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What happens to our PROTOLITH when acted on by AGENTS OF CHANGE??. Agents of Change T, P, fluids, stress, strain Metamorphic Reactions!!!! Solid-solid phase transformation Solid-solid net-transfer Dehydration Hydration Decarbonation Carbonation. Solid-solid phase transformation.
Jd Qtz Ab
En An Di And
If minerals contain volatiles, the volatiles must be conserved in the reaction so that no fluid phase is generated or consumed
For example, the reaction:
Mg3Si4O10(OH)2 + 4 MgSiO3 = Mg7Si8O22(OH)2
Talc Enstatite Anthophyllite
involves hydrous phases, but conserves H2O
It may therefore be treated as a solid-solid net-transfer reaction
Pyrophyllite And/Ky Quartz water
calcite quartz wollastonite
Reactions involving gas phases are also known as volatilization or devoltilization reactions
These reactions can also occur with other gases such as CH4 (methane), H2, H2S, O2, NH4+ (ammonia) – but they are not as common
Hunk o’ rock
by DG=DH – TDS
F = C - P + 2 the phase rule
P is the number of phases in the system
C is the number of components: the minimum number of chemical constituents required to specify every phase in the system
F is the number of degrees of freedom: the number of independently variable intensive parameters of state (such as temperature, pressure, the composition of each phase, etc.)
C = 1 (Al2SiO5)
(~ 0.37 GPa and 500oC)
Consider the following three scenarios:
Figure 21-9. The P-T phase diagram for the system Al2SiO5 calculated using the program TWQ (Berman, 1988, 1990, 1991). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
forsterite serpentine brucite
T O - T O - T O
Yellow = (OH)
Serpentine: Mg3 [Si2O5] (OH)4
T-layers and triocathedral (Mg2+) layers
(OH) at center of T-rings and fill base of VI layer
weak van der Waals bonds between T-O groups
Octahedra are a bit larger than tetrahedral match, so they cause bending of the T-O layers (after Klein and Hurlbut, 1999).
Antigorite maintains a sheet-like form by alternating segments of opposite curvature
Chrysotile does not do this and tends to roll into tubes
Veblen and Busek, 1979, Science 206, 1398-1400.
S = serpentine T = talc
Nagby and Faust (1956) Am. Mineralogist 41, 817-836.
The rolled tubes in chrysotile resolves the apparent paradox of asbestosform sheet silicates
Garnet (001) view blue = Si purple = A turquoise = B
Table 25-1. The definitive mineral assemblages that characterize each facies (for mafic rocks).
Miyashiro (1961) initially proposed five facies series, most of them named for a specific representative “type locality” The series were:
1. Contact Facies Series (very low-P)
2. Buchan or Abukuma Facies Series (low-P regional)
3. Barrovian Facies Series (medium-P regional)
4. Sanbagawa Facies Series (high-P, moderate-T)
5. Franciscan Facies Series (high-P, low T)
Fig. 25-3.Temperature-pressure diagram showing the three major types of metamorphic facies series proposed by Miyashiro (1973, 1994). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.