Mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (KFMASHTO) using thermocalc and its internally consistent thermodynamic dataset constrain the effect of TiO2 and Fe2O3 on greenschist and amphibolite facies mineral equilibria in metapelites. The end-member data and activity–composition relationships for biotite and chloritoid, calibrated with natural rock data, and activity–composition data for garnet, calibrated using experimental data, provide new constraints on the effects of TiO2 and Fe2O3 on the stability of these minerals. Thermodynamic models for ilmenite–hematite and magnetite–ulvospinel solid solutions accounting for order–disorder in these phases allow the distribution of TiO2 and Fe2O3 between oxide minerals and silicate minerals to be calculated. The calculations indicate that small to moderate amounts of TiO2 and Fe2O3 in typical metapelitic bulk compositions have little effect on silicate mineral equilibria in metapelites at greenschist to amphibolite facies, compared with those calculated in KFMASH. The addition of large amounts of TiO2 to typical pelitic bulk compositions has little effect on the stability of silicate assemblages; in contrast, rocks rich in Fe2O3 develop a markedly different metamorphic succession from that of common Barrovian sequences. In particular, Fe2O3-rich metapelites show a marked reduction in the stability fields of staurolite and garnet to higher pressures, in comparison to those predicted by KFMASH grids.

The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3

New activity–composition (a–x) relations for minerals commonly occurring in metapelites are presented for use with the internally consistent thermodynamic dataset of Holland & Powell (2011, Journal of Metamorphic Geology, 29, 333–383). The a–x relations include a broader consideration of Fe2O3 in minerals, changes to the formalism of several phases and order–disorder in all ferromagnesian minerals where Fe–Mg mixing occurs on multiple sites. The a–x relations for chlorite, biotite, garnet, chloritoid, staurolite, cordierite, orthopyroxene, muscovite, paragonite and margarite have been substantially reparameterized using the approach outlined in the companion paper in this issue. For the first time, the entire set of a–x relations for the common ferromagnesian minerals in metapelitic rocks is parameterized simultaneously, with attention paid to ensuring that they can be used together to calculate phase diagrams of geologically appropriate topology. The a–x relations developed are for use in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (NCKFMASHTO) system for both subsolidus and suprasolidus conditions. Petrogenetic grids in KFMASH and KFMASHTO are similar in topology to those produced with earlier end-member datasets and a–x relations, but with some notable differences. In particular, in subsolidus equilibria, the FeO/(FeO + MgO) of garnet is now greater than in coexisting staurolite, bringing a number of key staurolite-bearing equilibria into better agreement with inferences from field and petrographic observations. Furthermore, the addition of Fe3+ and Ti to a number of silicate phases allows more plausible equilibria to be calculated in relevant systems. Pseudosections calculated with the new a–x relations are also topologically similar to equivalent diagrams using earlier a–x relations, although with many low variance fields shifting in P–T space to somewhat lower pressure conditions.

New mineral activity-composition relations for thermodynamic calculations in metapelitic systems

This textbook provides a basic understanding of the formative processes of igneous and metamorphic rock through quantitative applications of simple physical and chemical principles. The book encourages a deeper comprehension of the subject by explaining the petrologic principles rather than simply presenting the student with petrologic facts and terminology. Assuming knowledge of only introductory college-level courses in physics, chemistry, and calculus, it lucidly outlines mathematical derivations fully and at an elementary level, and is ideal for intermediate and advanced courses in igneous and metamorphic petrology. The end-of-chapter quantitative problem sets facilitate student learning by working through simple applications. They also introduce several widely-used thermodynamic software programs for calculating igneous and metamorphic phase equilibria and image analysis software. With over 350 illustrations, this revised edition contains valuable new material on the structure of the Earth's mantle and core, the properties and behaviour of magmas, recent results from satellite imaging, and more.

Principles of igneous and metamorphic petrology

Building upon the award-winning second edition, this comprehensive textbook provides a fundamental understanding of the formative processes of igneous and metamorphic rocks. Encouraging a deeper comprehension of the subject by explaining the petrologic principles, and assuming knowledge of only introductory college-level courses in physics, chemistry, and calculus, it lucidly outlines mathematical derivations fully and at an elementary level, making this the ideal resource for intermediate and advanced courses in igneous and metamorphic petrology. With over 500 illustrations, many in color, this revised edition contains valuable new material and strengthened pedagogy, including boxed mathematical derivations allowing for a more accessible explanation of concepts, and more qualitative end-of-chapter questions to encourage discussion. With a new introductory chapter outlining the “bigger picture,” this fully updated resource will guide students to an even greater mastery of petrology.

