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1
Feininger, Tomas, and Alan K. Goodacre. "The eight classical Monteregian hills at depth and the mechanism of their intrusion." Canadian Journal of Earth Sciences 32, no. 9 (September 1, 1995): 1350–64. http://dx.doi.org/10.1139/e95-109.
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The eight classical Monteregian hills are monadnocks on the St. Lawrence Lowlands and adjacent Appalachian foothills in a swath that sweeps 80 km eastward from Montréal. Gravity anomalies suggest the presence of about 200 km3 of mafic and ultramafic Monteregian rocks at depth. Mounts Royal, Saint-Bruno, and Rougemont are interpreted to be pluglike intrusions atop large laccoliths that were fed by magma that spread laterally along the buried Precambrian–Paleozoic unconformity. Mounts Saint-Hilaire, Saint-Grégoire, and Yamaska lie at higher stratigraphic levels in flat-lying sedimentary host rocks. These six intrusions filled the lower parts of breccia pipes formed by the explosive upward escape of volatiles. Late-stage settling of the cooling intrusions dragged downward an encircling collar of baked host rocks. The two easternmost hills (Brome and Shefford) are interpreted to be thin intrusive sheets emplaced along Appalachian thrusts. Stepwise emplacement of magma in the thick cover rocks in the east promoted contamination and may account for the presence of quartz-bearing felsic rocks. Igneous rocks along the deeply buried unconformity in the east and felsic rocks, all undetectable by gravity, could add substantially to the total volume of the Monteregians. The absence of Monteregian intrusives west of Montréal (apart from Oka) is explained by the removal through erosion of Paleozoic cover rocks. The Monteregian intrusives developed only in cover rocks; feeders in the Precambrian basement are possibly small and may be covered by Quaternary deposits. Monteregian magmatism was a major event, out of all proportion to the small intrusions presently exposed, and may have emplaced as much as 1000 km3 of igneous rock.
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Dean, Mark T., and Nicholas Turner. "Conodont Colour Alteration Index (CAI) values for the Carboniferous of Scotland." Transactions of the Royal Society of Edinburgh: Earth Sciences 85, no. 3 (1994): 211–20. http://dx.doi.org/10.1017/s0263593300003606.
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AbstractConodont elements from Scottish Carboniferous rocks have been reviewed for Colour Alteration Index(CAI) data, and most values range between 1 and 1·5. Assuming a local average geothermal gradient similar to that of today, the observed and predicted CAI values generally fit well. Only a few of the samples analysed were influenced by local igneous intrusives. The CAI range shown lies within the immature (early dry gas) to mature (perhapsmid-oil window) stages of hydrocarbon generation, and this suggests that burial maturation (where CAI values are 1-5) could account for locally generated oil, where this occurred away from igneous intrusions. Alkali-dolerite and tholeiitic intrusives are, however, widespread in the Midland Valley of Scotland, and an understanding of their thermal effects has implications for both coal and petroleum exploration. The insensitivity of conodonts to low temperatures is noted, and the relevance, application and potential of various other palaeothermometers is discussed. Locally, the qualitative study of spore colour (SCI) appears useful.
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Lynas, B. D. T., C. C. Rundle, and R. W. Sanderson. "A note on the age and pyroxene chemistry of the igneous rocks of the Shelve Inlier, Welsh Borderland." Geological Magazine 122, no. 6 (November 1985): 641–47. http://dx.doi.org/10.1017/s0016756800032040.
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AbstractGeological survey, electron microprobe analyses of clinopyroxenes and isotopic age determinations have revealed that the intrusive dolerites and basic–intermediate lavas of the Shelve Ordovician Inlier are part of a co-magmatic suite which show transitional affinities between tholeiites and alkali basalts. The ages of most of the intrusives are shown to be mid-Ordovician.
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Sparlin, Mark A., and Richard D. Lewis. "Interpretation of the magnetic anomaly over the Omaha Oil Field, Gallatin County, Illinois." GEOPHYSICS 59, no. 7 (July 1994): 1092–99. http://dx.doi.org/10.1190/1.1443665.
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A 40 nanoTesla (nT) magnetic anomaly identified in an aeromagnetic survey over southern Illinois contours as a localized magnetic high on the west flank of a regional magnetic low. This magnetic anomaly is generally coincident with the Omaha Oil Field in northwest Gallatin County, Illinois. It was initially assumed that cultural sources of steel associated with this oil field were the primary source of the magnetic feature; however, similar oil fields overflown by the survey do not exhibit magnetic anomalies in the data set. The Luther Rister et ux ♯1 well, drilled near the apex of the Omaha structural dome, encountered two zones of ultramafic intrusive rock containing 9.0 percent by volume magnetite. These intrusives were identified to be alnöites which are a class of mantle‐derived ultramafic rock that can be associated with the incipient stages of crustal rifting. A ground magnetic survey verified the presence of the anomaly, and provided detailed data for 3-D modeling of the source. Petrophysical evaluations, magnetic susceptibility measurements and thin section modal analysis were made on drill cuttings from the ultramafic intrusives encountered in the Luther Rister ♯1 well. These measurements were made to constrain the 3-D magnetic modeling by the petrophysical characteristics of the source. After removal of the regional magnetic field, the resulting 140 nT residual magnetic anomaly was successfully modeled using two ultramafic sills with an igneous feeder plug. The two igneous sills adequately account for the structural closure exhibited in the Omaha Oil Field and raise the interesting possibility of other hydrocarbon trapping structures generated by intrusives emplaced into the sedimentary section.
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Ritchie, J. D., J. L. Swallow, J. G. Mitchell, and A. C. Morton. "Jurassic ages from intrusives and extrusives within the Forties igneous province." Scottish Journal of Geology 24, no. 1 (June 1988): 81–88. http://dx.doi.org/10.1144/sjg24010081.
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Ogunyele, Abimbola, Olatunde Adegbuyi, Miracle Odindu, and Tunde Erinfolami. "Geochemical Characteristics and Petrogenesis of Basement Rocks in Idoani Area, Ondo State, Southwestern Nigeria." International Journal of Advanced Geosciences 5, no. 2 (October 28, 2017): 102. http://dx.doi.org/10.14419/ijag.v5i2.8377.
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Idoani area of Ondo State is an extension of the Upper Proterozoic Igarra Schist Belt of the Southwestern Nigerian Basement Complex. The area comprises mainly of metasedimentary rocks with subordinate amount of intrusives. Quartz-mica schist, phyllite, quartzite and banded gneiss are the dominant rock types in the area. These metasediments are intruded by the Older granite and other minor intrusives (pegmatite, aplite, dolerite dyke, quartz vein). Idoani rocks, as revealed by petrographic studies, are rich in quartz, alkali and plagioclase feldspars and mica with a low amount of opaque minerals. Geochemical studies and petrochemical variation diagrams show that the rocks are sub-alkaline, medium-K calc-alkaline to shoshonitic, peraluminous, and characterized by intermediate-high silica content and low-moderate amount of mafic oxides. Petrological and geochemical studies revealed that the quartz-mica schist and phyllite are metapelites while the quartzite is a meta-arkose, derived from a granitic – quartz-monzonitic source. The banded gneisses were probably derived from a hybrid sedimentary–igneous protoliths while the granite is of magmatic origin.
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Ridgway, Jeff R., and Mark A. Zumberge. "Deep‐towed gravity surveys in the southern California Continental Borderland." GEOPHYSICS 67, no. 3 (May 2002): 777–87. http://dx.doi.org/10.1190/1.1484521.
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We surveyed two sites in the southern California continental borderland with a newly developed instrument, a towed deep ocean gravimeter—a gravity sensor that can be towed a few tens of meters above the sea floor. During its development phase, we used the instrument to survey two regions off the coast of southern California. The first was along two tracks in the San Diego Trough. The second was over a seamount‐like feature named Emery Knoll. Results of the trough survey reveal a basin with a geometry consistent with seismic data. We observed no significant density contrast across the San Diego Trough fault in the near‐surface sediments. The survey of Emery Knoll shed light on the question of the origin of this structure; modeling the knoll to determine its bulk density suggested a nearly uniform structure surrounded by sedimentary basins with a more massive central intrusive body. Derived densities of 2850 kg/m3 for the knoll and 3050 kg/m3 for the central intrusion assume that no deep unmodeled sources exist directly underneath the knoll. The gravity data favor a model of metamorphic basement rock uplifted and containing igneous intrusives.
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Klötzli, Urs, Jolanta Burda, Qiu-Li Li, Yu Liu, Gyula Jakab, Lucian Ionescu, and Paul Tibuleac. "Petrochronological Evidence for a Three-Stage Magmatic Evolution of the Youngest Nepheline Syenites from the Ditrău Alkaline Massif, Romania." Minerals 12, no. 5 (May 23, 2022): 657. http://dx.doi.org/10.3390/min12050657.
