Contrib Mineral Petrol (2002) 142: 679–699 DOI 10.1007/s00410-001-0316-7
John M. Ferry Æ Boswell A. Wing Sarah C. Penniston-Dorland Æ Douglas Rumble III
The direction of fluid flow during contact metamorphism of siliceous carbonate rocks: new data for the Monzoni and Predazzo aureoles, northern Italy, and a global review Received: 8 January 2001 / Accepted: 28 August 2001 / Published online: 1 November 2001 ! Springer-Verlag 2001
Abstract Periclase formed in siliceous dolomitic marbles during contact metamorphism in the Monzoni and Predazzo aureoles, the Dolomites, northern Italy, by infiltration of the carbonate rocks by chemically reactive, H2O-rich fluids at 500 bar and 565–710 "C. The spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time-integrated flux !5,000 and !300 mol fluid/cm2 rock in the Monzoni and Predazzo aureoles, respectively. The new results for Monzoni and Predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction, amount, and controls on the geometry of reactive fluid flow during contact metamorphism of siliceous carbonate rocks. Flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton. Fluid flow in two of the other three was primarily horizontal, directed from the pluton into the aureole. The direction of flow in the remaining aureole is uncertain. Earlier suggestions that fluid flow is often horizontal, directed toward the pluton, are likely explained by an erroneous assumption that widespread coexisting mineral reactants and prod-
J.M. Ferry (&) Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA E-mail:
[email protected] Tel.: +1-410-5168121 Fax: +1-410-5167933 B.A. Wing Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA S.C. Penniston-Dorland Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA D. Rumble III Geophysical Laboratory, 5251 Broad Branch Road NW, Washington, DC 20015-1305, USA Editorial responsibility: T.L. Grove
ucts represent arrested prograde decarbonation reactions. With the exception of three samples from one aureole, time-integrated fluid flux was in the range 102–104 mol/cm2. Both the amount and direction of fluid flow are consistent with hydrodynamic models of contact metamorphism. The orientation of bedding and lithologic contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal. Other pre-metamorphic structures, including dikes, faults, fold hinges, and fracture zones, served to channel fluid flow as well.
Introduction The important role that chemically reactive fluid flow plays in the mineralogical, isotopic, and chemical evolution of rocks during contact metamorphism has been firmly established by numerous studies beginning more than 20 years ago (e.g., Forster and Taylor 1977; Nabelek et al. 1984; Labotka et al. 1988; Jamtveit et al. 1992a, 1992b; Roselle et al. 1999; Cook and Bowman 2000). The direction of fluid flow, however, remains the subject of debate (Ferry and Dipple 1992; Nabelek and Labotka 1993; Hanson 1995a; Ferry 1995a). On the basis of petrologic and stable isotope data and hydrodynamic modeling, predicted directions of fluid flow include horizontal directed outward from the pluton into the contact aureole, horizontal directed from the aureole toward the pluton, and vertical upward. Application of transport theory to mineralogical, isotopic, and trace element data with the specific goal of determining the direction and amount of reactive fluid flow in contact aureoles has become routine only in the last decade. The controversy, in part, therefore, arose because until recently there was an insufficient number of case studies on which sound generalizations could be based. New petrologic and oxygen isotopic data are first presented that constrain the magnitude and geometry of fluid flow in the Monzoni and Predazzo aureoles,
680
northern Italy. A review of results for these and 13 other aureoles worldwide then leads to some generalizations about both the direction and amount of reactive fluid flow during contact metamorphism of siliceous carbonate rocks and about the essential factors that control the geometry of flow.
Geologic setting The Monzoni and Predazzo aureoles in the Dolomites of northern Italy are located 15 km apart and are developed in Permian–Triassic platform carbonate rocks. The geologic history of the region is summarized by Doglioni (1987) and Bosellini (1996), and geologic maps and cross sections for the aureoles have been presented by Del Monte et al. (1967), Bocchi and Morandi (1971), Castellarin et al. (1982), and Masch and Huckenholz (1993). This study focused on three formations that, from oldest to youngest, are the Permian Bellerophon Formation and the Triassic Werfen and Contrin Formations (Figs. 1, 2, 3, 4). The Bellerophon Formation is primarily composed of siliceous dolomitic limestone and limestone with minor evaporite horizons; the Werfen Formation is composed of siliceous dolomitic limestone and marl; and the Contrin Formation is primarily a siliceous dolomite with minor limestone. Contact metamorphism converted the sedimentary rocks to marble and hornfels. The Contrin Formation is overlain by the Buchenstein and Marmolada Formations, which are largely volcaniclastic rocks and limestone, respectively. The Buchenstein Formation is either very thin or absent in the Predazzo aureole. The Bellerophon Formation is underlain in the Monzoni aureole by Permian volcanic and terrestrial clastic rocks. For clarity, rocks older than the Bellerophon Formation or younger than the Contrin Formation are not differentiated in Figs. 1 and 2. The sedimentary rocks generally strike NE and dip 30–50"NW except
Fig. 1 Geologic sketch map of the Monzoni contact aureole (after Del Monte et al. 1967, Masch and Huckenholz 1993, this study). Numbers indicate sample locations in text, tables, and other figures
near their contact with the Monzoni intrusion, where they may be deformed by folds with steeply plunging axes. The Monzoni and Predazzo intrusions are composed primarily of diorite, monzonite, monzodiorite, and monzogabbro with subordinate gabbro and ultramafic rocks. The 232–238 Ma age of plutonism and metamorphism at Predazzo is well-constrained by U–Pb and 40Ar/39Ar dates of igneous minerals (Laurenzi and Visona 1996; Mundil et al. 1996; Visona 1997). Radiometric ages of 214–245 Ma for the Monzoni intrusive complex are similar but less precise (Borsi et al. 1968; Webb 1982). The effects of Triassic contact metamorphism were not overprinted by Alpine regional metamorphism.
