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Permeability anisotropy (the ratio of the horizontal to vertical permeability) develops in mudrocks at the macroscale due to heterogeneities such as layering and at the element scale (i.e., within a single homogeneous layer or unit) due to decreasing porosity and increasing platy particle alignment. This work describes new experimental methods and results from a laboratory program using cubic specimens to investigate the evolution of mudrock permeability and resistivity at the element scale. A systematic study analyzes the evolution of the permeability anisotropy and electrical resistivity anisotropy using resedimented Boston blue clay (RBBC) over a stress range of 0.4-40 MPa; additional measurements are presented for three other mudrocks within varying clay fraction and clay mineralogy within the stress range 1.2-10 MPa. The permeability anisotropy and the conductivity anisotropy (inverse of the resistivity anisotropy) of all four mudrocks studied ranges from 1 to 2.2 over the porosity range 0.55-0.30. A nearly 1:1 correlation between the electrical conductivity anisotropy and the permeability anisotropy is observed to be independent of clay fraction or clay mineralogy. Key words: permeability anisotropy, electrical conductivity anisotropy, resedimentation, resistivity anisotropy. L'anisotropie de permeabilite (le rapport de la permeabilite horizontale a la verticale) se developpe dans la pelite a l'echelle macro en raison de l'heterogeneite telle que la stratification et a l'echelle de l'element (par ex., dans une couche homogene unique ou unitaire) en raison de la porosite decroissante et l'alignement lamellaire croissante des particules. Cet ouvrage decrit les nouvelles methodes experimentales et les resultats d'un programme de laboratoire en utilisant des echantillons cubiques pour etudier l'evolution de la permeabilite et de la resistivite de la pelite a l'echelle de l'element. Une etude systematique analyse l'evolution de l'anisotropie de permeabilite et de l'anisotropie de la resistivite electrique utilisant l'argile Boston bleu resedimente (RBBC--resedimented Boston blue clay) sur une intervalle de contrainte de 0,4 a 40 MPa; des measures supplementaires sont presentees pour trois autres pelitesa fraction d'argile et a mineralogie d'argile variablesa l'interieur d'une intervalle de contrainte de 1,2 a 10 MPa. L'anisotropie de la permeabilite et l'anisotropie de conductivite (inverse de l'anisotropie de la resistivite) des quatre pelites etudiees varient de 1 a 2,2 a l'interieur d'une intervalle de porosite de 0,55 a 0,30. A peu pres une correlation 1:1 entre l'anisotropie de la conductivite electrique et l'anisotropie de la permeabilite s'avere etre independante de la fraction d'argile ou de la mineralogie d'argile. [Traduit par la Redaction] Mots-cles: anisotropie de la permeabilite, l'anisotropie de la conductivite electrique, resedimentation, l'anisotropie de resistivite., Introduction Permeability anisotropy (the ratio of the horizontal to vertical permeability) develops in mudrocks at the macroscale due to heterogeneities such as layering and at the element scale (i.e., within [...]