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The Ditrău Alkaline Massif (DAM) is an igneous massif in the Eastern Carpathian Mountains of Romania. Numerous geochronological and geochemical studies have proposed a long formation history (ca. 70 m.y.) of the DAM from Middle Triassic to Cretaceous times, which is hardly reconcilable with geochemical evolutionary models and the geotectonic environment during the Mesozoic in this part of the Eastern Carpathian Mountains. In order to put tighter age constraints on the igneous processes forming the DAM, two nepheline syenites from the so-called Ghiduţ and Lăzarea suites were investigated. Based on field and geochemical evidence, the two rock suites represent the younger part of the DAM intrusives. Detailed zircon characterization, in situ zircon SIMS U-Pb dating, and geochemical modelling were used to establish the timing of zircon crystallization and thus to set time constraints on the igneous formation of these parts of the DAM. The intrusion of the dated Ghiduţ suite sample took place at 232 ± 1 Ma in the Karnium, whereas the Lăzarea suite nepheline syenite sample was intruded at 225 ± 1 Ma in the Norium. Together with published geochemical and geochronological data, three different magmatic events can thus be identified: Ghiduţ suite at 231.1 ± 0.8 Ma, Ditrău suite at 230.7 ± 0.2 Ma, and Lăzarea suite at 224.9 ± 1.1 Ma. Although the ages of the events 1 and 2 are statistically indistinguishable, the combination of geochemical and petrochronological data certainly favor independent intrusion events. Thus, the igneous events forming the younger parts of the DAM encompassed a time span of ca. 13 m.y. Additionally, each igneous event can tentatively be divided in an older syenitic stage and a younger nepheline syenitic one, each with an age difference of some 100,000 years. No indication of any post 215 Ma igneous or hydrothermal activity was found. The new data and interpretation significantly improve our understanding of the temporal and geochemical evolution of the DAM and of alkaline complexes as such, demonstrating that the underlying igneous processes (melt generation, assimilation, fractionation, and the duration of plumbing systems) work on the same time scale for both sorts of magmatic rock suites.
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Nwachukwu, M. A., L. I. Nwosu, P. A. Uzoije, and C. A. Nwoko. "1D resistivity inversion technique in the mapping of igneous intrusives; A step to sustainable quarry development." Journal of Sustainable Mining 16, no. 4 (2017): 127–38. http://dx.doi.org/10.1016/j.jsm.2017.11.001.
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Ukpabi, N., and E. Etuk. "Petrographic Analysis and Total organic content (TOC) of Mudstone Inclusions in Igneous Intrusives in Lower Benue Trough, Nigeria." Advances in Research 3, no. 1 (January 10, 2015): 60–70. http://dx.doi.org/10.9734/air/2015/11962.
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Wade, C. E., J. L. Payne, K. Barovich, S. Gilbert, B. P. Wade, J. L. Crowley, A. Reid, and E. A. Jagodzinski. "ZIRCON TRACE ELEMENT GEOCHEMISTRY AS AN INDICATOR OF MAGMA FERTILITY IN IRON OXIDE COPPER-GOLD PROVINCES." Economic Geology 117, no. 3 (May 1, 2022): 703–18. http://dx.doi.org/10.5382/econgeo.4886.
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Abstract Extrusive and intrusive felsic magmas occur throughout the evolution of silicic-dominated large igneous province magmatism that is temporally related to numerous economically significant iron oxide copper-gold (IOCG) deposits in southern Australia. We investigate zircon trace element signatures of the felsic magmas to assess whether zircon composition can be related to fertility of the volcanic and intrusive suites within IOCG-hosted mineral provinces. Consistent with zircon forming in oxidizing magmatic conditions, the rare earth element (REE) patterns of zircon sourced from both extrusive and intrusive magmatic rocks are characterized by light REE depletions and a range of positive Ce and negative Eu anomalies. The timing of the major phase of IOCG mineralization overlaps with the early part of the first phase of Lower Gawler Range Volcanics magmatism (1593.6–1590.4 Ma) and older intrusive magmatism of the Hiltaba Suite (1593.06–1590.50 Ma). Zircon in these mineralization-related intrusives and extrusives is distinguished from zircon in younger, mineralization-absent rocks by higher Eu/Eu*, Ce/Ce*, and Ti values and separate magma evolution paths with respect to Hf. These zircon characteristics correspond to lower degrees of fractionation and/or crustal assimilation, more oxidizing magmatic conditions, and higher magmatic temperatures, respectively, in magmas coeval with mineralization. In this respect, we consider higher oxidation state, lower degrees of fractionation, and higher magmatic temperatures to be features of fertile magmas in southern Australian IOCG terrains. Similar zircon REE characteristics are shared between magmas associated with southern Australian IOCG and iron oxide-apatite (IOA) rhyolites from the St. Francois Mountains, Missouri, namely high Ce/Ce* and high Dy/Yb, indicative of oxidized and dry magmas, respectively. The dry and more fractionated nature of the IOCG- and IOA-associated magmas contrasts with the hydrous and unfractionated nature of fertile porphyry Cu deposit magmas. As indicated by high Ce/Ce* ratios, the oxidized nature is considered a key element in magma fertility in IOCG-IOA terrains. In both IOCG and IOA terrains, the trace element compositions of zircon are able to broadly differentiate fertile from nonfertile magmatic rocks.
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Assis, Omar Sebastian, Claudia Beatriz Zaffarana, Darío Orts, Carla Puigdomenech, Víctor Ruiz González, Gloria Gallastegui, Natalia Hauser, Ekaterina S. Kiseeva, José Francisco Molina, and Sebastián Pernich. "Emplacement conditions and exhumation of the Varvarco Tonalite and associated plutons from the Cordillera del Viento, Southern Central Andes." Geological Magazine 159, no. 5 (March 14, 2022): 645–72. http://dx.doi.org/10.1017/s0016756821001163.
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AbstractDuring the Late Cretaceous Andean orogeny, the compressive deformation associated with the shallowing of the subducting slab caused the development of the arc-related igneous rocks known as the Naunauco Belt. This study presents petrographic, mineralogical and anisotropy of magnetic susceptibility data for the Varvarco Intrusives (the Varvarco Tonalite, Butalón Tonalite and Radales Aplite), which crop out in the Cordillera del Viento, Neuquén Province, Argentina. The assembly of plutons was formed by mafic magma episodic injection. Amphibole and biotite compositions suggest that the Varvarco Tonalite is related to calc-alkaline, I-type magmas, typical of subduction environments. Different geothermobarometers based on amphibole and plagioclase compositions for the Varvarco Tonalite suggest shallow emplacement conditions (∼2–3 kbar, equivalent to ∼12 km depth). Apatite fission-track analyses give exhumation ages of 67.5 ± 8 Ma for the Varvarco Tonalite and 50.3 ± 5.9 Ma for the Butalón Tonalite. A calculated continuous fast exhumation rate of at least 330 °C Ma−1 is consistent with the shallow emplacement conditions, textural data and geobarometric estimations. In agreement with the thermal profile, the magmatic system was exhumed by ∼12 km within c. 2.1 Ma implying a geothermal gradient of ∼62.5 °C km−1. The last step of exhumation occurred between ∼65.3 and 56.9 Ma. The magmatic fabrics observed in the studied plutons reflect mostly magma chamber processes. The Varvarco Intrusives represent satellite calc-alkaline plutons of the North Patagonian Batholith which were emplaced syn- to post-tectonically with respect to a major deformation stage of the Southern Central Andes.
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Miller, Calvin F., John M. Hanchar, Joseph L. Wooden, Victoria C. Bennett, T. Mark Harrison, David A. Wark, and David A. Foster. "Source region of a granite batholith: evidence from lower crustal xenoliths and inherited accessory minerals." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 49–62. http://dx.doi.org/10.1017/s0263593300007744.
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ABSTRACTLike many granites, the Late Cretaceous intrusives of the eastern Mojave Desert, California, have heretofore provided useful but poorly focused images of their source regions. New studies of lower crustal xenoliths and inherited accessory minerals are sharpening these images.Xenoliths in Tertiary dykes in this region are the residues of an extensive partial melting event. Great diversity in their composition reflects initial heterogeneity (both igneous and sedimentary protoliths) and varying amounts of melt extraction (from <10% to >70%). Mineral assemblages and thermobarometry suggest that the melting event occurred at T ≥ 750°C at a depth of about 40 km. Present-day Sr, Nd, and Pb isotopic ratios indicate a Mojave Proterozoic heritage, but unrealistic model ages demonstrate the late Phanerozoic adjustment of parent/daughter ratios. A link between these xenoliths and the Late Cretaceous granites, though not fully documented, is probable; in any case, they provide invaluable clues concerning a crustal melting event, recording information about nature of source material (heterogeneous, supracrustal-rich), conditions of melting (moderately deep, moderately high T, accompanied by partial dehydration), and melt extraction (highly variable, locally extensive).The Old Woman-Piute granites contain a large fraction of inherited zircon and monazite. A SHRIMP ion probe investigation shows that these zircons record a Proterozoic history similar to that which affected the Mojave region. Zonation patterns in zircons, and to a lesser extent monazites and xenotimes, document multiple phases of igneous, metamorphic, and sedimentary growth and degradation, commonly several in a single grain. Low Y in portions of the cores of inherited zircons and monazites and in monazites and outer portions of zircons from the xenoliths appear to indicate growth in equilibrium with abundant garnet.
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Skilbrei, Jan Reidar, and Ola Kihle. "Display of residual profiles versus gridded image data in aeromagnetic study of sedimentary basins: A case history." GEOPHYSICS 64, no. 6 (November 1999): 1740–47. http://dx.doi.org/10.1190/1.1444679.
