Why ACF diagrams are not suitable for rocks and minerals with Fe Mg solid solutions?
One of the problems associated with ACF and AKF diagrams is that Fe and Mg are assumed to substitute for one another and act as a single component. We know, however, that in natural minerals the composition of Fe – Mg solid solutions is very much dependent on temperature and pressure.
What are AFM diagrams?
AFM diagram A three-component, triangular graph used to show how metamorphic mineral assemblages vary as a function of rock composition within one metamorphic facies. The components of the diagram are thus A (Al 2O 3), F (FeO), and M (MgO), with the projection geometry being accommodated on specially scaled axes.
How do you determine metamorphism grade?
Low-grade metamorphism begins at temperatures and pressures just above sedimentary rock conditions. The sequence slate→phyllite→schist→gneiss illustrates an increasing metamorphic grade. Geologists use index minerals that form at certain temperatures and pressures to identify metamorphic grade.
What is a metamorphic grade name the different metamorphic grades?
Metamorphic grade refers to the range of metamorphic change a rock undergoes, progressing from low (little metamorphic change) grade to high (significant metamorphic change) grade. Low-grade metamorphism begins at temperatures and pressures just above sedimentary rock conditions.
What is the difference between prograde and retrograde metamorphism?
In general, the changes in mineral assemblage and mineral composition that occur during burial and heating are referred to as prograde metamorphism, whereas those that occur during uplift and cooling of a rock represent retrograde metamorphism.
What is prograde metamorphism?
Prograde metamorphism involves the change of mineral assemblages (paragenesis) with increasing temperature and (usually) pressure conditions. These are solid state dehydration reactions, and involve the loss of volatiles such as water or carbon dioxide.
What is metamorphic phase rule?
Since metamorphism usually involves long periods of geologic time, most metamorphic rocks represent an equilibrium mineral assemblage. The Phase Rule for Metamorphism. Recall that the phase rule states that. F = C + 2 – P.
What is metamorphic facies series?
• A metamorphic facies series is a sequence of facies that. occurs across a metamorphic terrane due to differences in pressure and temperature (P/T) conditions. • Variations in P/T conditions are related to both space and. time.
What is the difference between high grade and low grade metamorphism?
Low-grade metamorphic rocks tend to be fine-grained (the newly formed metamorphic mineral grains that is). High-grade metamorphic rocks tend to be coarse-grained. Foliation in metamorphic rocks is related to the orientation of the applied stresses and not the original sedimentary or earlier metamorphic structures.
What is afafm diagram?
AFM diagram A three-component, triangular graph used to show how metamorphic mineral assemblages vary as a function of rock composition within one metamorphic facies. Besides SiO 2, the five most abundant oxides found in metamorphic rocks are Al 2 O 3, CaO, FeO, MgO, and K 2 O.
What are the mineral assemblages found in AFM?
The mineral assemblages will contain two or three minerals plus the excess phases Ms, Qtz and hydrous fluid. These will include variously biotite, chlorite, chloritoid, staurolite, cordierite, andalusite, sillimanite and kyanite. Look at the attached AFM diagram to see where these plot relative to one another.
What are metamorphic reactions on a ternary phase diagram?
Metamorphic Reactions on Ternary Phase Diagrams •In general the breakdown of a mineral because it is unstable at current PT conditions will cause a re-alignment of tie lines and new 3-phase stability fields. •An example would be the loss of staurolite in a schist due to the reaction: St + Ms + Q = Ga + Bi + Sil + H2O Metamorphic Reactions cont.
What is metamorphism of mafic & ultramafic rocks?
Metamorphism of Mafic & Ultramafic Rocks •Seafloor Metamorphism: hydrothermal seawater fluid circulates through new ocean lithosphere. •Mafic Low Grade: Chl + Ab-Pl + Act + Ep •Mafic Med. Grade: Pl + HBl + Ga •Mafic High Grade: Cpx + Opx + Garnet + Hbl Ultramafic Protoliths •Low grade: Chl + Ol + Talc + Trem •Med grade: Chl + Ol + Anth + Trem