Lithological Control on Fluid Composition and its Impact on Trace Element Mobility: Accessory Minerals in the Metamorphic Aureole of the Ballachulish

Igneous Complex

Stanley Hensley, TTU Dept. of Geosciences Masters of Science Thesis Proposal Advisor: Dr. Callum Hetherington Committee Members: Dr. Cal Barnes and Dr. Moira Ridley Introduction Accessory minerals are defined as mineral phases in a rock that are present in minor quantities,

typically less than 5% by volume. They commonly host a wide variety of trace elements, which

are defined as elements present in quantities of <0.01% by weight and not required to form major

rock-forming minerals (Shaw 2006). Relatively common accessory minerals such as zircon

(ZrSiO4), monazite ((LREE, Th, U)PO4), allanite ((Ca, REE)(Al2, Fe2+)SiO3O12(OH)), and

xenotime (YPO4) have been used to provide insight into magmatic and metamorphic processes

such as contact metamorphic aureole formation, fluid flow, and associated element mobility

(Geisler et al. 2007, Wing et al. 2003, Janots et al. 2008). Distribution and behavior of trace

elements is determined by a variety of factors including: (in)-compatibility, the preference of an

element for mineral or melt phases; chemical characteristics such as charge, ionic radius, or

chemical affinity (lithophile, chalcophile, and siderophile); and phase stability, affected by

temperature and pressure conditions as well as lithological and fluid compositions. The majority

of studies thus far have provided data in terms of mineral stability or solubility as a function of

fluid composition, temperature and pressure, and their reactivity in particular lithologies, with

studies being primarily focused on experimental petrology. These studies, while insightful, have

not documented the relative behavior of accessory phase assemblages as a function of lithology

and fluid composition in a well constrained P-T framework.

Accessory Mineral Stability and the Role of Fluids

Experimental petrology has played a key role in the understanding of accessory mineral stability

(Harlov et al. 2011, Hetherington et al. 2010, Hetherington and Harlov 2008, Budzyn et al. 2011,

Harlov and Wirth 2012, Harlov et al. 2005, Ayers et al. 2003, Geisler et al. 2003). Many of the

studies originated in response to questions posed from studies of natural geologic environments.

However, given the disparate nature of natural geologic settings, methodical experimentation can

only give a good approximation of expected natural results.

By comparison of natural and experimental systems, three diagnostic traits have been identified

as being indicative of mineral reactivity, as opposed to solubility, in the presence of fluids:

1. Element enrichment or depletion in accessory minerals: several studies indicate monazite and

xenotime are capable of compositional change as a result of fluid interaction (Harlov et al. 2011,

Hetherington et al. 2010, Harlov and Wirth 2012, Budzyn et al. 2011). While some fluid

compositions (KCl, H2O) showed minimal reactivity with monazite and xenotime, in the

presence of alkali-bearing fluids (NaOH, Na2Si2O5+H2O) constituent monazite and xenotime

showed significant compositional alteration. For example, Harlov et al. (2011) noted that in

experiments with Na2Si2O5+H2O light and dark compositional domains formed where light

domains had compositions comparable to that of the starting (constituent) monazite where dark

domains were found to be depleted in U, Th, Pb, and Ca.

Zircon has also been documented as capable of compositional change under experimental

conditions (Geisler et al. 2003, Rizvanova et al. 2000). Rizvanova et al. (2000) used carbonate-

bearing fluids to evaluate effects on the U-Pb system. At temperatures 200˚-300˚C, the ability of

U to migrate from metamict zircon is slightly higher than for Pb. At higher temperatures U-loss

was found to be masked by formation of U-enriched baddeleyite. Migration of U and Pb from

crystalline zircon was attributed to dissolution into carbonate fluid, though no trends as a

function of temperature or fluid composition were identified.