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High‐pass filtered aeromagnetic profiles from the Mid‐Norwegian continental shelf, displayed as shaded relief versions of color stripes, provide a lucid picture of sedimentary layering and structure not easily displayed by proper application of modern enhancement techniques to images of the gridded aeromagnetic data. We show that when the aim is to analyze anomalies related to sedimentary features, it is more useful to study shaded relief versions of the profile data than to study digitally enhanced images of high‐pass filtered or calculated gradient data; a reason for this is probably the loss of high‐wavenumber, very low amplitude, information in the gridding process. The reprocessed data sets reveal anomaly patterns that are interpreted to originate from the following magnetic sources: (1) Quaternary overburden and bathymetric features, (2) magnetic sedimentary rocks, the subcropping sedimentary rock units, (3) magnetic basement in the structural highs and in the coastal zone, and (4) igneous intrusives at relatively deep levels within sedimentary basins. West of the basement rocks along the coast, the subcropping wedge of Mesozoic to Tertiary sediments is characterized by a distinct set of subparallel anomalies. Also, sedimentary layering within the Tertiary can be resolved. Short to intermediate wavelength anomalies correlate with the Late Jurassic faults of the Halten Terrace.
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Green, T. H. "Experimental phase equilibrium studies of garnet-bearing I-type volcanics and high-level intrusives from Northland, New Zealand." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 429–38. http://dx.doi.org/10.1017/s0263593300008105.
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ABSTRACTRare garnet phenocrysts and garnet-bearing xenoliths occur in high-silica, metaluminous to peraluminous andesites and dacites (and their high-level intrusive quartz diorite equivalents) from a Miocene calc-alkaline province in Northland, New Zealand. These garnets are among the most Ca-rich (17–28 mol% grossular) garnets of igneous origin so far recorded in calc-alkaline suite rocks. Associated minerals are dominant hornblende and plagioclase and minor augite, occurring as phenocrysts in xenoliths and as inclusions in the garnet. This mineralogy points to the I-type character of the garnet-bearing host magma compositions, and contrasts this garnet occurrence with the more frequently recorded grossular-poor (3–10 mol%) garnets with hypersthene, plagioclase, biotite and cordierite, found in S-type volcanic and intrusive host rocks.Detailed experimental work on a glass prepared from one of the garnet-bearing dacites closely constrains the conditions under which the natural phenocryst and xenolith mineral assemblages formed. This work was conducted over a pressure-temperature range of 8–20 kbar, 800–1050°C with 3–10 wt% of added H2O, defining overall phase relationships for these conditions. Importantly, amphibole only appears at temperatures of 900°C or less and clinopyroxene at >900°C (with 3wt% H2O). Orthopyroxene occurs with garnet at lower pressure (∼15 kbar with 3wt% H2O; ∼>10kbar with 5wt% H2O). Absence of orthopyroxene from the natural garnet-bearing assemblages indicates pressures above these limits during crystallisation. Plagioclase is markedly suppressed (with respect to temperature) with increasing H2O content, and for pressures of 10–15 kbar, the maximum H2O content possible in the magma with retention of clinopyroxene and plagioclase together (as evident in xenoliths) is 5–6 wt%. Finally, the lack of quartz in any of the xenoliths suggests magma H2O content higher than 3% (where quartz appears with amphibole at 900°C), since the quartz liquidus temperature decreases with increasing H2O content, and with decreasing pressure. In experiments with 5wt% H2O, a quartz-free field of crystallisation of garnet-clinopyroxene-amphibole-plagioclase occurs between 10 and 15 kbar and temperatures between 850 and 900°C. In addition, detailed experimentally-determined garnet compositional trends, together with ferromagnesian mineral compositional data for specific experiments with 5 wt% H2O added and run at 10-13 kbar and ∼900°C, suggest that the natural assemblages formed at these conditions. This implies that the parental dacitic magma must have been derived at mantle depths (the Northland crust is ∼25 km thick), and any basaltic or basaltic andesite precursor must have contained ∼2–3 wt% H2O.The unique nature of the Northland volcanics and high-level intrusives, preserving evidence of relatively grossular-rich garnet fractionation in the high-pressure crystallisation history of an originally mantle-derived magma, is attributed to a combination of unusually hydrous conditions in the source region, complex tectonic history involving obduction and subduction, possible incorporation of crustal slivers in a mantle-crust interaction zone, and relatively thin (∼25 km) crust.
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Tuduri, Johann, Alain Chauvet, Luc Barbanson, Jean-Louis Bourdier, Mohamed Labriki, Aomar Ennaciri, Lakhlifi Badra, et al. "The Jbel Saghro Au(–Ag, Cu) and Ag–Hg Metallogenetic Province: Product of a Long-Lived Ediacaran Tectono-Magmatic Evolution in the Moroccan Anti-Atlas." Minerals 8, no. 12 (December 13, 2018): 592. http://dx.doi.org/10.3390/min8120592.
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The Jbel Saghro is interpreted as part of a long-lived silicic large igneous province. The area comprises two lithostructural complexes. The Lower Complex consists of folded metagreywackes and N070–090°E dextral shear zones, which roughly results from a NW–SE to NNW–SSE shortening direction related to a D1 transpressive tectonic stage. D1 is also combined with syntectonic plutons emplaced between ca. 615 and 575 Ma. The Upper Complex is defined by ash-flow caldera emplacements, thick and widespread ignimbrites, lavas and volcaniclastic sedimentary rocks with related intrusives that were emplaced in three main magmatic flare ups at ca. 575, 565 and 555 Ma. It lies unconformably on the Lower Complex units and was affected by a D2 trantensive tectonic stage. Between 550 and 540 Ma, the magmatic activity became slightly alkaline and of lower extent. Ore deposits show specific features, but remain controlled by the same structural setting: a NNW–SSE shortening direction related to both D1 and D2 stages. Porphyry Au(–Cu–Mo) and intrusion-related gold deposits were emplaced in an earlier stage between 580 and 565 Ma. Intermediate sulfidation epithermal deposits may have been emplaced during lull periods after the second and (or) the third flare-ups (560–550 Ma). Low sulfidation epithermal deposits were emplaced late during the felsic alkaline magmatic stage (550–520 Ma). The D2 stage, therefore, provided extensional structures that enabled fluid circulations and magmatic-hydrothermal ore forming processes.
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Tschirhart, Victoria, John A. Percival, and Charlie W. Jefferson. "Geophysical models of the Montresor metasedimentary belt and its environs, central Nunavut, Canada." Canadian Journal of Earth Sciences 52, no. 10 (October 2015): 833–45. http://dx.doi.org/10.1139/cjes-2015-0008.
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Recent identification of hydrothermally altered rocks and breccia in the underexplored Montresor belt of Paleoproterozoic metasedimentary rocks suggests the possible presence of undiscovered mineralization. This study examines potential field data from the region with the goal of identifying subsurface features that could be associated with or serve as vectors to mineralization (subsurface alteration zones, faulting and (or) igneous intrusions). Gravity data were used to model regional and local geological features using known geology and physical properties from the study area and environs as constraints, and documents dense intrusive bodies underlying the Paleoproterozoic sequences. Maps of transformed apparent magnetic susceptibility values outline corridors of weak magnetization that correspond to observed zones of non-magnetic breccia and epidote–hematite–quartz alteration. Imputing the apparent susceptibility and rock property information into a magnetic forward model defines the geometry of this alteration zone, which is best explained as a northerly dipping non-magnetic or demagnetized, metasomatized intrusive sheet. The presence of previously undocumented igneous intrusions, their association with demagnetized hydrothermal breccia, and the continuity of the demagnetized zone suggests additional prospective areas within the region. This geological–geophysical framework for the nature and geometry of the Montresor belt and its surrounds highlights the importance of integrated modelling for areas with limited data.
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Adams, Donald C., and G. Randy Keller. "Possible extension of the Midcontinent Rift in west Texas and eastern New Mexico." Canadian Journal of Earth Sciences 31, no. 4 (April 1, 1994): 709–20. http://dx.doi.org/10.1139/e94-063.
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The Midcontinent Rift System forms one of the most prominent gravity features in North America. The recognized geophysical anomaly extends in an arc from southern Oklahoma to Lake Superior and then into southern Michigan. The Midcontinent Rift System was active between 1185–1010 Ma, as indicated in the Lake Superior region by age determinations on intrusive igneous rocks. We suggest that the period of formation of the Midcontinent Rift was also a time of extensive igneous activity in Texas and New Mexico. This activity is represented by intrusions beneath the Central basin platform (Texas and New Mexico), intrusions which crop out at the Pajarito Mountain in the Sacramento Mountains (New Mexico), a basaltic debris flow in the Franklin Mountains (Texas), basalt flows at Van Horn (Texas), and the Crosbyton geophysical anomaly (east of Lubbock, Texas). These bodies and other bodies located by geophysical anomalies and wells drilled into mafic Precambrian rocks may be related to the Midcontinent Rift System. Alternatively this magmatism could be related to Grenville age tectonics in Texas. The mafic igneous rocks in this area form a 530 km diameter Middle Proterozoic igneous province, which formed between 1070 and 1220 Ma. Comparison of the Midcontinent Rift System and its extensions proposed here with the Mesozoic and Cenozoic African rift systems indicates that these features are of comparable scale and complexity.
