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1991 | Buch

Equilibrium and Kinetics in Contact Metamorphism

The Ballachulish Igneous Complex and Its Aureole

herausgegeben von: Professor Dr. Gerhard Voll, Dr. Jutta Töpel, Professor Dr. David R. M. Pattison, Professor Dr. Friedrich Seifert

Verlag: Springer Berlin Heidelberg

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With the new global tectonics approach in the Earth Sciences, the quan­ titative aspects of the dynamics of rock-forming processes came into focus: geologists are no longer satisfied knowing the pressure-tempera­ ture conditions of the formation of a metamorphic rock or of the emplace­ ment of a magmatic body, but instead would like to learn the time history of these rocks as well, i. e. , derive the temperature-pressure-time path and relate it to a tectonic process. To achieve this goal, a knowledge of both pressure-temperature-dependent equilibria and the time scales at which these equilibria may be attained are essential. However, the latter kinetic information is much more difficult to retrieve than that on equilibria: whereas equilibria are controlled by state variables, and proper laboratory experiments may be directly applied to equilibrium natural assemblages, kinetics also depends on factors other than state variables, such as grain size, dislocation density, and especially time (rate of heating, duration of annealing, rate of cooling). Extrapolation of kinetic data obtained at high temperatures on laboratory time scales to more realistic lower tempera­ tures and geological time scales are dangerous because, for example, of possible changes from an intrinsically controlled defect regime to an extrinsic one as temperature is lowered, or from an interface-controlled to a diffusion-controlled reaction mechanism.

Inhaltsverzeichnis

Frontmatter

Introduction

Frontmatter
1. The Setting of the Ballachulish Intrusive Igneous Complex in the Scottish Highlands
Abstract
The Ballachulish igneous complex is one of a series of relatively late granitoid complexes in the Caledonian orogenic zone and intrudes metasediments of the Dalradian Supergroup in the Scottish Highlands (Fig. 1.1). For those who are unfamiliar with the Scottish Highlands, the purpose of this chapter is to give some background to the nature of the Caledonian orogeny in Scotland, the Dalradian Supergroup and the late Caledonian granitoids. The aim, in conjunction with the following chapter on local regional geology, is to provide the reader with some background on crustal conditions and tectonic relations of intrusion, and on the broad history of development of the aureole rocks prior to contact metamorphism. Clearly these features are relevant to models of pressure-temperature-time relationships in the intrusive complex and its aureole, and to examining kinetic controls on the crystallization of the magmatic and metamorphic rocks.
B. Harte, G. Voll
2. Regional Geology of the Ballachulish Area
Abstract
The purpose of this chapter is to describe the stratigraphy, structure and regional metamorphism of the host rocks to the Ballachulish Igneous Complex. The chapter opens with a description of the geography of the Ballachulish area, and concludes with a discussion of pre-intrusion and post-intrusion uplift in the area.
D. R. M. Pattison, G. Voll

The Intrusive Complex

Frontmatter
3. Structure, Petrography and Emplacement of Plutonic Rocks
Abstract
The two-phase Ballachulish pluton is composed of a zoned monzodiorite - quartz diorite envelope with distinct flow- and deformation-foliation, surrounding a core of porphyritic granite with hybrid margins. Mesotype members of this suite are constituted of alkaline hypersthene diorites. This provides an unique opportunity to quantify the magmatic crystallization sequence within a relatively “dry” plutonic environment at upper crustal level, in terms of \( T - X - {f_{{o_2}}} \) evolution (Weiss and Troll, Chap. 4, this Vol.). The present chapter starts with a gross megascopic description of the igneous rocks. Section 3.2 deals with contact relationships, xenoliths and foliation structures, followed by a modal classification of the igneous units (Sect. 3.3.1). A detailed petrography of index minerals, their texture and areal distribution (Sect. 3.3.2) precede the synoptical Sect. 3.4 on magma emplacement and intrusion mechanics.
G. Troll, S. Weiss
4. Thermal Conditions and Crystallization Sequence, as Deduced from Whole-Rock and Mineral Chemistry
Abstract
This chapter presents new data on the chemistry of Ballachulish igneous rocks (Sects. 4.1.1, 4.1.2), considering the effects of assimilation and hybridization (Sect. 4.1.3). A section on solidus temperatures and the granite system (Sect. 4.1.4) introduces several condensed paragraphs on mineral chemistry, phase relationships and geothermometry (Sect. 4.2; see Weiss and Troll 1989 for further details). The implications for fluid activity and the order of crystallization (Sect. 4.3, Fig. 4.11) are given ahead of a comprehensive summary on the petrogenesis of the Ballachulish pluton (Sect. 4.4).
S. Weiss, G. Troll
5. Nucleation and Growth of Pyroxene in the Hypersthene Diorites
Abstract
For a detailed textural study on intermediate igneous rocks of Ballachulish complex, an area in the southeastern part of the pluton was selected, where hypersthene-bearing monzodiorites are nearest to the contact. These relatively ‘dry’ diorites are least affected by late- to post-magmatic hydration southeast of Sgorr Dhonuill, where a very fine-grained chilled marginal facies bordered quartzitic country rocks, before the emplacement of granitic rocks partially separated the diorites from the metasediments. The term ‘chilled margin’ is used here in a general sense, defined as a zone of “fine-grained rock, enclosing and grading into the relatively coarser inner parts of an intrusion” (Cox et al. 1979). Figure 5.1 attempts a reconstruction of the monzodiorite main zone before the emplacement of younger granites, omitting the large ring-dyke granite apophysis and correcting for later sinistral fault displacement (compare Fig. 3.13c).
S. Weiss
6. Microstructures and Thermal Behaviour of Igneous Pyroxenes
Abstract
The cooling history of rocks is manifested in the microstructures of their minerals, which are most conveniently observed by TEM. To help in their interpretation, X-ray diffraction of heated single crystals is applied.
H. Feuer, L. Schröpfer, H. Fuess
7. The Shape of the Intrusion Based on Geophysical Data
Abstract
Geological information about the geometric shape of a rock body is generally restricted to shallow depths. Concerning the Ballachulish pluton, it is the purpose of the present chapter to obtain information on the geological structure at larger depths by using geophysical methods. The following items will be investigated:
1.
Location of metamorphic contacts and of boundaries between different igneous rocks
 
