pseudosections A PT pseudosection is a PT map of the mineral assemblages developed in one rock composition (or equilibration-volume composition).

Transcription

1 pseudosections A PT pseudosection is a PT map of the mineral assemblaes developed in one rock composition (or equilibration-volume composition).

2 pseudosections A PT pseudosection is a PT map of the mineral assemblaes developed in one rock composition (or equilibration-volume composition). Tx and Px pseudosections are equivalently drawn for a composition vector, at constant P and T, respectively.

3 PT pseudosection example P(kbar) pl mu H 2O ky sill NCKFMASH (+q) solidus sill pl mu H 2O pl mu liq <0.03 sill pl mu liq sill pl mu liq sill ksp pl liq effective solidus sill ksp pl liq ksp pl mu liq als ksp mu liq cd ksp liq ky ksp liq sill cd ksp liq cd ksp liq cd liq opx cd liq sill liq liq 2 cd ksp pl H 2O cd ksp pl liq cd ksp pl liq sill ksp liq opx cd ksp liq sill ksp liq 0.4 melt modes 0.5 opx cd ksp pl liq opx cd ksp liq opx cd liq cd liq opx cd liq H 2O opx cd ksp pl H 2O cd liq H 2O T( C)

4 another PT pseudosection 35 ph cr jd + q/coe + H2O P kbar ph cr l jd ph jd ph cr l jd ph chl cr l jd i23 14 ct ph cr l jd ct ph l jd ct ph l pa jd ct ph l jd ph l pa jd ph l jd ph l ab jd ph lab ph jd ph l jd ph ab jd ph chl l pa jd ph l pa ab ph l pa jd ph ab l pa jd 3.40 ph ab l pa ph ab l pa ph ab pa ph ab l ph ab ph ab pa n1 ph ab ky/sill ab pa ab pa ab pa sill ab sill T C n

5 features of pseudosections

6 features of pseudosections modes of phases (proportions) chane continuously with PT around a pseudosection (except across univariant lines which in systems tend not to be seen very much)

7 features of pseudosections modes of phases (proportions) chane continuously with PT around a pseudosection (except across univariant lines which in systems tend not to be seen very much) phase compositions chane continuously with PT around a pseudosection.

8 NCKFMASH PT pseudosection P(kbar) pl mu H 2O ky sill NCKFMASH (+q) solidus sill pl mu H 2O pl mu liq <0.03 sill pl mu liq sill pl mu liq sill ksp pl liq effective solidus sill ksp pl liq ksp pl mu liq als ksp mu liq cd ksp liq ky ksp liq sill cd ksp liq cd ksp liq cd liq opx cd liq sill liq liq 2 cd ksp pl H 2O cd ksp pl liq cd ksp pl liq sill ksp liq opx cd ksp liq sill ksp liq 0.4 melt modes 0.5 opx cd ksp pl liq opx cd ksp liq opx cd liq cd liq opx cd liq H 2O opx cd ksp pl H 2O cd liq H 2O T( C)

9 more features of pseudosections the lines on pseudosections are phase boundaries not reactions

10 more features of pseudosections the lines on pseudosections are phase boundaries not reactions they are where a mode oes to zero

11 more features of pseudosections the lines on pseudosections are phase boundaries not reactions they are where a mode oes to zero except if the line is an actual univariant reaction but this view still holds if univariant lines are considered as zero width fields, themselves bounded by lines as we shall see)

12 more features of pseudosections the lines on pseudosections are phase boundaries not reactions they are where a mode oes to zero except if the line is an actual univariant reaction but this view still holds if univariant lines are considered as zero width fields, themselves bounded by lines as we shall see) variance chanes by just one across each line (i.e. the number of phases in the assemblae chanes by just one)

13 more features of pseudosections the lines on pseudosections are phase boundaries not reactions they are where a mode oes to zero except if the line is an actual univariant reaction but this view still holds if univariant lines are considered as zero width fields, themselves bounded by lines as we shall see) variance chanes by just one across each line (i.e. the number of phases in the assemblae chanes by just one) at a point, there are always just 4 lines, connectin fields of variance m, m + 2 and the two between them of variance m + 1.

