Journal articles: 'Contact aureoles'

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Owen, J. Victor. "Cordierite + spinel parageneses in pelitic gneiss from the contact aureoles of the Mistastin batholith (Quebec) and the Taylor Brook gabbro complex (Newfoundland)." Canadian Journal of Earth Sciences 28, no. 3 (March 1, 1991): 372–81. http://dx.doi.org/10.1139/e91-034.

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The contact aureoles of the Mistastin batholith and the Taylor Brook gabbro complex contain cordierite + spinel-bearing assemblages derived from quartz-, K-feldspar-, sillimanite-, garnet-, and biotite-bearing pelitic gneiss. Andalusite occurs locally. As a result of continuous, cordierite-forming reactions, garnet and biotite have recrystallized to relatively Fe-rich compositions compared with their counterparts outside the aureoles.Mosaics of fine-grained cordierite and spinel replace sillimanite and biotite throughout the Mistastin aureole. Similar assemblages and textures are preserved in metapelite in the outer part of the Taylor Brook aureole, where garnet adjacent to sillimanite is replaced by cordierite + spinel. The formation of spinel-free cordierite porphyroblasts by garnet-, sillimanite-, biotite-, and quartz-consuming reactions depleted metapelites in both aureoles in quartz, permitting the formation of the undersaturated assemblages. The undersaturated cordierite + spinel assemblages formed on a domainal scale (individually, a few hundred cubic millimetres in volume) and coexist metastably with saturated assemblages elsewhere in the same rock. Peak temperatures (700–750 °C) determined for both aureoles were insufficient to stabilize quartz + spinel parageneses owing to the low gahnite content of the oxide (ZnO < 2 wt.%).Metapelites in the innermost part of the Taylor Brook aureole appear to have been desilicified by the formation and fractionation of anatectic melt, yielding migmatitic rocks virtually devoid of quartz and K-feldspar. In contrast, migmatite in the inner part of the Mistastin aureole retains a quartz + two-feldspar mineralogy, so, as in the nonmigmatitic paragneiss, undersaturated assemblages are present only on a domainal scale.These aureole rocks demonstrate that undersaturated assemblages are not only characteristic of thermally- recrystallized low-grade pelites but also can occur in contact aureoles developed in granulite-facies paragneiss. Aluminous rocks can become undersaturated by subsolidus, quartz-consuming reactions yielding cordierite, or by the formation of anatectic liquids.

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Müller, Thomas, Lukas P. Baumgartner, C. T. Foster, and Torsten W. Vennemann. "Metastable prograde mineral reactions in contact aureoles." Geology 32, no. 9 (2004): 821. http://dx.doi.org/10.1130/g20576.1.

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Rowan, Lawrence C., Carmen Anton‐Pacheco, David W. Brickey, Marguerite J. Kingston, Alba Payas, Norma Vergo, and James K. Crowley. "Digital classification of contact metamorphic rocks in Extremadura, Spain, using Landsat thematic mapper data." GEOPHYSICS 52, no. 7 (July 1987): 885–97. http://dx.doi.org/10.1190/1.1442359.

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Landsat Thematic Mapper (TM) images of an extensively cultivated part of Extremadura, Spain, have been used to distinguish soil developed on contact metamorphic rocks in aureoles around late Hercynian granitic plutons from soil formed on stratigraphically equivalent Late Proterozoic slate and metagraywacke that has been regionally metamorphosed to the greenschist facies. Reflectance spectra of contact metamorphic soil have lower reflectance, especially in the 1.6 μm wavelength region, and weaker Al‐OH, Mg‐OH, and [Formula: see text] absorption features than do spectra of the slate‐metagraywacke soil. These spectral differences are attributed to highly absorbing carbonaceous material in the contact metamorphic soil that was subjected to high temperatures during emplacement of the plutons. These spectral reflectance differences are evident in a density‐sliced TM band 5 image, in color‐ratio composite images that incorporate TM 4 : 5, 4 : 3, and 3 : 1 ratios, and in principal‐component composite images. Digital classification of the numerous tilled, vegetation‐free fields was used to map the contact metamorphic soil in an August, 1984, TM scene of the Caceres study area. First, TM 4 : 3 was used to identify these fields. Then ranges of TM 5 and TM 3 : 1 values were determined for selected tilled fields within and outside the contact aureoles. Field evaluation of a classification map based on TM 5 plus TM 3 : 1 shows more extensive aureoles than published geologic maps and few misclassified areas. Similar results were achieved using TM 4 : 5 instead of TM 5. This approach was subsequently used to map two linear zones of contact metamorphic rocks in the San Nicolas mine area where only two small exposures of granite have been documented. Landsat Multispectral Scanner (MSS) images can also be used to map contact aureoles in the study areas, but extensive field evaluation is required because of more frequent misclassification.

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HOLNESS, M. B. "Contact metamorphism and anatexis of Torridonian arkose by minor intrusions of the Rum Igneous Complex, Inner Hebrides, Scotland." Geological Magazine 136, no. 5 (September 1999): 527–42. http://dx.doi.org/10.1017/s0016756899002988.

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Significant volumes of partial melt developed in the arkosic contact aureoles of two of the numerous mafic and ultramafic minor intrusions found in the northern parts of the Isle of Rum, Scotland. Melting was essentially static, with little movement of melt even on a thin-section scale, and no segregation. The relative proportions of (now inverted) tridymite and high quartz inferred to have crystallized in the silica primary-phase field constrain the pressure of metamorphism to 150 ± 50 bars. Melting attained 95 vol. %, and occurred up to 15 m from the contact with the 50 m diameter gabbro plug. Melting around the adjacent 200 m diameter peridotite plug reached ≈ 70 vol. %, and occurred up to 6 m from the contact. Simple thermal models for the two aureoles, based on the isograds given by the onset of melting, the breakdown of chlorite and the disordering of microcline, support the hypotheses that the peridotite plug was injected as a crystal-rich mush close to its solidus, whereas the gabbro plug was a relatively long-lived feeder conduit. Time scales for the melting events are of the order of forty years for the aureole of the gabbro and ten years for that surrounding the peridotite body. The melt distribution resulting from the heating part of the thermal history is controlled by reaction, and is far from textural equilibrium. Crystallization was abrupt, being complete in ten years for the gabbro, and in only four for the peridotite, resulting in a fine-grained cotectic intergrowth and preservation of the melt distribution.

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Zhou, Mei-Fu, John Malpas, Paul T. Robinson, and Peter H. Reynolds. "The dynamothermal aureole of the Donqiao ophiolite (northern Tibet)." Canadian Journal of Earth Sciences 34, no. 1 (January 1, 1997): 59–65. http://dx.doi.org/10.1139/e17-005.

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Metamorphic rocks found at the base of the Jurassic Donqiao ophiolite of northern Tibet are interpreted as a basal dynamothermal aureole produced during obduction of the massif. The rocks form a sequence some 8 m thick, varying from high-grade amphibolites at the contact with overlying harzburgites to greenschist facies metasedimentary rocks lower down. The mineral paragenesis is similar to other such aureoles, and indicates that temperatures in excess of 750 °C may have been reached during metamorphism. The lack of high-pressure minerals suggests that the rocks were produced by subcretion in a relatively shallow dipping subduction zone. Ar–Ar geochronology on amphibole separates provides dates of 175–180 Ma for the displacement of the ophiolite, significantly older than the age of emplacement estimated from stratigraphie relationships. The ophiolite was clearly obducted very soon after its formation in a suprasubduction zone environment.

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Ferry, John M., and Douglas Rumble III. "Formation and destruction of periclase by fluid flow in two contact aureoles." Contributions to Mineralogy and Petrology 128, no. 4 (August 14, 1997): 313–34. http://dx.doi.org/10.1007/s004100050312.

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van den Kerkhof, Alfons M., and Geoffrey H. Grantham. "Metamorphic charnockite in contact aureoles around intrusive enderbite from Natal, South Africa." Contributions to Mineralogy and Petrology 137, no. 1-2 (October 15, 1999): 115–32. http://dx.doi.org/10.1007/s004100050586.

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Marfin, Alexander E., Alexei V. Ivanov, Vadim S. Kamenetsky, Adam Abersteiner, Tamara Yu Yakich, and Timur V. Dudkin. "Contact Metamorphic and Metasomatic Processes at the Kharaelakh Intrusion, Oktyabrsk Deposit, Norilsk-Talnakh Ore District: Application of LA-ICP-MS Dating of Perovskite, Apatite, Garnet, and Titanite." Economic Geology 115, no. 6 (September 1, 2020): 1213–26. http://dx.doi.org/10.5382/econgeo.4744.