2.
Estimation of their dip angles
 
3.
Mean depth of the Ballachulish pluton
 
4.
The lateral extension of the pluton under the surrounding metamorphic rocks.
 
W. Rabbel, R. Meissner

The Contact Aureole and Its Rocks

Frontmatter
8. Petrography and Mineral Chemistry of Pelites
Abstract
This chapter describes the petrography and mineral chemistry of an exceptionally well-developed sequence of prograde mineral zones in pelitic and semipelitic rocks in the Ballachulish aureole. Two schematic petrogenetic grids are derived: the first is for mineral assemblages below the onset of partial melting, which define the mapped isograds in Maps 1 and 2 and Figure. 8.1; and the second is for high-grade mineral assemblages which occur sporadically within the zone of partial melting (Harte et al., Chap. 9, this Vol.) and within pelitic screens within the igneous complex. The two grids, when linked, provide a continuous petrogenetic grid from the lowest to highest grade in the aureole. In Pattison (Chap. 16, this Vol.) the continuous grid is calibrated in P-T space.
D. R. M. Pattison, B. Harte
9. Field Relations and Petrography of Partially Melted Pelitic and Semi-Pelitic Rocks
Abstract
Evidence of partial melting is seen in pelitic and semi-pelitic metasediments within the Ballachulish aureole in many locations immediately adjacent to the intrusive complex (within Zone V of Pattison and Harte 1985, and Chap. 8, this Vol.). In this chapter we summarize that evidence as seen both in the field and under the optical microscope. We endeavour in our presentation to largely keep description and interpretation in separate sub-sections, in an attempt to lay out the evidence for melting as objectively as possible. The chapter is concerned with textures and structures, their interpretation, and their implications for the rheological and crystallization behaviour of the melts. The reader is referred to Pattison and Harte (1985, 1988; Sect. 8.5, this Vol.) for notes concerning the melting reactions.
B. Harte, D. R. M. Pattison, C. M. Linklater
10. Decarbonation Reactions in Siliceous Dolomites and Impure Limestones
Abstract
In this chapter the petrography and mineral chemistry of carbonates of the Ballachulish aureole are presented. Carbonates are not widespread in the aureole, so the record of progressive metamorphism is incomplete. The outermost thermometamorphic reaction observed in the aureole leads to the appearance of talc + calcite in siliceous dolomites and impure limestones. In the inner aureole from the point where both forsterite and diopside are formed, the outcrop is continuous up to the formation of periclase.
L. Masch, S. Heuss-Aβbichler
11. Microtextures and Reaction Mechanisms of Carbonate Rocks: A Comparison Between the Thermoaureoles of Ballachulish and Monzoni (N. Italy)
Abstract
The kinetics of metamorphic reactions have become an important aspect of recent investigations. Attempts to determine the step which controls reaction progress are based primarily on experimental results and theoretical calculations (Fisher 1978; Walther and Wood 1984; Rubie and Thompson 1985; Lasaga 1986; Ridley and Thompson 1986). Field-related studies are mainly concerned with the formation of reaction bands (Vidale 1969; Fisher 1970; Joesten 1974, 1977; Sanford 1980; Walther 1983) and are based on detailed textural investigations. The latter treatment is also the basis of our study, which focuses on endothermic decarbonation reactions in the thermoaureoles of the intrusions of Ballachulish and Monzoni. A detailed petrographic and petrological examination was carried out; the results correlated with the temperature-time history in the thermoaureoles, which are characterized by varying heating rates dependent on the distance from the contact. The comparison of the microtextures in these two aureoles, which formed under different pressure conditions, permits the development of a more general theory of the evolution of microtextures during heating. The aim of this chapter is to work out the systematics of the evolution of the microtextures, to determine possible reaction mechanisms and to discuss the effect of changing boundary conditions (\( T, {X_{C{O_2}}} \) and volume of fluid phase) on their stabilization.