14 NCKFMASH PT pseudosection P(kbar) pl mu H 2O ky sill NCKFMASH (+q) solidus sill pl mu H 2O pl mu liq <0.03 sill pl mu liq sill pl mu liq sill ksp pl liq effective solidus sill ksp pl liq ksp pl mu liq als ksp mu liq cd ksp liq ky ksp liq sill cd ksp liq cd ksp liq cd liq opx cd liq sill liq liq 2 cd ksp pl H 2O cd ksp pl liq cd ksp pl liq sill ksp liq opx cd ksp liq sill ksp liq 0.4 melt modes 0.5 opx cd ksp pl liq opx cd ksp liq opx cd liq cd liq opx cd liq H 2O opx cd ksp pl H 2O cd liq H 2O T( C)

15 calculation of pseudosections lines and points are zero mode features (and can be calculated directly because of that)

16 calculation of pseudosections lines and points are zero mode features (and can be calculated directly because of that) variance chanes by just one across each line (i.e. the number of phases in the assemblae chanes by just one)

17 calculation of pseudosections lines and points are zero mode features (and can be calculated directly because of that) variance chanes by just one across each line (i.e. the number of phases in the assemblae chanes by just one) at a point, there are always just 4 lines, connectin fields of variance m, m + 2 and the two between them of variance m + 1

18 calculation of pseudosections lines and points are zero mode features (and can be calculated directly because of that) variance chanes by just one across each line (i.e. the number of phases in the assemblae chanes by just one) at a point, there are always just 4 lines, connectin fields of variance m, m + 2 and the two between them of variance m + 1 critical idea: followin a line there are two possilities: lose a phase (at a point), or ain a phase (at a point).

19 ain/lose a phase pseudosections line bein followed - a + b joined by c at point m+2 a m+1 m+1 ab ac ab(c) a(b) m abc a(c) ac(b) add a phase (c) m+1 ab lose a phase (b) a(b) ab(c) m abc m+2 a ac(b) a(c) m+1 ac line bein followed - mode of b oes to zero at point

20 ain/lose a phase let s look at these two situations more closely

21 ain/lose a phase let s look at these two situations more closely the losin of a phase is easy: the calculations alon a line will see the mode of the phase bein lost oin to zero

22 ain/lose a phase let s look at these two situations more closely the losin of a phase is easy: the calculations alon a line will see the mode of the phase bein lost oin to zero the ainin of a phase requires uessin which phase miht join the assemblae.

23 THERMOCALC now let s do some calculations in THERMOCALC, buildin up the phase relationships around the staurolite isorad reaction in KFMASH, startin with the univariant reaction itself

24 staurolite isorad: mode info when seen untitled text 2 Printed: Wednesday, 21 June :32:25 AM composition (from script) SiO2 Al2O3 MO FeO K2O <==================================================> phases : chl,, st,, (mu, q, fluid) P(kbar) T( C) x(chl) y(chl) Q(chl) x() y() Q() etc chl mu = st + 115q + 74H2O chl mu = st + 106q + 81H2O chl mu = st + 100q + 87H2O chl mu = st + 96q + 91H2O mode chl st mu q

25 untitled text 2 staurolite Printed: Wednesday, isorad: 21di/trivariants June :40:53 (where AM are holes ) P(kbar) T( C) x(chl) y(chl) Q(chl) x() y() Q() etc mode chl st mu q P(kbar) T( C) x(chl) y(chl) Q(chl) x() y() Q() mode chl st mu q P(kbar) T( C) x(chl) y(chl) Q(chl) x() y() Q() mode chl st mu q P(kbar) T( C) x(chl) y(chl) Q(chl) x() y() Q() mode chl st mu q holes then don't chane up P

26 staurolite isorad: addin qualitative boundaries P chl chl st chl chl st st st T

27 staurolite isorad: invariant as a thin polyonal field univariant as a this field chl chl st st P chl st chl st T

28 pseudosection construction AFM (+ mu + q + H2O) P (kbar) chl chl 4 chl chl st st chl st T ( C) 2 2 chl st chl chl st st ( chl) chl (st ) st st chl chl () chl chl () chl chl ( ) chl chl chl ( ) chl () chl chl () chl chl st

29 practical class time do make use of the documentation, and you can look at this lecture material (it is in the lectures directory/folder on the CD), and dave kelsey, johann diener, richard white and I are here to help. have fun!