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1
Larsen, L. M., W. S. Watt, and M. Watt. "Geology and petrology of the Lower Tertiary plateau basalts of the Scoresby Sund region, East Greenland." Bulletin Grønlands Geologiske Undersøgelse 157 (January 1, 1989): 1–164. http://dx.doi.org/10.34194/bullggu.v157.6699.
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The early Tertiary plateau basalts in East Greenland are situated on a continental margin and were erupted during continental break-up and initiation of sea-floor spreading in the North Atlantic. In the region stretching from Scoresby Sund southward to 69°N 40 000 km2of basalts with an average thickness of 1.5 km have been investigated by measuring and flow-to-flow sampling of 130 profiles, followed by major element geochemical analysis and microprobe analysis, trace element analysis and some Sr isotope data. The basalts rest on Mesozoic sediments in the east and on Precambrian gneiss in the west. Six basalt formations are defined: the Magga Dan, Milne Land and Geikie Plateau Formations form a lower regional sequence erupted in one volcanic episode from sites in the NW part of the region; the Rømer Fjord and Skrænterne Formations form an upper regional sequence erupted in a subsequent volcanic episode in which eruption sites moved SE to centres east of the present Atlantic coast; the Igtertivâ Formation and a coast-parallel dyke swarm formed in a third volcanic episode only recorded at the Atlantic coast. The lavas are essentially flat-lying; a narrow strip along the Atlantic coast is extensively block faulted. Single lava flows are extensive (max. 11 000 km2) and voluminous (max. 300 km3). They are well preserved, with metamorphism of the low zeolite facies. All the lavas and most of the dykes are fractionated tholeiitic basalts with Mg/(Mg+Fe2+) ratios of 0.66-0.39 and TiO2 = 1.2-4.5%. The major part (the 'main basalts', 96% by volume) have Mg ratios of 0.56-0.39, while only 4 vol.% are Mg-rich basalts with Mg ratios of 0.66-0.57. A nephelinitic tuff layer occurs at the base of the second sequence. A few dykes are alkaline. The Mg-rich basalts have microphenocrysts of olivine (FO90-70) and chromite, while the main basalts comprise both aphyric and porphyritic sequences. Phenocrysts of plagioclase (An88-37) are abundant, of olivine (FO80-57) are sparse but ubiquitous, and of augite (FS9-20) sparse and often absent. Groundmass phases are olivine (to FO3737), plagioclase (to An13, augite (to FS62), pigeonite (Fs26-50), titanomagnetite and ilmenite. All rocks contain several per cent fine-grained mesostasis. The phenocrysts frequently show disequilibrium textures and a wide range of compositions within one sample. Extrusion temperatures are calculated to 1280-1110°C, and densities to 2.68-2.78 g/cm3, increasing with fractionation. The volcanic episodes are demonstrated in systematic compositional variations with height in the basalt sequence. Each of the two major episodes started with a variety of lava compositions including Mg-rich basalts, followed by a thick sequence of 'main basalts' showing a systematic decrease of TiO2 and other incompatible elements with height, and ending with a reversal to higher TiO2 values. The third episode is not cyclic, and its products have changed incompatible element ratios. The Mg-rich basalts comprise depleted MORB type basalts, relatively enriched olivine tholeiites, and very enriched tholeiites (Mikis type basalt). Sr isotopes show 87Sr/86Sr ratios of 0.7034 in most basalts and 0.7045 in the Mikis type basalt, while some Si-rich basalts have ratios up to 0.7079. The East Greenland basalts are 'initial rifting' basalts very similar to those in Deccan. The magmas have equilibrated at low pressures in crustal magma chambers. The main basalts have fractionated ol + pl + cpx no matter whether they are aphyric or porphyritic. Simple crystal fractionation can account for sub-trends but not for the complete compositional variation of the main basalts. This is considered as resulting from fractionation in open magma chambers which were repeatedly filled, mixed and tapped. The decrease in TiO2 with height in each volcanic episode indicates increasing magma input rate and shorter residence time in the chamber, while the final reversal indicates the decline and cessation of activity. There is evidence for widespread crustal contamination (1-4%) in the magma chambers of the two lowest formations. Crustal contamination of magmas on the way to the surface occurred sporadically throughout both sequences. One case of magma mixing occurred when a Mg-rich basalt magma invaded the regional main basalt magma chamber. The Mg-rich basalts cannot be directly related to each other or to the main basalts. A petrogenetic scheme is suggested where the Mikis type basalt originated in, or contains an addition from, an undepleted or enriched mantle source. All the other magma types originated in a depleted mantle source by varying degrees and possibly depths of melting. Increasing degrees of melting are indicated for the types nephelinite - enriched olivine tholeiite – main basalt parent – MORB type basalt. The MORB type basalt may also be produced by melting of a residuum. The basalts of the third volcanic episode include another component of mantle or basaltic crust. The three recorded volcanic episodes are related to rifting events during the break-up of the North Atlantic continent, viewed as repeated attempts to straighten out a bend in the original line of opening. The two first rifting events failed while the third for a short while produced oceanic crust. Compared to other regions of the North Atlantic volcanic province the Scoresby Sund basalts are similar to basalts from Kangerdlugssuaq, northern East Greenland, West Greenland, the Faeroes, the Vøring Plateau and some basalts on lceland. The main magma source for the North Atlantic province was similar to that of the lceland hotspot, but enriched subcontinental lithosphere may also have participated in the stage of initial rifting. A correlation for the volcanic episodes throughout East Greenland and the Faeroes is proposed.
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Nelson, Faye E., René W. Barendregt, and Mike Villeneuve. "Stratigraphy of the Fort Selkirk Volcanogenic Complex in central Yukon and its paleoclimatic significance: Ar/Ar and paleomagnetic data." Canadian Journal of Earth Sciences 46, no. 5 (May 2009): 381–401. http://dx.doi.org/10.1139/e09-025.
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Brunhes, Matuyama, Kaena, and Mammoth age basaltic lava flows (Tertiary–Quaternary Selkirk Volcanics) were sampled in west-central Yukon. The mean characteristic remanent magnetization (ChRM) direction of the flows sampled in this and previous studies has a declination of 348.7° and an inclination of 70.8° (n = 42, k = 99.6, α95 = 2.2°) (all on lower hemisphere). The time range represented in this study (ca. 3.25 to ca. 0.004 Ma) is great enough to have confidently averaged secular variation. Sediment associated with the basalt has a mean declination of 7.6° and inclination of 78.8° (n = 5, k = 5.6, α95 = 35.7°). A new 40Ar–39Ar date on the reversely magnetized basal basalts at Ne Ch’e Ddhäwa places the eruption in the Mammoth subchron of the Gauss Normal Chron. The newly dated basal basalt at Ne Ch’e Ddhäwa precedes the initial continental glaciation in Yukon and is older than the Fort Selkirk vent (Lower Mushroom), which was previously thought to be the oldest eruption at Fort Selkirk Volcanic Complex (FSVC). This basal flow at Mushroom is dated at 1.82 ± 0.03 Ma and the uppermost flow is reproducibly dated at 1.36 ± 0.04 Ma. Till on the flanks of a subglacial volcanic mound called Ne Ch’e Ddhäwa (informal) is older than previously thought; its reverse magnetization indicates an Early Pleistocene age rather than the Reid glaciation, which falls during the Brunhes Normal Chron. The paleomagnetism of Tertiary–Quaternary Selkirk Volcanics outcrops outside the FSVC was studied for the first time. The ChRM direction of basalt at the northern edge of the northern Cordillera volcanic province agrees with FSVC directions, suggesting that this flow reflects the same period of volcanism. This suggests that an Eocene K–Ar date, previously thought to be unreliable, may well be correct.
3
Hald, N., and R. Waagstein. "The dykes and sills of the Early Tertiary Faeroe Island basalt plateau." Transactions of the Royal Society of Edinburgh: Earth Sciences 82, no. 4 (1991): 373–88. http://dx.doi.org/10.1017/s0263593300004211.
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ABSTRACTThe Early Tertiary basalt plateau of the Faeroe Islands is cut by dykes and sills. Chemical analyses show a two-fold division of the intrusive rocks into a group of low-TiO2 (0·73–1·93%), MORB-type tholeiitic basalts and a group of high-TiO2 (2·09–3·90%) tholeiitic basalts. The low-TiO2 group comprises about 15% picrites and olivine-phyric basalts and 85% plagioclase-phyric basalts, and shows a chemical range largely explicable in terms of low-pressure fractional crystallisation of olivine ± plagioclase ± clinopyroxene. The high-TiO2 group is strongly dominated by plagioclase-phyric basalts with only few olivine-phyric compositions. The chemical trends are less regular than those formed by the low-TiO2 basalt dykes and a number of subgroups may be identified on the basis of bulk rock chemistry. Dykes belonging to a specific subgroup were probably fed from the same magma chamber.Petrographically and chemically the dykes and sills are clearly related to the upper 2·5 km of the lava sequence. Field evidence suggests that some of the dykes were contemporaneous with the exposed lavas, while other dykes and the sills were intruded in response to a slight doming of the plateau during the final stages of volcanic activity. Our investigations demonstrate that high-TiO2 and low-TiO2 magmas were both emplaced until the very end of magmatism, with the latter being mainly concentrated in the northern part of the archipelago. We briefly sketch a possible relationship between the supposed NE-Atlantic mantle plume, the distribution of the various magma types and the location of the Early Tertiary continental splitting zone north of the islands.