2. Development of pores (µm-scale) and inclusion assemblages: experimental and natural

metasomatism have been shown to cause dissolution and the development of pore space, coupled

with the growth of secondary-phase inclusions in monazite and xenotime (Hetherington and

Harlov 2008, Budzyn et al. 2011, Harlov et al. 2011). Hetherington and Harlov (2008)

documented similar processes in granitic pegmatites associated with an anorthosite intrusion in

which thorite ((Th, U) SiO4) and uraninite (UO2) inclusions were found in host xenotime and

monazite.

3. Recrystallization and/or overgrowth of secondary mineral phases: overgrowths and

recrystallization have been experimentally determined to occur under a wide range of P-T

conditions and fluid compositions (Geisler et al. 2007, Budzyn et al. 2011, Hetherington et al.

2010). Budzyn et al. (2011) documented the growth of secondary monazite, allanite,

fluorapatite, britholite, REE-epidote, thorianite, and turkestanite. The identified phases were

dependent on the P-T conditions and fluid composition of the experiment.

An important and consistent result between experimental studies was that similar reaction

textures developed across a range of P-T conditions, thereby suggesting fluid composition is the

key determinant in accessory mineral reactivity and stability (Hetherington et al. 2010, Harlov et

al. 2011, Budzyn et al. 2011). While the experimental dataset for accessory mineral stability is

significant and continues to grow, it is not comprehensive in terms of stability of accessory

mineral assemblages, host-rock assemblage stability, or fluid composition. More importantly,

there are no existing studies that place the diversity of experimental data in the context of a

single natural system.

To test the hypothesis derived from experimental data against natural systems, a field locality

that meets a series of criteria should be identified. The criteria include:

1. A well constrained temperature, pressure, and petrologic framework

2. Lithological variation at constant P-T conditions

3. A mechanism for fluid flow

And, ideally:

4. Extensive prior study/publications

Figure 1- Regional geologic map of Scottish Highlands after Dempster et al. (2002). T, BV, M, and I are sample

localities not related to this study.

The Ballachulish Igneous Complex and its Thermal Aureole

The Ballachulish Igneous Complex and metamorphic aureole of the northwest Scottish

Highlands (Figure 1) is an example of a well-constrained natural laboratory, containing a wide

variety of metasedimentary lithologies that have been extensively described (Pattison and Harte,

1997). A constant pressure of 0.3 GPa was determined for the aureole (Troll and Weiss 1991),

meaning that accessory mineral stability may be evaluated in a two-dimensional grid where the

major variables are temperature and composition. Intrusion-wall rock contacts may be found

both parallel and sub-perpendicular to the strike of the metasedimentary units, which is roughly

northeast-southwest (Figure 2).

The Ballachulish Igneous Complex (Figure 2) consists of a pluton intruded into regionally

metamorphosed sedimentary units of the Paleozoic Ballachulish and Lochaber subgroups (Figure

3). Regional metamorphism occurred between ca. 520 and 490 Ma (Dempster 1985, Harte

1988), and grade increases from northwest to southeast. Chlorite grade through garnet is present

with increasing metamorphic grade to the southeast (Pattison and Harte 1985). Table 1

summarizes metasedimentary units in the area in terms of stratigraphic location and gives brief

unit descriptions. Magmatism in the area occurred ca. 426-400 Ma., with zircon ages for the

Ballachulish intrusive complex and nearby Glen Coe volcanic field being constrained to 426-420

Ma. and 412-400 Ma. (Fraser et al. 2004) respectively.

Group Subgroup Formation Brief Description Argyll (Middle Dalradian)

Creran Formation

Banded Leven Schists

Interbedded siltstones, dirty quartzites, and variably graphitic schists

Appin (Lower Dalradian)

Blair Atholl Cuil Bay Slate Dark gray slate Ballachulish Appin Phyllite Gray phyllite with flaggy interbeds

Appin Limestone Cream-colored, banded limestone. White dolomite

Appin Quartzite White, feldspathic, current-bedded quartzite Transition Zone Finely interbedded quartzite and black slate Ballachulish Slate Black, graphitic, sulfide-bearing slate Ballachulish Limestone

Dark pure limestone Calcareous schist Light-colored limestone

Lochaber Leven Schist Gray phyllites and semipelites Glen Coe Quartzite Fine-grained quartzite

Table 1- Summarizes the stratigraphic relation and gives a brief description of metapelitic units in the Ballachulish Complex. Table is after Pattison and Harte (1985) . Creran Formation information after Pattison and Voll (1991), Bailey and Maufe (1960), and Litherland (1980).