The contact aureole at the eastern margin of the South Mountain Batholith (Halifax Pluton) underlies most of the city of Halifax, Nova Scotia. The Halifax Group in the study area includes two lithological units, the Cunard and Bluestone formations. Before intrusion, both had been affected by greenschist facies regional metamorphism and deformed into northeast-southwest-trending, regional upright folds associated with a strong slaty cleavage. Contact metamorphic isograds trend obliquely across the Halifax peninsula, at a high angle to regional structural trends. At 2.5-3 km from the intrusive contact, sparse cordierite spots mark the outer limit of the contact aureole. The biotite-in isograd is marked by the development of biotite within chlorite + muscovite stacks inherited from regional metamorphism. Pyrrhotite is the dominant sulphide mineral throughout the contact aureole. With increasing metamorphic grade, assemblages in both units are marked by increasing modal abundance of cordierite and biotite, with K-feldspar variably developed within ca. 600 m of the contact. However, there is a marked difference in the distribution and appearance of andalusite between the two units. In aluminous pelites of the Cunard formation, idioblastic chiastolite appears before biotite more than 1500 m from the contact. In the less aluminous Bluestone formation, andalusite is present only within ca. 500 m of the contact, where it forms xenoblastic, spongy crystals. In both units, the assemblage andalusite + biotite + K-feldspar [+ or -] cordierite is developed near the contact, with local fibrolite and evidence of incipient partial melting. Petrographic constraints suggest pressure-temperature conditions at the contact of ca. 2.5-3.0 kbar (1 kbar = 100 MPa) at ca. 650°C. La ville de Halifax, Nouvelle-Ecosse, se retrouve presque entierement batie sur l'aureole de contact a la limite est du batholite de South Mountain (pluton Halifax). Le Groupe de Halifax dans le secteur a l'etude comprend deux unites lithologiques, soit les formations de Cunard et de Bluestone. Avant l'intrusion, ces deux unites avaient ete affectees par un metamorphisme regional au facies des schistes verts et deformees en plis regionaux droits de tendance nord-est-sud-ouest auxquels on associe un fort clivage ardoisier. Les isogrades de metamorphisme de contact ont une tendance oblique a travers la peninsule de Halifax, a un angle eleve par rapport aux tendances structurales regionales. A une distance de 2.53 km du contact intrusif, des taches eparses de cordierite marquent la limite externe de l'aureole de contact. L'isograde d'inclusion de la biotite est marque par le developpement de la biotite dans des monticules de chlorite + muscovite herites du metamorphisme regional. La pyrrhotite est le mineral sulfure dominant a travers toute l'aureole de contact. Avec l'accroissement du grade de metamorphisme, les assemblages dans les deux unites sont marques par une abondance modale croissante de cordierite et de biotite; le feldspath-K se developpant de maniere variable a moins de 600 m du contact. Toutefois, la distribution et l'apparence de l'andalousite sont tres differentes dans les deux unites. Dans les pelites alumineuses de la Formation de Cunard, une chiastolite idiomorphe apparait avant la biotite a plus de 1500 m du contact. Dans la Formation de Bluestone, moins alumineuse, l'andalousite n'est presente que dans les 500 m a proximite du contact ou elle forme des cristaux xenoblastiques spongieux. Dans les deux unites, l'assemblage andalousite + biotite + feldspathK ± cordierite s'est developpe a proximite du contact, avec presence locale de fibrolite et des preuves de debut d'une fusion partielle. Les contraintes petrographiques suggerent, au contact, des conditions de temperature et de pression d'environ 650°C et de 2.5-3.0 kbar (1 kbar = 100 MPa). [Traduit par la Redaction], Introduction The geology, stratigraphy, and petrology of the sedimentary and igneous units of the Meguma terrane of southern Nova Scotia have been the subject of numerous detailed studies and regional [...]