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Emeleus, C. H. "The Tertiary lavas and sediments of northwest Rhum, Inner Hebrides." Geological Magazine 122, no. 5 (September 1985): 419–37. http://dx.doi.org/10.1017/s0016756800035342.
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AbstractSeveral small outliers of Tertiary lavas and sediments rest with strong unconformity on a buried landscape eroded from Torridonian sediments and Tertiary granophyre. Erosion continued during the period of sediment and lava accumulation. Four formations are recognized; these are, in order of increasing age, the Orval Formation (hawaiite and basaltic hawaiite lavas), the Guirdil Formation (icelandite lavas, interbedded conglomerates), the Upper Fionchra Formation (tholeiitic basaltic andesite lavas, hyaloclastite deposits, basal conglomerate) and the Lower Fionchra Formation (alkali and transitional basalt, basaltic hawaiite and hawaiite lava flows, basal conglomerate); each is separated by an erosional interval. Clasts in the conglomerates reveal a history of erosion of a terrain exposing gneisses, Torridonian sediments, igneous rocks derived from the Rhum Tertiary Central Complex (including allivalites), and Tertiary lavas of local origin but also including, in the oldest conglomerates, tholeiitic basalts not now preserved on or near Rhum. Prior to and during lava and sediment accumulation, erosion on Rhum had cut down to a level similar to that of the present day, although not to the extent that high-grade thermally altered rocks, which are a marked feature of the Central Complex, were being eroded in any quantity. A sequence of east–west trending valleys, possibly initiated on the line of the earlier Main Ring Fault, drained the area of the Central Complex which then, as now, must have been high ground. Small lakes occasionally formed in the valleys allowing the accumulation of fine-grained sediment with plant remains, and promoting the formation of hyaloclastite deposits when buried by later flows. No source for any of the lava formations is preserved on Rhum; they are thought to have come from feeders north of Rhum, possibly near Canna, and to have ponded against the hills and valleys near and in the Central Complex.The oldest tholeiitic lavas, not now found in situ, were followed by alkali and transitional flows compositionally similar to the Skye Main Lava Series but characteristically feldsparphyric; the most mafic also contain phenocrysts of magnesian olivine (with included Cr-Al-rich spinels) and aluminous spinel. Both the early alkalic/transitional basalts and the youngest hawaiites and basaltic hawaiites equilibrated at pressures < 9 kb; the tholeiitic basaltic andesites and icelandites equilibrated at relatively shallows depths.Apart from a few N–S to NW–SE-trending basalt dykes, the lava formations represent the youngest Tertiary igneous event on Rhum.
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Watt, W. S. "Stratigraphy and correlation of the Tertiary plateau basalts in North-East Greenland." Rapport Grønlands Geologiske Undersøgelse 162 (January 1, 1994): 185–94. http://dx.doi.org/10.34194/rapggu.v162.8261.
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The Hold with Hope – Wollaston Forland area with the adjacent islands is partly covered by Tertiary plateau basalts. The area is divided into structural blocks by NNE–SSW faults with apparent eastward down-step and the basalt succession of the mainland is repeated on the islands to the east. Individual profiles are correlated using distinctive features of the development of their chemistry with height. A succession of 600–700 m of uniform tholeiitic lavas compose a lower sequence which extends over the whole area. This is overlain locally by an intervolcanic conglomerate followed by 500 m of variable tholeiites and alkali-basalt lavas. This upper sequence is restricted to the southern part of the volcanic area. The northerly occurrence of a dyke chemically associated with the upper sequence suggests that this sequence originally extended much further north than its present outcrop.
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Baksi, Ajoy K. "Timing and duration of Mesozoic-Tertiary flood-basalt volcanism." Eos, Transactions American Geophysical Union 71, no. 49 (1990): 1835. http://dx.doi.org/10.1029/eo071i049p01835-01.
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Chen, X. M., M. Zhao, and Z. L. Dong. "Coronas of corundum xenocryst in the Tertiary alkali basalt." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A99. http://dx.doi.org/10.1016/j.gca.2006.06.111.
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Baldreel, L. O., and M. S. Andersen. "Tertiary development of the Faeroe-Rockall Plateau based on reflection seismic data." Bulletin of the Geological Society of Denmark 41 (November 30, 1994): 162–80. http://dx.doi.org/10.37570/bgsd-1995-41-15.
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The Faeroe-Rockall Plateau is located in the NE Atlantic Ocean between Iceland and Scotland and is characterized by a late Paleocene-early Eocene basalt cover, which was extruded in association with the incipient opening of the NE Atlantic. The Faeroe-Rockall Plateau is separated from the NW European continental shelf by the Rockall Trough and the FaeroeShetland Channel, whose nature and age is still debated. Reflector configuration within the basalt allows volcanic seismic facies inteipretation to be carried out. The thickness of the basalt cover is estimated from reflection seismic data. Subbasalt geological structures are identified below subaerially extruded basalt on recently acquired as well as reprocessed seismic profiles. Overlying the basalt are early Eocene and younger Sediments. The distribution of these sedi- . ments is largely controlled by 1) the topography after the cessation of the volcanism, 2) the post volcanic subsidence of the area which is estimated from the depth to the breakpoints located on prim¥)' volcanic escaipments, 3) the Eocene-Miocene compressional tectonics which formed ridge& and minor basins, and 4) bottom currents of Norwegian Sea Deep Water (NSDW) which in the Neogene flowed into the North Atlantic south of the Greenland-Iceland-Faeroe-Scotland Ridg,e. A considerable part of the NSDW flows east and south of th
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Baumhauer, Roland. "Basaltic Bedding Conditions of the Tertiary Brown-Coal Formation in the Rhön and Vogelsberg Area (Tertiary Basaltic Volcanoes)." Zeitschrift der Deutschen Geologischen Gesellschaft 141, no. 1 (January 1, 1990): 79–86. http://dx.doi.org/10.1127/zdgg/141/1990/79.
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Jensen, Aage. "Cupriferous pseudobrookite in a Tertiary basalt from the Faeroe Islands." Bulletin of the Geological Society of Denmark 34 (December 19, 1985): 87–95. http://dx.doi.org/10.37570/bgsd-1985-34-09.
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Forty-five electron microprobe analyses have been carried out on pseudobrookite occurring in a basalt from the Faeroe Islands. It is shown that pseudobrookite formed after ilmenite contains between 1 and 3% CuO, whereas pseudobrookite formed after titanomagnetite does not contain Cu. This difference in Cu content is not inherited from the original ilmenite and titanomagnetite, but arises during the formation of the pseudobrookite. The pseudobrookite in this basalt, regardless of whether it formed from ilmenite or from titanomagnetite, is richer in Ti than in the formula Fe2TiO5, the surplus Ti4+ being balanced by the presence of divalent ions such as Mg, Mn, Fe and Cu. Mg and Cu dominate in pseudobrookite after ilmenite, Fe and Mg dominate in pseudobrookite after titanomagnetite. Pseudobrookite after titanomagnetite is richer in Ti than pseudobrookite after ilmenite. The pseudobrookite is not homogeneous. Both pseudobrookite formed from ilmenite and that formed from titanomagnetite contain small blebs of hematite and rutile, and furthermore pseudobrookite after titanomagnetite is intergrown with larger coherent areas of hematite. The hematite blebs in pseudobrookite after ilmenite can contain up to more than 5% CuO, but there is virtually no copper in either type of hematite in the pseudobrookite after titanomagnetite, nor do the rutile blebs contain copper.
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Sutherland, F. L., D. F. Hendry, B. J. Barron, W. L. Matthews, and J. D. Hollis. "An unusual Tasmanian Tertiary basalt sequence, near Boat Harbour, northwest Tasmania." Records of the Australian Museum 48, no. 2 (September 18, 1996): 131–61. http://dx.doi.org/10.3853/j.0067-1975.48.1996.285.
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Whittaker, R. C. "A preliminary seismic interpretation of an area with extensive Tertiary basalts offshore central West Greenland." Bulletin Grønlands Geologiske Undersøgelse 172 (January 1, 1996): 28–31. http://dx.doi.org/10.34194/bullggu.v172.6739.
