of minerals
   

• chemical weathering – strongly linked to physical weathering and the relative stability of minerals
   

• abrasion (during transport) – related to mechanical stability
   

• hydrodynamic sorting – sorting by water - related to density and shape

• authigenesis – (definition: The process by which new minerals form in place within a rock during or after its formation, as by replacement or recrystallization, or by secondary enlargement of quartz overgrowths.)
   

•  burial diagenesis (important in sedimentary and metasedimentary rocks)
   

• metamorphism – metamorphic recrystallization and metamorphic reactions

Dynamics of physical and chemical weathering

• If all minerals were subject to the same degree of weathering the types and proportions of minerals would only be a function of
  • the mineralogical composition of the source rocks
  • hydrodynamic properties of the minerals
     
• However, not all minerals are the same
  • different minerals undergo weathering to different degrees and rates
  • some minerals are robust (e.g. quartz) and some are reactive (e.g. olivine)
  • knowledge of the relative stability gives information on the sedimentary processes

The magnitude of the effects of physical and chemical weathering are controlled by factors such as

• climate of the source region
• relief of the source region
• transport distance
• time in transit
• climate conditions during transport
• energetic environment during transport
• energetic conditions as point of deposition

Modifications associated with transport and deposition obscure provenance information. However, they are strongly related to the environment in which the sediment developed – primarily a topic for other sedimentology courses.

Can we see through these overprints? This is what we will try to answer in this course.