Methods of investigation Fifty-seven samples were collected at 29 locations in the Monzoni aureole, including 22 samples from the Bellerophon Formation, 14 from the Werfen Formation, 20 from the Contrin Formation and 1 from the Marmolada Formation (Figs. 1, 2, 3). Samples from the eastern and western portions of the Monzoni aureole are distinguished by ‘‘E’’ and ‘‘W’’ prefixes, respectively. Twenty-one samples collected from the Contrin Formation at 12 locations in the Predazzo aureole are denoted by a ‘‘P’’ prefix (Fig. 4). Sample locations and geological contacts in Figs. 2, 3, 4 were mapped using a laser rangefinder equipped with a digital fluxgate compass. Uncertainties in distances between locations in Fig. 2 increase from several decimeter for samples no more than 100 m apart to ±12 m for samples 1 km apart; uncertainties in distances between locations in Figs. 3 and 4 are several centimeters. Mineral assemblages were identified by optical and scanning electron microscopy of thin sections. Minerals that showed detectable deviation from ideal compositions were quantitatively analyzed with the JEOL JXA-8600 electron microprobe at Johns Hopkins University using wavelength dispersive spectrometry (WDS), natural silicate and carbonate standards, and a ZAF correction scheme (Armstrong 1988). Modes of 21 samples of siliceous
681
Fig. 3 Geologic sketch map of the western portion of the Monzoni aureole. Numbers with ‘‘W’’ prefix denote sample locations in text, tables, and other figures. Letters trailing sample location numbers are explained in the caption to Fig. 2 Fig. 2 Geologic sketch map of the eastern portion of the Monzoni contact aureole. Numbers with ‘‘E’’ prefix denote sample locations in text, tables, and other figures. Letters trailing sample location numbers distinguish multiple samples from the same location or traverse. Samples E10B–E10E are located along the line connecting locations E10A and E10F. The Per isograd is located beneath alluvium between locations E15 and E18. Estimates or upper bounds on peak T (in "C) at locations E1, E21, and E22 calculated from mineral–fluid equilibria. Elevation difference between locations E18 and E19 sets a lower limit on the amount of fluid flow during metamorphism at the Per isograd (see text) carbonate rock and marble from the Bellerophon and Contrin Formations were measured by counting ‡2,000 points in thin section with back-scattered electron imaging. Any uncertainty in the identification of a particular point was resolved by obtaining an EDS X-ray spectrum. Modes for 14 samples are listed in Table 1. Compositions of analyzed minerals in the 14 specimens, along with compositions of selected minerals in eight additional samples that were used for geothermometry, appear in Tables 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. Carbonate from 54 samples from the Bellerophon, Werfen, Contrin, and Marmolada Formations was analyzed for oxygen and carbon isotope composition following procedures described by Rumble et al. (1991). Approximately 2–3 mg of finely powdered calcite or dolomite was obtained with a 2-mm diamond-tipped drill from a polished rock slab stained to distinguish calcite from dolomite. Carbonate was dissolved in phosphoric acid (McCrea 1950) in evacuated reaction vessels at 100 "C. Evolved CO2 was analyzed with the Finnigan MAT 252 mass spectrometer at the Geophysical Laboratory. The acid fractionation factor for calcite analyses was computed from the expression in Swart et al. (1991) using their calibration for sealed reaction vessels. The acid fractionation factor for dolomite analyses was computed using the value at 25 "C from Sharma and Clayton (1965) and the temperature-dependence of Rosenbaum and Sheppard (1986). All results were normalized to the composition of calcite standard NBS-19 (d18O=28.65&, VSMOW;
Fig. 4 Geologic sketch map of the Canzoccoli quarry in the Predazzo aureole. Area is located at 46"18¢30¢¢ north latitude and 11"35¢20¢¢ east longitude. Numbers with ‘‘P’’ prefix denote sample locations in text, tables and, other figures. Letters trailing sample location numbers are explained in the caption to Fig. 2. Elevation difference between locations P9 and P11 sets a lower limit on the amount of fluid flow during metamorphism at the Per isograd (see text) d13C=1.95&, VPDB, Coplen 1988, 1996). Analyses of NBS-19 and other standards indicate that analytical precision for both oxygen and carbon isotopes is approximately ±0.1&.
682 All calculations of mineral-fluid equilibria used Berman’s (1988) thermodynamic data base updated August 1990. Fluids were considered CO2–H2O solutions that obey the Kerrick and Jacobs (1981) equation of state. Activities of components in mineral solid solutions were computed using ideal ionic mixing models assuming short range cation disorder (except in diopside and fassaite); expressions used for biotite and amphibole are those listed in Holland and Powell (1990). Activities of the CaMgSi2O6 and CaAl2SiO6 components in calcic pyroxene were computed assuming short range order (Wood 1976). Molar volumes of minerals were taken from Berman (1988).