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A seismic and geological interpretation of the area between latitudes 67°30'N and 73°N offshore West Greenland, was completed in 1995 and has been published as an Open File Series report (Whittaker, 1995). The area is characterised by extensive Early Tertiary basalts which are the seaward extension of the plateau basalts exposed in the Disko - Nuussuaq - Svartenhuk Halvø area onshore (Clarke & Pedersen, 1976). These basalts present special problems in the processing and interpretation of seismic data. The interpretation incorporates all the seismic data acquired prior to the 1995 field season, inc1uding those lines acquired during the first phase of exploration in the 1970s. Ties to two of the exploration wells drilled offshore southem West Greenland have led to a greater understanding of the timing and kinematics of teetonie events during the Tertiary period; such events are not recorded in the onshore area. The area is considered to have significant exploration potential and warrants additional studies to determine the thickness of the basalt formation in the area.
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Clarke, D. B., B. I. Cameron, G. K. Muecke, and J. L. Bates. "Early Tertiary basalts from the Labrador Sea floor and Davis Strait region." Canadian Journal of Earth Sciences 26, no. 5 (May 1, 1989): 956–68. http://dx.doi.org/10.1139/e89-077.
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Fine- to medium-grained, phyric and aphyric basalt samples from ODP Leg 105, site 647A, in the Labrador Sea show little evidence of alteration. Chemically, these rocks are low-potassium (0.01–0.09 wt.% K2O), olivine- to quartz-normative tholeiites that compare closely with the very depleted terrestrial Paleocene volcanic rocks in the Davis Strait region of Baffin Island and West Greenland. However, differences exist in the Sr–Nd isotope systematics of the two suites; the Labrador Sea samples have ε Nd values (+9.3) indicative of a more depleted source, and are higher in 87Sr/86Sr (0.7040), relative to the Davis Strait basalts (ε Nd +2.54 to +8.97; mean 87Sr/86Sr 0.7034). The higher 87Sr/86Sr in the Labrador Sea samples may reflect seawater exchange despite no petrographic evidence for significant alteration. The Labrador Sea and early Davis Strait basalts may have been derived from a similar depleted mantle source composition; however, the later Davis Strait magmas were generated from a different mantle. None of the Baffin Island, West Greenland, or Labrador Sea samples show unequivocal geochemical evidence for contamination with continental crust.
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Kitchen, D. E. "The partial melting of basalt and its enclosed mineral-filled cavities at Scawt Hill, Co. Antrim." Mineralogical Magazine 49, no. 354 (December 1985): 655–62. http://dx.doi.org/10.1180/minmag.1985.049.354.04.
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AbstractPartially melted basalts enclosing amygdales which have been completely melted formed at Scawt Hill adjacent to a Tertiary dolerite plug. Melting of the basalts commenced in a clay-rich mesostasis to produce a feldspathic liquid which then crystallized to an assemblage of dendritic olivine, skeletal hypersthene, opaque oxide and Mg-hercynite in a microcrystalline plagioclase matrix. An original mineral assemblage of zeolite, calcite, and saponite-nontronite in the amygdales melted and quenched to a brown glass now containing complexly zoned pyroxenes with plagioclase and opaque oxide. Melting commenced between 700–800°C, reaching a maximum temperature of 1168°C, and was followed by rapid cooling. The assimilation of remelted basalt may alter the course of crystallization of contaminated magmas.
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Anketell, J. M., and S. M. Ghellali. "Stratigraphic Relationships of Basalt Lava Flows to the Pleistocene Sedimentary Sequence of the Mizdah Region, Tripolitania, S.P.L.A.J." Libyan Studies 21 (1990): 61–63. http://dx.doi.org/10.1017/s0263718900001473.
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AbstractCalcreted debris flow breccias which form the lowermost Pleistocene deposits in the Hammadah Al Hamrah region are locally overlain by well cemented conglomerates of the Old Wadi Terraces. These are commonly capped by a younger, mature calcrete which is also found patchily developed on the Tertiary and Mesozoic limestone bedrock. Basalt lava flows rest either on an eroded surface in the conglomerates or directly on the debris flows; however, their relationship to the younger calcrete is rarely seen. In the area north-east of Mizdah a pre-younger calcrete age for the basalts is proposed on the basis of calcrete-filled fissures which invade the topmost part of the lava sequence. Similarity of the Mizdah sequence to that at Wadi Ghan in the Jabal Nafusah supports correlation of the conglomerates and basalt with Unit Q2 and the younger calcrete event with the upper calcrete of the Jifarah/Wadi Ghan areas. The calcreted breccia/debris flow deposits in turn correlate with Unit Q1 and the lower calcrete.
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DePaolo, Donald J., Frank V. Perry, and W. Scott Baldridge. "Crustal versus mantle sources of granitic magmas: a two-parameter model based on Nd isotopic studies." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 439–46. http://dx.doi.org/10.1017/s0263593300008117.
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ABSTRACTTemporal and spatial variations in the Nd isotopic compositions of Tertiary caldera-forming rhyolite tuffs, and Cretaceous and Tertiary granites of the western U.S.A. are used as a basis for a model that accounts for the observed proportions of crustal versus mantle contributions to silicic magmas in terms of two parameters: the ambient crustal temperature and the rate of supply of basaltic magma from the mantle. The crustal contribution to silicic igneous rocks is measured in terms of the Neodymium Crustal Index (NCI). The relationships between crustal temperature, basalt supply and NCI are quantified using a model of a magma chamber undergoing continuous recharge, wall-rock assimilation and fractional crystallisation. From the model, a critical value of the ratio of basalt recharge-to-assimilation, (r/a)c, is deduced, which increases with decreasing crustal temperature. The r/a value must exceed (r/a)c to allow the volume of differentiated magma to increase, a prerequisite for developing large volumes of silicic magma. Strongly peraluminous (or S-type) magmas (NCI = 0·8–1), form under conditions of high crustal temperature and low basalt supply. Metaluminous or I-type granites form over a wide range of conditions (NCI = 0·1–1), generally where basalt supply is substantial. In individual long-lived volcanic centres, the large-volume high-silica ignimbrites are associated with the highest r/a and lowest NCI values, indicating that these magmas are typically differentiates of mantle-derived basaltic parents.
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MOGHAZI, ABDEL-KADER M. "Geochemistry of a Tertiary continental basalt suite, Red Sea coastal plain, Egypt: petrogenesis and characteristics of the mantle source region." Geological Magazine 140, no. 1 (January 2003): 11–24. http://dx.doi.org/10.1017/s0016756802006994.
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Major and trace element data on Tertiary continental basalt flows from the Shalatein area, Red Sea coastal plain of Egypt, have been presented and used to obtain more information about their source region and the processes involved in their generation. The rocks are mainly alkali olivine basalt with MgO and Mg no. in the range of 9.8–5 wt % and 65–46, respectively. They display wide variations in incompatible element concentrations, particularly LREE, Zr, Nb, K, Y, Ba and Sr. There is no evidence of significant crustal contamination or a lithospheric mantle signature in these rocks. Normalized trace element patterns and diagnostic elemental ratios are very similar to those of modern ocean-island basalts (OIB) a feature which suggests that the mantle source region was the asthenosphere. Comparison with the different types of OIB indicates that the basalts may be derived from a high U/Pb (HIMU) source with slightly elevated K and Ba contents. The basalts show general trends of increasing incompatible elements (K2O, Nb, Y, Sr and Yb), and decreasing contents of compatible elements (Cr, Ni, Sc and Ca) with decreasing Mg no. Furthermore, TiO2, P2O5, LREE and Th define maxima at about Mg no.=56, suggesting late fractionation of Fe–Ti oxides and apatite. Although these variations are consistent with fractional crystallization processes, the wide variations in LREE contents and the incompatible trace element ratios Ce/Y (1.2–3.8), Zr/Nb (2.3–7.1) and Nb/Y (0.6–4) in the least fractionated samples (Mg no. > 56) suggest that fractional crystallization involving the observed phenocryst assemblage (olivine and clinopyroxene) cannot fully explain such compositional variations. Modelling of the mafic rocks (Mg no. > 56) using REE suggests varying degrees of partial melting of an enriched mantle source region in the garnet stability field. Partial melting is attributed to plume-related mantle upwelling beneath the Red Sea rift system.
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Larsen, H. C., R. S. Duncan, J. F. Allan, and ODP Leg 163 shipboard party. "ODP Leg 163, South-East Greenland volcanic rifted margin." Bulletin Grønlands Geologiske Undersøgelse 172 (January 1, 1996): 103–12. http://dx.doi.org/10.34194/bullggu.v172.6753.
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The South-East Greenland margin is a type example of a volcanic rifted margin. The margin is characterised by a broad seaward-dipping reflector sequence (SDRS) composed of basalt that onlaps continental (mainly Precambrian) crust to the west and terminates eastward in oceanic crust of early Tertiary age (Figs 1, 2).
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Okrusch, Martin, Ulrich Schüssler, Paul Van Den Bogaard, Nikola Koglin, Helene Brätz, Joachim Lorenz, Cliff Karbusicka, and Tobias Spiegl. "Isolated alkaline basalt occurrences in the northern Spessart, Germany: Outposts of the Early Miocene Vogelsberg shield volcano?" Neues Jahrbuch für Mineralogie - Abhandlungen Journal of Mineralogy and Geochemistry 196, no. 3 (July 1, 2020): 199–219. http://dx.doi.org/10.1127/njma/2020/0194.