Iron oxide -Cu ± Au ± U ± Co (IOCG) mineralization is associated with numerous Proterozoic breccia bodies, collectively known as Wernecke Breccia, in Yukon Territory, Canada. Multiphase breccia zones occur in areas underlain by Paleoproterozoic Wernecke Supergroup metasedimentary rocks and are associated with widespread sodic, potassic, and carbonate alteration assemblages. Fluid inclusion data indicate syn-breccia fluids were hot (185-350°C) saline (24-12 wt.% NaCl equivalent) NaCl-Ca[Cl.sub.2]-[H.sub.2]O brines. Estimates of fluid pressure vary from 0.4 to 2.4 kbar (1 kbar = 100 MPa). Carbon and oxygen isotopic compositions of breccia-related carbonates range from ~-11 ‰ to +1.5 ‰ (Pee Dee belemnite (PDB)) and -2 ‰ to 20 ‰ (Vienna standard mean ocean water (V-SMOW); [δ.sup.18] [O.sub.water] ~-8 ‰ to +15 ‰), respectively. δ[sup.13]C and δ[sup.18]O values for host Wernecke Supergroup limestone/dolostone vary from ~-2 ‰ to 1.6 ‰ and 12 ‰ to 25 ‰, respectively. Sulfur isotopic compositions of hydrothermal sulfides and sulfate vary from ~-12 ‰ to +13 ‰ and +8 ‰ to +17 ‰ (Canon Diablo Troilite (CDT)), respectively. Syn-breccia biotite, muscovite, and actinolite have δD and δ[sup.18]O values of ~-141 ‰ to -18 ‰ and +7 ‰ to +12 ‰ (V-SMOW; [δ.sup.18][O.sub.water] ~7 ‰ to 11 ‰), respectively. The Wernecke Breccias and the associated IOCG mineralization appear to have formed from largely nonmagmatic fluids--based on isotopic, fluid inclusion, and geological data. The emerging hypothesis is that periodic overpressuring of dominantly formational/metamorphic water led to repeated brecciation and mineral precipitation. The weight of overlying sedimentary rocks led to elevated fluid temperatures and pressures; fluid flow may have been driven by tectonics and (or) gravity with metals scavenged from host strata. Une mineralisation d'oxyde de fer--Cu ± Au ± U ± Co (IOCG) est associee a de nombreux amas de breches datant du Proterozoique, connus ensemble sous le nom de breches de Wernecke, dans le Territoire du Yukon, Canada. Des zones de breches a plusieurs phases se retrouvent dans les secteurs reposant sur des roches metasedimentaires du supergroupe de Wernecke (Paleoproterozoique) et ces zones sont associees a des assemblages etendus d'alteration sodique, potassique et de carbonate. Des donnees sur des inclusions de fluides indiquent que les fluides contemporains des breches etaient des saumures NaCl-Ca[Cl.sub.2]-[H.sub.2]O chaudes (185-350°C) et salines (24-42 % poids equivalent NaCl). Des estimations de la pression des fluides varient de 0,4 a 2,4 kbar (1 kbar = 100 MPa). Les compositions isotopiques en carbone et en oxygene des carbonates relies aux breches varient respectivement de ~-11 ‰ a +1,5 ‰ (Pee Dee belemnite (PDB)) et -2 ‰ a 20 ‰ (Vienna standard mean ocean water (V-SMOW); δ[sup.18]O eau ~-8 ‰ a +15 ‰). Les valeurs δ[sup.13]C et δ[sup.18]O pour les dolomies/calcaires encaissants du supergroupe de Wernecke varient respectivement de ~-2 ‰ a 1,6 ‰ et de 12 ‰ a 25 ‰. Les compositions isotopiques du soufre des sulfures et sulfates hydrothermaux varient respectivement de ~-12 ‰ a +13 ‰ et de +8 ‰ a +17 ‰ (Canon Diablo Troilite (CDT)). La biotite, la muscovite et l' actinote contemporaines de la breche ont respectivement des valeurs δD et δ[sup.18]O de ~-141 ‰ a -18 ‰ et de +7 ‰ a +12 ‰ (V-SMOW; δ[sup.18]O eau :7 ‰ a 11 ‰). En se basant sur des donnees d'isotopes, d'inclusion de fluides et geologiques, il semblerait que les breches de Wernecke et la mineralisation IOCG associee aient ete formees a partir de fluides en grande partie non magmatiques. L'hypothese resultante est que la surpression periodique de l'eau, surtout de formation/metamorphique, a conduit a beaucoup de brechification et de precipitation de mineraux. Le poids des roches sedimentaires sus-jacentes a mene a des temperatures et a des pressions elevees dans les fluides; les fluides peuvent avoir ete pousses a couler par tectonisme et (ou) par gravite et contenir des metaux recuperes des strates hotes. [Traduit par la Redaction], Introduction Numerous Proterozoic breccia bodies, collectively known as Wernecke Breccia, occur over large areas in the north-central Yukon Territory, Canada (Fig. 1; e.g., Bell and Delaney 1977; Archer et al. [...]