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Seifert, Karl E., Zell E. Peterman, and Scott E. Thieben. "Possible crustal contamination of Midcontinent Rift igneous rocks: examples from the Mineral Lake intrusions, Wisconsin." Canadian Journal of Earth Sciences 29, no. 6 (June 1, 1992): 1140–53. http://dx.doi.org/10.1139/e92-092.
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Interlayered mafic–telsic intrusions from the Mineral Lake intrusive complex in northwest Wisconsin reflect the typical bimodal basalt–rhyolite compositional pattern of the Midcontinent Rift flood basalt province in the Lake Superior region. The later felsic intrusions were emplaced between the mafic intrusions and overlying basalt flows, and postemplacement fractional crystallization produced gradational mineralogical and geochemical variations. Isotopic and trace-element data for the Mineral Lake intrusions are consistent with mantle sources for both mafic and felsic intrusions, with compositional differences explained by the extent of fractional crystallization and crustal contamination or mantle source characteristics.εNd–εSr plots of analyzed Midcontinent Rift igneous rocks define three largely separate isotopic fields that suggest separate sources. However, the spread in isotopic data and a spider diagram plot of mafic samples from the εNd = εSr = 0 field suggest a crustal component and derivation from depleted rather than chondritic mantle. Evolved felsic rocks plotting in two negative εNd – positive εSr fields can be explained by derivation from separate enriched mantle sources or crustal contamination or both.
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Mytrokhyn, O., V. Bakhmutov, A. Aleksieienko, T. Mytrokhina, and O. Marushchenko. "INTRUSIVE-MAGMATIC COMPLEXES OF WILHELM ARCHIPELAGO, WEST ANTARCTICA (PART 1 – INTRUSIONS OF GABBROIDS, DIORITES AND GRANITOIDS)." Visnyk of Taras Shevchenko National University of Kyiv. Geology, no. 4(95) (2021): 6–15. http://dx.doi.org/10.17721/1728-2713.95.01.
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The Wilhelm Archipelago and the adjacent coast of Graham Land are typical areas of calc-alkaline magmatism associated with the protracted evolution of the Antarctic Peninsula igneous belt. The authors studied intrusive complexes of the Wilhelm Archipelago (WA) in order to characterize their geographical distribution, geological occurrence and age, mineralogical and petrographical features. Geological surveys revealed that gabbro, diorite, and granitoid intrusions are widespread on the WA. Due to the processes of tectonic uplift and exhumation, both apical and bottom parts of individual intrusive bodies can be exposed on the modern erosion level. Recent geological observations have shown that plutons of different ages intersect each other in a complex sequence. This made it possible to determine their relative geological age and reconstruct the general direction of the deep magmatic development from the Early Cretaceous to the Early Paleogene, inclusive. It has been proved that the oldest massifs of gabbroids are parts of much larger intrusive bodies. They were formed in the period between the Jurassic and the Early Cretaceous periods. Crystallization differentiation of basaltic magmas gave them various scale layering. In the bottom parts of gabroid intrusions there were conditions for the formation of Fe-Ti-V and Cu-Ni-EPG mineralization. Diorite and granitoid intrusions occupy much larger areas compared to gabbroids. The formation of diorite intrusions took place in the period between the Early Cretaceous and the Paleocene. Although the oldest gabbroids were formed much earlier than diorites, the phenomena of magmatic mingling in the latter indicate that magmas of basic and intermediate composition could also synchronously intrude in common magmatic chambers. Granitoid magmatism on the WA covers the Late Cretaceous and the Paleogene periods. Most granitoid intrusions formed in the Paleocene after the main phase of tectonic deformations. Cu-Mo mineralization may be associated with these intrusions.
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Holm, Paul Martin, Eva Degn Egeberg, and Niels-Ole Prægel. "Multiple syenite intrusions at Kærven, Kangerdlugssuaq, East Greenland: Evidence from the 1986 field work." Bulletin of the Geological Society of Denmark 38 (February 18, 1991): 173–81. http://dx.doi.org/10.37570/bgsd-1990-38-17.
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Tue Kærven Syenite Complex is recognized as the earliest intrusive body in the Kangerdlugssuaq region associated with the opening of the proto-Atlantic Ocean in the Lower Tertiary. Earlier investigations of the geology of the Kærven Syenite Complex have interpreted the intrusion as a single igneous body, emplaced subsequent to the Kærven Gabbro and in turn cut by the Kangerdlugssuaq intrusion. Preliminary sampling on Kærven in 1977 revealed a relatively large range of rock types in the complex (syenite - alkali feldspar syenite - alkali feldspar granite). Tue field work conducted in 1986 has verified these findings and enabled the distinction of 8 intrusive events within the complex. Further, a preliminary geological map has been produced. An igneous breccia separates the complex from the earlier Kærven Gabbro along parts of the eastern and southern margins. The central part of the Kærven Syenite Complex include an hitherto unrecognized slice of Precambrian basement gneisses with numerous approximately N-S trending basaltic dykes. This is multiply intruded by syenite. Most notably in the eastern part of the complex, intimate associations of brecciated and remobilized basement gneiss and melts of syenitic through monzonitic to tonalitic compositions are found. The form of the intrusive bodies are more or less dyke-shaped and N-S trending. Toere is a general stratigraphic younging to the SW, which is matched by the tater adjacent Kangerdlugssuaq intrusion. Tue intrusive sequence and trend of the intrusions are thought to be closely related to an extentional tectonic regime present in this part of the fjord for a considerable period onwards from the earliest Tertiary magmatic activity in the area.
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Curtis, Michael S., Simon P. Holford, Mark A. Bunch, and Nick J. Schofield. "Seismic, petrophysical and petrological constraints on the alteration of igneous rocks in the Northern Carnarvon Basin, Western Australia: implications for petroleum exploration and drilling operations." APPEA Journal 62, no. 1 (May 13, 2022): 196–222. http://dx.doi.org/10.1071/aj21172.
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The Northern Carnarvon Basin (NCB) hosts an extensive record of Jurassic–Cretaceous rift-related igneous activity, manifested by a >45 000 km2 intrusive complex and series of volcanic centres constrained by seismic mapping. However, there are relatively few well penetrations of these igneous rocks (<1% of ~1500 exploration wells) in comparison to other basins that witness extensive magmatism, and thus, their lithological and petrophysical characteristics are poorly understood. Here, we describe the properties of igneous rocks encountered in nine petroleum exploration wells and scientific boreholes in the NCB and evaluate their impacts on exploration and development issues. Igneous rocks in the NCB are characterised by pervasive alteration, with ramifications for seismic imaging and drilling. For example, low acoustic velocities in mafic lavas altered to clays in Toro-1 were mistaken for overpressure, whilst intrusive rocks in Palta-1 were initially unrecorded and only recognised due to subsequent post-drilling thermal history analysis. The alteration of mafic igneous rocks to clays reduces acoustic impedance contrasts relative to sedimentary host rocks, making their identification prior to drilling more challenging. Whilst the preferential emplacement of intrusive rocks in Triassic strata deeper than reservoir targets is primarily responsible for the paucity of well penetrations, our findings of extensive alteration of igneous rocks in the NCB suggests that additional wells may intersect as yet unrecognised intrusive or extrusive sequences.
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ROBERTS, R. J., F. CORFU, T. H. TORSVIK, L. D. ASHWAL, and D. M. RAMSAY. "Short-lived mafic magmatism at 560–570 Ma in the northern Norwegian Caledonides: U–Pb zircon ages from the Seiland Igneous Province." Geological Magazine 143, no. 6 (September 18, 2006): 887–903. http://dx.doi.org/10.1017/s0016756806002512.
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The Seiland Igneous Province (SIP) of northern Norway comprises a suite of mainly gabbroic plutons, with subordinate ultramafic, syenitic and felsic intrusions. Several intrusions from the Seiland Igneous Province have been dated by ID-TIMS U–Pb zircon and monazite analyses. The Hasvik Gabbro on the island of Sørøy, previously assigned an age of 700±33 Ma by Sm–Nd, yields a U–Pb zircon age of 562±6 Ma, within error of the Storelv Gabbro (569±5 Ma) and a diorite associated with the Breivikbotn Gabbro (571±4 Ma). Various intrusions on the Øksfjord peninsula give nearly identical ages of 565±9 Ma (gabbro), 566±4 Ma (monzonite), 565±5 Ma (monzodiorite), 570±9 Ma (norite), and 566±1 Ma (orthopyroxenite). These ages overlap with those from Sørøy, and define a single and short-lived period of gabbroic (to felsic) magmatism for the region between 570 and 560 Ma, pre-dating a subordinate episode of alkalic magmatism at 530–520 Ma. The U–Pb ages contradict the previous geochronological interpretation for the Finnmark area, which implied a period of 250 m.y. for the emplacement of the SIP intrusions. The new age data also clearly distinguish the Seiland intrusions, emplaced into the Sørøy Group metasediments of the Kalak Nappe Complex, from several older granitic intrusions (c. 850 to 600 Ma) that cut the Sørøy Group farther east and south. The coincident ages of the different Seiland intrusive bodies also contradict the previous structural model for the area, which posits that the different gabbro bodies were emplaced at intervals, with compressional deformation affecting the gabbros between periods of intrusion. The short time span between the main plutonic phases strongly suggests that the mechanism for the emplacement of mafic magma operated in a single, probably extensional, tectonic regime. The mafic intrusions were later deformed and metamorphosed to at least amphibolite facies, most likely by the Scandian (420 Ma) phase of the Caledonian Orogeny.