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Abstract The Norilsk-Talnakh ore district in the northwestern Siberian platform contains globally unique reserves of Cu-Ni-sulfides with Pt and, especially, Pd. The Oktyabrsk deposit, which is one of the largest in the district, is spatially and genetically associated with the Kharaelakh mafic-ultramafic intrusion and its exceptionally large metamorphic and metasomatic aureoles. In this study, we employed in situ laser ablation-inductively coupled plasma-mass spectrometry U-Pb isotope dating of apatite, titanite, garnet, and perovskite that cocrystallize with disseminated sulfides within the aureole of metasomatic and contact metamorphic rocks. The calculated isotopic ages for apatite (257.3 ± 4.5 and 248.9 ± 5.1 Ma), titanite (248.6 ± 6.8 and 249.1 ± 2.9 Ma), garnet (260.0 ± 11.0 Ma), and perovskite (247.3 ± 8.2 Ma), though with large uncertainties, indicate that sulfide mineralization within metasomatic and contact-metamorphic rocks is coeval with the emplacement of the Kharaelakh intrusion. These isotopic dates are in complete agreement with the published isotope dilution-thermal ionization mass spectrometry U-Pb zircon ages for the Norilsk intrusions and, at the same time, notably older than available Re-Os isochron ages of sulfides. The latter ages have been long interpreted as evidence for a prolonged duration of magmatic ore-forming processes; however, our data narrow their life span. Trace elements in titanite and garnet allow distinguishing late- and postmagmatic grains, which show indistinguishable U-Pb isotope ages.

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Cui, Xiaojun, Peter I. Nabelek, and Mian Liu. "Heat and fluid flow in contact metamorphic aureoles with layered and transient permeability, with application to the Notch Peak aureole, Utah." Journal of Geophysical Research: Solid Earth 106, B4 (April 10, 2001): 6477–91. http://dx.doi.org/10.1029/2000jb900418.

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VOLDMAN, GUSTAVO G., GUILLERMO L. ALBANESI, and MARGARITA DO CAMPO. "Conodont palaeothermometry of contact metamorphism in Middle Ordovician rocks from the Precordillera of western Argentina." Geological Magazine 145, no. 4 (March 27, 2008): 449–62. http://dx.doi.org/10.1017/s001675680800455x.

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AbstractThe Yerba Loca Formation (Middle–Upper Ordovician), exposed in the Western Precordillera, San Juan, Argentina, is made up of clastic–carbonate turbidites, and basic–ultrabasic rocks. It is affected by regional Siluro-Devonian very low-grade metamorphism that locally reaches greenschist facies. At Ancaucha creek, 45 conodont samples were taken from two sections that include 30 to 50 m thick sills. In order to analyse the thermal alteration patterns produced by these intrusive bodies, conodont Colour Alteration Index (CAI) is contrasted with optical petrography and X-ray diffraction analyses of clay minerals. The intrusions are dated as post-Darriwilian (Da2), as determined by conodont biostratigraphy of the host rock, which indicates theParoistodus horridusSubzone of theLenodus variabilisZone. The distribution of CAI values defines a thermal aureole of about 2.5 times intrusion thickness that prevailed over the later very low-grade metamorphism. Metasomatism at Ancaucha creek is recorded by CAI values of 4 to 7, particularly restricted to a few layers close to the intrusions, as indicated by conodont textures and rock fabric. One-dimensional thermal computer simulation conforms to empirical data indicating temperatures greater than 600 °C for the contact zone, although it points out slightly narrower thermal aureoles. The clay mineral assemblage of most of the analysed samples (chlorite, illite, smectite and I/S mixed-layers) is complex and probably derives from several superimposed processes, thus representing non-equilibrium assemblages. In turn, KI values (0.27–0.32) indicate anchizone metamorphism, in agreement with regional CAI values of 4; consequently, the occurrence of smectite and I/S probably resulted from retrograde diagenesis processes.

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FESTA, VINCENZO, ALFREDO CAGGIANELLI, ANTONIO LANGONE, and GIACOMO PROSSER. "Time–space relationships among structural and metamorphic aureoles related to granite emplacement: a case study from the Serre Massif (southern Italy)." Geological Magazine 150, no. 3 (November 16, 2012): 441–54. http://dx.doi.org/10.1017/s0016756812000714.

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AbstractTectonic and thermal perturbations, related to emplacement of granodiorite in the upper continental crust, have been investigated in the late-Hercynian basement exposed in southern Calabria (Italy). Here, the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km. Geometrical analysis of the structural aureole and related foliations, lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact. This pattern is compatible with a laccolith-like mode of magma emplacement, related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks. The metamorphic aureole, about 1800 m wide, is characterized by biotite, cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact. The peak assemblage equilibrated between 535 and 590°C at pressures between 175 and 200 MPa, confirmed by Al-in-hornblende barometry on granodiorite. Microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations. With the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations. This estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 × 10−14 s−1 within the country rocks during granodiorite intrusion.

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Zi, Jian-Wei, Birger Rasmussen, Janet R. Muhling, Wolfgang D. Maier, and Ian R. Fletcher. "U-Pb monazite ages of the Kabanga mafic-ultramafic intrusions and contact aureoles, central Africa: Geochronological and tectonic implications." GSA Bulletin 131, no. 11-12 (April 15, 2019): 1857–70. http://dx.doi.org/10.1130/b35142.1.

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AbstractMafic-ultramafic rocks of the Kabanga-Musongati alignment in the East African nickel belt occur as Bushveld-type layered intrusions emplaced in metasedimentary sequences. The age of the mafic-ultramafic intrusions remains poorly constrained, though they are regarded to be part of ca. 1375 Ma bimodal magmatism dominated by voluminous S-type granites. In this study, we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole. The monazite shows contrasting crystal morphology, chemical composition, and U-Pb ages. Monazite that formed by contact metamorphism in response to emplacement of mafic-ultramafic melts is characterized by extremely high Th and U and yielded a weighted mean 207Pb/206Pb age of 1402 ± 9 Ma, which is in agreement with dates from the igneous monazite and zircon. The ages indicate that the intrusion of ultramafic melts was substantially earlier (by ∼25 m.y., 95% confidence) than the prevailing S-type granites, calling for a reappraisal of the previously suggested model of coeval, bimodal magmatism. Monazite in the metapelitic rocks also records two younger growth events at ca. 1375 Ma and ca. 990 Ma, coeval with metamorphism during emplacement of S-type granites and tin-bearing granites, respectively. In conjunction with available geologic evidence, we propose that the Kabanga-Musongati mafic-ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to Nuna breakup, which culminated during the ca. 1375 Ma Kibaran event, manifested as extensive intracrustal melting in the adjoining Karagwe-Ankole belt, producing voluminous S-type granites. The Grenvillian-aged (ca. 990 Ma) tin-bearing granite and related Sn mineralization appear to be the far-field record of tectonothermal events associated with collision along the Irumide belt during Rodinia assembly. Since monazite is a ubiquitous trace phase in pelitic sedimentary rocks, in contact aureoles of mafic-ultramafic intrusions, and in regional metamorphic belts, our study highlights the potential of using metamorphic monazite to determine ages of mafic-ultramafic intrusions, and to reconstruct postemplacement metamorphic history of the host terranes.

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Wang, Wei-(RZ), Geoffrey Clarke, Nathan R. Daczko, and Yue Zhao. "Modelling the partial melting of metasediments in a low-pressure regional contact aureole: the effect of water and whole-rock composition." Geological Magazine 156, no. 08 (December 3, 2018): 1400–1424. http://dx.doi.org/10.1017/s001675681800078x.

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AbstractLow-pressure regional aureoles with steep metamorphic field gradients are critical to understanding progressive metamorphism in high-temperature metasedimentary rocks. Delicately layered pelitic and psammitic metasedimentary rocks at Mt Stafford, central Australia, record a greenschist- to granulite-facies Palaeoproterozoic regional aureole, associated with S-type granite plutons, reflecting metamorphism in the range 500–800 °C and at ∼3 kbar. The rocks experienced minimal deformation during metamorphism and partial melting. Partial melting textures evolve progressively along the steep metamorphic field gradient from the incipient stages of melting marked by cuspate grains with low dihedral angles, to melt proportions sufficient to form diatexite with schollen. Phase equilibria modelling in the NCKFMASHTO system for pelitic, semi-pelitic and high- and low-ferromagnesian psammitic samples quantitatively illustrates the dependence of partial melting on rock composition and water volume. Pelitic compositions are more fertile than psammitic compositions when the water content in the rocks is low, especially during the early stages of melting. The whole-rock ferromagnesian component additionally influences melt fertility, with ferromagnesian-rich psammite being more fertile than psammite with a lower ferromagnesian component. Subtle variations in free water content can result in obvious changes in melt volume but limited variation in melt composition. Distinct melting histories of pelitic and psammitic rocks inferred from field relationships may be partially attributed to potential differences in water volume retained to super-solidus conditions. Melt composition is more dependent on the rock composition than the variation in water content.