In 2008, a Vibroseis seismic reflection survey was acquired by Geoscience BC across the eastern part of the volcanic- covered Nechako basin in central British Columbia, where Cretaceous sedimentary rocks have been exhumed along a NNW trend. Good signal penetration through the volcanic cover is indicated by lower crustal reflections at 8-12 s, which were recorded by the entire seismic survey. Comparison of the 2008 seismic survey with data from a previous survey indicates that the lack of reflectivity in the earlier surveys is generally representative of the subsurface geology. The seismic data show that ~1700 and ~2900 m thick sub-basins are present at the northern and southern ends of this trend, but the intervening Cretaceous rocks are discontinuous and relatively thin. The creation of a passive-roof duplex by Campanian or later low-angle thrusting is inferred within the thickest Cretaceous strata, but elsewhere faulting is likely related to Eocene extension or transtension. Seismic reflections are also recorded from folded volcanic stratigraphy, the base of the surface volcanic rocks, an underlying volcaniclastic stratigraphy, and intrusions projecting into a Quaternary volcanic cone. Seismic interpretation is complemented by coincident audiofrequency magnetotelluric surveys, from which faulting is inferred at offsets in a regional conductor. No regionally extensive stratigraphy can be identified within the seismic data, and the central Nechako basin appears to be a complex network of small, deformed sub-basins, rather than a single large basin. En 2008, Geoscience BC a acquis un releve sismique reflexion Vibroseis portant sur la partie est du bassin Nechako, recouvert de roches volcaniques; ce bassin est situe dans le centre de la Colombie-Britannique, ou des roches sedimentaires datant du Cretace ont ete exhumees le long d'une tendance NNO. Une bonne penetration du signal a travers le couvert volcanique est indiquee par les reflexions sur la croute inferieure a 8-12 s, lesquelles sont enregistrees dans tout le releve sismique. Une comparaison entre le releve sismique de 2008 et les donnees d'un releve anterieur indique que le manque de reflectivite dans les anciens releves est generalement representatif de la geologie souterraine. Les donnees sismiques montrent que des sous-bassins d'une epaisseur ~1700 et ~2900 m sont presents aux extremites nord et sud de cette tendance, mais que les roches cretacees entre les extremites sont discontinues et relativement minces. La creation, vers le Campanien ou plus tard, d' un << duplex >> a toit passif par chevauchement a angle faible est inferee dans les strates cretacees les plus epaisses, mais ailleurs, les failles sont plus probablement reliees a l'extension a l'Eocene ou a de la transtension. Des reflexions sismiques sont aussi enregistrees a partir de la stratigraphie de roches volcaniques pliees, de la base des roches volcaniques en surface, d'une stratigraphie volcano-clastique sous-jacente et a partir d'intrusions se projetant dans un cone volcanique quaternaire. L'interpretation sismique est completee par des releves magnetotelluriques de frequences audio coincidents, a partir desquels les failles sont inferees aux points de decalage dans un conducteur regional. Aucune stratigraphie regionale extensive ne peut etre identifiee dans les donnees sismiques et le bassin Nechako central semble etre un reseau complexe de petits bassins deformes plutot qu'un seul grand bassin. [Traduit par la Redaction], Introduction The Nechako basin, which is located in the interior plateau of British Columbia between the Coast Mountains and the Rocky Mountains (Fig. 1), has seen very little exploration for [...]

A combination of sediment petrography, detrital zircon U-Pb, and fission-track dating is used to show that provenance of the Paleogene sedimentary rocks exposed in the Makran region of southern Iran and the Katawaz basin of Pakistan is consistent with a source from the nascent western Himalaya and associated magmatic arc. Results from this important archive show that Paleogene erosion was focused mainly on the arc and northern Indian margin, and, in contrast to the east-central Himalaya, we have not detected widespread rapid exhumation indicative of strong forcing by climate-driven erosion at that time. doi: 10.1130/G31087.1

For the last three decades, the position of the Triassic-Jurassic boundary (TJB) in nonmarine strata has largely been based on its palynostratigraphic placement just below the oldest basalts of the Central Atlantic magmatic province (CAMP) in the Newark Supergroup of eastern North America. This boundary, however, is demonstrably older than the TJB as it is defined in marine strata. Thus, the palynostratigraphic change used to place this TJB in the Newark most resembles a late Norian change in the European section and does not correspond to any palynological event at the marine-defined TJB. Conchostracan biostratigraphy suggests that the TJB is in the Newark extrusive zone above the oldest CAMP basalt, and vertebrate biostratigraphy is consistent with this placement of the TJB. Radioisotopic ages indicate that the TJB defined in marine strata is no older than 200 MA, but the oldest CAMP basalts of the Newark Supergroup consistently yield ages averaging about 201 Ma. Magnetostratigraphic correlation of the Newark section to the TJB section at St. Audrie's Bay in England also indicates that the onset of CAMP volcanism in the Newark Supergroup is older than the marine TJB. Correlations based on carbon and osmium isotopes are also consistent with this correlation. Thus, all data indicate that the TJB in the Newark Supergroup is above the lowest CAMP basalt in the Newark extrusive zone. Correct placement of the TJB in the Newark Supergroup allows key nonmarine and marine events to be sequenced across the TJB, indicating the following succession of events: crurotarsan ('thecodont') extinction, the palynofloral turnover in the Newark, the first CAMP eruptions, the extinctions of Rhaetian ammonites and conodonts, and the first appearance of Jurassic psiloceratid ammonites. Keywords: Triassic; Jurassic; Newark Supergroup; mass extinction