Formation of periclase and the periclase isograd The focus of study in the Monzoni and Predazzo aureoles was formation of periclase in dolomitic marbles from the Bellerophon and Contrin Formations because the development of periclase can effectively constrain the direction
and amount of reactive fluid flow during contact metamorphism (Ferry 1996; Ferry and Rumble 1997; Cook and Bowman 2000). Periclase typically forms in contact aureoles by a simple infiltration-driven reaction, CaMgðCO3 Þ2 dolomite
¼
MgO þ periclase
CaCO3 calcite
þ
CO2 fluid
ð1Þ
The distribution of periclase-bearing rocks then directly images the flow path of reactive fluid flow in an aureole. Because the minerals that participate in the reaction have well-known thermodynamic properties, quantitative interpretation of the effects of reaction (1) with thermodynamics and transport theory is straightforward. Field, petrologic, and isotopic data can all be brought to bear on the question of the direction and amount of metamorphic fluid flow.
Table 1 Modes of selected samples from the Monzoni and Predazzo aureolesa Sampleb Aureole Formation Rock type
E8A Monzoni Bellerophon D-C marblec
E10A Monzoni Contrin Per marble
E10F Monzoni Contrin Per marble
E12A Monzoni Contrin Per marble
E16A Monzoni Contrin dolomite
E19B Monzoni Contrin Per marble
W2D Monzoni Bellerophon Per marble
Dolomite Calcite Brucite Forsterite Clinohumite Spinel Geikielite Baddeleyite Apatite Phlogopite Pyrrhotite Serpentine Chlorite Quartz Muscovite Trace otherd
34.62 63.47 0 0 0 tr 0 tr tr 0.52 0 0 0.88 0.40 0.12
tr 68.43 31.13 tr 0 tr 0 0 tr 0 0 0.44 0 0 0 e,f
4.10 62.28 33.02 tr tr tr 0 0 tr 0 0 0.59 0 0 0
0.60 67.27 32.13 0 0 tr 0 0 tr 0 0 tr 0 0 0 g,h
87.53 12.37 0 0 0 0 0 0 0.10 0 0 0 0 0 0 i
0.20 64.85 34.71 0 0 tr 0 0 tr 0 0 0.25 0 0 0 j
1.11 66.11 21.28 1.27 1.95 0.24 tr tr tr 0 0.08 7.96 0 0 0 j,k
Sampleb Aureole Formation Rock type
W2J Monzoni Bellerophon Per marble
W8B Monzoni Bellerophon Per marble
P1C Predazzo Contrin Dol marble
P6B Predazzo Contrin Per marble
P9D Predazzo Contrin Per marble
P10A Predazzo Contrin Per marble
P11A Predazzo Contrin Per marble
Dolomite Calcite Brucite Forsterite Clinohumite Spinel Geikielite Baddeleyite Apatite Phlogopite Pyrrhotite Serpentine Chlorite Quartz Muscovite Trace otherd
1.54 60.84 33.25 0.05 2.03 0.20 0 tr tr 0 tr 2.08 0 0 0 g,l
7.90 66.42 22.77 0.10 1.60 0.29 0 tr 0.05 0 0.10 0.78 0 0 0
93.01 3.03 0 0.20 1.71 0.59 tr tr 0 0 0.10 1.37 0 0 0
7.39 58.65 33.02 0 0 tr 0 0 tr 0 0 0.94 0 0 0 m
0.99 60.16 35.98 0.05 0 0.10 0.05 0 0 0 tr 2.68 0 0 0 f
tr 69.35 29.07 tr tr 0.05 0 0 tr 0 0 1.53 0 0 0 f
5.93 63.39 30.43 0 0 tr 0 0 tr 0 0 0.25 0 0 0 h
a
c
b
d
Volume percent, tr100i
7, 8 2 9, 10, 11
Utah California California California
SD QCS SDL, SL SD
32–42 Ma 89 Ma 91 Ma 173 Ma
625" 560" 600" 680"
1,500 1,500 1500 1500
H NV NV 50"-V
Ex’ve None None Some
3,000–4,000 1,700–3,700 250–1,600 >!400j
12, 13, 14 15 16, 17 18, 19
Utah
165 Ma
600"
1,500–2,000
NH-A
Ex’ve
Canada
108–109 Ma
650"
2,200
!35"
Some
Scotland
SDL, SL
!412 Ma
750"
3,000
NV
None
NV–U + H–O V–U
!2,000 or !20,000 !300–400
20, 21, 22, 23
Horsethief Creek Ballachulish
Marl, SDL SD
H–O NV–U NV–U NV–U + H–O H ± VU?