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Four isolated occurrences of Tertiary volcanic rocks in the northern Spessart at Beilstein, Hoher Berg, Madstein and Kasselgrund are relics of volcanic vents or dikes. They display alkaline basalts (s. l.) with mainly trachybasaltic composition, which, from normative mineral contents, may be designated as nepheline-bearing alkali-olivine basalts and basanites. In part, centimetre-sized xenoliths of spinel lherzolite occur. According to Ar-Ar dating, the alkaline basalts (s. l.) from Kasselgrund have erupted at 18.1 ± 0.3 or 19.3 ± 0.4 Ma, those of Hoher Berg between c. 18 and c. 21 Ma. These ages correspond to the Vogelsberg eruption stage I. A slightly younger Ar-Ar age of 16.8 ± 0.3 Ma was recorded for the Beilstein basalt, which is in chronological accordance to the turn of Vogelsberg eruption stages II and III. Samples of all four occurrences reveal major and trace element compositions, which are different from those of the Vogelsberg basalts. Compositions of basalts of the stage III from Vogelsberg coincide most with the Spessart basalts. This signals a special position of the northern Spessart volcanic rocks either as a discrete spatial part of the Vogelsberg volcanic suite or as smaller, independent eruption centres.
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Anderson, Robert G., Jonah Resnick, James K. Russell, G. J. Woodsworth, Michael E. Villeneuve, and Nancy C. Grainger. "The Cheslatta Lake suite: Miocene mafic, alkaline magmatism in central British Columbia." Canadian Journal of Earth Sciences 38, no. 4 (April 1, 2001): 697–717. http://dx.doi.org/10.1139/e00-121.
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New mapping, mineralogical, and geochemical studies help characterize late Tertiary primitive, alkaline, sodic basanite, alkali olivine basalt, transitional basalt, and diabase in the Nechako River, Whitesail Lake, and McLeod Lake map areas of central British Columbia and distinguish the Miocene Cheslatta Lake suite. The suite encompasses scattered erosional remnants of topographically distinct, columnar-jointed, olivine-phyric basalt and diabase volcanic necks, dykes, and associated lava flows north of the Anahim volcanic belt and west of the Pinchi Fault. Volcanic centres at Alasla Mountain and at Cutoff Creek, near Cheslatta Lake, are proposed as type areas. Olivine, plagioclase, and pyroxene phenocrysts, megacrysts, and (or) xenocrysts; common ultramafic xenoliths; and rare but significant plutonic and metamorphic xenoliths are characteristic. Basanite, transitional basalt, and alkali olivine basalt groundmass contain plagioclase, clinopyroxene, Fe-Ti oxides, feldspathoid, olivine, and apatite. The Cheslatta Lake suite is characterized by its alkaline character, olivine-rich (>10 wt.%) normative mineralogy, and silica-undersaturated nature (>1 wt.% normative nepheline; hypersthene-normative rocks are uncommon). Mg numbers vary between 7242. Some samples encompass near-primitive mantle melt compositions. Cheslatta Lake suite rocks in the Nechako River area are distinguished from the underlying Eocene Endako and stratigraphically higher Neogene Chilcotin groups basaltic andesite lavas within the study area, and from the Chilcotin Group basalt in the type area south of the Anahim volcanic belt, by form, preserved thickness, phenocrystxenocryst mineralogy, amygdule abundance, included xenoliths, isotopic age, and major and incompatible, high field strength, and rare-earth trace element contents.
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Hamilton, T. S., and J. Dostal. "Melting of heterogeneous mantle in a slab window environment: examples from the middle Tertiary Masset basalts, Queen Charlotte Islands, British Columbia." Canadian Journal of Earth Sciences 38, no. 5 (May 1, 2001): 825–38. http://dx.doi.org/10.1139/e00-095.
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Voluminous basalts dominate a middle Tertiary bimodal volcanic assemblage in the Queen Charlotte Islands, British Columbia, Canada. These moderately enriched mid-ocean-ridge basalt (MORB-)like magmas were associated with significant crustal extension related to the subduction of the PacificFarallon ridge and the initiation of a slab window environment, which persisted for 35 Ma. These asthenospheric melts were derived from a low degree of melting of a heterogeneous peridotite source mainly in the spinel stability field, as inferred from fractional melting inversion calculations. The basaltic magmas in turn gave rise to both tholeiitic and calc-alkaline volcanic strata up to 3.5 km thick in local grabens. The tholeiitic basalts resemble MORB, with rare-earth element (REE) patterns ranging from slightly depleted to enriched in light REE (LREE). The calc-alkaline basaltic andesites are enriched in LREE, but are not strongly depleted in Nb. The rocks have overlapping Nd, Sr, and Pb isotopic compositions, similar to those of intraplate basalts from the adjacent northeast Pacific seamounts and Cordillera. The difference between the tholeiitic and calc-alkaline rocks is, in part, attributed to polybaric fractional crystallization of different proportions of plagioclase to mafic minerals from a similar tholeiitic magma. This marginal-basin subalkaline volcanic sequence and its genesis describe the slab window environment for the Tertiary tectonics of the western Canadian continental margin and provide a model for older combined tholeiitic and calc-alkaline volcanic successions.
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Hurai, V., M. Huraiová, P. Konečný, and R. Thomas. "Mineral-melt-fluid composition of carbonate-bearing cumulate xenoliths in Tertiary alkali basalts of southern Slovakia." Mineralogical Magazine 71, no. 1 (February 2007): 63–79. http://dx.doi.org/10.1180/minmag.2007.071.1.63.
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AbstractTwo types of carbonatic cumulate xenoliths occur in alkali basalts of the northern part of the Carpatho-Pannonian region, Central Europe. One is dominated by Ca-Fe-Mg carbonates with randomly distributed bisulphide globules (Fe1+xS2, x = 0–0.1), Mg-Al spinel, augite, rhönite, Ni-Co-rich chalcopyrite, and a Fe(Ni,Fe)2S4 phase. The second, carbonatic pyroxenite xenolith type, is composed of diopside, subordinate fluorapatite, interstitial Fe-Mg carbonates, and accessory K-pargasite, F-Al-rich ferroan phlogopite, Mg-Al spinel, albite and K-feldspar. All accessory minerals occur in ultrapotassic dacite-trachydacite glass in primary silicate melt inclusions in diopside, together with calcio-carbonatite and CO2-N2-CO inclusions. Textural evidence is provided for multiphase fluid-melt immiscibility in both xenolith types. The carbonatic pyroxenite type is inferred to have accumulated from differentiated, volatile-rich, ultrapotassic magma derived by a very low-degree partial melting of strongly metasomatized mantle. Mineral indicators point to a genetic link between the carbonatite xenolith with olivine-fractionated, silica-undersaturated alkalic basalt ponded at the mantle-crust boundary.
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Shahin, Hassan A. A., and Masoud S. Masoud. "Geology and geochemistry of Tertiary basalt in south Wadi Hodein area, South Eastern Desert, Egypt." Arabian Journal of Geosciences 6, no. 8 (February 15, 2012): 2777–87. http://dx.doi.org/10.1007/s12517-012-0525-6.
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Livingstone, A. "Low-temperature, hydrothermal garnet associated with zeolites, from basalt lavas near Beith, Ayrshire." Mineralogical Magazine 53, no. 369 (March 1989): 125–29. http://dx.doi.org/10.1180/minmag.1989.053.369.17.
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A Working quarry, at Loanhead (NS363557) within the Clyde Plateau Carboniferous lavas, is traversed by a tholeiitic Tertiary dyke some 25-30 m wide. Throughout the quarry the lavas are extensively altered and the most prominent secondary minerals are calcite and prehnite. Adjacent to the dyke is an indefinite alteration zone within which garnet has developed in close association with analcime and thomsonite. Contact metamorphism is not apparent. Secondary minerals in the quarried lavas and from the alteration zone have been described by Meikle (1989). The most salient feature of secondary mineral formation central to this paper is that grossular and andradite occur, in situ, in close proximity to the dyke, and only in the amygdales.
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Ochadlick, Andrew R. "Magnetic exploration of ocean crust for craters of impact origin: Model results." GEOPHYSICS 56, no. 8 (August 1991): 1153–57. http://dx.doi.org/10.1190/1.1443134.
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Magnetic data sets over deep ocean areas may contain clues to the existence of craters formed by the impact of an extraterrestrial body with the Earth’s ocean crust. To aid in the magnetic exploration of the ocean crust for oceanic impact craters, basic but effective computations from an impact model are studied from an aeromagnetic point of view. The main assumption of the analysis is that a sufficiently large impact can excavate large volumes of magnetized basalt, vaporize basalt, and raise basalt to temperatures above the Curie temperature (approximately 500°C) to alter the preimpact magnetization of the ocean floor and result in a magnetic anomaly being associated with an oceanic impact crater. In the absence of an existing theory on the influence of impacts on ocean crustal magnetization, the representation of a crater on the ocean floor by a simple potential provides, apparently for the first time, quantitative estimates of the crater’s magnetic anomaly along a horizontal surface. Numerical results from the model suggest that the detection of the anomaly of a Cretaceous‐Tertiary (K-T) type of impact is well within the capabilities of aeromagnetic technology.