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Webster, Ewan Russell, and David R. M. Pattison. "Spatially overlapping episodes of deformation, metamorphism, and magmatism in the southern Omineca Belt, southeastern British Columbia." Canadian Journal of Earth Sciences 55, no. 1 (January 2018): 84–110. http://dx.doi.org/10.1139/cjes-2017-0036.

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The southeastern Omineca Belt of the Canadian Cordillera preserves a record of overlapping Barrovian and Buchan metamorphism spanning 180–50 Ma. This paper documents the timing, character, and spatial relationships that define separate domains of Middle Jurassic, Early Cretaceous, and Late Cretaceous deformation and metamorphism, and the nature of the geological interfaces that exist between them. A domain of Early Jurassic deformation (D1) and regional greenschist-facies metamorphism (M1) is cross-cut by Middle Jurassic (174–161 Ma) intrusions. Associated contact aureoles are divided into lower pressure (cordierite-dominated; ∼2.5–3.3 kbar; 1 kbar = 100 MPa) and higher pressure (staurolite-bearing; 3.5–4.2 kbar) subtypes; contact metamorphic kyanite occurs rarely in some staurolite-bearing aureoles. Jurassic structures are progressively overprinted northwards by Early Cretaceous deformation and metamorphism (D2M2), manifested in a tightening of Jurassic structures, development of more pervasive ductile fabrics, and Barrovian metamorphism. The D2M2 domain is the southerly continuation of the 600 km long Selkirk–Monashee–Cariboo metamorphic belt. Mid-Cretaceous intrusions (118–90 Ma) were emplaced throughout the D2M2 domain, the earliest of which contain D2 fabrics, but cut M2 isograds. The D2M2 domain makes a continuous, southeasterly transition into a domain of Late Cretaceous regional Barrovian metamorphism and deformation (D3M3; 94–76 Ma). The interface between these two domains is obscured by the coaxial nature of the deformation and the apparent continuity of the metamorphic zones, resulting in a complex and cryptic interface. Similarities between the D3M3 domain and the Selkirk Crest of Idaho and Washington suggest that this domain is the northerly continuation of the northward-plunging Priest River Complex.

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Lazzarotto, Manuele, David R. M. Pattison, Simon Gagné, and Paul G. Starr. "Metamorphic and structural evolution of the Flin Flon – Athapapuskow Lake area, west-central Manitoba." Canadian Journal of Earth Sciences 57, no. 11 (November 2020): 1269–88. http://dx.doi.org/10.1139/cjes-2019-0136.

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The Flin Flon – Athapapuskow Lake area, situated in the Flin Flon Greenstone Belt, Manitoba, consists of ocean-floor and island-arc assemblages, deformed and metamorphosed during the Trans-Hudson Orogeny (∼1.86–1.69 Ga). A new map of metamorphic mineral assemblages and isograds has been compiled that reveals a largely coherent regional metamorphic sequence increasing in metamorphic grade from prehnite–pumpellyite to amphibolite facies. Regional metamorphism postdates most of the deformation within the area, with the exception of the reactivation of major block-bounding faults. The regional prograde sequence has been subdivided into 10 metamorphic zones, separated by 9 isograds, that describe the transition from prehnite–pumpellyite to greenschist to amphibolite facies. The formation of contact metamorphic aureoles, pre-dating regional metamorphism, record conditions up to amphibolite facies. Equilibrium phase diagrams for the island-arc (low-Mg) and ocean-floor (high-Mg) assemblages were calculated and allow for the evaluation of the modelling techniques and determination of pressure–temperature conditions. Discrepancies between the modelling predictions and natural observations occur due to (1) limitations in the thermodynamic models for some of the complex minerals (e.g., amphibole); and (2) metastable persistence of some minerals to higher grade due to sluggish reaction kinetics. Notwithstanding these discrepancies, the modelling suggests that metamorphosed mafic rocks in the Flin Flon – Athapapuskow Lake area reached about 430–480 °C and 3.0–4.5 kbar. Peak metamorphic conditions within contact aureoles that preceded regional metamorphism did not exceed 500 °C (at a pressure between 2.7 and 4.4 kbar). The metamorphic field gradient records a transition from 250–300 °C/1.5–2.3 kbar to 430–480 °C/3–4.5 kbar (100–150 °C/kbar), defining a geothermal gradient of approximately 25–31 °C/km.

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Gieré, Reto. "Hydrothermal mobility of Ti, Zr and REE: examples from the Bergell and Adamello contact aureoles (Italy)." Terra Nova 2, no. 1 (January 1990): 60–67. http://dx.doi.org/10.1111/j.1365-3121.1990.tb00037.x.

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Liu, Xiao-Ming, Roberta L. Rudnick, Saswata Hier-Majumder, and Mona-Liza C. Sirbescu. "Processes controlling lithium isotopic distribution in contact aureoles: A case study of the Florence County pegmatites, Wisconsin." Geochemistry, Geophysics, Geosystems 11, no. 8 (August 2010): n/a. http://dx.doi.org/10.1029/2010gc003063.

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GIBSON, RICHARD G., and J. A. SPEER. "Contact aureoles as constraints on regional P-T trajectories: an example from the Northern Alabama Piedmont, USA." Journal of Metamorphic Geology 4, no. 3 (August 1986): 285–308. http://dx.doi.org/10.1111/j.1525-1314.1986.tb00352.x.

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Mason, Roger, and Rong Liu. "The Origin of Spots in Contact Aureoles and Over-Heating of Country Rock Next to a Dyke." Journal of Earth Science 29, no. 5 (October 2018): 1005–9. http://dx.doi.org/10.1007/s12583-018-0882-5.

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Powell, Wayne G., and Edward D. Ghent. "Low-pressure metamorphism of the mafic volcanic rocks of the Rossland Group, southeastern British Columbia." Canadian Journal of Earth Sciences 33, no. 10 (October 1, 1996): 1402–9. http://dx.doi.org/10.1139/e96-105.

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Mafic volcanic rocks of the Rossland Group have been metamorphosed in the subgreenschist to lower amphibolite faciès. Subgreenschist-facies regional metamorphic rocks are subdivided into prehnite–pumpeilyite zone and prehnite–epidote zone. Fluid inclusions in two subgreenschist-facies veins yielded mean homogenization temperatures of 139 and 151 °C. Assuming a reasonable maximum temperature limit of 275 °C for the subgreenschist fades, the fluid-inclusion isochores indicate a pressure <250 MPa for regional metamorphism in the subgreenschist facies. This is consistent with the widespread occurrence of prehnite–chlorite-bearing assemblages. Metamorphic grade increases sharply northward approaching the large plutons of the Nelson suite. The contact aureoles of the Nelson batholith and the related Bonnington pluton encompass most of the region, producing an extensive region underlain by rocks within the hornblende–oligoclasc zone. Intrusion of the Nelson plutonic suite overlapped with the development of the Hall Creek syncline and Silver King shear zone. The pattern of isograds across the Rossland Group indicates superimposed contact and regional metamorphism rather than progressively deeper structural levels northward.

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Nabelek, Peter I. "Fluid evolution and kinetics of metamorphic reactions in calc-silicate contact aureoles—From H2O to CO2 and back." Geology 35, no. 10 (2007): 927. http://dx.doi.org/10.1130/g24051a.1.

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Crowley, J. L., E. D. Ghent, and R. L. Brown. "Metamorphism in the Clachnacudainn terrane and implications for tectonic setting in the southern Omineca Belt, Canadian Cordillera." Canadian Journal of Earth Sciences 33, no. 11 (November 1, 1996): 1570–82. http://dx.doi.org/10.1139/e96-119.

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New and previously published metamorphic data suggest that the Clachnacudainn terrane of the southern Omineca Belt has tectonic affinities with the overlying Selkirk allochthon, rather than the underlying Shuswap metamorphic complex. This interpretation is based on relationships between metamorphic minerals and deformation phases, plutons, and the upper boundary of the terrane, the Standfast Creek fault. Regional kyanite and staurolite zones in the structurally lowest part of the terrane are overlain by a garnet zone that is continuous upward across the Standfast Creek fault into the Selkirk allochthon. This metamorphism is inferred to be Jurassic age based mainly on the continuity of these zones with those of known age in the allochthon. Textural relationships show that metamorphism occurred at different times relative to deformation across the terrane. Thermobarometry and a petrogenetic grid indicate that the terrane attained lower to middle amphibolitc facies conditions. Sillimanite and andalusite zones in the contact aureoles of posttectonic mid-Cretaceous plutons overprint the regional metamorphic zones and the Standfast Creek fault. Comparison of estimated pressures shows that approximately 5–10 km of exhumation occurred between regional and contact metamorphism. These metamorphic data are interpreted to indicate that the Standfast Creek fault had minor displacement after regional metamorphism and negligible displacement after contact metamorphism. Therefore, the fault cannot be an Eocene ductile to ductile–brittle shear zone that appressed or omitted metamorphic isograds and rapidly exhumed the Clachnacudainn terrane in its footwall, as was previously proposed.