S. Heuss-Aβbichler, L. Masch
12. Quartz Grain Coarsening by Collective Crystallization in Contact Quartzites
Abstract
Clastic minerals of the Appin Quartzite are: ca. 85 vol % quartz, ca. 15% alkali feldspars, heavy minerals (zircone, rutile — partly formed from titanomagnetite during diagenesis, and apatite and tourmaline as very rare exceptions.
G. Buntebarth, G. Voll
13. Disordering, Re-Ordering and Unmixing in Alkali Feldspars from Contact-Metamorphosed Quartzites
Abstract
For kinetic reasons it is difficult to study the sanidine ⇄ microcline transition in the laboratory. A contact aureole, however, in which K-feldspars have passed the transition at rising and falling temperatures provides the opportunity to examine the disordering and re-ordering processes in some detail.
H. Kroll, C. Krause, G. Voll
14. A Search for Variations in the Structural States of Cordierite in Contact-Metamorphosed Pelites
Abstract
The mineral cordierite is an important rock constituent of pelites that has developed throughout the Ballachulish aureole as a consequence of contact metamorphism. Cordierite is a framework silicate with distinct similarities to ring silicates, whereby rings of six (Al,Si)-tetrahedra are linked by additional (Al,Si)-tetrahedra to form a three-dimensional framework. The rings are stacked in the crystallographic c-direction to form the large open channels that are permeable to rock fluids and cationic species of various compositions and types, leading to the unusual crystal chemical properties and thermodynamic behaviour observed for this mineral. The general structural formula has been summarized by Schreyer (1986) as follows:
$$ \eqalign{ & (\text{Na,K})_{0 - 1} ^{[\text{CHANNEL}]} \;(Mg,Fe^{2 + },\text{Mn}^{2 + },\text{Li})_2 ^{[6]} \cr & [(Si,Al,\text{Be},\text{Fe}^{3 + } )_9 ^{[4]} \text{O}_{18} ]\; \bullet \;(H_2 O,CO_2,\text{Ar}...)^{[\text{CHANNEL}]}, \cr} $$
where the most important site occupants found in nature are italicized.
W. V. Maresch, P. Blümel, W. Schreyer
15. Detrital Quartz and K-Feldspar in Quartzites as Indicators of Oxygen Isotope Exchange Kinetics
Abstract
Oxygen isotope fractionation between coexisting minerals may indicate equilibrium or disequilibrium, provided the temperature of formation is known. Depending on the time of blocking of specific 18O/16O ratios, the fractionations contain information on:
1.
Pre-peak-metamorphic conditions as assumed by Wenner and Taylor (1973) for serpentine-magnetite fractionations or by Hoernes and Hoffer (1979) for metamorphic parageneses in a more general sense. In this case oxygen isotope temperatures represent formation temperatures.
 
2.
Peak-metamorphic conditions; equilibrium is thought to be reached by exchange reactions via a fluid phase, by recrystallization (Hoernes and Friedrichsen 1978), or by mineral reactions.
 
3.
Post-peak-metamorphic conditions; based on different rates of oxygen diffusion in different minerals, it is thought that 18O/16O ratios are fixed at different temperatures during cooling, as demonstrated by Deines (1977) for specific minerals and recently discussed by Giletti (1986). The postmagmatic exchange reactions discussed in Hoernes et al. (Chap. 17, this Vol.) belong in this category. For further discussion see Hoefs (1987), O’Neil (1986), Valley (1986).
 