Figure 2- Geologic map of the Ballachulish Igneous Complex. Red lines represent transects on which samples are to

be collected (see Sample Collection) and numbers correspond to information given in table 2. Map is after Voll et al. (1991)

The Ballachulish Igneous Complex is a zoned pluton with an estimated emplacement depth of 10

km (Pattison 1991). Troll and Weiss (1991) proposed an emplacement model that shows initial

intrusion of a diorite magma that becomes zonally modified by convective fractionation and

host-rock assimilation, forced intrusion of granitic magma and its subsequent expansion, and

fault displacement lending to the pluton’s current state. Petrologically, this results in a small

leucogranitic center surrounded by granites (including hybrid marginal facies), quartz diorites,

and monzodiorites (Troll and Weiss 1991, Pattison and Harte 1997).

Intrusion of the igneous complex resulted in a contact metamorphic assemblage overprinting the

regional metamorphic pattern. Approximate peak temperatures were documented by Pattison

and Harte (1985) and are defined on the basis of the following reactions in metapelites:

(1) Muscovite + Chlorite + Quartz = Cordierite + Biotite + V

(2) Muscovite + Biotite + Quartz = Cordierite + K-feldspar + V

OR

Muscovite + Cordierite = Quartz + Biotite + Al-silicate + V

(3) Muscovite + Quartz = Al-silicate + K-feldspar + V

(4) Quartz + Biotite + Al-silicate = Cordierite + K-feldspar + V

OR

Muscovite + Cordierite = Biotite + Al-silicate + K-feldspar + V

(5) Muscovite = Corundum + K-feldspar + V

(6) Biotite + Al-silicate = Corundum + K-feldspar + Cordierite + V

-Reactions reproduced from Pattison and Harte (1985)

In addition to traditional metamorphic isograds and zones, Pattison and Harte (1991) defined

four broad zones specific to metamorphism of the Ballachulish aureole. Additionally, Fraser et

al. (2004) described the appearance, habit, and distribution of monazite in the context of these

zones. The following is a brief summary:

Zone I- Includes marginal schist and phyllite that show no (or little) evidence of having

undergone contact metamorphism. With few exceptions, biotite in the samples is oriented

parallel to regional metamorphic fabrics suggesting it is of regional metamorphic origin; samples

with randomly oriented porphyroblasts were not considered to be important. Garnet is present,

but dependent on relationships between regional garnet isograd and lithology.

Monazite of zone I varies from the outer part to the inner part. Outer zone I monazite was

described as ragged, anhedral, and deeply embayed. It occurred as large clusters made up of

smaller crystals. Inner zone I monazite (slightly higher grade) was found to be similar in habit,

but proportionally less abundant. In addition to similar occurrence as inner zone I monazite, it

was also found to occur along mica cleavage or intergrown with host iron oxides.

Zone II- This zone is marked mineralogically by the first appearance of ellipsoidal cordierite.

This appearance varies with distance from contact from <400 m in the north to 1700 m in the

east and southwest. New biotite growth envelops ilmenite grains or occurs on chlorite grain

edges. Primary chlorite shows an abrupt decrease in abundance in zone II.

No marked change in monazite distribution or habit was noticed by Fraser and Pattison (2004)

between zones I and II.

Zone III- Zone III is marked by the absence of primary chlorite in all pelitic and semi-pelitic

units. An increase in modal abundance and size of cordierite is also indicative of the zone. Zone

III varies in width from <200 m. in the north to 700 m. in the east and southwest.

Monazite morphology change is observed between the monazite from zones I and II and zone III.