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THÓRARINSSON, SIGURJÓN B., PAUL M. HOLM, SEBASTIAN TAPPE, LARRY M. HEAMAN, and NIELS-OLE PRÆGEL. "U–Pb geochronology of the Eocene Kærven intrusive complex, East Greenland: constraints on the Iceland hotspot track during the rift-to-drift transition." Geological Magazine 153, no. 1 (July 3, 2015): 128–42. http://dx.doi.org/10.1017/s0016756815000448.
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AbstractSeveral major tholeiitic (e.g. the Skaergaard intrusion) and alkaline (e.g. the Kangerlussuaq Syenite) intrusive complexes of the North Atlantic Large Igneous Province are exposed along the Kangerlussuaq Fjord in East Greenland. The Kærven Complex forms a satellite intrusion to the Kangerlussuaq Syenite and includes early tholeiitic gabbros and a series of cross-cutting alkaline intrusions ranging from monzonite to alkali granite. The alkaline intrusions cut the gabbros, and are cut by the outer nordmarkite zone of the Kangerlussuaq Syenite. This study presents the first U–Pb zircon ages from the alkaline units of the Kærven Complex. Fourteen multi-grain zircon fractions have been analysed by thermal ionization mass spectrometry (TIMS). Absolute age differences could not be resolved between the different units, suggesting a relatively rapid succession of intrusions betweenc. 53.5 and 53.3 Ma. Our compilation of precise radiometric age data shows that most of the alkaline magmatism in the Kangerlussuaq Fjord occurred prior to 50 Ma. Moreover, pre-50 Ma alkaline intrusions and lavas show a SSE-younging trend, which is interpreted as the track of the Iceland hotspot during the rift-to-drift transition of the North Atlantic.
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Bina, Mehdi, Mohammad Ali Arian, Mohsen Pourkermani, and Mohammad Hasan Bazoobandi. "GEOCHEMISTRY AND PETROGENESIS OF SILLS IN LAVASANAT REGION, TEHRAN, IRAN." Geosaberes 11 (July 5, 2020): 480. http://dx.doi.org/10.26895/geosaberes.v11i0.1049.
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The study area is located in Lavasanat region in the east of Tehran Province in the Central Alborz zone. The outcrops in this region are mainly associated with Karaj formation and belong to the upper Eocene to Oligocene periods. These outcrops consist of two intrusions: one in the north and the other in the northeast of Lavasanat. These outcrops are scattered over an area of approximately 337km2. In the study region, there are various intrusive igneous rocks, while numerous intrusive igneous rocks are scattered in the form of sills and dikes. These rocks include a range of rocks from diorite gabbro to diorite, monzonite, and syenite. The weathered colors of these rocks are black, brown and gray. The outcrops of these sills are mainly present in the middle-northern part of the quadrangle geological map of the east of Tehran. In different diagrams of the magma series, the study rocks are classified as alkaline, calc-alkaline, and shoshonite, which may indicate magma contamination. An analysis of the variations of the classical elements and trace elements, the spider plots, and interpretations of these plots confirms the relationship of these rocks with the subduction zone and continental arc. To find the tectonic position of the sills in the study area based on the geochemical diagrams, we selected samples from the within-plate (WIP) and arc zones.
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Scott, J. M. J., T. D. Peterson, W. J. Davis, C. W. Jefferson, and B. L. Cousens. "Petrology and geochronology of Paleoproterozoic intrusive rocks, Kiggavik uranium camp, Nunavut." Canadian Journal of Earth Sciences 52, no. 7 (July 2015): 495–518. http://dx.doi.org/10.1139/cjes-2014-0153.
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We investigated the age and petrology of Paleoproterozoic granitic intrusions in the area of the Kiggavik uranium exploration camp, near the southeast margin of the Aberdeen subbasin of the Thelon Basin. A subset of these intrusions (e.g., the Lone Gull stock) is spatially associated with and mineralized by basement hosted, unconformity-related uranium deposits. Surface (outcrop) samples have field relations, textures, and compositions consistent with Hudson Suite granitoids and mixtures of monzogranite with minette. We obtained U–Pb (zircon) ages ranging from ca. 1818 to 1840 Ma, within the known range of the Hudson Suite and cogenetic minettes of the Baker Lake Group (1.80–1.84 Ga). Core samples of granitic rocks adjacent to mineralized zones are more complex and indicate an influence from the younger Nueltin Granite (Kivalliq Igneous Suite, ca. 1.77–1.73 Ga). One sample from the Lone Gull stock contains two zircon populations in texturally distinctive domains, one at 1806 ± 41 Ma and the other at 1748 ± 9.4 Ma. A porphyritic hypabyssal syenite below the Bong deposit yielded a U–Pb zircon age of 1837.8 ± 7.7 Ma and a U–Pb titanite age of 1758.5 ± 44 Ma. We recognize a Kivalliq-age overprint in the form of metasomatism and partial remelting or melt infiltration in the drill core samples, which is not evident at the surface and is consistent with the presence of a Nueltin Granite intrusive complex at depth. The geochemistry and primary igneous textures of the Bong syenite, including its euhedral zircons, resemble those of lava flows near the base of the Baker Lake Group, and we recognize a mixed magma (i.e., Martell Syenite) continuum between intrusive Hudson granitoids and minette with extrusive equivalents in the lower felsic minette member of the Christopher Island Formation.
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Lockley, Martin G., R. Farley Fleming, Karen Houck, Seong‐Young Yang, and Seong‐K Lim. "Dinosaur tracks in intrusive igneous rock." Ichnos 2, no. 3 (April 1993): 213–16. http://dx.doi.org/10.1080/10420949309380094.
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Emeleus, C. H., and V. R. Troll. "The Rum Igneous Centre, Scotland." Mineralogical Magazine 78, no. 4 (August 2014): 805–39. http://dx.doi.org/10.1180/minmag.2014.078.4.04.
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AbstractThe publication of the British Geological Survey memoir on Rum and the Small Isles in 1997 was followed by a period of intense petrological and mineralogical research, leading to some 40 papers, books and other publications. The research progress since then is reviewed here and integrated with the information previously available to provide an overview of the current status of understanding of the centre. New data on the acidic and mixed acid/basic magmas of the early Rum caldera demonstrate that frequent mafic replenishments were the main driver for magmatic activity at Rum right from its initial stages. The caldera is bound by the Main Ring Fault, a structure which probably also exercised an influence on the emplacement of the subsequent basic and ultrabasic intrusions. The later emplacement of gabbros and ultrabasic rocks caused only limited thermal metamorphism of the surrounding Torridonian sandstones, contrasting markedly with the crustal isotope signatures of the early intracaldera ignimbrite magmas and the intense alteration of uplifted masses of Lewisian gneiss within the ring fault. Rare picritic dykes provide an indication of the possible parent magma for the mafic and ultrabasic rocks, but these, as with most other magmatic rocks on Rum, have undergone varying degrees of crustal contamination, involving both Lewisian granulite and amphibolite-type crust but, notably, no Moine metasedimentary compositions as is the case at the nearby Ardnamurchan centre. Detailed textural studies on the gabbroic and ultrabasic rocks allow a distinction between intrusive peridotites and peridotite that forms part of the classic layered cumulate units of Rum and, furthermore, this work and that on the chromite seams and veins in these rocks shows that movement of trapped magma and magma derived from later intrusions, may produce textures regarded previously as of primary cumulate origin. Sulfides in the chromitite seams and ultrabasic rocks, in turn, show possible influences from assimilated Mesozoic sediments. Igneous activity on Rum was short-lived, possibly only between 0.5 and 1 m.y. in duration and commenced at ∼60.5 Ma. The Rum Central Complex was extinct by the time the main activity at the nearby Skye Central Complex commenced (∼59 Ma). From recent apatite fission-track studies it seems probable that Rum, in common with other Palaeogene centres, underwent a brief, but significantly later heating event (∼45 Ma).
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Holford, Simon, Mark Bunch, Nick Schofield, and Michael Curtis. "Application of a probability model to detect unrecognised igneous intrusions in sedimentary basins." APPEA Journal 62, no. 2 (May 13, 2022): S426—S430. http://dx.doi.org/10.1071/aj21051.
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Mafic igneous intrusions are a common feature in extensional sedimentary basins, particularly those located at volcanic rifted margins, and are important in both exploration and development contexts due to their range of interactions with the petroleum system and their role as potential drilling hazards. Experience from a range of basins containing mafic igneous intrusions suggests that seismically resolvable intrusions are typically accompanied by a large number of intrusions that are too thin to be confidently identified and interpreted from seismic reflection surveys. The increased vertical resolution of wireline log data affords an opportunity to identify such sub-seismic-scale intrusions, though in many wells with full wireline suites igneous intrusions are often misidentified as sedimentary units, including felsic intrusions whose physical properties are more similar to sedimentary rocks. Here we apply a wireline-log-based probability model to well data from a number of basins. In previous applications, the model has proven highly effective in predicting the occurrence of carbonate cementation zones in sandstones in comparison to neural network approaches. We demonstrate its ability to predict the presence of igneous intrusions that were not previously identified by either seismic interpretation, or through the analysis of well-derived datasets. The broader application of this model to large suites of legacy data could lead to improved knowledge of the occurrence of intrusions in basins with implications for basin modelling and well planning.