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Dallmeyer, R. D., and J. D. Keppie. "Polyphase late Paleozoic tectonothermal evolution of the southwestern Meguma Terrane, Nova Scotia: evidence from 40Ar/39Ar mineral ages." Canadian Journal of Earth Sciences 24, no. 6 (June 1, 1987): 1242–54. http://dx.doi.org/10.1139/e87-118.

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40Ar/39Ar incremental-release ages of hornblende, muscovite, and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late Paleozoic tectonothermal evolution for the southwestern Meguma Terrane. Regional D1 folding with cleavage formation under greenschist – lower amphibolite facies, M1 metamorphic conditions, occurred at ca. 400–410 Ma and was followed by emplacement of a series of granitic stocks ranging in age between ca. 375 and 315 Ma. These were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade. These are locally superposed on M1 regional metamorphic assemblages and result in a complex isograd pattern. 40Ar/39Ar mineral ages suggest episodes of contact metamorphism occurred at (1) 360–375 Ma (possibly related to emplacement of the South Mountain Batholith or temporal equivalents), (2) 350–356 Ma around the Port Mouton Pluton and northeastern Shelburne Pluton, (3) ca. 315–325 Ma near the Wedgeport Pluton and in several other isolated localities, and (4) ca. 287 Ma along the northern margin of a large, low gravity anomaly located off the southwestern coast of Nova Scotia (inferred to reflect a subsurface pluton). Dextral shear deformation was locally associated with all of these thermal events. It is suggested that the Meguma Terrane experienced a similar stress system throughout the Late Devonian – Permian, with shear deformation localized in areas where increased temperatures resulted in decreased viscosity.

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Najoui, Khalid, Andre Francois Leyreloup, and Patrick Monie. "Conditions et ages 40 Ar/ 39 Ar de mise en place des granitoides de la zone externe sud du Massif central francais; exemple des granodiorites de St-Guiral et du Liron (Cevennes, France)." Bulletin de la Société Géologique de France 171, no. 5 (September 1, 2000): 495–510. http://dx.doi.org/10.2113/171.5.495.

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Abstract The St-Guiral and the Liron laccolithic granodiorites outcropping in the southeastern area of the French Massif Central intrude the Cambro-Ordovician low grade series of the western Cevennes. The petrological study of their contact aureoles shows that these plutons emplaced at low depth (1-2 kb; 690-700 degrees C). The laser probe 40 Ar/ 39 Ar allows us to suggest a minimum age of 324 Ma for the emplacement of the St-Guiral granodiorite. This emplacement seems synchronous with the LP-HT regional metamorphism in the western Cevennes for which the cooling ages are identical. The Liron granodiorite (310 Ma) is younger and crosscuts the thermal structures of the LP-HT regional metamorphism. Accordingly these plutons emplaced at the Namurian-early Westphalian during the extensional phases related to the generalised gravitational collapse of the previously thickened Hercynian belt. The detachment of the subducted lithosphere (slab detachment) could be related to these phenomena and could explain the granitization of the south external area of the Hercynian belt as well as the migration of the magmatism towards the south of the belt.

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Nabelek, Peter I., Anne M. Hofmeister, and Alan G. Whittington. "The influence of temperature-dependent thermal diffusivity on the conductive cooling rates of plutons and temperature-time paths in contact aureoles." Earth and Planetary Science Letters 317-318 (February 2012): 157–64. http://dx.doi.org/10.1016/j.epsl.2011.11.009.

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Pang, Kwan-Nang, Nicholas Arndt, Henrik Svensen, Sverre Planke, Alexander Polozov, Stephane Polteau, Yoshiyuki Iizuka, and Sun-Lin Chung. "A petrologic, geochemical and Sr–Nd isotopic study on contact metamorphism and degassing of Devonian evaporites in the Norilsk aureoles, Siberia." Contributions to Mineralogy and Petrology 165, no. 4 (November 21, 2012): 683–704. http://dx.doi.org/10.1007/s00410-012-0830-9.

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Svensen, Henrik H., Sergei Frolov, Grigorii G. Akhmanov, Alexander G. Polozov, Dougal A. Jerram, Olga V. Shiganova, Nikolay V. Melnikov, Karthik Iyer, and Sverre Planke. "Sills and gas generation in the Siberian Traps." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2130 (September 3, 2018): 20170080. http://dx.doi.org/10.1098/rsta.2017.0080.

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On its way to the surface, the Siberian Traps magma created a complex sub-volcanic plumbing system. This resulted in a large-scale sill emplacement within the Tunguska Basin and subsequent release of sediment-derived volatiles during contact metamorphism. The distribution of sills and the released sediment-stored gas volume is, however, poorly constrained. In this paper, results from a study of nearly 300 deep boreholes intersecting sills are presented. The results show that sills with thicknesses above 100 m are abundant throughout the upper part of the sedimentary succession. A high proportion of the sills was emplaced within the Cambrian evaporites with average thicknesses in the 115–130 m range and a maximum thickness of 428 m. Thermal modelling of the cooling of the sills shows that the contact metamorphic aureoles are capable of generating 52–80 tonnes of CO 2 m −2 with contributions from both marine and terrestrial carbon. When up-scaling these borehole results, an area of 12–19 000 km 2 is required to generate 1000 Gt CO 2 . This represents only 0.7–1.2% of the total area in the Tunguska Basin affected by sills, emphasizing the importance of metamorphic gas generation in the Siberian Traps. These results strengthen the hypothesis of a sub-volcanic trigger and driver for the environmental perturbations during the End-Permian crisis. This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.

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Marsh, Erin E., Richard J. Goldfarb, Craig J. R. Hart, and Craig A. Johnson. "Geology and geochemistry of the Clear Creek intrusion-related gold occurrences, Tintina Gold Province, Yukon, Canada." Canadian Journal of Earth Sciences 40, no. 5 (May 1, 2003): 681–99. http://dx.doi.org/10.1139/e03-018.

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The Clear Creek gold occurrences lie within deformed lower greenschist-facies rocks of the western Selwyn basin. They consist of auriferous, sheeted quartz veins that cut six Cretaceous stocks and their hornfels. The veins contain 12% combined pyrite and arsenopyrite, with lesser pyrrhotite, bismuthinite, and scheelite, as well as 25 g/t Au. New 40Ar/39Ar geochronology of hydrothermal micas indicates that the veins formed within 12 million years of granitoid emplacement. Fluid inclusion microthermometry defines a parent ore fluid of ~81 mol.% H2O, 14 mol.% CO2, 4 mol.% NaCl ± KCl, and 1 mol.% CH4, which unmixed into a low- and high-salinity immiscible pair. This suggests a more saline parent fluid and a greater degree of fluid unmixing relative to the other occurrences in the eastern Tintina Gold Province. Inclusions trapped in As- and Bi-rich, high-gold grade veins have homogenization temperatures of 300350°C, whereas inclusions found in more Ag- and Pb-rich veins are characterized by temperatures of 250300°C. Fluid inclusion geobarometry suggests hydro-fracturing and gold deposition at 57 km depth. The δ18O values of quartz samples range from 1316 (per mil) and δ34S for sulfides are also consistent between 3.0 and 0, with the exception of some outliers from the Contact Zone of the Pukelman stock that indicate a lower temperature second phase of mineralization. It remains uncertain as to whether the Clear Creek ore fluids were exsolved from magmas at depth or from devolatilization reactions within the contact metamorphic aureoles of the intrusions.

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Cui, X., P. I. Nabelek, and M. Liu. "Reactive flow of mixed CO2-H2O fluid and progress of calc-silicate reactions in contact metamorphic aureoles: insights from two-dimensional numerical modelling." Journal of Metamorphic Geology 21, no. 7 (August 29, 2003): 663–84. http://dx.doi.org/10.1046/j.1525-1314.2003.00475.x.

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30

Heinrich, Wilhelm, Sergey S. Churakov, and Matthias Gottschalk. "Mineral-fluid equilibria in the system CaO?MgO?SiO2?H2O?CO2?NaCl and the record of reactive fluid flow in contact metamorphic aureoles." Contributions to Mineralogy and Petrology 148, no. 2 (August 5, 2004): 131–49. http://dx.doi.org/10.1007/s00410-004-0598-7.