Bergell
Italy
OCR
30–32 Ma
680"
3,500
NV
Some
V–U
a
(mol/cm2)
100–400 (SDL) > 1,000 (SL) 1,000–70,000
24 25, 26
27, 28, 29
Country or state if within USA SD Siliceous dolomite; SDL siliceous dolomitic limestone; SL siliceous limestone; QCS quartz–calcite sandstone; OCR ophicarbonate rock c Overall dip of lithologic layering, NV nearly vertical; NH nearly horizontal; H horizontal; NH-A nearly horizontal away from pluton d Oxygen isotope alteration: Ex’ve extensive e V–U Vertical, upward; H–O horizontal, outward from pluton; NV–U nearly vertical, upward; H horizontal f References: 1 Holness (1992); 2 Rumble and Ferry (1997); 3 Masch and Huckenholz (1993); 4 this study; 5 Jamtveit et al. (1992a); 6 Jamveit et al. (1992b); 7 Bowman and Essene (1982); 8 Bowman et al. (1985); 9 Heinrich (1993); 10 Heinrich and Gottschalk (1994); 11 Heinrich et al. (1995); 12 Bowman et al. (1994); 13 Cook et al. (1997); 14 Cook and Bowman (2000); 15 Ferry et al. (2001); 16 Hanson et al. (1993); 17 Ferry et al. (1998); 18 Roselle (1997); 19
Roselle et al. (1999); 20 Nabelek et al. (1984); 21 Labotka et al. (1988); 22 Ferry and Dipple (1992); 23 Nabelek and Labotka (1993); 24 Dipple and Niermann (1997); 25 Masch and HeussAßbichler (1991); 26 Ferry (1996); 27 Trommsdorff and Evans (1977); 28 Ferry (1995b); 29 Pozzorini and Fru¨h-Green (1996) g Based on occurrence of Per marble with unaltered O-isotope composition 1 cm from the marble-pluton contact h Based on the absence of prograde diopside and talc (Ferry 1994, his Fig. 7) i Based on estimated location of an O-isotope alteration front in siliceous marbles 17 m from the marble-pluton contact. Lower bound from inference that siliceous marbles were less permeable than chert interbeds j Based on estimated whole-system volumetric fluid–rock ratio =0.18 and reactive fluid flow over a distance on the order of 1 km. Lower bound from inference that fluid flow was heterogeneous and focused within tube-shaped channels
Monzoni). On the other hand, horizontal flow toward the Notch Peak pluton would be unlike inferred flow geometries in all the other 14 aureoles in Table 17 and may be difficult to understand in terms of hydrodynamics (Hanson 1995b). If there was no significant infiltration, mass transport by diffusion would have had to occur over a distance (400–500 m) an order of magnitude larger than documented in any other metamorphic terrain. Resolution of the debate over the mechanism of mass transport and flow direction (if flow occurred) in the Notch Peak aureole calls for additional field, petrologic, isotopic, and trace-element geochemical studies. Because the direction of fluid flow in the Notch Peak aureole is uncertain, so is the source and amount of fluid and the mechanism of decarbonation reaction. Therefore, the Notch Peak aureole was not considered further in the discussions of contact metamorphic fluid flow that follow. Earlier reviews of contact metamorphism argued that fluid flow through siliceous carbonate rocks in many
cases was directed from the aureole toward the pluton (Ferry 1991, 1994). The conclusion was based on reports of the widespread distributions of coexisting reactants and products of decarbonation reactions in contact aureoles (e.g., Rice 1977a, 1977b; Suzuki 1977; Masch and Heuss-Aßbichler 1991; Holness 1992), and the assumption that the distributions represent arrested prograde decarbonation reactions. More recent studies, however, either have failed to observe the widespread occurrence of coexisting reactants or products (e.g., Cook and Bowman 2000), or have interpreted them as arrested retrograde carbonation reactions rather than as the result of prograde metamorphism (e.g., Ferry 1996; Ferry and Rumble 1997; Roselle 1997; Ferry et al. 1998). Coexisting reactants and products of a retrograde mineral-fluid reaction can be simply explained by continued fluid flow as aureoles cool in the same direction as during prograde metamorphism, i.e., in the direction of decreasing T, vertical or horizontal (Ferry 2000). The
b
696
directions of fluid flow listed in Table 17 all refer to portions of the inner aureole close to the pluton. Alternatively, at least some widespread occurrences of coexisting reactants and products of low-grade decarbonation reactions, such as those in aureoles associated with the Boulder batholith (Rice 1977a, 1977b), may, in fact, represent arrested prograde reactions. The occurrences then might define a flow system during prograde metamorphism in the outer portion of a contact aureole with geometry different from that in the inner part of the aureole. It will be a challenge to determine if the direction of fluid flow differs between the inner and outer portions of contact aureoles because the outer portions almost never show any isotopic or trace element effects of reactive fluid flow. There are many examples of hydrothermal systems that involve flow of meteoric water into plutons through their contact aureoles (e.g., review by Criss and Taylor 1986). These systems, which obviously involve fluid flow with a significant horizontal component directed toward the pluton, appear to be fundamentally different from the carbonate-hosted metamorphic flow systems summarized in Table 17. The difference may be explained by the mechanical properties of their host rocks. Meteoric-hydrothermal systems commonly develop in highly fractured competent rocks such as volcanics, and the fracture network assures hydrostatic P. At hydrostatic P, surface waters may be drawn downward and into the thermal anomaly generated by a cooling pluton (Norton and Knight 1977). Because of their greater ductility, fluid flow systems in carbonate rocks during metamorphism are probably at or close to lithostatic P (Dipple 2001). Flow in hydrothermal systems at or near lithostatic P does not have a significant downward component (Hanson 1992). Several aureoles listed in Table 17 show O-isotope evidence for late-stage infiltration by meteoric water (e.g., Elkhorn, Oslo Rift). As contact aureoles in carbonate rocks cool, they evidently may pass through the brittle– ductile transition, fracture, assume hydrostatic P, and become open to flow of surface waters toward the pluton.
during contact metamorphism and channel fluid flow along them, including dikes (e.g., Beinn an Dubhaich, Mt. Morrison), faults (Olso Rift, Mt. Morrison), fold hinges (Mt. Morrison), and fracture zones (Bergell). The control of pre-metamorphic structures on fluid flow is of a passive nature in contrast to the active role that deformation can play in focusing metamorphic fluid flow as envisioned, for example, by Ord and Oliver (1997) and Holness (1997).