U-Pb detrital zircon geochronology from the upper Cambrian to Devonian part of the Ellsworth Mountains succession, Antarctica, yields dominant late Mesoproterozoic and late Neoproterozoic-Cambrian age populations that are consistent with a provenance from within Gondwana. Hf isotope compositions reveal a source predominantly within west Gondwana and identify a change in provenance up-stratigraphy that coincides with the change of sedimentation setting from active rift to passive margin, which has been independently determined by stratigraphic, structural, and geochemical arguments. For the Late Cambrian Frasier Ridge Formation, late Mesoproterozoic grains have positive [[epsilon].sub.Hf] values, suggesting derivation from juvenile crust, and late Neoproterozoic-Cambrian grains have [[epsilon].sub.Hf] values greater than -5, consistent with remelting of similar juvenile late Mesoproterozoic crust during the Pan African-Ross orogenies. Provenance during rifting was from proximal sources from within west Gondwana, most likely, southernmost Africa and basement to the Ellsworth-Whitmore Mountains block. At higher stratigraphic levels where deposition occurred along a passive margin, in the early Ordovician Mount Twiss Member and middle Devonian Mount Wyatt Earp Formation, late Neo-proterozoic-Cambrian grains have [[epsilon].sub.Hf] values less than -5; this means that early Mesoproterozoic-Archean crust was remelted to generate these zircons. Provenance was from a more expansive source region within west Gondwana, and probably included the Kaapvaal and Congo cratons of south and west Africa. Isolated outcrops of sedimentary rock of uncertain age at Mount Woollard and the Whitmore Mountains have detrital zircon signatures similar to the Frasier Ridge Formation, suggesting correlation with these Late Cambrian deposits. Sedimentary rock from the Stewart Hills contains some late Mesoproterozoic grains with lower [[epsilon].sub.Hf] values than the previously mentioned samples. This suggests that the Stewart Hills sample has a provenance from within east Gondwana and was possibly deposited on the East Antarctic craton prior to the Ross orogeny and is not part of the displaced Ellsworth-Whitmore Mountains crustal block. Keywords: Antarctica, absolute age, U-Pb. Hf, zircon provenance.

Chimneys around hydrothermal vents at a depth of c. 140 m in the Horomatangi Reefs area in Lake Taupo, New Zealand, are composed of amorphous silica (opal-A) with lesser amounts of Mn-, Fe-, and Hg-rich precipitates. Detrital quartz and feldspar grains are found in the surrounding sediments. The associated biota includes fish, bacteria, sponges, crayfish, amphipods, copepods, ostracodes, annelids, and other unidentified organisms. Much of this biota, however, is not preserved in the opal-A deposits. Instead, the silicified biota includes filamentous microbes and diatoms, scattered coccoid microbes, fungal hyphae and spores, rare sponge spicules, and rare worm(?) tubes. The diatoms, coccoid microbes, and fungi were brought into the area with the detrital sediment. In ancient successions, distinction between sublacustrine, terrestrial, and some marine hot spring deposits may be difficult because the precipitates share many similarities. Distinction based on the biota is viable only if palaeoecological information can be inferred from accurately identified organisms. Unfortunately, silicification commonly disguises microbes and precludes their accurate identification. Diagenetic transformation of opal-A to its more stable polymorphs also destroys many original depositional fabrics and silicified microbes. Distinction between the different types of spring deposit may therefore depend on the interpretation of their overall sedimentological and stratigraphic setting.

A previously inexplicable difference between the Highland Border Complex, Scotland, and its correlative in Ireland, the Clew Bay Complex, is that rocks of Caradoc-Ashgill age occur only in the former. We reject evidence from supposed chitinozoa for this dichotomy: no sedimentary rocks of proven age younger than Arenig occur in the Highland Border Complex. Consequentially, the stratigraphy must be totally recast, and the 'exotic terrane model' replaced by one in which a largely autoehthonous Highland Border Complex in stratigraphical continuity with the Dalradian (Grampian terrane), was overridden by the Highland Border ophiolite (Midland Valley terrane). Tectonic models for SE Laurentia are thereby considerably simplified.