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PIPER, J. D. A., N. J. McARDLE, and Y. ALMASKERI. "Palaeomagnetic study of the Cairnsmoor of Fleet Granite and Criffel-Dalbeattie granodiorite contact aureoles: Caledonian tectonics of the Southern Uplands of Scotland and Devonian palaeogeography." Geological Magazine 144, no. 5 (June 19, 2007): 811–35. http://dx.doi.org/10.1017/s0016756807003536.

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The plutons of Cairnsmoor of Fleet (392±2 Ma) and Criffel-Dalbeattie (397±2 Ma, both mineral isochron ages) comprise two of four major post-tectonic granitic complexes emplaced into the Southern Uplands, an Ordovician–Silurian back-arc and foreland basin complex formed at the northern margin of the Iapetus Suture. To expand the palaeomagnetic record of the Southern Uplands we have studied palaeomagnetism and magnetic fabrics in traverses spanning contacts of these intrusions with host mudrocks. A uniform anisotropy of magnetic susceptibility (AMS) fabric across the Cairnsmoor of Fleet contact has been enhanced by recrystallization into hornfels near the contact and records a late Acadian regional stress operative during, or soon after, emplacement of the pluton in Middle Devonian times. Magnetization during slow cooling recorded a dual polarity (‘A’) remanence in granite and hornfels with mean direction D/I = 92/−2° (α95 = 6.5°) yielding a palaeopole (Q = 6) at 2°N, 265°E linked to cooling at c. 392 Ma. Subsidiary magnetizations are overprints imparted during Variscan tectonism (‘B’, D/I = 194/6°) and Jurassic rifting within the adjoining Irish Sea Basin (‘C’, c. 160–140 Ma, D/I = 172/−52°). The Criffel-Dalbeattie pluton has more complex AMS fabrics recording both deformation and emplacement effects. Hematite of secondary hydrothermal origin is a significant feature of the rock magnetic record in the aureole, which is otherwise dominated by paramagnetism. The granodiorite is more strongly magnetized than the country rocks, accounting for a positive aeromagnetic anomaly. A fairly dispersed dual polarity remanence (mean D/I = 115/55°, α95 = 18°) in granodiorite and late tectonic porphyrite dykes is probably the oldest magnetization preserved in this pluton because it correlates with an excursion of Britain into southerly palaeolatitudes at c. 410 Ma and indicates an Early Devonian emplacement age. The palaeofield at c. 397 Ma, the currently accepted isotopic age, is recorded by a minority overprinted remanence (mean D/I = 272/2°, α95 = 12°) similar to the record in the Cairnsmoor of Fleet pluton and granites from the adjoining Lake District terrane. Granite complexes of the Southern Uplands Block collectively record regional rotation and excursion of Britain into southerly latitudes between c. 410 and 390 Ma. Comparable Silurian–Devonian palaeomagnetic poles identify common apparent polar wander (APW) in paratectonic and orthotectonic terranes from the Variscan Front in the south to the Laurentian foreland in the north following climactic Acadian deformation. APW between 430 and 390 Ma embracing the (post-closure) history of the Caledonian orogen is a loop executed at rates much higher than typical rates of plate motion and appears to record a component of true polar wander. The ∼110° arc length is identical to polar shift identified between mid-Silurian and Lower–Middle Devonian poles from Gondwana. The two paths superimpose to show that the western margin of Gondwana was in proximity to the SE margin of Laurentia during Acadian deformation in Early–Middle Devonian times and remote from the Caledonides; the residual Rheic Ocean subsequently closed by a combination of pivotal and left lateral strike-slip motions.

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32

Chorlton, Lesley. "Regional setting of vein-style gold mineralization around the Goldlund mine, Sandybeach Lake area, northwestern Ontario." Canadian Journal of Earth Sciences 27, no. 12 (December 1, 1990): 1590–608. http://dx.doi.org/10.1139/e90-170.

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The Sandybeach Lake area was deformed in four stages. Stage 1 produced gently south-southeast-dipping foliations at low angles to bedding. Stage 2 involved draping of these planes and formation of contact-strain aureoles related to the emplacement of granitoid stocks. Stage 3 produced doubly plunging folds, steep foliations, and shear zones, which resulted from regional transpression, with a sinistral lateral shear sense along this arm of the Wabigoon greenstone belt. Stage 4 produced minor folds and shear displacements in some places and final tightening of stage 3 folds in others, compatible with final regional convergence.Regional quartz veins, including those carrying gold, appear to have filled tensional fractures related to bulk belt-perpendicular shortening and belt-parallel extension, sinistral shear, and tightening of folds in sheetlike competent bodies. Veins and mineralization thus coincided with late stage 3 deformation, possibly overlapping stage 4.Auriferous vein occurrences at the Goldlund mine display geometries similar to those of veins in the surrounding region. The main body of auriferous vein mineralization is hosted by a thick, composite metatonalite–metadiorite sheet. The vein system of this zone likely originated during the steepening and axial-plane transposition of the southeast-dipping limb near the southwest-plunging end of a stage 3 fold.

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Heimdal, Thea H., Morgan T. Jones, and Henrik H. Svensen. "Thermogenic carbon release from the Central Atlantic magmatic province caused major end-Triassic carbon cycle perturbations." Proceedings of the National Academy of Sciences 117, no. 22 (May 18, 2020): 11968–74. http://dx.doi.org/10.1073/pnas.2000095117.

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The Central Atlantic magmatic province (CAMP), the end-Triassic mass extinction (ETE), and associated major carbon cycle perturbations occurred synchronously around the Triassic–Jurassic (T–J) boundary (201 Ma). Negative carbon isotope excursions (CIEs) recorded in marine and terrestrial sediments attest to the input of isotopically light carbon, although the carbon sources remain debated. Here, we explore the effects of mantle-derived and thermogenic carbon released from the emplacement of CAMP using the long-term ocean–atmosphere–sediment carbon cycle reservoir (LOSCAR) model. We have tested a detailed emission scenario grounded by numerous complementary boundary conditions, aiming to model the full extent of the carbon cycle perturbations around the T–J boundary. These include three negative CIEs (i.e., Marshi/Precursor, Spelae/Initial, Tilmanni/Main) with sharp positive CIEs in between. We show that a total of ∼24,000 Gt C (including ∼12,000 Gt thermogenic C) replicates the proxy data. These results indicate that thermogenic carbon generated from the contact aureoles around CAMP sills represents a credible source for the negative CIEs. An extremely isotopically depleted carbon source, such as marine methane clathrates, is therefore not required. Furthermore, we also find that significant organic carbon burial, in addition to silicate weathering, is necessary to account for the positive δ13C intervals following the negative CIEs.

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Brown, P. E., T. J. Dempster, T. N. Harrison, and D. H. W. Hutton. "The rapakivi granites of S Greenland—crustal melting in response to extensional tectonics and magmatic underplating." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 173–78. http://dx.doi.org/10.1017/s0263593300007860.

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ABSTRACTEarly Proterozoic rapakivi intrusions in S Greenland occur as thick sheets which have ramp–flat geometry and were intruded along the median planes of active ductile extensional shear zones. These shear zones and their intrusions were linked via transfer zones in a major three-dimensional framework. At high structural levels (c. 6 km) the rapakivi intrusions developed thermal aureoles which overprint the regional assemblages, whereas at deeper levels in the regional structure they are contemporaneous with regional metamorphism. Thermobarometry on the regional and contact assemblages indicates low pressure granulite facies conditions (200–400 MPa, 650°-800°C) suggesting very high thermal gradients. The rapakivi suite and associated norites have low initial 87Sr/86Sr together with positive εNd values, indicating the involvement of predominantly young crust and/or mantle component in the generation of the igneous suite. It is considered that the voluminous norites are closely related to the mafic melts which underplated the juvenile crust to trigger the generation of the monzonitic rapakivi suite. Taken together, the data are consistent with a model of Proterozoic lithospheric extension, thinning of relatively juvenile continental crust and compression of mantle isotherms, resulting in high crustal heat flow, mafic underplating, and crustal melting with emplacement of magmas along a linked network of extensional shear zones.

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Paterson, Scott R., T. Kenneth Fowler, and Robert B. Miller. "Pluton emplacement in arcs: a crustal-scale exchange process." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 87, no. 1-2 (1996): 115–23. http://dx.doi.org/10.1017/s0263593300006532.