Structural control of fluid flow
The time-integrated fluxes of prograde contact metamorphism
The most fundamental division in fluid flow direction among the aureoles listed in Table 17 is between those in which there was a large vertical component to fluid flow and those in which the flow was horizontal or largely so. The division is explained by the essential role that premetamorphic structures play in controlling the geometry of reactive fluid flow during contact metamorphism. Strong channeling of reactive fluid flow by bedding and lithologic contacts is almost universally reported in the studies summarized in Table 17. Correspondingly, the aureoles that record horizontal flow are the only aureoles in which lithologic layering is horizontal or nearly so. In all others, layering is inclined 30" or more from horizontal. Numerous additional structures evidently are more permeable than immediately surrounding rocks
Reaction mechanisms and sources of reactive fluid Decarbonation reactions in 13 of the aureoles listed in Table 17 were driven by infiltration of the aureole by a fluid that was out of equilibrium with rock at the inlet to the metamorphic flow system. The Bergell aureole is the single definite example of prograde mineral-fluid reaction driven by fluid flow along a T gradient with rocks and fluid in or close to equilibrium at every point in the flow system. The difference in reaction mechanism between the Bergell aureole and the other 13 is explained by the source of fluid. Reactive fluids in all but the Bergell aureole are believed to have had a magmatic source. Magmatic fluids are far from chemical equilibrium with siliceous carbonate rocks at any condition of elevated T. Fluids that infiltrated ophicarbonate rocks of the Bergell aureole, however, were internally generated below the present level of exposure by dehydration– decarbonation reactions involving Cal, Srp, Di, Fo, and Tr. As fluids rose vertically in the fracture zone that hosts the ophicarbonate rocks, Di + Srp reacted to Tr + Cal in response to decreasing T along the flow path. Therefore, the prograde reaction involved a carbonation reaction rather than the more usual decarbonation reaction. In this regard, the mechanism for prograde formation of Tr in ophicarbonate rocks of the Bergell aureole closely resembles the mechanism for formation of Tr, Cal, Qtz, Brc, Srp, and Dol in siliceous dolomites and limestones during retrograde metamorphism in many of the other aureoles (Ferry 2000).
Estimates of time-integrated flux listed in Table 17 are taken from the literature, except where indicated in the footnotes. If values were reported in volume units, they were converted to mole units using inferred molar volumes of the fluid. Values of q are almost all in the range 102–104 mol fluid/cm2 rock. Only three samples from the Bergell aureole record q>104 mol/cm2. Hydrodynamic models of contact metamorphic fluid flow independently predict time-integrated fluid flux in the range 103– 104 mol/cm2 (e.g., Hanson 1992; Hanson et al. 1993; Cook et al. 1997). The amount of fluid flow computed from the mineralogical and O-isotope effects of reactive fluid flow in contact aureoles, therefore, appears to be fully consistent with that predicted by the physics of
697
fluid flow in porous media. The hydrodynamic models assume uniform rock properties at the scale of 50– 1,000 m. Because of the heterogeneity in permeability of metamorphic rocks at much smaller scales and consequent focusing of fluid flow, it is no surprise that individual samples of metamorphic rocks can record q>104 or !5,000 mol/cm2, mineral reaction fronts that produce Per and Fo in siliceous dolomites and Wo in siliceous limestones will outpace the O-isotope alteration front (Ferry 1994, his Figs. 7 and 8). In aureoles where reactive fluid flow was largely horizontal out of the pluton into the aureole, rocks that contain Fo ± Per or Wo and that exhibit O-isotope alteration should, therefore, occur closest to the pluton, rocks that contain Fo ± Per or Wo, but that exhibit no isotope alteration, should occur further away, and rocks that lack Fo, Per, Wo, and isotope alteration should lie further yet from the pluton. The predicted pattern is observed exactly in the Alta and Bufa del Diente aureoles. If reactive fluid flow was largely vertical, individual aureoles or portions of aureoles should either (1) contain Fo ± Per or Wo and exhibit O-isotope alteration (if mineral reaction and isotope alteration fronts passed through the present level of exposure and are now eroded away), (2) contain Fo ± Per or Wo but exhibit no O-isotope alteration (if the present level of exposure lies between a buried isotope front and mineral reaction fronts that passed through and are eroded away), or (3) contain neither Per nor Wo and exhibit no O-isotope alteration in samples close to the contact (if the Per- or Wo-forming mineral reaction and isotope alteration fronts are still buried beneath the present level of exposure). All aureoles that contain evidence for reactive fluid flow with a significant vertical component conform to the predicted systematics. Silver Star, Oslo Rift, and portions of the Beinn an Dubhaich, Monzoni, Ubehebe Peak, and Horsethief Creek exhibit type (1) relations; Predazzo, Elkhorn, Mt. Morrison, Ritter Range, Ballachulish, and portions of Monzoni, Ubehebe Peak, and Horsethief Creek exhibit type (2) systematics; and portions of Beinn an Dubhaich, Horsethief Creek, and Ubehebe Peak exhibit type (3) systematics. No aureole shows evidence for significant O-isotope alteration of siliceous carbonate rocks in the absence of mineral reactions that produced Per, Fo, or Wo. The difference in velocity between the mineral reaction fronts and the O-isotope alteration front explains why many of the aureoles listed in Table 17 contain abundant mineralogical evidence for infiltration of chemically reactive
fluids during metamorphism but limited or no O-isotope evidence. As a corollary, the absence of O-isotope evidence for reactive fluid flow in a contact aureole should never be misinterpreted as the absence of reactive flow. Acknowledgments Research supported by the National Science Foundation, Division of Earth Sciences, grant EAR-9805346. We thank Martha Gerdes for assistance with fieldwork and Greg Dipple and an anonymous reviewer for their comments on the manuscript.