Diamondoids were detected in the extracts of a series of coals and rocks varying in maturity, lithology, source input, and depositional enviromnent. At the same maturity level, diamondoids are generally about a magnitude more abundant in source rocks than in coals. The concentrations of diamondoids are maturity dependent. However, while diamondoids become more abundant with the increasing thermal maturity, a diminution in diamondoid concentrations is observed at the maturity value of about [R.sub.o] = 4.0% in both coals and rocks. The occurrence of diamantane destruction at 550 [degrees]C during pyrolysis suggests that diamondoids may be eventually destroyed at high temperatures in the Earth. Here we propose three main phases of diamondoid life in nature: diamondoid generation (phase I, [R.sub.o] < 1.1%), diamondoid generation and enrichment (phase II, 1.1% [less than or equal to] [R.sub.o] [less than or equal to] 4.0%), and diamondoid destruction (phase III, [R.sub.o] > 4.0%). Keywords: diamondoids, thermal maturity, coals, source rocks, oil cracking, vitrinite reflectance, diamondoid destruction.

The Dariv Basin is an actively evolving intracontinental transpressional basin located on the eastern flank of the Mongolian Altai. The basin occupies a complex tectonic position between a restraining bend, a thrusted basement block, and two major conjugate strike-slip fault systems. Structures and sedimentary strata exposed within the Dariv Basin suggest a Mesozoic and Cenozoic two-stage evolution. Jurassic--Cretaceous strata fine upward and record alluvial fan, fluvial and lacustrine depositional environments. The distribution of Mesozoic sedimentary rocks and the presence of a suspected Jurassic normal fault array suggest that the Dariv Basin initially formed as an extensional basin. Following Palaeogene tectonic quiescence, Oligocene--Recent basin fill is dominated by alluvial fan sediments derived from basin-flanking ranges. The modern basin is deforming by thrusting, normal fault inversion and folding along discrete belts expressed as intrabasinal ridges and domes. These belts define a rhomboid of active deformation that compartmentalizes the basin. Sediments derived from these discrete deforming belts and from basin flanking ranges continue to accumulate in the basin centre. Thus, modern fans contain reworked older basin fill and competing processes of sedimentation, deformation, erosion and resedimentation can be observed. The Dariv Basin is an excellent example of a transpressional piggyback basin in the early stages of basin inversion and destruction.

Finite strain analysis of deformed elastic sedimentary rocks below and above the Acadian unconformity on the Dingle Peninsula, SW Ireland, reveals that this boundary represents a significant bulk strain discontinuity. The Late Emsian Acadian event is primarily responsible for penetrative cleavage development and high strain in rocks below the unconformity and not, as previously held, the later Variscan event, which overprinted the peninsula with a weak and localized disjunctive cleavage. The presence of apparent anticlockwise transecting cleavage and implied dextral closure of the Dingle Basin during the Acadian event is compatible with northward convergence of Armorica with respect to Eastern Avalonia.

The simultaneous use of several thermochronological methods on replicate sedimentary rock samples can reveal their pre- and postdepositional history. Single grain U/Pb dating of zircon, zircon and apatite fission track dating, and vitrinite reflectance measurements were performed on Cretaceous through Miocene sedimentary rocks of the Great Valley Group and the Temblor Formation near Coalinga and New Idria, California. The data show that the Sierra Nevada was exhumed and cooled at ~0.5-1 km/m.y. or ~20 [degrees]C/m.y. during the Cretaceous. After deposition in the Great Valley forearc basin, Sierra Nevada erosional products were buried at great depth under low thermal gradients. At ca. 12-14 Ma, northward progression of the Mendocino triple junction triggered folding on the eastern flanks of the California Coast Ranges and rapid exhumation of the New Idria serpentinite diapir. This middle Miocene event caused the deposition of spectacular deposits of sedimentary serpentinite (Big Blue Formation). The rapid rise of the hot serpentinite body created a thermal pulse that may have provided the enigmatic heat source for oil fields in the shallow Vallecitos syncline, a few kilometers north of New Idria. Keywords: detrital thermochronology, fission track, Great Valley Group, serpentinite, Sierra Nevada, exhumation.

