Lecture 1 - Sedimentary course notes PDF

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Lecture 1: Clastic Provenance- Provenance is what type the rock comes fromand what tectonic setting- Depositional environmental is where the rockis going to- Pettijohn scheme used to classifysedimentary rocksi — Quartz category:- Near-perfect hexagonal quartz crystal- Abraded quartz grains, as commo...

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Lecture 1: Clastic Provenance

- Provenance is what type the rock comes from and what tectonic setting

- Depositional environmental is where the rock is going to

- Pettijohn scheme used to classify sedimentary rocks i — Quartz category: - Near-perfect hexagonal quartz crystal - Abraded quartz grains, as commonly seen in sediments - Polycrystalline quartz (Qp) — is a lithic fragment or mono crystalline quartz (Qm) or Cryptocrystalline silica (Ls) - If look at these quartz and go under XPL some will undergo Undulose extinction — are imperfections, grain has been strained in the crystal lattice — seen as a shadow when you rotate - The strain has caused the quartz crystal to deform into domains with slightly different extinction angles — not truly polycrystalline - Rocks with most undulose extinction are low grade metamorphic rocks — picking up a lot of applied strain, low pressures and temperature so the lattice pick up the deformation quickly - Higher grade metamorphic rocks recover from this strain as more temperature and pressure, grains grow into each other and form perfect 3 point boundaries - Plutonic rocks have the least undulose extinction due to the reduction of shear — unstrained - Can tell where a quartz is from now if it from low, high metamorphic or plutonic rocks

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Type of boundaries that can occur: - Sutured grain boundaries — low grade metamorphic rocks - Annealed texture — higher grade metamorphic rocks — close to 120 degrees grain boundaries (most stable) - Stretched quartz — find in rocks such as quartzite mylonites — high grade close to major faults Other things to identify in Quartz: - Fluid inclusions: normally in plutonic rocks, trains of fluid filled bubbles in a quartz grain — characteristic of hydrothermal origin - Find high pressure forms of quartz e.g. Coesite and Stishovite - Find cathodoluminescence — bombard electrons and measure photons emitted — show different colours —> - Cathodoluminescence is good to see zoning

ii — Feldspar category: - Plagioclase (Ca-Na feldspars) — sure the Michel - Levy plagioclase method to see which feldspar it is — help to see which kind of rock it comes from - Orthoclase tend to be in gneiss and plutonic - Sericite is a product of hydrolysis of feldspar — look very similar to muscovite but fine grained, alteration product, but PPL it appears very cloudy quartz — these are from very fresh faced rocks — weathering took place in a humid/warm place - If no sericite probably weathered in a very arid environment - Zoning of plagioclase feldspars — show magma mixing

- Broken plagioclase feldspars — show explosive activity iii — Lithic grain category: - Normally in lower grade rocks - Pretty easy to identify

iv - Heavy metals category: - Some like rutile, apatite and tourmaline are igneous - Staurolite, garnet and epidote are normally metamorphic - Zircon are extremely hard, very good survival rate, useful for dating — found in many different settings of time as are so hard Provenance: - Can see where the rock has come from - Can see different tectonic settings fro where the rock came from...