References Anovitz LM, Essene EJ (1987) Phase equilibria in the system CaCO3–MgCO3–FeCO3. J Petrol 28:389–414 Armstrong JT (1988) Quantitative analysis of silicate and oxide minerals: Comparison of Monte Carlo, ZAF and phi-rho-z procedures. In: Newbury DE (ed) Microbeam analysis – 1988. San Francisco Press, San Francisco, pp 239–246 Baumgartner LP, Ferry JM (1991) A model for coupled fluid-flow and mixed-volatile mineral reactions with applications to regional metamorphism. Contrib Mineral Petrol 106:273–285 Berman RG (1988) Internally-consistent thermodynamic data for minerals in the system Na2O–K2O–CaO–MgO–FeO–Fe2O3– Al2O3–SiO2–TiO2–H2O–CO2. J Petrol 29:445–522 Bocchi G, Morandi N (1971) Sulla distribuzione della brucite (stima quantitativa in DTA) nella ‘‘predazzite’’ di Canzoccoli (Predazzo, nord Italia). Mineral Petrogr Acta 17:135–148 Borsi S, Ferrara G, Paganelli L, Simboli G (1968) Isotopic age measurements of the M. Monzoni intrusive complex. Mineral Petrog Acta 14:171–183 Bosellini A (1996) Geologia della Dolomiti. Casa Editrice Athesia, Bolzano-Bozen Bowman JR, Essene EJ (1982) P–T–X(CO2) conditions of contact metamorphism in the Black Butte aureole, Elkhorn, Montana. Am J Sci 282:311–340 Bowman JR, O’Neil JR, Essene EJ (1985) Contact skarn formation at Elkhorn, Montana. II: origin and evolution of C–O–H skarn fluids. Am J Sci 285:621–660 Bowman JR, Willett SD, Cook SJ (1994) Oxygen isotopic transport and exchange during fluid flow: one-dimensional models and applications. Am J Sci 294:1–55 Castellarin A, Lucchini F, Rossi PL, Sartori R, Simboli G, Sommavilla E (1982) Note geologiche sulle intrusioni di Predazzo e dei M. Monzoni. Guida alla Geologia del Sudalpino Centro-orientale. Societa Geologica Italiana, Bologna, pp 211–220 Cook SJ, Bowman JR (2000) Mineralogical evidence for fluid-rock interaction accompanying prograde contact metamorphism of siliceous dolomites: Alta stock aureole, Utah, USA. J Petrol 41:739–757 Cook SJ, Bowman JR, Forster CB (1997) Contact metamorphism surrounding the Alta stock: finite element model simulation of heat- and 18O/16O mass-transport during prograde metamorphism. Am J Sci 297:1–55 Coplen TB (1988) Normalization of oxygen and hydrogen isotope data. Chem Geol 72:293–297 Coplen TB (1996) New guidelines for reporting stable hydrogen, carbon, and oxygen isotope-ratio data. Geochim Cosmochim Acta 60:3359–3360 Criss RE, Taylor HP Jr (1986) Meteoric-hydrothermal systems. Mineral Soc Am Rev Mineral 16:373–424 Del Monte M, Paganelli L, Simboli G (1967) The Monzoni intrusive rocks. A modal and chemical study. Mineral Petrogr Acta 13:75–118 Dipple GM (2001) The persistence of near lithostatic fluid pressure during infiltration metamorphism in the Horsethief Creek contact aureole, British Columbia. In Eleventh Annual V.M. Goldschmidt Conference, Abstract #3420. LPI Contribution no. 1088, Lunar and Planetary Institute, Houston, CD-ROM
698 Dipple GM, Ferry JM (1992) Fluid flow and stable isotopic alteration of rocks at elevated temperatures with applications to metamorphism. Geochim Cosmochim Acta 56:3539–3550 Dipple GM, Niermann MC (1997) Permeability structure of the contact metamorphic–hydrothermal system at Horsethief Creek, British Columbia, Canada. In: Hendry JP, Carey PF, Parnell J, Ruffell AH, Worden RH, (eds) GeoFluids II: contributions to the second international conference on fluid evolution, migration and interaction in sedimentary basins and orogenic belts. Queen’s University, Belfast, pp 244–246 Doglioni C (1987) Tectonics of the Dolomites (Southern Alps, northern Italy). J Struct Geol 9:181–193 Ferry JM (1991) Dehydration and decarbonation reactions as a record of fluid infiltration. Mineral Soc Am Rev Mineral 26:351–393 Ferry JM (1994) Role of fluid flow in the contact metamorphism of siliceous dolomitic limestones. Am Mineral 79:719–736 Ferry JM (1995a) Role of fluid flow in the contact metamorphism of siliceous dolomitic limestones – reply to Hanson. Am Mineral 80:1226–1228 Ferry JM (1995b) Fluid flow during contact metamorphism of ophicarbonate rocks in the Bergell aureole, Val Malenco, Italian Alps. J Petrol 36:1039–1053 Ferry JM (1996) Prograde and retrograde fluid flow during contact metamorphism of siliceous carbonate rocks from the Ballachulish