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ABSTRACT:Buddington (1959) pointed out that the construction of large crustal magma chambers involves complex internal processes as well as multiple country rock material transfer processes (MTPs), which reflect large horizontal, vertical and temporal gradients in physical conditions. Thus, we have attempted to determine the relative importance of different magmatic and country rock MTPs at various crustal depths, and whether country rock MTPs largely transport material vertically or horizontally, rather than seeking a single model of magma ascent and emplacement.Partially preserved roofs of nine plutons and in some cases roof–wall transitions with roof emplacement depths of 1·5–11 km were mapped. During emplacement, these roofs were not deformed in a ductile manner, detached or extended by faults, or significantly uplifted. Instead, sharp, irregular, discordant contacts are the rule with stoped blocks often preserved immediately below the roof, even at depths of 10 km. The upper portions of these magma chambers are varied, sometimes preserving the crests of more evolved magmas or local zones of volatile-rich phases and complex zones of dyking and magma mingling. Magmatic structures near roofs display a wide variety of patterns and generally formed after emplacement. Transitions from gently dipping roofs to steep walls are abrupt. At shallow crustal levels, steep wall contacts have sharp, discordant, stepped patterns with locally preserved stoped blocks indicating that the chamber grew sideways in part by stoping. Around deeper plutons, an abrupt transition (sometimes within hundreds of metres) occurs in the country rock from discordant, brittle roofs to moderately concordant, walls deformed in a ductile manner defining narrow structural aureoles. Brittle or ductile faults are not present at roof–wall joins.Near steep wall contacts at shallow to mid-crustal depths (5–15 km), vertical and horizontal deflections of pre-emplacement markers (e.g. bedding, faults, dykes), and ductile strains in narrow aureoles (0·1–0·3 body radii) give a complete range of bulk strain values that account for 0–100% of the needed space, but average around 30%, or less, particularly for larger batholiths. A lack of far-field deflection of these same markers rules out significant horizontal displacement outside the aureoles and requires that any near-field lateral shortening is accommodated by vertical flow. Lateral variations from ductile (inner aureole) to brittle (outer aureole) MTPs are typically observed. Compositional zoning is widespread within these magma bodies and is thought to represent separately evolved pulses that travelled up the same magma plumbing system. Magmatic foliations and lineations commonly cross-cut contacts between pulses and reflect the strain caused either by the late flow of melt or regional deformation.Country rocks near the few examined mid- to deep crustal walls (10–30 km) are extensively deformed, with both discordant and concordant contacts present; however, the distinction between regional and emplacement-related deformation is less clear than for shallower plutons. Internal sheeting is more common, although elliptical masses are present. Lateral compositional variations are as large as vertical variations at shallower depths and occur over shorter distances. Magmatic foliations and lineations often reflect regional deformation rather than emplacement processes.The lack of evidence for horizontal displacement outside the narrow, shallow to mid-crustal aureoles and the lack of lateral or upwards displacement of pluton roofs indicate that during emplacement most country rock is transported downwards in the region now occupied by the magma body and its aureole. The internal sheeting and zoning indicate that during the downwards flow of country rock, multiple pulses of magma travelled up the same magma system. If these relationships are widespread in arcs, magma emplacement is the driving mechanism for a huge crustal-scale exchange process.

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Ferry, John M., Boswell A. Wing, Sarah C. Penniston-Dorland, and Douglas Rumble. "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." Contributions to Mineralogy and Petrology 142, no. 6 (November 1, 2001): 679–99. http://dx.doi.org/10.1007/s00410-001-0316-7.

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37

Shawwa, Nabil A., Robert P. Raeside, David W. A. McMullin, and Christopher R. M. McFarlane. "Employing contact metamorphism to assess the conditions of pluton emplacement and timing of recrystallization in southwestern Kellys Mountain, Cape Breton Island, Nova Scotia." Canadian Journal of Earth Sciences 54, no. 11 (November 2017): 1165–78. http://dx.doi.org/10.1139/cjes-2017-0052.

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At Kellys Mountain, Cape Breton Island, Nova Scotia, the late Neoproterozoic Glen Tosh formation (a low-grade metapsammite–metapelite unit of the George River Metamorphic Suite) has been intruded by diorite, granodiorite, and granite plutons, and the diorite hosts a narrow contact metamorphic aureole. New mapping and sampling in the contact aureole reveals that the metasedimentary rocks have reached amphibolite-facies metamorphism resulting in the development of neoformed biotite, muscovite, cordierite, ilmenite, garnet, andalusite, sillimanite, monazite, and spinel within the meta-pelite, a mineral assemblage also found in the Kellys Mountain Gneiss as a result of low-pressure regional metamorphism. Neoformed minerals and the disappearance of foliation defines a contact metamorphic aureole within 300 m of the pluton contacts. Petrographic and microprobe analyses of equilibrium assemblages in metapelitic units of the contact aureole yielded metamorphic pressures of 250 MPa, implying an intrusion depth of ∼9 km, with temperatures ranging from 365 to 590 °C. The presence of earlier-formed andalusite and garnet indicates the rocks may have initially undergone a low-pressure regional metamorphic event prior to contact metamorphism. Monazite in the contact aureole was dated using in-situ U–Pb methods and yielded an age of 480.9 ± 3.7 Ma, interpreted as the time of formation of the contact metamorphic aureole.

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38

Hafeez, Amer, Sverre Planke, Dougal A. Jerram, John M. Millett, Dwarika Maharjan, and Tore Prestvik. "Upper Paleocene ultramafic igneous rocks offshore mid-Norway: Reinterpretation of the Vestbrona Formation as a sill complex." Interpretation 5, no. 3 (August 31, 2017): SK103—SK120. http://dx.doi.org/10.1190/int-2016-0143.1.

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Continental breakup between northwest Europe and Greenland (approximately 56 Ma) was associated with widespread magmatism. Silica undersaturated alkaline porphyritic igneous rocks of a similar age have previously been dredged near the mid-Norwegian coast. These igneous rocks of the Vestbrona Formation have previously been interpreted as either igneous plugs or volcanic flows. New 3D seismic data indicate that relatively small sill complexes are abundant in the same region. In total, 36 sills with a size of [Formula: see text] have been mapped. In addition, 10 seismic horizons were interpreted and tied to nearby wells to obtain a robust stratigraphic framework. The sills mainly intrude Cretaceous and Paleocene sequences; however, one sill is also identified in the pre-Cretaceous sequences. The sills locally form erosional remnants on the seabed due to massive uplifting and erosion of the continental margin. Vintage igneous and sedimentary dredge samples have been reanalyzed, including petrography, geochemistry (X-ray fluorescence [XRF], X-ray diffraction [XRD]), biostratigraphy, and Ar-Ar geochronology. The new Ar-Ar data suggest that the sills are 1–2 Ma older than breakup (approximately 57–58 Ma). Furthermore, the biostratigraphy and petrography of two sediment samples suggest that the samples were collected from near in situ subcrops and not of an ice rafted origin. The sediment samples are of Danian age and are strongly metamorphosed, most likely by contact metamorphism resulting from heating during sill emplacement. The newly identified sills have implications for the petroleum prospectivity of the study area including source rock maturation within thermal aureoles and the long-term alteration of fluid migration pathways.

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Friedman, G. M., and D. J. Schultz. "Precipitation of vaterite (CaCO3) during oil field drilling." Mineralogical Magazine 58, no. 392 (September 1994): 401–8. http://dx.doi.org/10.1180/minmag.1994.058.392.05.

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AbstractVaterite, a CaCO3 polymorph, is a rare mineral that is said to be metastable under all known conditions. According to the literature, vaterite precipitated from carbonate solution recrystallizes spontaneously to calcite or aragonite. Yet vaterite has been identified in hard tissues of organisms, in gallstones, in contact metamorphic aureoles, in zones of thermal metamorphism, in a meteorite, and in cone-in-cone concretions. Newly precipitated vaterite has formed at the expense of carbonate rock in drilling fluids in wells of New York, Michigan, Nevada, Texas, and New Zealand. Petrographic examination reveals a light brown core of Ca3SiO5 surrounded by a colourless rim of vaterite. The δ18OPDB of New York vaterite is −12.4‰ and that of the Michigan vaterite is −17.6‰, which reflect the oxygen isotopic composition of meteoric freshwater used in drilling. The δ13CPDB value of −19.2‰ for New York vaterite and that of −17.6‰ for Michigan vaterite suggest that natural gas dissolved original carbonate in the subsurface. Drilling records from both wells indicate that natural gas was released into the drilling muds from the formations exposed at the time vaterite was encountered. Crossplots of the oxygen and carbon isotopic ratios overlap those of spurrite rocks in thermal metamorphic zones in Israel. A C-14 radiocarbon analysis of the Michigan vaterite gave an age of 953±39 yr. BP. 88.8±0.6% is modern carbon and 11.2% is dead carbon. Hence this carbon, and therefore the vaterite, is essentially modern. A sample of the New York vaterite yielded a modern age.