S. Hoernes, G. Voll

Interactions Between the Intrusion and the Contact Aureole

Frontmatter
16. P-T-a(H2O) Conditions in the Thermal Aureole
Abstract
In this chapter estimates are made of the pressure of emplacement of the Ballachulish Igneous Complex and the range of maximum temperatures in the surrounding thermal aureole. Using these P-T estimates, quantitative estimates of a(H2O) are made for pelites at different grades in the aureole. Activity of H2O is shown to vary between pelites above and below the onset of partial melting, and between graphitic and non-graphitic pelites at the same grade.
D. R. M. Pattison
17. Stable Isotope Geochemistry on the Intrusive Complex and Its Metamorphic Aureole
Abstract
Variations in stable isotope ratios can be particularly helpful in studying the origins of igneous rocks, as well as the fluid interactions that may accompany magma generation or which may occur during and after magma emplacement and solidification (see e.g., the recent review in Valley et al. 1986). In certain instances, and to certain extents, granitic magmas may inherit and preserve the isotopic composition of their source region (O’Neil and Chappel 1977; O’Neil et al. 1977; Chivas et al. 1982; Vidal et al. 1984; Hill et al. 1986). More commonly, mafic partial melts may interact with isotopically evolved crust during magma ascent through AFC-type processes which produce correlated stable-radiogenic isotope covariations within genetically related plutonic suites (Michard-Vitrac et al. 1980; Halliday et al. 1980; Clayburn et al. 1983; Fleck and Criss 1985). Finally, interaction with externally derived fluids at either magmatic or subsolidus stages can be an important process (Friedman et al. 1964; Forester and Taylor 1976,1977; Hildreth et al. 1984; Fourcade and Javoy 1985; Wickham and Taylor 1987; Bickle et al. 1988).
S. Hoernes, S. MacLeod-Kinsel, R. S. Harmon, D. Pattison, D. F. Strong
18. Thermal Models of Cooling
Abstract
The Ballachulish intrusion consists of concentric rings of quartz diorite, monzodiorite and granite in the centre. This suite of rocks intruded Lower Dalradian metasediments, consisting mainly of pelite with minor quartzite. Petrological investigations (Pattison, Chap. 16; Troll and Weiss, Chap. 3, this Vol.) estimate an emplacement depth of the intrusion of 10 km, and a pre-intrusion temperature of the metasediments as approximately 250 but not more than 300°C (Pattison and Voll, Chap. 2, this Vol.).
G. Buntebarth

Concluding Discussion

Frontmatter
19. Evidence of Fluid Phase Behaviour and Controls in the Intrusive Complex and Its Aureole
Abstract
This chapter brings together evidence pertaining to the presence, composition, influence and mobility of fluids rich in volatile species (principally H2O and CO2) in the development of the Ballachulish intrusive complex and its aureole. We examine fluid-mineral-rock interactions over the complete range of scales from that of the small-scale systems represented by individual rocks, to that of the large-scale system represented by the combined intrusive complex and its aureole. This will allow comparison with models of fluid behaviour identified in other low- to high-grade metamorphic situations (see reviews in Walther and Wood 1986; and Valley 1986), such as the hydrothermal circulation system of the Hebridean intrusive complexes (Taylor and Forester 1971; Forester and Taylor 1977), and the high fluid-pressure model of regional metamorphism in orogenic belts (Etheridge et al. 1983, 1984).
B. Harte, D. R. M. Pattison, S. Heuss-Aβbichler, S. Hoernes, L. Masch, S. Weiss
20. Intracrystalline Processes
Abstract
The thermal history of minerals may be recorded by examining intracrystalline processes, notably, ordering and exsolution. We will deal in this paper with both these processes, using K-feldspar, cordierite, Mg-calcite and pyroxenes as examples. The discussion is based on the contributions by Kroll et al. (Chap. 13, this Vol.), Maresch et al. (Chap. 14, this Vol.), Masch and Heuss-Aβbichler (Chap. 10, this Vol.) and Feuer et al. (Chap. 6, this Vol.). H. Feuer, Frankfurt, provided additional personal communication on pyroxenes.
H. Kroll
21. Summary and Outlook
Summary
The multidisciplinary study of the Ballachulish Igneous Complex and thermal aureole represents the most comprehensive investigation of contact metamorphism yet published. The aim of this study was to investigate equilibrium and kinetic aspects of mineral- and rock forming processes in a well-constrained natural setting. The Ballachulish Igneous Complex and its aureole were chosen because of the simple shape of the intrusion and the lack of any later episodes of metamorphism, deformation or retrogression that postdates emplacement and cooling of the complex. A great variety of metasedimentary rocks run into the thermal aureole: feldspathic quartzites, psammopelites with and without graphite and pyrite, impure limestones and dolomites. All rock types experienced regional upper greenschist-lower amphibolite metamorphism and acquired fine-grained equilibrium mineral assemblages prior to emplacement of the complex. Regional structures are simple and uniform. The psammopelites show a penetrative slaty cleavage and heat was transferred either parallel or normal to it in different parts of the contact; thus, the effects of different heat conductivities and anisotropy effects could be assessed.
G. Voll
Backmatter
Metadaten
Titel
Equilibrium and Kinetics in Contact Metamorphism
herausgegeben von
Professor Dr. Gerhard Voll
Dr. Jutta Töpel
Professor Dr. David R. M. Pattison
Professor Dr. Friedrich Seifert
Copyright-Jahr
1991
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-642-76145-4
Print ISBN
978-3-642-76147-8
DOI
https://doi.org/10.1007/978-3-642-76145-4