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Bird, D. K., M. T. Rosing, C. E. Manning, and N. M. Rose. "Geologic field studies of the Miki Fjord Area, East Greenland." Bulletin of the Geological Society of Denmark 34 (December 20, 1985): 219–36. http://dx.doi.org/10.37570/bgsd-1985-34-18.
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Field relations between Tertiary intrusions and the lithologic units near Miki Fjord provide a record of physical and chemical processes associated with crustal extension and the formation of the East Greenland continental margin. At several localities the Precambrian basement has been remobilized and partly incorporated in the large macrodikes northeast of the Skaergaard intrusion. Blocks of vesicular basalts sank into the macroÂdike magma and were metamorphosed to equigranular aggregates of olivine and ortho- and clinopyroxÂenes with concentrations of plagioclase filling amygdale-like structures. We suggest that contact metamorÂphic dehydration of hydrous alteration minerals in the basaltic xenoliths and diffusion of this water into the macrodike magma were responsible for the abundant rhythmic layering that occurs near swarms of the xenoliths in a manner similar to that proposed by Taylor & Forester (1979) and Mc Birney & Noyes (1979) for the Skaergaard intrusion. Concentrations of xenoliths of leucogabbro and migmatitic basement gneisÂses are found near the top of one macrodike and in six smaller mafic dikes and sills that intrude the lower lavas. In contrast to the basalt blocks, the leucocratic xenoliths appear to have floated to the top of these mafic intrusions, thus providing an effective mechanism for transport of basement material during the early stages of crustal extension. Basement rocks and Tertiary basalts of the area have undergone hydrothermal alteration that is conÂcentrated in fracture systems near the intrusive bodies. Alteration mineralogy in the basalts consists of calc-silicate assemblages similar to those found in active geothermal systems in Iceland. Extensive calcium metasomatism is evident in a number of coast parallel dolerite dikes that are mineralized by iron-rich prehnite. Thermodynamic analysis of the dehydration of prehnite to form epidote and garnet indicates that the fluids responsible for the formation of prehnite mineralized dikes were at temperatures less than about 250°C. Mineralized shear zones and mafic dikes of presumed Proterozoic age define a pronounced structural trend in the basement of the area. This east - west trend is parallel with the coastal dike swarm north of 68°N and with topographical trends within the basalts. We therefore suggest that the pre-Tertiary strucÂtures may in part control the deflection of the coastline at 68°N and other aspects of the Tertiary structural and intrusive development.
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Kitchen, D. E. "The disequilibrium partial melting and assimilation of Caledonian granite by Tertiary basalt at Barnesmore, Co. Donegal." Geological Magazine 126, no. 4 (July 1989): 397–405. http://dx.doi.org/10.1017/s0016756800006580.
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AbstractA regional Tertiary basaltic dyke swarm intensifies within a Caledonian granite at Barnesmore, Co. Donegal. Rapid heating along the contact of one (possible feeder) dyke resulted in disequilibrium partial melting of granite wall-rock and the generation of a range in melt composition by the in situ melting of feldspar. The compositional variability of the melt is preserved in a glass containing feldspar spherulites and other quench phases which suggest rapid cooling. During partial melting the trace elements, Rb, Sr, and Ba were mobile and have been concentrated in glassy melted granite close to the contact of one dyke. The textures, mineralogy and geochemistry of dolerite in two dykes indicate localized bulk contamination and mixing with melted granite. This had a particularly marked effect on the crystallization of pyroxene and resulted in a wide range in mineral composition reflecting the degree of contamination. The intensification of a regional dyke swarm in well-jointed granite might control the siting of some major intrusive centres. Granite melted and mixed with basaltic magma may contribute to the evolution of granites in such centres.
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KIØRBOE, L. "Stratigraphic relationships of the Lower Tertiary of the Faeroe Basalt Plateau and the Faeroe–Shetland Basin." Geological Society, London, Petroleum Geology Conference series 5, no. 1 (1999): 559–71. http://dx.doi.org/10.1144/0050559.
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Brown, P. E., I. B. Evans, and S. M. Becker. "The Prince of Wales Formation - post-flood basalt alkali volcanism in the Tertiary of East Greenland." Contributions to Mineralogy and Petrology 123, no. 4 (May 20, 1996): 424–34. http://dx.doi.org/10.1007/s004100050166.
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Pedersen, A. K., and L. M. Larsen. "Early Tertiary volcanic rocks from eastern Disko and south-eastern Nûgssuaq." Rapport Grønlands Geologiske Undersøgelse 135 (December 31, 1987): 11–17. http://dx.doi.org/10.34194/rapggu.v135.7992.
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As part of an integrated study of the interaction between sedimentary and volcanic facies in the Cretaceous-Tertiary West Greenland basin, early Tertiary extrusive and intrusive basic igneous rocks have been investigated in eastern Disko and south-eastern Nûgssuaq (fig. 1). The volcanic activity started in the early Tertiary. It was centred in the western regions of Disko and Nûgssuaq and west of the present land areas, and consequently western Disko and western Nûgssuaq have a thick and complete volcanic succession, the Vaigat and Maligât Formations (Hald & Pedersen, 1975; Pedersen, 1975a, 1985). The coeval deposits in the eastern part of the basin are clastic sediments of the Upper Atanikerdluk Formation (Koch, 1959). With time, the volcanic deposits prograded eastwards, and eventually the whole area was covered by a coherent basalt plateau. The present study attempts to extend the established volcanic stratigraphy from western Disko and the geological map sheets 1:100 000 Qutdligssat (published in 1976) and Mellemfjord (published in 1987) into eastern Disko and eastern Nûgssuaq where volcanic rocks and sediments interfinger.
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Ueng, W. C., T. P. Fox, D. K. Larue, and J. T. Wilband. "Geochemistry and petrogenesis of the early Proterozoic Hemlock volcanic rocks and the Kiernan sills, southern Lake Superior region." Canadian Journal of Earth Sciences 25, no. 4 (April 1, 1988): 528–46. http://dx.doi.org/10.1139/e88-052.
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During the early Proterozoic, the 2 km thick differentiated gabbroic Kiernan sills were emplaced into a thick accumulation of pillow basalt and associated deep-water strata, the Hemlock Formation, in the southern Lake Superior region. On the basis of major elements and trace elements (including rare-earth-element data), the Kiernan sills and the hosting volcanic rocks of the Hemlock Formation were determined to be comagmatic in origin, and both evolved from assimilation – crystal fractionation processes. The major assimilated components in these igneous rocks are identified as terrigenous sedimentary rocks. Assimilation affected the abundance of Nb, Ta, light rare-earth elements, and most likely P, Rb, Th, and K in the magma. The effect of chemical contamination from wall-rock assimilation accumulates with increasing differentiation.With wall-rock contamination carefully evaluated, a series of tectonic discriminating methods utilizing immobile trace elements indicates that the source magma was a high-Ti tholeiitic basalt similar to present-day mid-ocean-ridge basalts (MORB). It is suggested from this study that most of the enriched large-ion lithophile elements and LREE of the magma were not inherited from the mantle but from assimilation of supracrustal rocks. Chemical signatures of these rocks are distinctively different from those of arc-related volcanics. A rifting tectonic regime analogous to the opening of the North Atlantic Ocean and extrusion of North Atlantic Tertiary volcanics best fits the criteria revealed by this study.
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Linthout, K., H. Paulick, and J. R. Wijbrans. "Provenance of basalt blocks from Roman sites in Vleuten-De Meern (the Netherlands) traced to the Tertiary Siebengebirge (Germany): a geoarchaeological quest using petrological and geochemical methods." Netherlands Journal of Geosciences - Geologie en Mijnbouw 88, no. 1 (March 2009): 55–74. http://dx.doi.org/10.1017/s0016774600000998.