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Bayer, P., H. A. Horn, B. Lammerer, R. Schmidt-Thome, K. Weber-Diefenbach, and C. Wiedemann. "The Brasiliano Mobile Belt in Southern Espírito Santo (Brazil) and its Igneous Intrusions." Zentralblatt für Geologie und Paläontologie, Teil I 1985, no. 9-10 (July 9, 1986): 1429–39. http://dx.doi.org/10.1127/zbl_geol_pal_1/1985/1986/1429.
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Wrona, T., C. Magee, H. Fossen, R. L. Gawthorpe, R. E. Bell, C. A. L. Jackson, and J. I. Faleide. "3-D seismic images of an extensive igneous sill in the lower crust." Geology 47, no. 8 (May 31, 2019): 729–33. http://dx.doi.org/10.1130/g46150.1.
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Abstract When continents rift, magmatism can produce large volumes of melt that migrate upwards from deep below the Earth’s surface. To understand how magmatism impacts rifting, it is critical to understand how much melt is generated and how it transits the crust. Estimating melt volumes and pathways is difficult, however, particularly in the lower crust where the resolution of geophysical techniques is limited. New broadband seismic reflection data allow us to image the three-dimensional (3-D) geometry of magma crystallized in the lower crust (17.5–22 km depth) of the northern North Sea, in an area previously considered a magma-poor rift. The subhorizontal igneous sill is ∼97 km long (north-south), ∼62 km wide (east-west), and 180 ± 40 m thick. We estimate that 472 ± 161 km3 of magma was emplaced within this intrusion, suggesting that the northern North Sea contains a higher volume of igneous intrusions than previously thought. The significant areal extent of the intrusion (∼2700 km2), as well as the presence of intrusive steps, indicate that sills can facilitate widespread lateral magma transport in the lower crust.
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Ekwok, Stephen E., Anthony E. Akpan, Ogiji-Idaga M. Achadu, Cherish E. Thompson, Ahmed M. Eldosouky, Kamal Abdelrahman, and Peter Andráš. "Towards Understanding the Source of Brine Mineralization in Southeast Nigeria: Evidence from High-Resolution Airborne Magnetic and Gravity Data." Minerals 12, no. 2 (January 25, 2022): 146. http://dx.doi.org/10.3390/min12020146.
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Investigation into understanding the genesis of brines in southeast Nigeria was carried out utilizing high-resolution potential field (HRPF) data. This study reveals that igneous intrusions and associated hydrothermal fluids are responsible for brine generation. The obtained result of the analytic signal revealed the locations and spatial distribution of short- and long-wavelength geologic structures associated with igneous intrusions. The low pass filtering, upward continuation, and 2D modelling procedures showed key synclinal structures which coincided well with the location of brine fields. The results showed that salt ponds are common in the neighborhood of igneous intrusions. To validate this finding, a conceptual model describing igneous-related hydrothermal circulation systems that are driven by convective cells of the hydrothermal fluid and overburden loads was generated. This model fits reasonably well into the overall stratigraphic and geologic framework of the study area.
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Wilson, Penelope I. R., Robert W. Wilson, David J. Sanderson, Ian Jarvis, and Kenneth J. W. McCaffrey. "Analysis of deformation bands associated with the Trachyte Mesa intrusion, Henry Mountains, Utah: implications for reservoir connectivity and fluid flow around sill intrusions." Solid Earth 12, no. 1 (January 20, 2021): 95–117. http://dx.doi.org/10.5194/se-12-95-2021.
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Abstract. Shallow-level igneous intrusions are a common feature of many sedimentary basins, and there is increased recognition of the syn-emplacement deformation structures in the host rock that help to accommodate this magma addition. However, the sub-seismic structure and reservoir-scale implications of igneous intrusions remain poorly understood. The Trachyte Mesa intrusion is a small (∼1.5 km2), NE–SW trending satellite intrusion to the Oligocene-age Mount Hillers intrusive complex in the Henry Mountains, Utah. It is emplaced within the highly porous, aeolian Entrada Sandstone Formation (Jurassic), producing a network of conjugate sets of NE–SW striking deformation bands trending parallel to the intrusion margins. The network was characterized by defining a series of nodes and branches, from which the topology, frequency, intensity, spacing, characteristic length, and dimensionless intensity of the deformation band traces and branches were determined. These quantitative geometric and topological measures were supplemented by petrological, porosity and microstructural analyses. Results show a marked increase in deformation band intensity and significant porosity reduction with increasing proximity to the intrusion. The deformation bands are likely to impede fluid flow, forming barriers and baffles within the Entrada reservoir unit. A corresponding increase in Y- and X-nodes highlights the significant increase in deformation band connectivity, which in turn will significantly reduce the permeability of the sandstone. This study indicates that fluid flow in deformed host rocks around igneous bodies may vary significantly from that in the undeformed host rock. A better understanding of the variability of deformation structures, and their association with intrusion geometry, will have important implications for industries where fluid flow within naturally fractured reservoirs adds value (e.g. hydrocarbon reservoir deliverability, hydrology, geothermal energy and carbon sequestration).
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Berzina, A. N., A. P. Berzina, and V. O. Gimon. "The Aksug Porphyry Cu–Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma." Russian Geology and Geophysics 62, no. 4 (April 1, 2021): 445–59. http://dx.doi.org/10.2113/rgg20194115.
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Abstract ––Two stages are recognized in the evolution of the Aksug ore-magmatic system (OMS): (1) formation of the Aksug granitoid pluton and (2) emplacement of small ore-bearing intrusions. Intrusive bodies of the two stages are composed of rocks of the same type and bear copper mineralization: poor dispersed and large-scale veinlet-disseminated, respectively. The pluton and small intrusions are formed by gabbroid and granitoid rocks, with similar petrogeochemical characteristics of igneous rocks of the same type. The plutonic gabbroic association includes gabbro, gabbrodiorites, and pyroxene–amphibole diorites/quartz diorites. The small subvolcanic gabbroic intrusions are gabbrodiorite and diorite porphyrites. The trace element patterns of the gabbroids are similar to those of igneous rocks in subduction zones. The gabbroids are characterized by isotope parameters εNd(500) = +6.1 to +7.2 and (87Sr/86Sr)500 = 0.7022–0.7030 and model age TNd(DM) = 0.85–0.74 Ga. As follows from the geochemical parameters, the depleted mantle metasomatized by subduction fluids was the source of basaltic magma. The plutonic granitoid association includes tonalites, plagiogranites, and amphibole diorites/quartz diorites; the small subvolcanic granitoid intrusions are tonalite porphyry and quartz diorite porphyrites. The trace element patterns and Nd and Sr isotope compositions of the granitoids are much similar to those of the gabbroids. According to the geochemical parameters, tonalitic and plagiogranitic magmas formed through the melting of juvenile mafic crust, and dioritic magma resulted from the mixing of basaltic and tonalitic/plagiogranitic magmas. In the course of the OMS formation, metals and volatiles were introduced by basaltic and granitoid magmas from the metasomatized mantle and juvenile mafic crust. The compression setting during the pluton formation hampered the separation of ore-bearing fluids, which led to poor dispersed mineralization. The extension setting during the emplacement of small intrusions favored the intense separation of ore-bearing fluids. The interaction of magma and fluids of the small intrusions with rocks of the pluton was accompanied by the removal of metals from the latter and their involvement in the ore-forming process. This increased the ore potential of the magmatic system and favored the formation of rich mineralization at the final stage of its evolution.
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Skyttä, P., T. Hermansson, J. Andersson, and P. Weihed. "New zircon data supporting models of short-lived igneous activity at 1.89 Ga in the western Skellefte District, central Fennoscandian Shield." Solid Earth Discussions 3, no. 1 (April 1, 2011): 355–83. http://dx.doi.org/10.5194/sed-3-355-2011.
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Abstract. New U-Th-Pb zircon data (SIMS) from three intrusive phases of the Palaeoproterozoic Viterliden intrusion in the western Skellefte District, central Fennoscandian Shield, dates igneous emplacement in a narrow time interval at about 1.89 Ga. A locally occurring quartz-plagioclase porphyritic tonalite, here dated at 1889 ± 3 Ma, is, based on the new age data and field evidence, considered the youngest of the intrusive units. This supports an existing interpretation of its fault-controlled emplacement after intrusion of the dominating hornblende-tonalite units, in this study dated at 1892 ± 3 Ma. The Viterliden magmatism was synchronous with the oldest units of the Jörn type early-orogenic intrusions in the eastern part of the district (1.89–1.88 Ga; cf. Gonzàles Roldán, 2010). A U-Pb zircon age for a felsic metavolcanic rock from the hanging-wall to the Kristineberg VMS deposit, immediately south of the Viterliden intrusion, is in this study constrained in the 1.89–1.88 Ga time interval. It provides a minimum age for the Kristineberg ore deposit and suggests contemporaneous igneous/volcanic activity throughout the Skellefte District. Furthermore, it supports the view that the Skellefte Group defines a laterally continuous belt throughout this "ore district". Tentative correlation of the 1889 ± 3 Ma quartz-plagioclase porphyritic tonalite with the Kristineberg "mine porphyry", which cuts the altered ore-hosting metavolcanic rocks, further constrain the minimum age for ore deposition at 1889 ± 3 Ma. Based on the new age determinations, the Viterliden intrusion may equally well have intruded into, or locally acted as a basement for the ore-hosting Skellefte Group volcanic rocks.