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Héroux, Y., and R. Bertrand. "Maturation thermique de la matière organique dans un bassin du Paléozoïque inférieur, basses-terres du Saint-Laurent, Québec, Canada." Canadian Journal of Earth Sciences 28, no. 7 (July 1, 1991): 1019–30. http://dx.doi.org/10.1139/e91-093.

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The organic matter (OM) sampled in 15 oil exploration wells and 102 outcrops of Cambrian-Ordovician rocks in the St. Lawrence Lowlands consists of zooclasts (chitinozoans, graptolites, and scolecodonts) and solid bitumen (mainly pyrobitumen). The reflectance of pyrobitumen, transformed in vitrinite-equivalent (Ro-Std-B), indicates that the upper part of the platform sequence is mature (condensate zone) in the Québec area, but overmature in the Montréal area.The platform is divided into three domains based on optical texture of OM and types of bitumen: domain 1, south of Montréal, contains a highly reflecting and coked pyrobitumen showing alteration rims; domain 3, east of Trois-Rivières, contains low-reflecting, late solid bitumen commonly associated with oil impregnations; domain 2, located midway, contains a pyrobitumen with moderate reflectance and, locally, fine mosaic texture. The thermal maturation in the autochthonous sequences of the St. Lawrence Lowlands and in the Appalachian allochthons increases from the north-east toward the south-west and in the direction of the Appalachian belt. In wells, the gradient of Ro-Std-B with depth decrease from the autochthonous zone toward the Appalachian belt, and is inversely related with thickness of the sequences. Isoreflectance values parallel the outline of the Chambly–Fortierville Syncline in the central and eastern parts of the basin. Consequently, thermal maturation predates folding. Reflectance jumps observed between the Lowlands and the first Appalachian overthrusts, and observed when crossing Logan's Line, demonstrate that the maximum burial of Appalachian sequences predates the tectonic transport. The Ro-Std-B in allochthonous zones shows higher values in the St-Francis River cross-section than in structural equivalent units of the Québec area. Therefore the increase of thermal maturation observed from the northeast toward the southwest, in the St. Lawrence Lowlands, is also developed in the Appalachian allochthonous units. A post-Taconic regional thermal event explains this similarity in both autochthonous and allochthonous sequences, with the sequences of the Connecticut Valley – Gaspé Synclinorium being the most thermally mature.Zones of highest thermal maturation, locally observed in the Montréal area, are explained by (i) hydrothermal activity (Ro-Std = 3–4%), accounted for by sulfate and sulfide mineralization (Ba, Zn, Pb) and by (ii) contact metamorphism, related to alkaline intrusions (Ro-Std-B = 13%). The contact metamorphism is restricted to aureoles less than 5 km wide around the Monteregian alkaline intrusions, but the hydrothermal alteration, apparently not related to contact metamorphism, covers an area of 10 km around mineralized domains.

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Daigneault, R., P. St-Julien, and G. O. Allard. "Tectonic evolution of the northeast portion of the Archean Abitibi greenstone belt, Chibougamau area, Quebec." Canadian Journal of Earth Sciences 27, no. 12 (December 1, 1990): 1714–36. http://dx.doi.org/10.1139/e90-178.

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The Chibougamau area, occupying the northeastern part of the Abitibi greenstone belt is a large synclinorium of volcanic and sedimentary rocks enclosed within tonalitic gneisses. Several east–west–trending regional folds within this synclinorium are responsible for the vertical attitude of the strata. Synclinal structures, with youngest sediments within the core, possess axial-plane schistosity. Anticlines, on the other hand, either form domes with a core occupied by earlier tonalitic to dioritic plutons or are transected by a series of east–west-trending ductile faults (the Waconichi tectonic zone).An early deformation phase of low intensity (D1) generated broad, north–south folds without schistosity. The subsequent regional deformation, event D2, produced the large east–west folds. These deformations, in combination, produced the regional interference pattern of domes and basins. North–south horizontal shortening generated an east–west-trending schistosity associated with a vertical stretching lineation. Regional deformation at its climax produced a tightening of folds and rotation of fold axes parallel to the stretching lineation.Plutons deflected the regional east–west schistosity and formed concentric trajectories associated with "contact-strain aureoles." This produced small interaction zones or triple points characterized by strong vertical extension. These relations suggest an interference between a regional stress field, which produced north–south horizontal shortening, and local stress fields, controlled or deflected by granitoid plutons acting as competent bodies.East–west-trending ductile shear zones represent the final stage of the regional deformation. The observed northward and southward reverse movement along these east–west faults, their parallelism to the axial trace of folds, and the regional schistosity are probable evidence of a regime dominated by a coaxial strain.

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Chown, E. H., Réal Daigneault, Wulf Mueller, and J. K. Mortensen. "Tectonic evolution of the Northern Volcanic Zone, Abitibi belt, Quebec." Canadian Journal of Earth Sciences 29, no. 10 (October 1, 1992): 2211–25. http://dx.doi.org/10.1139/e92-175.

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The Archean Abitibi Subprovince has been divided formally into a Northern Volcanic Zone (NVZ), including the entire northern part of the subprovince, and a Southern Volcanic Zone (SVZ) on the basis of distinct volcano-sedimentary successions, related plutonic suites, and precise U–Pb age determinations. The NVZ has been further formally subdivided into (i) a Monocyclic Volcanic Segment (MVS) composed of an extensive subaqueous basalt plain with scattered felsic volcanic complexes (2730–2725 Ma), interstratified with or overlain by linear volcaniclastic sedimentary basins; and (ii) a Polycyclic Volcanic Segment (PVS) comprising a second mafic–felsic volcanic cycle (2722–2711 Ma) and a sedimentary assemblage with local shoshonitic volcanic rocks.A sequence of deformational events (D1–D6) over a period of 25 Ma in the NVZ is consistent with a major compressional event. North–south shortening was first accommodated by near-vertical east-trending folds and, with continued deformation, was concentrated along major east-trending fault zones and contact-strain aureoles around synvolcanic intrusions, both with a downdip movement. Subsequent dextral strike-slip movement occurred on southeast-trending faults and major east-trending faults which controlled the emplacement of syntectonic plutons (2703–2690 Ma).This study suggests that the NVZ, which is a coherent geotectonic unit, initially formed as a diffuse volcanic arc, represented by the MVZ, in which the northern part, represented by the PVS, evolved into a mature arc as documented by a second volcanic and sedimentary cycle associated with major plutonic accretion. Volcano-sedimentary evolution and associated plutonism, as well as structural evolution, are best explained by a plate-tectonic model involving oblique convergence.

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Bhattacharyya, P. K., and Subimal Mukherjee. "Granulites in and around the Bengal anorthosite, eastern India; genesis of coronal garnet, and evolution of the granulite-anorthosite complex." Geological Magazine 124, no. 1 (January 1987): 21–32. http://dx.doi.org/10.1017/s0016756800015752.

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AbstractGranulites occur in and around an anorthosite massif (commonly referred to as the Bengal anorthosite) in eastern India. The central part of the anorthosite is massive in nature with locally developed ‘fluxion structure’ in isolated blocks. Banding in the peripheral part is typical of that of the massif anorthosites of Anderson & Morin. The granulites bear imprints of polyphase deformation, and the xenoliths of granulites within the anorthositic massif maintain their regional structural alignment. The Anorthosite, syntectonic with the second fold movement in the terrane, has developed second generation structures.Hornblende, orthopyroxene, clinopyroxene, plagioclase and quartz with or without garnet and other minor phases consitute the granulites. In the anorthosites, orthopyroxene, clinopyroxene, hornblende, and magnetite with or without garnet may constitute more than 15% of the mode. Garnet, when present in the rocks, is a late overprint. Symplectitic growth of garnet with one or more of the phases such as ilmenite, quartz, clinopyroxene and sodic plagioclase indicates genesis of garnet through decomposition of orthopyroxene and/or prograde hornblende in the presence of calcic plagioclase. The garnet formed during prograde dehydration reactions, rather than cooling of the complex.Chemical characteristics of the mafic phases in the rocks indicate attainment of exchange equilibrium with respect to the major cations in closely associated hornblende, clinopyroxene, orthopyroxene and garnet. Estimated physical conditions of metamorphism from contrasted assemblages suggest a final equilibration of different granulitic assemblages as well as of the anorthositic assemblages under similar conditions. There was, however, belated building up of water pressure in the anorthositic domains stabilizing a late hornblende during cooling of the complex. Absence of chilled margins in the anorthosite as well as absence of contact aureoles in the enveloping and enclosed granulites indicate emplacement of the anorthosite in a hot environment, prior to cooling of the complex.