Principles of Igneous and Metamorphic Petrology

A quantitative petrogenetic grid for pelitic schists in the system KFMASH that includes the phases garnet, chlorite, biotite, chloritoid, cordierite, staurolite, talc, kyanite, andalusite, sillimanite, and pyrophyllite (with quartz, H2O and muscovite or K-feldspar in excess) is presented. The grid is based on thermodynamic data of Berman et al. (1985) and Berman (1988) for endmember KFASH and KMASH equilibria and natural Fe-Mg partitioning for the KFMASH system. Calculation of P-T slopes and the change in Fe/(Fe+Mg) along reactions in the KFMASH system were made using the Gibbs method. In addition, the effect on the grid of MnO and CaO is evaluated quantitatively. The resulting grid is consistent with typical Buchan and Barrovian parageneses at medium to high grades. At low grades, the grid predicts an extensive stability field for the paragenesis chloritoid+biotite which arises because of the unusual facing of the reaction chloritoid+biotite + quartz+H2O = garnet+chlorite+muscovite, which proceeds to the right with increasing T in the KFMASH system. However, the reaction proceeds to the left with increasing T in the MnKFASH system so the assemblage chloritoid + biotite is restricted to bulk compositions with high Fe/(Fe+Mg+Mn). Typical metapelites will therefore contain garnet+chlorite at low grades rather than chloritoid + biotite.

A petrogenetic grid for pelitic schists in the system SiO 2 -Al 2 O 3 -FeO-MgO-K 2 O-H 2 O

Summary An attempt is made to synthesise data on the regional metamorphism of pelites in the eastern Scottish Dalradian. Zonal sequences (facies series) of mineral assemblages are presented and variants of the traditionally recognised Barrovian and Buchan metamorphism are separated. A Schreinemakers net and petrogenetic grid for the system KFMASH is presented and fixed in P-T space using experimental data. The P-T data for the various facies series are used in conjunction with other constraints to develop a model of isotherm and isobar distribution in the region, and the effects of post metamorphic folding of the isopleths are noted. P-T gradients normal to isobars suggest overall ‘geothermal’ gradients for most of the area to be convex to the T-axis, and it is suggested that they result from magma intrusion at depth. The region adjacent to the Highland Boundary fault shows strong horizontal and vertical temperature gradients which are tentatively interpreted to indicate the presence of a synmetamorphic tectonic boundary to the Dalradian metamorphic belt.

Pelite facies series and the temperatures and pressures of Dalradian metamorphism in E Scotland

Phase equilibria calculated with THERMOCALC for simplified mantle ultrabasic and basic bulk compositions in Na O-CaO-FeO- MgO-Al O -SiO (NCFMAS) at depths down to the Transition Zone and uppermost lower mantle are presented here for the first time. This capitalizes on a new equation of state for solid phases and ties in deep mantle phases (wadsleyite, ringwoodite, akimotoite, garnet, MgSi-perovskite, CaSi-perovskite, cf phase, ferropericlase, nal, corundum and stishovite) to the thermodynamic dataset used at lower pressures in THERMOCALC. Activity-composition relationships for these complex phases are formulated that combine the end-member properties, allowing such phase equilibria to be calculated. The results are presented in the form of P-Tand P-X pseudosections showing the dependence of mineral assemblage on conditions of formation and composition in basic and ultrabasic compositions, and also in terms of modal proportion and mineral composition diagrams. Such thermodynamic calculations will allow quantitative assessment of the mineral assemblages in the mantle, as well as in subducting lithospheric slabs. The results will be a key input into geophysical modelling, allowing questions such as the controls on the penetration of subducted slabs into the lower mantle to be addressed. The calculated mineral assemblages can also help in the interpretation of deep mantle phase inclusions trapped within diamonds. Calculations are made more realistic than in pre-existing models by inclusion in this study of a chemically complex nal phase as well as inclusion of a wide range of substitutions in the cf phase and in both the Mg- and Ca-perovskite phases. © The Author 2013. Published by Oxford University Press. All rights reserved. 2 2 3 2

New Thermodynamic Models and Calculated Phase Equilibria in NCFMAS for Basic and Ultrabasic Compositions through the Transition Zone into the Uppermost Lower Mantle

K 2 O-poor, aluminous assemblages from the Buchan Dalradian, and the variety of orthoamphibole assemblages in aluminous bulk compositions in the amphibolite facies