It coincides with the onset of dehydration reactions, and corresponding temperature is 560-

600˚C. There is a greater abundance of monazite in higher grade zones, however smaller grain

sizes were noted. The smaller grains occurred as clusters of ovoid blebs included in host

minerals such as cordierite, quartz, biotite, and andalusite.

Zone IV- Zone IV metapelites mark the appearance of either andalusite or K-feldspar; both are

indicative of zone IV and, therefore, represent the same metamorphic grade. Andalusite-bearing

samples were all found to be from the graphitic Ballachulish Slate, whereas K-feldspar-bearing

samples were only found in the Appin Phyllite, Leven Schist, and Creran Succession.

Change in monazite morphology is minor between zones III and IV. Fraser et al. (2004) only

note that bleb clusters described for zone III are “particularly abundant” in zone IV.

Zone V- Both quartz-bearing and quartz-absent assemblages are present in zone V. The

characteristic assemblage in both cases includes Aluminosilicate + K-feldspar.

Monazite occurrence only changes in the migmatitic portion of zone V. Here, ovoid monazite

blebs were found to occur in trails. This was thought to represent Zone II or III type monazite

formation, but minor ductile deformation caused disruption and/or smearing.

Fraser et al. (2004) found distinct changes in morphology and an increase in abundance of

monazite within the Ballachulish aureole, suggesting new metamorphic monazite growth in the

560-600˚C temperature range. This is broadly consistent with observations made in other natural

systems. Wing et al. (2003) described metamorphic monazite growth at the aluminosilicate

isograd, and Janots et al. (2008) found the same growth at ~556-580˚C. This is a commonly

observed relationship, and has been attributed to the breakdown of allanite and the growth of

new monazite (Williams et al. 2007, Wing et al. 2003). Conversely, it has also been suggested

the primary cause of new monazite growth is the breakdown of garnet near the staurolite-in

isograd (Pyle and Spear 2003). With the progressive breakdown of xenotime, it is possible for

both metamorphic monazite and garnet to grow (Pyle and Spear 1999). Upon xenotime

depletion, monazite and garnet must have corresponding growth and breakdown reactions

because both phases are reservoirs for Y in pelitic rocks (Williams et al. 2007).

Proposed Research The following questions will guide research focusing on accessory phase assemblage stability as

a function of temperature, fluid availability, and fluid composition in metapelites of the contact

aureole of the Ballachulish:

1. What is the compositional variation in the metapelites surrounding the Ballachulish

Igneous Complex?

2. To what extent do compositional and peak metamorphic temperature variations control

accessory mineral assemblage stability and trace element abundances?

3. How did metamorphic fluid flow contribute to the formation of the contact aureole of the

Ballachulish Igneous Complex?

4. Assuming a contribution from fluid flow to the formation of the aureole, what was the

composition of the fluid(s)?

5. What do textural relationships between non-silicate assemblages and accessory phase

assemblages indicate about their respective stabilities?

6. Can non-silicate assemblages be used to evaluate fluid flow in the aureole?

To address these research questions, the following work will be conducted:

Sample Collection

Based on well-established geologic, metamorphic, and temperature constraints (Pattison and

Harte 1985, Pattison 1989, Fraser et al. 2004) sample suites will be collected along transects

perpendicular to pluton-wall rock contact. Transects along a single rock unit will limit

compositional variation, thus making temperature change the dominant variable. Transects will

be followed beyond the limits of the aureole, allowing for comparison with host rock prior to

thermal metamorphism. Transects parallel to the pluton contact that cross several lithologies are

ideal to evaluate lithological control on fluid composition and activity at a constant temperature.

Thermally metamorphosed rocks will be distinguished from regionally metamorphosed rocks on

the basis of major silicate assemblages and the different ages of metamorphism; the intrusion is

426-420 Ma (Fraser et al. 2004) whereas the regional metamorphism is ~70 m.y. older

(Dempster 1985, Fraser et al. 2004).