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Skyttä, P., T. Hermansson, J. Andersson, M. Whitehouse, and P. Weihed. "New zircon data supporting models of short-lived igneous activity at 1.89 Ga in the western Skellefte District, central Fennoscandian Shield." Solid Earth 2, no. 2 (October 26, 2011): 205–17. http://dx.doi.org/10.5194/se-2-205-2011.
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Abstract. New U-Th-Pb zircon data (SIMS) from three intrusive phases of the Palaeoproterozoic Viterliden intrusion in the western Skellefte District, central Fennoscandian Shield, dates igneous emplacement in a narrow time interval at about 1.89 Ga. A locally occurring quartz-plagioclase porphyritic tonalite, here dated at 1889 ± 3 Ma, is considered the youngest of the intrusive units, based on the new age data and field evidence. This supports an existing interpretation of its fault-controlled emplacement after intrusion of the dominating hornblende-tonalite units, in this study dated at 1892 ± 3 Ma. The Viterliden magmatism was synchronous with the oldest units of the Jörn type early-orogenic intrusions in the eastern part of the district (1.89–1.88 Ga; cf. Gonzàles Roldán, 2010). A U-Pb zircon age for a felsic metavolcanic rock from the hanging-wall to the Kristineberg VMS deposit, immediately south of the Viterliden intrusion, is constrained at 1883 ± 6 Ma in this study. It provides a minimum age for the Kristineberg ore deposit and suggests contemporaneous igneous/volcanic activity throughout the Skellefte District. Furthermore, it supports the view that the Skellefte Group defines a laterally continuous belt throughout this "ore district". Tentative correlation of the 1889 ± 3 Ma quartz-plagioclase porphyritic tonalite with the Kristineberg "mine porphyry" suggests that these units are coeval at about 1.89 Ga. Based on the new age determinations, the Viterliden intrusion may equally well have intruded into or locally acted as a basement for the ore-hosting Skellefte Group volcanic rocks.
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Sparks, R. S. J. "Igneous petrology: Discordance in layered intrusions." Nature 315, no. 6019 (June 1985): 460. http://dx.doi.org/10.1038/315460a0.
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Schofield, Nick, Simon Holford, Alex Edwards, Niall Mark, and Stefano Pugliese. "Overpressure transmission through interconnected igneous intrusions." AAPG Bulletin 104, no. 2 (February 2020): 285–303. http://dx.doi.org/10.1306/05091918193.
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Gurevich, A. B., and S. B. Shishlov. "IGNEOUS INTRUSIONS IN COAL-BEARING SEQUENCES." International Geology Review 29, no. 8 (August 1987): 951–58. http://dx.doi.org/10.1080/00206818709466190.
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Evenchick, Carol A., Jennifer M. Galloway, Benoit M. Saumur, and William J. Davis. "A revised stratigraphic framework for Cretaceous sedimentary and igneous rocks at Mokka Fiord, Axel Heiberg Island, Nunavut, with implications for the Cretaceous Normal Superchron." Canadian Journal of Earth Sciences 56, no. 2 (February 2019): 158–74. http://dx.doi.org/10.1139/cjes-2018-0129.
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New data and interpretations on geological relationships of igneous rocks at Mokka Fiord, Axel Heiberg Island, Nunavut, provide insight into the timing and nature of magmatism associated with the Sverdrup Basin and High Arctic Large Igneous Province (HALIP). Field relationships indicate that the igneous rocks, previously interpreted to be volcanic flows, are most likely an intrusive unit discordant to regional bedding. An intrusive origin helps resolve chronostratigraphic inconsistencies in previous work. The host rocks are palynologically constrained to be late Barremian to late Aptian in age and are interpreted to be Paterson Island or Walker Island member of the Isachsen Formation. If the igneous body is intrusive, it’s previously reported Ar–Ar age (102.5 ± 2.6 Ma) is no longer in conflict with accepted stratigraphic interpretations and probably reflects the emplacement age of the intrusion. Lingering uncertainties in interpreting the normal and reverse magnetic polarities determined in the previous work remain, and both are considered viable. Although this uncertainty precludes definitive conclusions on the significance of paleomagnetic data at Mokka Fiord, examination of the stratigraphic, paleomagnetic, and geochronologic relationships there highlight potential for the study of excursions, or reversed magnetic polarity subchrons, in the Cretaceous Normal Superchron elsewhere in the HALIP.
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Horsman, Eric, Sven Morgan, Michel de Saint-Blanquat, Guillaume Habert, Andrew Nugent, Robert A. Hunter, and Basil Tikoff. "Emplacement and assembly of shallow intrusions from multiple magma pulses, Henry Mountains, Utah." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 1-2 (March 2009): 117–32. http://dx.doi.org/10.1017/s1755691009016089.
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ABSTRACTThis paper describes three mid-Tertiary intrusions from the Henry Mountains (Utah, USA) that were assembled from amalgamation of multiple horizontal sheet-like magma pulses in the absence of regional deformation. The three-dimensional intrusion geometries are exceptionally well preserved and include: (1) a highly lobate sill; (2) a laccolith; and (3) a bysmalith (a cylindrical, fault-bounded, piston-like laccolith). Individual intrusive sheets are recognised on the margins of the bodies by stacked lobate contacts, and within the intrusions by both intercalated sedimentary wallrock and formation of solid-state fabrics. Finally, conduits feeding these intrusions were mostly sub-horizontal and pipe-like, as determined by both direct observation and modelling of geophysical data.%The intrusion geometries, in aggregate, are interpreted to reflect the time evolution of an idealised upper crustal pluton. These intrusions initiate as sills, evolve into laccoliths, and eventually become piston-like bysmaliths. The emplacement of multiple magma sheets was rapid and pulsed; the largest intrusion was assembled in less than 100 years. The magmatic fabrics are interpreted as recording the internal flow of the sheets preserved by fast cooling rates in the upper crust. Because there are multiple magma sheets, fabrics may vary vertically as different sheets are traversed. These bodies provide unambiguous evidence that some intrusions are emplaced in multiple pulses, and that igneous assembly can be highly heterogeneous in both space and time. The features diagnostic of pulsed assembly observed in these small intrusions can be easily destroyed in larger plutons, particularly in tectonically active regions.
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Milner, Simon C., Anton P. Le Roex, and Ronald T. Watkins. "Rb-Sr age determinations of rocks from the Okenyenya igneous complex, northwestern Namibia." Geological Magazine 130, no. 3 (May 1993): 335–43. http://dx.doi.org/10.1017/s001675680002001x.
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AbstractThe Okenyenya igneous complex is one of a suite of intrusions which define a prominent northeast-trending linear feature in Damaraland, northwestern Namibia. Precise Rb–Sr internal isochron ages range from 128.6 ± 1 to 123.4 ± 1.4 Ma for the major phases of intrusion identified within the complex. The tholeiitic gabbros forming the outer rings of the complex, and the later alkali gabbros which form the central hills, cannot be distinguished in terms of Rb–Sr ages, although field relations clearly indicate the younger age of the latter. The intrusionsof nepheline-syenite and essexite comprising the mountain of Okenyenya Bergon the northern edge of the complex give ages of 123.4 ± 1.4 and 126.3 ± 1 Ma, respectively, and form the final major phase of intrusion. The ages obtained for early and late intrusive phases define a minimum magmatic ‘life-span’ of approximately 5 Ma for the complex. The determined age of the Okenyenya igneous complex (129–123 Ma), when taken together with the few reliable published ages for other Damaraland complexes (130–134 Ma), suggests that these sub-volcanic complexes were emplaced contemporaneously with the widespread Etendeka volcanics (˜ 130 Ma), and relate to magmatism associated with the breakup of southern Africa and South America with the opening of the South Atlantic Ocean. The linear distributionof intrusions in Damaraland is interpreted to be due to magmatism resultingfrom the upwelling Tristan plume being focused along a structural discontinuity between the Pan-African, Damaran terrain to the south, and Proterozoiccratonic basement to the north.
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Legault, Marc I., and Keiko Hattori. "Provenance of igneous clasts in conglomerates of the Archaean Timiskaming Group, Kirkland Lake area, Abitibi greenstone belt, Canada." Canadian Journal of Earth Sciences 31, no. 12 (December 1, 1994): 1749–62. http://dx.doi.org/10.1139/e94-156.