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AbstractUnshaped basalt blocks from archaeological sites along the border of the Roman Empire (limes) in the lower Rhine area near Vleuten-De Meern (Utrecht) have been studied petrographically, analysed by XRF for major and trace elements, and dated by the 40Ar/39Ar method. The blocks are from a revetment in the bank of a fossil branch of the Rhine and a contiguous ship De Meern 4, both built around 100 AD. All nineteen blocks are alkali olivine basalt (AOB) with xenoliths of peridotite derived from the upper mantle and quartz xenocrysts from the continental crust; eighteen blocks contain resorbed plagioclase xenocrysts as well. Abundances of major and trace elements show that those eighteen samples form a chemically coherent group. The outlier, different in chemistry and without plagioclase xenocrysts, is from the ship. A basalt block from ship De Meern 1 (148 AD) conforms compositionally to the defined group. AOB lumps from a limes watchtower (2nd-3rd century) form a chemically distinct group.Low SiO2 contents (<46 wt.%) and high abundances of Mg, Ti, Ni, and Sr indicate a within-plate origin, directly from primitive melts; proportions of selected trace elements point at a continental rift setting. In the archaeological context, the most likely source region for the blocks is the Cenozoic European Volcanic Province, upstream along the Rhine and its tributaries.The petrographic and analytical data of the blocks have been compared with 432 published analyses of German AOB. On petrographic grounds, the Eifel can be ruled out as a source area since typical Eifel basalt minerals, amphibole, biotite, K-feldspar and feldspatoids, are absent in the blocks. Applying seven geochemical criteria, based on abundances of major elements in the Roman blocks, twelve sites with matching AOB were found in the Siebengebirge, seven in the Vogelsberg, and one in the Westerwald.The ages of the blocks (26.3 - 28.5 Ma) are compatible with ages determined for AOB from the Siebengebirge (27.4 - 29.9 Ma), and preclude their provenance from the Vogelsberg (< 18 Ma). The matching Westerwald sample is from 60 km beyond the limes, a prohibitive distance from the perspective of Roman logistics.AOB quarries of optimal logistic position are located adjacent to the Rhine, between Bonn and Remagen, a zone with significant Roman settlements from the first century AD. Geochemical correlation indicates AOB bodies at Rolandsbogen and Godesburg (S of Bonn) as potential sources of the blocks from the 100 AD revetment and ships. Similarly, the Erpeler Ley (E of Remagen) is indicated as the likely source for the blocks from a 2nd-3rd century AD watchtower.As the Godesburg basalt is at 1.6 km from the Rhine today, it is not obvious how the blocks were transported from there. However, it may be that the adjacent, now sanded, branch of the old Rhine river system, was navigable for flat-bottomed vessels in Roman times.Our study demonstrates that substantial detailed information regarding ancient mining and trading activities can be retrieved from seemingly indistinctive basalt blocks.
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Carpenter, Chris. "Sub-Basalt Imaging Reveals Deeper Plays Offshore India." Journal of Petroleum Technology 73, no. 02 (February 1, 2021): 66–67. http://dx.doi.org/10.2118/0221-0066-jpt.
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30279, “Revealing Deeper Plays, Offshore Kutch, India: A Success Story of Sub-Basalt Imaging,” by S.K. Biswal, N.N.B. Naidu, and S. Basu, ONGC, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2-6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. The Deccan Traps volcanic province of India is considered one of the largest basalt-covered regions in the world but is essentially unexplored because of the limitations of conventional marine streamer P-wave seismic acquisition in imaging structures both intrabasalt and sub-basalt. In the complete paper, the authors demonstrate that, even with legacy marine streamer surveys, an appropriate work flow of combining suitable advanced technologies can help to overcome the long-standing challenges of sub-basalt imaging. The reprocessed data show clear uplift in sub-basalt imaging, and inversion results validate the quality of the new data in relation to the well logs. Introduction The Kutch offshore basin is characterized by the presence of the Deccan Traps, a large igneous province of up to 2000-m-thick basalt lava flows. These lava flows have hindered successful imaging of sub-basalt Mesozoic sediments for hydrocarbon exploration. To date, no single technique has been found to produce considerable improvements in deeper image quality. The solution lies in an appropriate combination of advanced technologies. The project consists of three legacy data sets acquired in 2004, 2010, and 2014 in the shallow-water area (water depth ranges from 25 to 50 m). Two of the surveys were shot in the north/south direction with six streamers having 100-m separation, 25-m shot spacing, 12.5-m receiver spacing, and 6-second record length. The third survey was acquired oblique to these with a similar acquisition geometry; however, it featured sparser 25-m receiver spacing and 8- second record length. These surveys were matched and merged before migration to ensure a seamless image across the surveys in the post-migration domain. A tailored processing work flow improved existing data quality significantly and provided new insights into the sub-basalt geology, thereby opening a new play to exploration and production. Challenges and Work Flow Sub-basalt imaging challenges include transmission losses, scattering, complex wave kinematics, prevalent multiples, interference effects, and variable illumination caused by high and variable acoustic impedance of thick heterogeneous basalt layers. The tertiary sedimentary sequences overlying the Deccan Trap consist predominantly of carbonates, shale, and fine-grained clastic sediments, accompanied by channels and nearly vertical faulting. The geological complexities from the water bottom to the base of the basalt present a substantial geophysical challenge to successful deeper imaging and require an appropriate work flow to mitigate them. Broadband processing, including de-ghosting, can increase the signal-to-noise ratio across the broad range of frequencies in the seismic bandwidth and can enhance the lower frequencies required to achieve enhanced imaging at sub-basalt targets. Demultiple methods can reduce the presence of surface-related and interbed multiples that prohibit reliable interpretation of Mesozoic sediment; imaging methods can focus the recorded data when used in conjunction with an accurate Earth model that captures the velocity complexities of carbonates, shale, basalt, channel, and faults.
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Kiss, Gabriella, Ferenc Molnar, and Ladislav A. Palinkaš. "Volcanic facies and hydrothermal processes in Triassic pillow basalts from the Darnó Unit, NE Hungary." Geologia Croatica 61, no. 2-3 (December 25, 2008): 385–94. http://dx.doi.org/10.4154/gc.2008.30.
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The Darnó Unit within the Zagorje-Mid-Transdanubian Megaunit is an allochtonous part of Dinarides in NE-Hungary and represents a relict of the Neotethyan accretionary complex. It contains blocks of submarine basalts of Triassic age in turbiditic sediments (olistrostrome) of Jurassic age. The lava clogged in the lime mud at the original site of volcanism and developed closely packed pillow, pillow fragment hyaloclastite breccia, and peperite facies. Interaction between the lava and the sea water produced mostly chloritic alteration of basalt and precipitation of hydrothermal calcite in amygdales, feeding channels of lava lobes and hyaloclastite breccia cements. Calcite is associated with chlorite, epidote, hematite and pyrite. Fluid inclusions in calcite infillings record conditions of fluid/rock interaction. Salinities of fluid inclusions (3.2 – 5.6 wt.% NaCl equiv. wt.%.) are close to the salinity of recent sea water and their homogenization temperatures in the range of 80 – 150oC. Fluid inclusion data support interpretation that volcanic facies represent rapidly cooled distal zones away from the submarine volcanic centre. This is also confirmed by the comparison to the volcanic and hydrothermal alteration facies of the submarine basalt lava-flow complex and associated pillow lava formation of Triassic age in the Hruškovec quarry in the Kalnik Mts., NW-Croatia. The obtained data contribute to understanding of the early history of Neotethyan evolution, i.e. dilemma about rifting or oceanization in Triassic time and offer new aspects of correlation between units of Dinaridic origin which had been displaced from their original setting by large scale Tertiary tectonic processes.
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Watt, W. S., L. M. Larsen, and M. Watt. "Volcanic history of the Lower Tertiary plateau basalts in the Scoresby Sund region, East Greenland." Rapport Grønlands Geologiske Undersøgelse 128 (December 31, 1986): 147–56. http://dx.doi.org/10.34194/rapggu.v128.7931.
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The extensive plateau basalt lava pile in the Scoresby Sund region has a stratigraphic thickness of 3200 m and an overall average thickness of 1500 m. The pile thins inland from the Atlantic coast and laps onto basement gneisses and Jurassic sediments in the inner fjord region. The lavas are divisible into five formations which form two separate lava sequences. The lower sequence is best developed in the inner fjord region, while the upper sequence dominates the regions near the Atlantic coast. The sequences are interpreted as produced in two vo\canic episodes in connection with failed rifting episodes during the opening of the North Atlantic Ocean. At the Atlantic coast remains of a third separate lava sequence apparently forrned during active spreading.
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Prasad, Guntupalli V. R. "Vertebrate biodiversity of the Deccan volcanic province of India: A review." Bulletin de la Société Géologique de France 183, no. 6 (December 1, 2012): 597–610. http://dx.doi.org/10.2113/gssgfbull.183.6.597.
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Abstract The Deccan Traps of peninsular India, representing one of the largest flood basalt eruptions on the earth's surface, have been a subject of intensive research in the last three decades because of the attributed link between the Deccan Traps and the Cretaceous-Tertiary boundary mass extinctions. In this context, the biota from the sedimentary beds intercalated with the volcanic flows and underlying the oldest volcanic flow are more important for understanding the faunal diversity and palaeobiogeography of India during the time span of volcanic eruptions. A detailed review of the vertebrate faunal diversity of the Deccan volcanic province is presented here.
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Pedersen, A. K., L. M. Larsen, G. K. Pedersen, and K. S. Dueholm. "Filling and plugging of a marine basin by volcanic rocks: the Tunoqqu Member of the Lower Tertiary Vaigat Formation on Nuussuaq, central West Greenland." Bulletin Grønlands Geologiske Undersøgelse 171 (January 1, 1996): 5–28. http://dx.doi.org/10.34194/bullggu.v171.6731.