aureole, Scotland. Contrib Mineral Petrol 124:235–254 Ferry JM (2000) Patterns of mineral occurrence in metamorphic rocks. Am Mineral 85:1573–1588 Ferry JM (2001) Calcite inclusions in forsterite. Am Mineral 86:773–779 Ferry JM, Dipple GM (1992) Models for coupled fluid flow, mineral reaction, and isotopic alteration during contact metamorphism: the Notch Peak aureole, Utah. Am Mineral 77:577–591 Ferry JM, Gerdes ML (1998) Chemically reactive fluid flow during metamorphism. Annu Rev Earth Planet Sci 26:255–287 Ferry JM, Rumble D (1997) Formation and destruction of periclase by fluid flow in two contact aureoles. Contrib Mineral Petrol 128:313–334 Ferry JM, Sorensen SS, Rumble D (1998) Structurally controlled fluid flow during contact metamorphism in the Ritter Range pendant, California, USA. Contrib Mineral Petrol 130:358–378 Ferry JM, Wing BA, Rumble D (2001) Formation of wollastonite by chemically reactive fluid flow during contact metamorphism, Mt. Morrison pendant, Sierra Nevada, California, USA. J Petrol 42: 1705–1728 Forester RW, Taylor HP Jr. (1977) 18O/16O, D/H, and 13C/12C studies of the Tertiary igneous complex of Skye, Scotland. Am J Sci 277:136–177 Hanson RB (1992) Effects of fluid production on fluid flow during regional and contact metamorphism. J Metamorph Geol 10:87– 97 Hanson RB (1995a) Role of fluid flow in the contact metamorphism of siliceous dolomitic limestones – discussion. Am Mineral 80:1222–1225 Hanson RB (1995b) The hydrodynamics of contact metamorphism. Geol Soc Am Bull 107:595–611 Hanson RB, Sorensen SS, Barton MD, Fiske RS (1993) Long-term evolution of fluid–rock interactions in magmatic arcs: evidence from the Ritter Range pendant, Sierra Nevada, California, and numerical modeling. J Petrol 34:23–62 Harris MT (1988) Margin and foreslope deposits of the Latemar carbonate buildup (Middle Triassic), the Dolomites, northern Italy. PhD Thesis, Johns Hopkins University, Baltimore, Maryland Heinrich W (1993) Fluid infiltration through metachert layers at the contact aureole of the Bufa del Diente intrusion, northeast Mexico: implications for wollastonite formation and fluid immiscibility. Am Mineral 78:804–818 Heinrich W, Gottschalk M (1994) Fluid flow patterns and infiltration isograds in melilite marbles from the Bufa del Diente
contact metamorphic aureole, north-east Mexico. J Metamorph Geol 12:345–359 Heinrich W, Hoffbauer R, Hubberton H-W (1995) Contrasting fluid flow patterns at the Bufa del Diente metamorphic aureole, north-east Mexico: evidence from stable isotopes. Contrib Mineral Petrol 119:362–376 Holland TJB, Powell R (1990) An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O–Na2O–CaO–MgO–MnO–FeO– Fe2O3–Al2O3–SiO2–TiO2–C–H2–O2. J Metamorph Geol 8: 89–124 Holness MB (1992) Metamorphism and fluid infiltration of the calc-silicate aureole of the Beinn an Dubhaich granite, Skye. J Petrol 33:1261–1293 Holness MB (1997) Fluid flow paths and mechanisms of fluid infiltration in carbonates during contact metamorphism: the Beinn an Dubhaich aureole, Skye. J Metamorph Geol 15: 59–70 Jamtveit B, Bucher-Nurminen K, Stijfhoorn DE (1992a) Contact metamorphism of layered shale–carbonate sequences in the Oslo rift: I. buffering, infiltration, and the mechanisms of mass transport. J Petrol 33:377–422 Jamtveit B, Grorud HF, Bucher-Nurminen K (1992b) Contact metamorphism of layered carbonate–shale sequences in the Oslo Rift. II: Migration of isotopic and reaction fronts around cooling plutons. Earth Planet Sci Lett 114:131–148 Kerrick DM, Jacobs GK (1981) A modified Redlich–Kwong equation for H2O, CO2, and H2O–CO2 mixtures at elevated pressures and temperatures. Am J Sci 281:735–767 Kretz R (1983) Symbols for rock-forming minerals. Am Mineral 68:277–279 Labotka TC, Nabelek PI, Papike JJ (1988) Fluid infiltration through the Big Horse Limestone Member in the Notch Peak contact-metamorphic aureole, Utah. Am Mineral 73: 1302-1324 Laurenzi MA, Visona D (1996) 40Ar/39Ar chronology of Predazzo magmatic complex (Southern Alps, Italy). Geologia delle Dolomiti, 78a Riunione Estiva. Societa Geologica Italiana, Bologna Masch L, Heuss-Aßbichler S (1991) Decarbonation reactions in siliceous dolomites and impure limestones. In: Voll G, To¨pel J, Pattison DRM, Seifert F (eds) Equilibrium and kinetics in contact metamorphism. The