The [X.sub.C[O.sub.2]] recorded by mineral-fluid equilibria in contact metamorphosed siliceous carbonates commonly defines two groups of rocks in the same aureole. One group records relatively low [X.sub.C[O.sub.2]], that results from infiltration of chemically reactive [H.sub.2]O-rich fluid. The other records relatively high [X.sub.C[O.sub.2]], up to 0.99, that results from decarbonation reactions with little or no infiltration. A complementary dichotomy in apatite compositions exists in five contact aureoles in Italy, Scotland, and the U.S.A. Apatite in the low-[X.sub.C[O.sub.2]] group is close to an F-OH solid solution. Apatite in the high-[X.sub.C[O.sub.2]] group is a relatively Cl-rich Cl-F--OH solution. The halogen content of fluid coexisting with analyzed apatite was characterized in two aureoles to determine the origin and significance of the dichotomy in apatite composition. Calculated [a.sub.HF]/[[a.sub.[H.sub.2].sub.O], [a.sub.HF]/[a.sub.HCl], [a.sub.HF], and [m.sub.[F.sub.T]] (the total F molality of fluid) are systematically higher in fluid coexisting with the low-[X.sub.[co.sub.2]] group. In contrast, [a.sub.HCl]/[[a.sub.[H.sub.2].sub.O] in the high-[X.sub.C[O.sub.2]] group may be higher than or overlap with [[a.sub.HCl]/[a.sub.H].sub.2].sub.O] in the low-[X.sub.C[O.sub.2]] group. Calculated [a.sub.HCl] and [m.sub.Cl].sub.T] in the high-[X.sub.[co.sub.2]] group are lower than or overlap with [a.sub.HCl] and [m.sub.Cl].sub.T] in the low-[X.sub.[co.sub.2]] group. The Cl-rich apatites in the high-[X.sub.C[O.sub.2]] group are explained by crystallization at relatively low [[a.sub.[H.sub.2].sub.O], any, and [m.sub.F].sub.T]] rather than at high [a.sub.HCl] or [m.sub.Cl].sub.T]]. In comparison, the F-OH apatites in the low-[X.sub.[co.sub.2]] group formed by infiltration of rock by and equilibration with relatively [H.sub.2]O-rich, high [m.sub.F].sub.T]]/[m.sub.Cl].sub.T]] fluid, reflecting the same metasomatic process responsible for F-rich humite-group minerals and skarns in many contact aureoles. Calculated halogen contents indicate that the non-C[O.sub.2] fraction of fluid in equilibrium with both groups had modest, seawater-like salinity, and that the reactive [H.sub.2]O- and F-rich fluid that infiltrated the low-[X.sub.C[O.sub.2]] group had a plutonic source.

The Paleoproterozoic Proven Igneous Complex (PIC) in West Greenland extends from ca. 72[degrees]15' to 73[degrees]10'N, approximately 500 km north of the subduction-related intrusive complex in the core of the +1100 km wide, asymmetric collisional Nagssugtoqidian-Rinkian Orogen. A new U-Pb SHRIMP age for the PIC of 1869 [+ or -] 9 Ma indicates that it intruded synchronously with the main collisional phase of the orogen into the passive margin side of the collision. Sm-Nd and Lu-Hf isotopic and A-type geochemical signatures are compatible with its derivation from melted Archean lower crustal material contaminated to varying degrees by pelitic sedimentary rocks of the Karrat Group. The timing, petrogenesis and position of the PIC within the orogen support a model of collisionally induced delamination of the mantle lithosphere following initial collision. Upwelling asthenospheric mantle replacing the partially or completely detached mantle lithosphere caused widespread partial melting of lower crust that resulted in the areally extensive (~ 250,000 [km.sup.2]) Cumberland-Proven intrusive complexes of Baffin Island and West Greenland. Emplacement of the PIC at 1.87 Ga caused a high-temperature low- to medium-pressure metamorphic aureole that contrasts the regional, overprinting higher-pressure amphibolite facies metamorphism. The consequent high-temperature garnet-orthopyroxene-biotite-bearing assemblages occurring within the margin of the intrusion in the aureole are attributed to the intrusion event. Garnet-controlled Sm-Nd and Lu-Hf ages of 1.82-1.80 Ga require efficient diffusion of these elements during orogenic reheating at this time. This age range overlaps the post-collisional, north-south shortening in the Nagssugtoqidian Orogen to the south and serves to confirm the recently proposed genetic link between these two orogens. These new data infer that garnet-controlled isochrons based on the Lu-Hf and Sm-Nd systems cannot date high-grade events in slowly cooled or significantly reheated terrains in rocks possessing other phases that close at low temperatures.