Table 2 summarizes the two proposed transects (Figure 2) with their location relative to the

intrusion, units crossed, mineralogic isograds crossed, and corresponding peak metamorphic

temperatures (assumes a constant pressure of 0.3GPa; Pattison and Harte 1985). Transect 1

(Figure 2) is ideal to evaluate element mobility on the microscopic level as the lithology does not

vary and peak metamorphic temperature varies drastically. In contrast, transect 2 passes through

several rock units and mineralogic isograds. Additionally, the transects run parallel and adjacent

to one another and represent the transition from biotite zone (transect 1) to garnet zone (transect

2). Transects are based on the geologic map from Voll et al. (1991) (Figure 2).

Table 2 – Summary of conditions present for traverses made in the thermal aureole Transect # Mineralogic

Isograds Relation to Metasediment Strike

Lithologies Traversed

Metapelitic Zone

Igneous Type Adjacent

1 1, 2, 3a, 4 Parallel CS, LS Biotite Qtz. Diorite 2 2, 3b, 4, ±5 Parallel BS, AQ, AL, ± AP,

BL, CS Garnet Fine-grained

Diorite Lithology Abbreviations: AP- Appin Phyllite, BS- Ballachulish Slate, AL- Appin Limestone, AQ- Appin Quartzite, CS- Creran Succession, LS- Leven Schist, BL- Ballachulish Limestone. Mineralogic Isograds: (1) Liquid K-feldspar + Quartz; 670-720˚C, (2) Andalusite + K-feldspar Muscovite + Quartz; 625-640˚C, (3a) Muscovite + Biotite + Quartz Cordierite + K-feldspar; 600-620˚C, (3b) Muscovite + Cordierite Quartz + Biotite + Andalusite; 600-620˚C, (4) Muscovite + Chlorite + Quartz Cordierite + Biotite (± Chlorite-out); 550-560˚C, (5) Dolomite + Quartz Talc + Calcite. Transect numbers correspond to transects shown on figure 2.

Analytical Methods

To meet the proposed research goals, geochemical data will be gathered on both micro-

(individual mineral grains) and meso- to macro-scales (whole rock) from both within and beyond

the contact aureole. For small-scale domains, the mineral assemblage and textural relationships

must be documented prior to dating and compositional analysis. Whole rock composition of

thermally altered rocks will be compared with whole rock composition of the same unit outside

the thermal aureole to document compositional change.

Petrography- Standard petrographic procedures will be used to identify major rock-forming

mineral assemblages. These will be compared with temperature ranges of Pattison and Harte

(1985) to place each sample within the petrogenetic grid.

QEMSCAN- Quantitative evaluation of minerals using scanning electron microscopy

(QEMSCAN) will be used in identification of accessory mineral assemblages. Given the fine-

grained nature of metapelites, this procedure will give a much more accurate (and useful)

determination of accessory phase distribution in samples. Estimates of relative volumes of rock-

forming and accessory phase minerals can be obtained by comparing surface area of a mineral

phase against the total surface area of the section. These will be used for comparison with future

whole-rock compositional data. Additionally, optically opaque minerals may be identified.

Scanning Electron Microscopy (SEM)- Backscattered electron (BSE) and cathodoluminescence

(CL) detectors will be used to identify accessory phase assemblages and textural relations

between and within grains. The size and textural relationships of the identifiable domains will be

used to guide future in situ analysis. Energy-dispersive X-ray Spectroscopy (EDS) will also be

used to confirm the identity of major and accessory phase minerals.

Electron Probe Microanalysis (EPMA)- With spots determined from previous methods (SEM,

QEMSCAN), EPMA will be used to quantify accessory mineral compositions. Standard

elemental abundances in accessory phase minerals will be determined using the SX50 at the

University of Oklahoma. Monazite and xenotime metamorphic domain ages will be determined

by EPMA of trace elements (Th, U, Pb) using the SX100 Ultrachron at the University of

Massachusetts – Amherst.