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The volcanic Tunoqqu Member formed at the end of the second of three volcanic cycles in the Paleocene Vaigat Formation. The Tunoqqu Member consists of brown aphyric and feldspar-phyric basalts and forms a marker horizon within the grey picritic rocks of the Vaigat Formation. Most of the basalts are siliceous and were produced by contamination with crustal rocks of magmas ranging in composition from picrite to evolved basalt. Some of the basalts were erupted from local volcanic centres of which four have been identified, whereas other basalts form more regional flows. The four identified eruption centres are located along fault lines and zones of uplift and subsidence, indicating tectonic control. Tectonic control is also inferred to be important in terminating the volcanic cycle and causing the development of high-level magma chambers where the magmas stagnated, fractionated, and became contaminated. The basalts of the Tunoqqu Member form subaerial lava flows in western Nuussuaq. Central Nuussuaq constituted a marine embayment in which the volcanics were deposited as eastward prograding foreset-bedded hyaloclastite breccia fans which indicate water depths of up to 160 m. Eastern Nuussuaq was a gneiss highland with a more than 700 m high NW-SE-elongated gneiss promontory stretching into the sea. During Tunoqqu Member time the volcanic rocks reached the gneiss promontory and blocked the outlet from the south to the sea in the north. This resulted in increased water levels in the enclosed embayment and transformation of the outlet into a torrential river. This river eroded the concomitantly forming Tunoqqu Member volcanics and the gneiss promontory and deposited the material in up to more than 250 m thick foreset-bedded boulder conglomerates in the sea where the north coast of Nuussuaq is now situated.
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Steinthorsson, S., Ö. Helgason, M. B. Madsen, C. Bender Koch, M. D. Bentzon, and S. Mørup. "Maghemite in Icelandic basalts." Mineralogical Magazine 56, no. 383 (June 1992): 185–99. http://dx.doi.org/10.1180/minmag.1992.056.383.05.
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AbstractCurie temperatures indicating non-titaniferous magnetite are common in Icelandic basalts of all ages, especially Tertiary ones. Yet, microprobe analyses of such samples have shown high titanium in the magnetite. To resolve this paradox, and the mechanism at work, the magnetic mineral fraction of eight basalt samples with Js-T curves characteristic for pure magnetite was subjected to a multi-disciplinary analysis including Mössbauer spectroscopy and X-ray diffraction. In most of the samples titanium in the magnetite, as analysed with the microprobe, ranged between 16 and 28 wt.%, indicating submicroscopic solvus exsolution in the titanomagnetite, beyond the power of resolution for the microprobe. More unexpectedly in view of the reversible Js-T curves, Mössbauer spectroscopy showed appreciable proportion of maghemite in the magnetic fraction. A three-stage mechanism is proposed for the formation of the mineral assemblages observed: (1) limited high-temperature oxyexsolution; (2) solvus exsolution during low-temperature hydrothermal alteration; and (3) maghemitization of the magnetite. Finally, the maghemite may transform to hematite with time. It is concluded that maghemite is much more common in Icelandic rocks than hitherto believed.
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Keays, Reid R., and Peter C. Lightfoot. "Siderophile and chalcophile metal variations in Tertiary picrites and basalts from West Greenland with implications for the sulphide saturation history of continental flood basalt magmas." Mineralium Deposita 42, no. 4 (December 15, 2006): 319–36. http://dx.doi.org/10.1007/s00126-006-0112-4.
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Stefánsson, S. M., J. S. Ólafsson, H. Adalsteinsson, and G. M. Gíslason. "The structure of chironomid and simuliid communities in direct run-off rivers on Tertiary basalt bedrock in Iceland." SIL Proceedings, 1922-2010 29, no. 4 (October 2006): 2015–20. http://dx.doi.org/10.1080/03680770.2006.11903043.
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Comin-Chiaramonti, Piero, Angelo De Min, Aldo Cundari, Vicente A. V. Girardi, Marcia Ernesto, Celso B. Gomes, and Claudio Riccomini. "Magmatism in the Asunción-Sapucai-Villarrica Graben (Eastern Paraguay) Revisited: Petrological, Geophysical, Geochemical, and Geodynamic Inferences." Journal of Geological Research 2013 (May 16, 2013): 1–22. http://dx.doi.org/10.1155/2013/590835.
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The Asunción-Sapucai-Villarrica graben (ASV) in Eastern Paraguay at the westernmost part of the Paraná Basin was the site of intense magmatic activity in Mesozoic and Tertiary times. Geological, petrological, mineralogical, and geochemical results indicate that the following magmatic events are dominant in the area: (1) tholeiitic basalt and basaltic andesites, flows and sills of low- and high-titanium types; (2) K-alkaline magmatism, where two suites are distinguished, that is, basanite to phonolite and alkali basalt to trachyte and their intrusive analogues; (3) ankaratrite to phonolite with strong Na-alkaline affinity, where mantle xenoliths in ultramafic rocks are high- and low-potassium suites, respectively. The structural and geophysical data show extensional characteristics for ASV. On the whole, the geochemical features imply different mantle sources, consistently with Sr-Nd isotopes that are Rb-Nd enriched and depleted for the potassic and sodic rocks, respectively. Nd model ages suggest that some notional distinct “metasomatic events” may have occurred during Paleoproterozoic to Neoproterozoic times as precursor to the alkaline and tholeiitic magmas. It seems, therefore, that the genesis of the ASV magmatism is dominated by a lithospheric mantle, characterized by small-scale heterogeneity.
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Gibb, F. G. F., R. Kanaris-Sotiriou, and R. Neves. "A new Tertiary sill complex of mid-ocean ridge basalt type NNE of the Shetland Isles: a preliminary report." Transactions of the Royal Society of Edinburgh: Earth Sciences 77, no. 3 (1986): 223–30. http://dx.doi.org/10.1017/s0263593300010853.
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ABSTRACTBasic intrusive rocks recently encountered in wells N and NNE of the Shetland Isles are probably parts of a single large sill complex which extends for over 130 km along the edge of the Faeroe-Shetland Trough. The sills intrude thick Mesozoic sediments which almost certainly overlie continental crust but the complex also appears to underlie, and extend beyond the SE edge of, the Faeroes basaltic lava plateau. Petrographic and geochemical analyses of drill core samples recovered from some of these sills reveal that they are of mid-ocean ridge basalt (MORB) type; an observation which provides evidence regarding the plate tectonic history of this area of the North Atlantic and has major implications for the nature of the continental/oceanic crust transition.
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Tran Nhu, Huy, San Ngo Thuong, Binh Kieu Nguyen, Xuan Tran Van, Kha Nguyen Xuan, Huy Nguyen Xuan, and Tuan Nguyen Van. "The tectonic evolution and hydrocarbon potential in the boundaries of Vietnam continental shelf." Science and Technology Development Journal 17, no. 3 (September 30, 2014): 126–31. http://dx.doi.org/10.32508/stdj.v17i3.1490.
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Recent survey results indicate the presence of Tertiary sedimentary basins with hydrocarbon potential in the boundaries of Vietnam continental shelf. These basins were perhaps formed in the Early Oligocene on the Mesozoic basement of continental crust and were filled with mainly deltaic clastic sediments. From very early Miocene these basins have linked together and became wider. Sediments of marine and prograding delta facies accumulated and widespreaded on the whole continental shelf. At the Middle Miocene to present-day the opening of the Bien Dong Sea (Vietnam East Sea), the regional tectonic subsidence and the eustatic fluctuation had created sedimentary formations of open and deep marine facies with turbidite shale, platform carbonate including reef build-up. Andesite and basalt extrusion occurred in form of dykes resulting from tectonic inversions in Late Oligocene, in the beginning of Middle Miocene, particularly in Late Miocene-Pliocene. These Tertiary sedimentary basins are expected to have hydrocarbon potential and need to be investigated and explorated adequately. The main risk is the drilling technology, the exploitation in the deep sea and high investment cost.
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Mitchell, J. G., and P. Mohr. "Carboniferous dikes of West Connacht, Ireland." Transactions of the Royal Society of Edinburgh: Earth Sciences 78, no. 3 (1987): 133–51. http://dx.doi.org/10.1017/s0263593300011068.
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ABSTRACTVigorous Carboniferous extensional tectonism and associated igneous activity is a feature of Ireland and the neighbouring areas of Newfoundland and Britain. In West Connacht, Ireland, dolerite dikes of late Carboniferous age are newly recognised and distinguished from Tertiary dolerites. In the N, the 320 Ma-old Logmor dike trends N–S across the Ordovician South Mayo Trough, and has an evolved, mildly alkaline basalt geochemistry. In the S, in Connemara, a diffuse and arcuate swarm of ENE–NE trending, 305 Ma-old dolerite dikes, the Teach Doite swarm, cuts the Galway Granite batholith and its envelope of Dalradian gneisses. These more tholeiitic dolerites reveal the mineralogical and geochemical effects of varying degrees of pervasive hydrothermal alteration, imposed on an original magmatic composition similar to that of mid-ocean ridge basalts. Variscan overprinting on k–Ar ages from West Connacht dolerites clusters at 300, 245 and 205 Ma. Overprinting is also a feature of much of the Galway Granite. Carboniferous diking in West Connacht may have responded to nascent opening of the proximate North Atlantic, its pattern related to domal uplift adjacent to the rifted zone.