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Nabelek, Peter I., Anne M. Hofmeister, and Alan G. Whittington. "Corrigendum to ‘The influence of temperature-dependent thermal diffusivity on the conductive cooling rates of plutons and temperature-time paths in contact aureoles’ [Earth Planet. Sci. Lett. 317–318 (2012) 157–164]." Earth and Planetary Science Letters 413 (March 2015): 214. http://dx.doi.org/10.1016/j.epsl.2015.01.011.

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Wang, Dayong. "Comparable study on the effect of errors and uncertainties of heat transfer models on quantitative evaluation of thermal alteration in contact metamorphic aureoles: Thermophysical parameters, intrusion mechanism, pore-water volatilization and mathematical equations." International Journal of Coal Geology 95 (June 2012): 12–19. http://dx.doi.org/10.1016/j.coal.2012.02.002.

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Park, Youngdo, and Changwhan Oh. "CONTACT2: A Macintosh program for calculating heat conduction in a contact aureole." Computers & Geosciences 24, no. 9 (November 1998): 901–4. http://dx.doi.org/10.1016/s0098-3004(97)00135-0.

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Piazolo, Sandra, David J. Prior, M. D. Holness, and Andreas O. Harstad. "Annealing in a Natural Laboratory: an EBSD and Cl Study of Calcite and Quartz Growth from Volumes of Rock Heated by a Nearby Melt Intrusion." Materials Science Forum 550 (July 2007): 333–38. http://dx.doi.org/10.4028/www.scientific.net/msf.550.333.

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Annealing is an important mechanism of microstructural modification both in rocks and metals. In order to relate directly changes in crystallographic orientation to migrating boundaries the researcher has the option to investigate either samples where the grain boundary motion can be directly tracked or a series of samples exhibiting successively higher degrees of annealing. Here we present results from rock samples collected from two well characterised contact aureoles (a volume of rock heated by the intrusion of a melt in its vicinity): One quartz sample in which patterns revealed by Cathodoluminescence (CL) indicate the movement of grain boundaries and a series of calcite samples of known temperature history. Electron backscatter diffraction (EBSD) analysis is used to link the movement of grain, twin boundaries and substructures with the crystallographic orientation / misorientation of a respective boundary. Results from the quartz bearing rock show: (a) propagation of substructures and twin boundaries in swept areas both parallel and at an angle to the growth direction, (b) development of slightly different crystallographic orientations and new twin boundaries at both the growth interfaces and within the swept area, and (c) a gradual change in crystallographic orientation in the direction of growth. Observations are compatible with a growth mechanism where single atoms are attached and detached both at random and at preferential sites i.e. crystallographically controlled sites or kinks in boundary ledges. Strain fields caused by defects and/or trace element incorporation may facilitate nucleation sites for new crystallographic orientations at distinct growth interfaces but also at continuously migrating boundaries. Calcite samples show with increasing duration and temperature of annealing: (a) systematic decrease of the relative frequency of low angle grain boundaries (gbs), (b) decrease in lattice distortion within grains, (c) development of distinct subgrains with little internal lattice distortion, (d) change in lobateness of gbs and frequency of facet parallel gbs and (e) change in position of second phase particles. These observations point to an increasing influence of grain boundary anisotropy with increasing annealing temperature, while at the same time the influence of second phase particles and subtle driving-force variations decrease. This study illustrates the usefulness of using samples from natural laboratories and combining different analysis techniques in microprocess analysis.

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Mattsson, Tobias, Steffi Burchardt, Karen Mair, and Joachim Place. "Host-rock deformation during the emplacement of the Mourne Mountains granite pluton: Insights from the regional fracture pattern." Geosphere 16, no. 1 (December 16, 2019): 182–209. http://dx.doi.org/10.1130/ges02148.1.

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Abstract The Mourne Mountains magmatic center in Northern Ireland consists of five successively intruded granites emplaced in the upper crust. The Mourne granite pluton has classically been viewed as a type locality of a magma body emplaced by cauldron subsidence. Cauldron subsidence makes space for magma through the emplacement of ring dikes and floor subsidence. However, the Mourne granites were more recently re-interpreted as laccoliths and bysmaliths. Laccolith intrusions form by inflation and dome their host rock. Here we perform a detailed study of the deformation in the host rock to the Mourne granite pluton in order to test its emplacement mechanism. We use the host-rock fracture pattern as a passive marker and microstructures in the contact-metamorphic aureole to constrain large-scale magma emplacement-related deformation. The dip and azimuth of the fractures are very consistent on the roof of the intrusion and can be separated into four steeply inclined sets dominantly striking SE, S, NE, and E, which rules out pluton-wide doming. In contrast, fracture orientations in the northeastern wall to the granites suggest shear parallel to the contact. Additionally, contact-metamorphic segregations along the northeastern contact are brecciated. Based on the host-rock fracture pattern, the contact aureole deformation, and the north-eastward–inclined granite-granite contacts, we propose that mechanisms involving either asymmetric “trap-door” floor subsidence or laccolith and bysmalith intrusion along an inclined or curved floor accommodated the emplacement of the granites and led to deflection of the northeastern wall of the intrusion.

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Selyatitskii, A. Yu, O. P. Polyansky, and R. A. Shelepaev. "A High-Pressure Thermal Aureole of the Bayan-Kol Gabbro–Monzodiorite Intrusion (Western Sangilen, Southeastern Tuva): Evidence for Lower-Crust Mafic Magma Chambers." Russian Geology and Geophysics 62, no. 9 (September 1, 2021): 987–1005. http://dx.doi.org/10.2113/rgg20194157.

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Abstract —Thermal metamorphism produced an aureole near the early Paleozoic Bayan-Kol gabbro–monzodiorite intrusion in the Erzin shear zone of western Sangilen (Tuva–Mongolia microcontinent, Central Asian Orogenic Belt). Field observation of intrusive contact, structure–textural and mineral transformations of metamorphic rocks, regular changes in the chemical composition of minerals with approaching the intrusive contact, and high temperature gradient from intrusive to wallrocks verified the occurrence of a contact aureole near the Bayan-Kol intrusion. The high-gradient thermal metamorphism (M2) affected garnet–staurolite–kyanite schists that formed during earlier regional metamorphism (M1) at 6.2–7.9 kbar and 600–670 ºC. The 0.5 km wide M2 metamorphic aureole mapped along the northwestern intrusion margin consists of a muscovite–sillimanite zone adjacent to the sedimentary country rocks and a cordierite–K-feldspar zone on the side of the intrusion. The M2 metamorphic reactions occurred within the granulite facies temperature range 880–910 ºC along the contact with monzodiorites and at ~950 ºC along the boundary with gabbronorites; the temperature on the aureole periphery was about 640 ºC. Pressure estimates indicate deep-seated high-grade metamorphism at 6.9–7.8 kbar, while the intrusion itself crystallized at 7.7–7.8 kbar. The suggested numerical model implying the formation of a thermal aureole at a depth of 26 km (7 kbar) in the lower crust is consistent with the temperature pattern determined by geothermobarometry for several key points of the metamorphic zoning and confirms its deep-level origin. Thus, the aureole near the Bayan-Kol intrusion represents a rare case of contact metamorphism in the lower continental crust. The obtained results, along with published petrological and geochronological evidence, reveal two depth levels of the early Paleozoic M2 metamorphism in the Sangilen area: upper (7–15 km, 2–4 kbar) and lower (26–30 km, 7–8 kbar) crust. The Bayan-Kol gabbro–monzodiorite intrusion is likely a small apophysis or a fragment of a deep-crust intermediate magma chamber, while the moderate-pressure (7–8 kbar) M2 granulites in the Erzin shear zone are products of high-gradient metamorphism related to the Cambrian–Ordovician collisional mafic magmatism in the Sangilen area.

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Mouchos, E., L. Papadopoulou, B. J. Williamson, and G. Christofides. "MARIALITIC SCAPOLITE OCCURENCES FROM THE KIMMERIA-LEFKOPETRA METAMORPHIC CONTACT, XANTHI (N. GREECE)." Bulletin of the Geological Society of Greece 50, no. 4 (July 28, 2017): 1943. http://dx.doi.org/10.12681/bgsg.14244.

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Emplacement of the Xanthi Plutonic Complex within the Rhodope Massif of N. Greece created an extensive metamorphic aureole around the plutonite. The aureole contains two areas of intense scapolitization in the contacts between granodiorite and biotitegneiss and between monzonite and sandstone, the latter cross-cut by andesite dykes. This paper reports the results of a mineralogical and geochemical study into the formation of the scapolites and particularly the nature of the plutonite-derived hydrothermal fluids from which scapolites were formed.

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Journal articles on the topic 'Contact aureoles'

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