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)- Zircon may be

subjected to standard separation procedures or analyzed in situ on polished thin sections. Dates

and compositions will be determined. Large domains of other accessory minerals (monazite,

xenotime) will also be analyzed for ages and compositions. Trace element abundances in major

silicate assemblages will be collected.

X-Ray Fluorescence (XRF)- Whole rock compositional analysis by XRF will be used to evaluate

major and trace element distribution on a large scale, this is in contrast to the smaller scales

determined by EPMA and LA-ICP-MS.

Volatile Quantification- Anionic species that may have been important during thermal

metamorphism will be identified on the basis of EPMA analyses of hydrous minerals. Once

identified, the relative abundance of individual species will be quantified using a combination of

ion-electrode or combustion infrared spectroscopy at Actilabs, Ancaster, Canada.

Additionally, minerals such as quartz, carbonates, sulfides, and fluorites commonly contain fluid

inclusions (paleofluids) and will be separated and prepared for crush-leaching. This process

involves crushing and sieving minerals from the thermal metamorphic assemblage to obtain a

0.5-1.5 mm fraction, and then picking and cleaning them to minimize contamination from other

mineral phases.

Paleofluids are extracted from minerals by crushing 0.5g of sample in an agate mortar and pestle

and then leaching the sample in 3 ml of doubly distilled de-ionized water. Samples for cation ion

analyses are leached in a La-doped solution to prevent absorption on mineral surfaces. The

leachate is centrifuged and may be analyzed by ion chromatography (IC) to obtain Cl, Br, F,

SO4; major cations and trace elements may be analyzed by Inductively Coupled Plasma- Atomic

Emission Spectroscopy.

Integration of Analytical Results to Meet Research Objectives Results of standard petrographic analysis will yield major rock-forming assemblage data. This

will be integrated with QEMSCAN data to identify the spatial distribution of accessory minerals

in metapelites of the aureole. QEMSCAN data will also be the basis of accessory mineral

volume estimates. By comparing the relative abundance and molar proportions of accessory

minerals with whole rock major and trace element abundances, accessory mineral stability as a

function of metamorphic conditions will be determined. The same data, when compared to the

major and trace element compositions of non-thermally metamorphosed metasediments will also

be used to quantify thermal, metamorphism-induced changes in element abundance and spatial

distribution as a function of temperature. Greater constraints on the processes may be attained

using core-to-rim relationships in certain accessory phases (e.g. monazite, xenotime, and zircon).

If fluid flow was key in development of the aureole, LA-ICP-MS and EPMA should provide

trace element abundance data with a distinguishable pattern going away from pluton-wallrock

contact. This pattern may be identifiable based on a combination of mineralogic isograds and

changes in lithology, and may form a “peak.” This would be taken to represent the point where

fluid flow ceased to be a dominant process, with all the elements previously mobile

incorporating into various mineral phases. Combining this data with whole-rock XRF data,

elemental balance should be achievable. This assumes elemental abundances were originally

constant within individual lithologies. Overlaying this same data with dominant anionic species

abundances will allow for identification of the prevailing fluid flow directions and paths.

Additionally, it will allow for spatial consideration of fluid compositions present. Fluid

compositional variation will be considered as both a function of temperature and lithology.

Fluid compositions and paths will be integrated with accessory phase stability, composition, and

distribution data to compare with previous petrologic and experimental observations (Fraser et

al. 2004, Pattison and Harte 1985, Pattison and Harte 1991, Pattison and Harte 1997, Wing et al.

2003, Williams et al. 2007, Harlov et al. 2011, Hetherington et al. 2010, Harlov and Wirth 2012,

Budzyn et al. 2011) and conclusions about fluid flow and mineral assemblage stability as a

function of temperature and lithology in the development of the thermal aureole will be made.