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Four types of igneous clasts from Timiskaming conglomerates of the Kirkland Lake area are identified: calc-alkaline porphyry, trachyte (K2O + N2O > 7.25 wt.%), trondhjemite, and tholeiitic basalt. Clasts derived from quartz–carbonate veins and carbonatized porphyries and komatiites indicate CO2-rich hydrothermal activity along the Larder Lake – Cadillac Fault before sedimentation. Calc-alkaline porphyry, the predominant clast, is similar in appearance to feldspar porphyry intrusions widely exposed in the area, but the two are not related. The porphyry clasts are cogenetic with diorite–granodiorite intrusions and volcanic rocks of the greenstone belt. Andesite clasts are only observed near the base of the assemblage, and the ratio of basalt to andesite increases up stratigraphic sections. The change suggests progressive erosion of arc-related volcanic rocks during sedimentation. Composition, texture, and mineralogy of the trondhjemite clasts are consistent with their derivation from the marginal phases of the Round Lake batholith. Intrusive rocks of the Timiskaming Group (coarse-grained holocrystalline syenitic–monzonitic rocks, biotite-bearing feldspar porphyries, and mica-rich lamprophyres) were not observed in the clasts, which suggests sedimentation prior to unroofing of these rocks. Sedimentation of the conglomerates postdated unroofing of underlying plagioclase porphyry (~2685 Ma), but predated unroofing of Timiskaming intrusions. The distribution of alkaline clasts only in proximity to the fault implies that alkaline magmatism was confined along the fault. Derivation of clasts from both sides of the fault and proximity of inferred sources support a pull-apart basin for sedimentation with minor strike-slip movement during and after the sedimentation.
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Holford, Simon, Nick Schofield, Justin MacDonald, Ian Duddy, and Paul Green. "Seismic analysis of igneous systems in sedimentary basins and their impacts on hydrocarbon prospectivity: examples from the southern Australian margin." APPEA Journal 52, no. 1 (2012): 229. http://dx.doi.org/10.1071/aj11017.
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The increasing availability of 3D seismic data from sedimentary basins at volcanic and non-volcanic continental margins has provided fundamental new insights into both the storage and transport of magma in the continental crust. As global hydrocarbon exploration increasingly focuses on passive margin basins with evidence for past intrusive and extrusive igneous activity, constraining the distribution, timing and pathways of magmatism in these basins is essential to reduce exploration risk. Producing and prospective Australian passive margin basins where igneous systems have been identified include the Bight, Otway, Bass, Gippsland and Sorell basins of the southern margin. This paper reviews both the impacts of volcanic activity on sedimentary basin hydrocarbon prospectivity (e.g. advective heating, reservoir compartmentalisation and diagenesis), and the styles, distribution and timing of late Cretaceous–Recent extrusive and intrusive igneous activity along basins of the southern Australian margin, providing illustrative examples based on 2D and 3D seismic reflection data.
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Gibson, S. A., R. N. Thompson, O. H. Leonardos, S. E. Turner, J. G. Mitchell, and A. P. Dickin. "The Serra do Bueno potassic diatreme: a possible hypabyssal equivalent of the ultramafic alkaline volcanics in the Late Cretaceous Alto Paranaίba Igneous Province, SE Brazil." Mineralogical Magazine 58, no. 392 (September 1994): 357–73. http://dx.doi.org/10.1180/minmag.1994.058.392.02.
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AbstractCretaceous, strongly alkaline mafic igneous provinces occur around the margins of the Ordovician to Cretaceous Paraná sedimentary basin of southern Brazil. The Serra do Bueno diatreme is situated in the southern portion of the largest of these alkaline provinces, the Alto Paranaíba Igneous Province in Minas Gerais. The well-exposed diatreme crops out close to the south-west surface limit of the São Francisco craton and is adjacent to several other poorly exposed ultramafic alkaline pipes, previously described variously as kimberlites (Barbosa, 1991) and lamproites (Ramsay and Tompkins, in press). The diatreme has two distinct facies: (1) a crater facies dominated by lapilli tuffs; and (2) a magmatic hypabyssal facies formed by a relatively fresh ultramafic (MgO = 15 wt.%) potassic (K2O/Na2O = ∼ 1.5) intrusion that contains xenoliths of meta-sediments, feldspathic gneiss and dunite. It is massive and porphyritic, with large olivine phenocrysts (Fo87) and smaller crystals of diopside (Ca50Mg44Fe6), phlogopite, perovskite, ilmenite and zeolites in a fine-grained groundmass that contains altered leucite and up to 20% devitrified glass. The Serra do Bueno intrusion shows a strong enrichment in light relative to heavy rare earth elements, with La/Yb of ∼85. Its initial 87Sr/86Sr (0.705176) and 143Nd/144Nd (0.512312) isotopic ratios are similar to those of other intrusions (e.g. Limeira 2) and lavas (e.g. Presidente Olegário) in the Alto Paranaíba Igneous Province. This suggests that these Late Cretaceous alkaline magmas were all derived from a similar source, predominantly within the subcontinental lithospheric mantle.Laser 40Ar/39Ar analyses have yielded an isochron of 90 ± 4 Ma for the Serra do Bueno intrusion. This age is higher than the corresponding K/Ar bulk-rock age for the same sample but similar to K/Ar ages determined on mica separates from both intrusive and extrusive rocks in the Alto Paranaíba Igneous Province.
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Stephens, Tara, Richard Walker, David Healy, and Alodie Bubeck. "Segment tip geometry of sheet intrusions, II: Field observations of tip geometries and a model for evolving emplacement mechanisms." Volcanica 4, no. 2 (October 18, 2021): 203–25. http://dx.doi.org/10.30909/vol.04.02.203225.
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Igneous sheet intrusions are segmented across several orders of magnitude, with segment tip geometry commonly considered indicative of the propagation mechanism (brittle or non-brittle). Proposed propagation mechanisms are inferred to represent host rock mechanical properties during initial magma emplacement; typically, these models do not account for segment sets that show a range of tip geometries within the same lithology. We present a detailed structural characterization of basaltic sill segments and their associated host rock deformation from the Little Minch Sill Complex, Isle of Skye, UK, and a broader comparison with segment geometries in three additional intrusive suites (Utah, USA; and Mull and Orkney, UK). Each separate host lithology shows multiple tip geometries and styles of host rock deformation, from elastic-brittle fracture, to viscous indentation and fluidisation. We attribute this range of host rock deformations to evolving conditions that occur at the tips both during sheet growth and arrest.
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Pharaoh, T. C., T. S. Brewer, and P. C. Webb. "Subduction-related magmatism of late Ordovician age in eastern England." Geological Magazine 130, no. 5 (September 1993): 647–56. http://dx.doi.org/10.1017/s0016756800020951.
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AbstractDeep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.
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ROBINS, BRIAN. "The mode of emplacement of the Honningsvåg Intrusive Suite, Magerøya, northern Norway." Geological Magazine 135, no. 2 (March 1998): 231–44. http://dx.doi.org/10.1017/s0016756898008395.
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The Honningsvåg Intrusive Suite consists of several layered mafic/ultramafic intrusions and a transgressive body of igneous breccia that appears to represent a magma conduit. It is emplaced into a Silurian, flysch-type sedimentary sequence that is thermally metamorphosed to spotted slate, cordierite–andalusite or pyroxene hornfels and agmatitic migmatite. Folds and flattened reduction spots in the hornfelses suggest that emplacement took place after Caledonian deformation and development of a slaty cleavage. Tectonic rotation subsequent to emplacement has led to exposure of the Honningsvåg Intrusive Suite in a natural cross-section corresponding to ∼10 km of crustal depth. Basaltic magma was initially emplaced as a several-kilometre-tall pipe that crystallized to form Intrusion 1. A second magma chamber was initiated alongside this pipe and subsequently expanded laterally into a sill-like magma body as batches of olivine-saturated basalt were added. A later magma chamber, represented by Intrusion 4, developed largely within the cumulates forming the upper part of Intrusion 2 and appears to have been accompanied by opening of a broad inclined feeder into which blocks and slabs of older cumulates collapsed. The resulting igneous breccias of Intrusion 3 are chaotic and largely clast-dominated in the lower part of the conduit, but enclosed slabs are matrix supported and orientated parallel to an originally subhorizontal banding in the feldspathic peridotite matrix in the upper part. The core of the breccia body has a troctolite matrix and contains blocks of older breccia, suggesting re-opening of the conduit, either during the crystallization of Intrusion 4 or possibly during the development of chambers represented by the younger layered intrusions. The cumulates in Intrusion 4 subsided sufficiently to invert marginal parts of the Layered Series before a further magma chamber was initiated in its roof rocks. The last major magma chamber opened alongside Intrusion 5 and extended upwards as a pipe or broad dyke to the highest structural levels exposed. Cross-cutting relationships show that the Honningsvåg magma chambers were not active simultaneously but were emplaced sequentially, generally at successively higher structural levels. Olivine tholeiite magma initially pooled in a crustal zone where it had neutral buoyancy. Subsequent chambers are suggested to have been initiated by emplacement of magma along the density discontinuities that existed above and around crystallized intrusions and their associated hornfelses. Chambers evolved by fractional crystallization, assimilation of country rocks and periodic replenishment. The abandonment of magma chambers may have resulted from the expulsion of low-density residual melts.
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Singh, Rajendra, A. K. Singh, and P. K. Mandal. "Cuttability of coal seams with igneous intrusions." Engineering Geology 67, no. 1-2 (December 2002): 127–37. http://dx.doi.org/10.1016/s0013-7952(02)00149-7.
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Mark, Niall, Nick Schofield, David Gardiner, Liam Holt, Clayton Grove, Douglas Watson, Andy Alexander, and Heather Poore. "Overthickening of sedimentary sequences by igneous intrusions." Journal of the Geological Society 176, no. 1 (September 24, 2018): 46–60. http://dx.doi.org/10.1144/jgs2018-112.
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