The Inzie Head gneisses of the NE Dalradian are syntectonic metapelitic migmatites containing numerous sill-like bodies of granite. Leucosomes preserve evidence for efficient deformation-controlled segregation and interconnection of melt, from intergranular pockets to sheets of leucogranite hundreds of metres thick. Although the physico-chemical system is complex, the geochemistry of in situ decimetre-scale leucosomes and discrete metre- to decametre-scale leucogranite sheets within the migmatites suggests derivation from a common metapelitic source. A comparison with spatially and temporally related Grampian Granite plutons and garnet-bearing aplites that occur at shallower crustal levels supports a genetic granite–migmatite link. The compositions of the granitic rocks are interpreted to be linked via fractional crystallization of a parental magma and escape of the fugitive melt from a cumulate residue. Leucogranite sheets within the migmatites have compositions that are similar to experimentally determined first-formed melts at the appropriate P – T conditions, and are interpreted to approximate parental liquids. Smaller-scale leucosomes contain the accumulated products of fractional crystallization and variable quantities of entrained solids, principally biotite. The Grampian Granites and aplites represent evolved liquids that segregated from source. The evolution of Grampian Granite melts involved varying degrees of K-feldspar-dominated fractional crystallization that is consistent with magma ascent; removal of a maximum of 15–20% cumulate material is implied. The composition of the aplites suggests a multistage evolution that involved plagioclase-dominated fractionation of a fugitive melt batch.

Evidence for a genetic granite–migmatite link in the Dalradian of NE Scotland

The chapter reviews the worldwide occurrence of inclusions in diamonds which involve Si-rich minerals and which appear to come mainly from depths in the range ca 550 to 800 km. They are referred to collectively as the Perovskite and Periclase Suite. Attention is focussed upon distinguishing retrograde and primary minerals, and upon identifying associations of different primary minerals within single diamonds; this provides potential equilibrium inclusion assemblages whose depths of formation may be estimated with reference to experimental studies. Associations in the same diamond of separate inclusions of (Mg,Fe)SiO3, (Mg,Fe)O and (Mg,Fe)2SiO4—potentially representing the original phases MgSi-perovskite(mPv), ferropericlase (fPer) and ringwoodite (rw)—indicate formation at the Upper/Lower Mantle boundary. Associations involving MgSi-perovskite and ferropericlase, without ringwoodite, are taken to indicate Lower Mantle assemblages of ultrabasic bulk composition, and these are divided into two: those with low-Al MgSi-perovskite, mPv, from the shallowest Lower Mantle, and those with high-Al MgSi-perovskite, mPv(Al), from greater depths. In assemblages of basic bulk composition, the primary phases of mPv(Al), sodic majoritic garnet (maj-grt), new Al–silicate phase (NAL) and the calcium ferrite structured phase (CF) are all represented by composite inclusions, which include a variety of retrograde products such as olivine, spinel, tetragonal almandine-pyrope phase (TAPP), NaAl-rich pyroxene phase (NaAl-pyrox) and nepheline. In both ultrabasic and basic bulk compositions, the principal Ca-bearing phase appears to be CaSi-perovskite (cPv). The chemical compositions of the primary phases show considerable coherency, including relatively constant Fe–Mg partition coefficients. The postulated mineral assemblages conform well with experimental investigations, and a series of different depths of formation are indicated. In the inclusion assemblages of basic bulk composition, a transition from assemblages with sodic majoritic garnet (maj-grt) to ones with mPv(Al), NAL and CF is believed to approximately coincide with the change from mPv to mPv(Al) in ultrabasic assemblages. The eight minerals mPv–mPv(Al), fPer-mW, maj-grt, NAL, CF, cPv, corundum (crn) and stishovite (stv) [where mPv–mPv(Al) and fPer-mW indicate solid solutions] potentially define an invariant point in the 6-component composition space MgO–FeO–Al2O3–SiO2–CaO–Na2O, giving rise to a series of univariant and divariant mineral assemblages in pressure–temperature space. Consideration of the available experimental data indicates that this invariant point is probably in the pressure range 24–28 GPa under the range of temperatures expected in the uppermost Lower Mantle.

Neil F. C. Hudson

Papers

Pelite facies series and the temperatures and pressures of Dalradian metamorphism in E Scotland

New Thermodynamic Models and Calculated Phase Equilibria in NCFMAS for Basic and Ultrabasic Compositions through the Transition Zone into the Uppermost Lower Mantle

K 2 O-poor, aluminous assemblages from the Buchan Dalradian, and the variety of orthoamphibole assemblages in aluminous bulk compositions in the amphibolite facies

Evidence for a genetic granite–migmatite link in the Dalradian of NE Scotland

Mineral Associations in Diamonds from the Lowermost Upper Mantle and Uppermost Lower Mantle