Intellectual Merit and Broader Impacts Trace elements, despite being of very small proportions, can be crucial in characterizing the

development of igneous and metamorphic systems. Their mobility, or lack thereof, in the

development of a thermal aureole such as the Ballachulish will provide insight into accessory

phase stability on the micro-scale and help evaluate the possibility of fluid flow on the macro-

scale. To date, other relevant studies have been purely experimental or limited by P-T-X

conditions, lithological homogeneity, or lack of a dynamic fluid composition. This study will

test hypotheses based on natural and experimental observations and provide a comprehensive

dataset in terms of fluid composition and accessory phase stability over a variety of metamorphic

conditions in metapelites.

This project will provide the opportunity for a M.S. student to travel abroad and study field

relations in a well-documented thermal aureole. With sample preparation being done in

Scotland, this will simultaneously allow for international collaboration with researchers from the

University of St. Andrews. Additionally, the variety of analytical work to be done (BSE-SEM,

QEMSCAN, LA-ICP-MS, EPMA, XRF) will provide exposure to both traditional and newer

techniques.

References Ayers, J.C., DeLaCruz, K., Miller, C., and Switzer, O. (2003) Experimental study of zircon coarsening in quartzite ±H2O at 1.0 GPa and 1000 ˚C, with implications for

geochronological studies of high-grade metamorphism. American Mineralogist, 88, 365- 376. Bailey, E.B. and Maufe, H.B. (1960) The geology of Ben Nevis and Glen Coe and the surrounding country: explanation of Sheet 53- update of 1916 memoir. Mem. Geol. Surv. Scot. H.M.S.O., Edinburgh, 307 pp. Budzyn, B., Harlov., Williams., and Jercinovic, M.J. (2011) Experimental determination of stability relations between monazite, fluorapatite, allanite, and REE-epidote as a function of pressure, temperature, and fluid composition. American Mineralogist, 96, 1547-1567. Dempster, T.J., Rogers, G., Tanner, P.W.G., Bluck, B.J., Muir, R.J., Redwood, S.D., Ireland, T.R., and Paterson, B.A. (2002) Timing of deposition, orogenesis and glaciation within the Dalradian rocks of Scotland: constraints from U-Pb zircon ages. Journal of the Geological Society, London, 159, 83-94. Dempster, T.J. (1985) Uplift patterns and orogenic evolution in the Scottish Dalradian. Journal of the Geological Society, 142, 111-128. Fraser, G.L., Pattison, D.R.M., and Heaman, L.M. (2004) Age of the Ballachulish and Glencoe Igneous Complexes (Scottish Highlands), and paragenesis of zircon, monazite, and baddeleyite in the Ballachulish Aureole. Journal of the Geological Society, London, 161, 447-462. Geisler, T., Schaltegger, U., and Tomascheck, F. (2007) Re-equilibration of Zircon in Aqueous Fluids and Melts. Elements, 3, 43-50. Geisler, T., Pidgeon, R.T., Kurtz, R., Van Bronswijk, W., and Schleicher, H. (2003) Experimental hydrothermal alteration of partially metamic zircon. American Mineralogist, 88, 1496-1513. Harlov, D.E. and Wirth, R. (2012) Experimental incorporation of Th into xenotime at middle to lower crustal P-T utilizing alkali-bearing fluids. American Mineralogist, 97, 641-652. Harlov, D.E, Wirth, R., and Hetherington, C.J. (2011) Fluid-mediated partial alteration in monazite: the role of coupled dissolution-reprecipitation in element redistribution and mass transfer. Contributions to Mineralogy and Petrology, 162, 329-348. Harlov, D.E., Wirth, R., and Forster, H.J. (2005) An experimental study of dissolution- reprecipitation if fluorapatite: infiltration and the formation of monazite. Contributions to Mineralogy and Petrology, 150, 268-286. Harte, B. (1988) Lower Paleozoic metamorphism in the Moine-Dalradian belt of the British Isles. In Harris, A.L. and Fettes, D.J. (eds.) The Caledonian-Appalachian Orogen. Geological Society, London, Special Publications, 38, 123-134. Hetherington, C.J., Harlov, D.E., and Budzyn, B. (2010) Experimental metasomatism of monazite and xenotime: mineral stability, REE mobility and fluid composition. Mineralogy and Petrology, 99, 165-184. Hetherington, C.J. and Harlov, D.E. (2008) Metasomatic thorite and uraninite inclusion in xenotime and monazite from granitic pegmatites, Hidra anorthosite massif, southwestern Norway: Mechanics and fluid chemistry. 93, 806-820. Janots, E., Engi, M., Berger, A., Allaz, J., Schwarz, J.O., and Spandler, C. (2008) Prograde metamorphic sequence of REE minerals in pelitic rocks of the Central Alps: implications for allanite-monazite-xenotime phase relations from 250 to 610˚C. Journal of Metamorphic Geology, 26, 509-526. Litherland, M. (1980) The stratigraphy of the Dalradian rocks around Lock Creran, Argyllshire. Scottish Journal of Geology, 16, 105-123.