Ballachulish Igneous Complex and its aureole. Springer, Berlin Heidelberg New York, pp 211–227 Masch L, Huckenholz HG (1993) Der intusivkomplex von Monzoni und seine thermometamorphe aureole. Beih Eur J Mineral 5:81–135 McCrea JM (1950) On the isotopic chemistry of carbonates and a paleotemperature scale. J Chem Phys 18:849–857 Mundil R, Brack P, Laurenzi MA (1996) High resolution U–Pb single-zircon age determinations: new constraints on the timing of Middle Triassic magmatism in the Southern Alps. Geologia delle Dolomiti, 78a Riunione Estiva. Societa Geologica Italiana, Bologna Nabelek PI, Labotka TC (1993) Implications of geochemical fronts in the Notch Peak contact-metamorphic aureole, Utah, USA. Earth Planet Sci Lett 119:539–559 Nabelek PI, Labotka TC, O’Neil JR, Papike JJ (1984) Contrasting fluid/rock interaction between the Notch Peak granitic intrusion and argillites and limestones in western Utah: evidence from stable isotopes and phase assemblages. Contrib Mineral Petrol 86:25–34 Norton D, Knight J (1977) Transport phenomena in hydrothermal systems: cooling plutons. Am J Sci 277:937–98 Ord A, Oliver NHS (1997) Mechanical controls on fluid flow during regional metamorphism: numerical models. J Metamorph Geol 15:345–359 Pozzorini D, Fru¨h-Green GL (1996) Stable isotope systematics of the Ventina ophicarbonate zone, Bergell contact aureole. Schweiz Mineral Petrogr Mitt 76:549–564
699 Rice JM (1977a) Progressive metamorphism of impure dolomitic limestones in the Marysville aureole, Montana. Am J Sci 277: 1–24 Rice JM (1977b) Contact metamorphism of impure dolomitic limestone in the Boulder aureole, Montana. Contrib Mineral Petrol 59:237–259 Roselle GT (1997) Integrated petrologic, stable isotopic, and statistical study of fluid-flow in carbonates of the Ubehebe Peak contact aureole, Death Valley National Park, California. PhD Thesis, University of Wisconsin, Madison, Wisconsin Roselle GT, Baumgartner LP, Valley JW (1999) Stable isotope evidence for heterogeneous fluid infiltration at the Ubehebe Peak contact aureole, Death Valley National Park, California. Am J Sci 299:93–138 Rosenbaum J, Sheppard SMF (1986) An isotopic study of siderites, dolomites and ankerites at high temperatures. Geochim Cosmochim Acta 50:1147–1150 Rumble D (1982) Stable isotope fractionation during metamorphic devolatilization reactions. Mineral Soc Am Rev Mineral 10:327–353 Rumble D, Oliver NHS, Ferry JM, Hoering TC (1991) Carbon and oxygen isotope geochemistry of chlorite-zone rocks of the Waterville limestone, Maine, USA. Am Mineral 76:857–866 Sharma T, Clayton RN (1965) Measurement of O18/O16 ratios of total oxygen in carbonates. Geochim Cosmochim Acta 29:1347–1353 Suzuki K (1977) Local equilibrium during the contact metamorphism of siliceous dolomites in Kasuga-Mura, Gifu-ken, Japan. Contrib Mineral Petrol 61:79–89
Swart PK, Burns SJ, Leder JJ (1991) Fractionation of the stable isotopes of oxygen and carbon in carbon dioxide during the reaction of calcite with phosphoric acid as a function of temperature and technique. Chem Geol 86:89–96 Taylor HP Jr, Sheppard SMF (1986) Igneous rocks: I. isotope fractionation and isotope systematics. Mineral Soc Am Rev Mineral 16:227–271 Trommsdorff V, Evans BW (1977) Antigorite–ophicarbonates: contact metamorphism in Valmalenco, Italy. Contrib Mineral Petrol 62:301–312 Veizer J, Hoefs J (1976) The nature of O18/O16 and C13/C12 secular trends in sedimentary carbonate rocks. Geochim Cosmochim Acta 40:1387–1395 Visona D (1997) The Predazzo multipulse intrusive body (Western Dolomites, Italy). Field and mineralogical studies. Mem Sci Geol 49:117–125 Walther JV, Orville PM (1982) Volatile production and transport in regional metamorphism. Contrib Mineral Petrol 79: 252–257 Warner RD, Luth WC (1973) Two-phase data for the join monticellite (CaMgSiO4)–forsterite (Mg2SiO4): experimental results and numerical analysis. Am Mineral 58:998–1008 Webb JA (1982) A Carnian age from the Mt. Monzoni intrusive complex, western Dolomites, Italy. In: Odin GS (ed) Numerical dating in stratigraphy. Wiley, New York, pp 875–876 Wood BJ (1976) Mixing properties of tschermakitic clinopyroxenes. Am Mineral 61:599–602 Yardley BWD, Lloyd GE (1995) Why metasomatic fronts are really metasomatic sides. Geology 23:53–56