Pattison, D.R.M. (1991) P-T-a(H2O) Conditions in the Thermal Aureole. In G. Voll, J. Topel, D.R.M. Pattison, and F. Seifert, Eds. Equilibrium and kinetics in contact metamorphism: the ballachulish Igneous Complex and its aureole, p. 327-350. Springer, Berlin. Pattison, D.R.M. (1989) P-T Conditions and the Influence of Graphite on Pelitic Phase Relations in the Ballachulish Aureole, Scotland. Journal of Petrology, 30, 1219-1244. Pattison, D.R.M., and Harte, B. (1985) A petrogenetic grid for pelites in the Ballachulish and other Scottish thermal aureoles. Journal of the Geological Society, London, 142, 7-28. Pattison, D.R.M., and Harte, B. (1997) The geology and evolution of the Ballachulish Igneous Complex and Aureole. Scottish Journal of Geology, 33, 1-29. Pattison, D.R.M. and Voll, G. (1991) Regional Geology of the Ballachulish Area. In G. Voll, J. Topel, D.R.M. Pattison, and F. Seifert, Eds. Equilibrium and kinetics in contact metamorphism: the ballachulish Igneous Complex and its aureole, p. 19-36. Springer, Berlin. Pyle, J.M., and Spear, F.S. (2003) Four generations of accessory phase growth in low-pressure migmatites from SW New Hampshire. American Mineralogist, 88, 338-351. Pyle, J.M. and Spear, F.S. (1999) Yttrium zoning in garnet: coupling of major and accessory phases during metamorphic reactions. Geological Materials Research, 1(6), 1-49. Rizvanova, N.G., Levchenkov, O.A., Belous, N.I., Bezmen, N.I., Maslenikov, A.V., Komarow, A.N.K., Makeev, A.F. and Levskiy, L.K. (2000) Zircon reaction and stability of the U- Pb isotope system during interaction with carbonate fluid: experimental hydrothermal study. Contributions to Mineralogy and Petrology, 139, 101-114. Shaw, D.M., 2006, Trace Elements in Magmas, Cambridge University Press, New York City, 243 p. Troll, G., and Weiss, S. (1991) Structure, Petrography, and Emplacement of Plutonic Rocks. In G. Voll, J. Topel, D.R.M. Pattison, and F. Seifert, Eds. Equilibrium and kinetics in contact metamorphism: the ballachulish Igneous Complex and its aureole, p. 39-66. Springer, Berlin. Voll, G., Topel, J., Pattison, D.R.M., and Seifert, F. (eds) (1991). Equilibrium and kinetics in contact metamorphism: The Ballachulish Igneous Complex and its aureole. Springer- Verlag, Berlin. Williams, M.L., Jercinovic, M.J., and Hetherington, C.J. (2007) Microprobe Monazite Geochronology: Understanding Geologic Processes by Integrating Composition and Chronology. Annual Reviews Earth Planet Science, 35, 37-75. Wing, B.A., Ferry, J.M., and Harrison, M.T. (2003) Prograde destruction and formation of monazite and allanite during contact and regional metamorphism of pelites: petrology and geochronology. Contributions to Mineralogy and Petrology, 145, 228-250.