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Felix-Henningsen, Peter. "Field Trip D (27 September 2018): characteristics and development of the Mesozoic–Tertiary weathering mantle and Pleistocene periglacial slope deposits in the Hintertaunus mountainous region." DEUQUA Special Publications 1 (August 20, 2018): 53–77. http://dx.doi.org/10.5194/deuquasp-1-53-2018.
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Abstract. The Devonian slates and sandstones of the Rhenish Massif were subject to deep and intensive weathering under (sub)tropical climate conditions during the Cretaceous, the Paleogene and the Neogene, which caused the development of a weathering mantle (regolith) >100 m thick, consisting of kaolinitic saprolite and paleosols as well as correlated sediments. Especially the tectonic uplift of the Rhenish Massif and climate change during the Neogene and the Pleistocene led to a vast denudation of the weathering mantle. Only in less uplifted areas of the mountainous region did thick remnants of saprolites remain, and they were covered by Neogene sediments as well as Quaternary periglacial slope deposits. As the kaolinitic weathering products serve as raw materials for the clay industry, unique exposures are available in the Hintertaunus which offer impressive insights into the landscape development of the past ∼80 million years: the excursion proceeds from Giessen to Limburg and further south and southwest to the eastern and western Hintertaunus area. At site 1 near the village of Langhecke, characteristics and properties of the fresh, unweathered slates will be demonstrated. Excursion sites 2 and 3 are situated near the village of Eisenbach. In two open-cast clay mines, both a terrestrial and a semi-terrestrial saprolite from silt slate, covered by periglacial layers, are exposed. Properties and genesis will be discussed on the basis of morphological characteristics and mineralogical and geochemical analyses, as well as isovolumetric elemental mass balances. At site 4 a former basalt quarry near the village of Biebrich exposes a Paleogene Plinthosol above saprolite. The autochthonous paleosol was preserved below Upper Oligocene basalt tuff and periglacial layers. Site 5 is situated within a huge pit for mining of Upper Oligocene to Miocene quartz gravel near the village of Wasenbach. A Miocene Plinthosol developed from alluvial sediments on top of the gravel beds and was covered by periglacial slope deposits. At nearly all sites the basal layers of the periglacial cover beds consist of kaolinitic paleosol/saprolite material, which has an important influence on the site properties of the Holocene soils.
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Adem, Anwar A., Gashaw G. Addis, Dessalew W. Aynalem, Seifu A. Tilahun, Wolde Mekuria, Mulugeta Azeze, and Tammo S. Steenhuis. "Hydrogeology of Volcanic Highlands Affects Prioritization of Land Management Practices." Water 12, no. 10 (September 27, 2020): 2702. http://dx.doi.org/10.3390/w12102702.
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Volcanic highlands supply water to 40% of the world’s population. Soil degradation threatens this water supply. Studies on geohydrology that affect the effectiveness of land and water management (LWM) practices in reducing soil degradations are limited. To aid in the effectiveness of LWM practices, we conducted a field experiment in the Gomit watershed in the semihumid Ethiopian Highlands on the interaction of hydrogeology and LWM practices. We found that in a watershed with strongly faulted tertiary basalt, 30% of the rainfall was drained through faults to another basin. Consequently, the discharge at the outlet was less than half of that of other watersheds with quaternary basalts. Despite the high sediment concentration, i.e., around 15 g L−1, in the Gomit watershed, the sediment yield of less than 4 Mg ha−1 a−1 was below average for the agricultural watershed in Ethiopia because of the low runoff response. While some faults facilitated drainage, others acted as a barrier. Groundwater stored behind the barriers was used as a municipal potable water source. Since the effectiveness of LWM practices depends on the amount of erosion that can be prevented, considerations of country-wide prioritizing of investments in land and water management practices should include the geology of the watersheds.
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Nelson, JoAnne L. "The Sylvester Allochthon: upper Paleozoic marginal-basin and island-arc terranes in northern British Columbia." Canadian Journal of Earth Sciences 30, no. 3 (March 1, 1993): 631–43. http://dx.doi.org/10.1139/e93-048.
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The Sylvester Allochthon is a composite klippe of upper Paleozoic ophiolitic, island-arc, and pericratonic assemblages, which rests directly on the Cassiar terrane, a displaced sliver of Ancestral North America. Each tectonic assemblage occurs at a distinct and consistent structural level within the allochthon. They are assigned, respectively, to the Slide Mountain, Harper Ranch, and Yukon–Tanana terranes. The Sylvester Allochthon provides a view of the structural relationships between these terranes prior to Early Cretaceous – early Tertiary strike-slip dismemberment, as well as possible sedimentological links to late Paleozoic North America. Slide Mountain Terrane assemblages, designated divisions I and II, form the lowest structural panels. Chert – quartz sandstones are interbedded with Lower Mississippian deep-water sediments in division I and ocean-floor basalts and deep-water sediments in division II. They are similar in age and character to sandstones in the autochthonous Earn Group. Division II assemblages represent atypical oceanic crust and upper mantle assemblages. Continuous basalt–sedimentary sequences, well dated by conodont faunas, span Early Mississippian to mid-Permian time. Feeders for the basalts are sills rather than sheeted dyke swarms, suggesting very slow spreading and high(?) sedimentation rates in a marginal-basin setting. These supracrustal sequences are thrust-imbricated with ultramafite–gabbro panels. Division II is in part overlain by a Triassic siliciclastic and limy sedimentary sequence, which resembles the basal Takla Group, Slocan Group, and autochthonous Triassic units. Division III occupies the highest structural levels in the allochthon. With one exception, thrust sheets within it consist of Pennsylvanian to Upper Permian mixed calc-alkaline volcanic and plutonic rocks, chert, tuff, and limestone, assigned to the Harper Ranch Terrane. One panel, assigned to the Yukon–Tanana Terrane, consists of an Early Mississippian quartz diorite pluton with Precambrian inheritance that intrudes older volcanogenic sediments, pyroclastics, limestone, and siliciclastic sediments. Preferred pre-Mesozoic restoration of these terrane elements shows a Harper Ranch arc, built partly on pericratonic Yukon–Tanana and partly on primitive oceanic basement (division III), which is separated from North America by the Slide Mountain marginal basin (divisions I and II).
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Jiang, Kai Yu, Jing Cao, and Yue Ma. "Slope Stability Analysis Based on Limit Equilibrium and Numerical Analysis." Applied Mechanics and Materials 256-259 (December 2012): 198–202. http://dx.doi.org/10.4028/www.scientific.net/amm.256-259.198.
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Based on the background of a foundation pit slope of the tertiary strong weathered basalt(TSWB), a quantitative analysis of the slope stability is proposed by combination of the limit equilibrium and the numerical analysis. The analysis also considers the effects of the natural state and soaking state Then, as an example, an ultra-deep foundation pit slope (UFPS) is analyzed under the background of TSWB. The Janbu method is used in the limit equilibrium because it can meet all the equilibrium conditions, including the force and moment equilibrium equation. The Lagrangian difference method which based on shear strength reduction is adopted in numerical analysis. Some meaningful conclusions can be obtained through comparing analysis the calculation results of Janbu method with finite difference method. These conclusions can be given a reference to similar projects.
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BERNSTEIN, STEFAN, and DENNIS K. BIRD. "Formation of wehrlites through dehydration of metabasalt xenoliths in layered gabbros of the Noe-Nygaard Intrusion, Southeast Greenland." Geological Magazine 137, no. 2 (March 2000): 109–28. http://dx.doi.org/10.1017/s0016756800003794.
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The Noe-Nygaard Intrusion is a 4 × 2.5 km stock composed of layered gabbros and wehrlites within the Precambrian basement of the coastal mountains west of the Kialineq Plutonic Complex. Transgressive relationships to Tertiary mafic dykes and the occurrence of abundant metabasaltic xenoliths signify a Tertiary age for the intrusion. The intrusion is characterized by alternating zones of gabbro and wehrlite; gabbro is both intruded and replaced by wehrlite, and the wehrlite zones are characterized by abundant metabasaltic xenoliths. Based on 87Sr/86Sr ratios, mica, olivine and oxide gabbros are all cumulates, crystallized at different differentiation stages from a common parental magma. Field relations, together with similarities in strontium isotope ratios, and in the major and rare earth element (REE) mineral chemistry between gabbros and wehrlites, indicate that the wehrlite bodies were formed by the dissolution of plagioclase from a gabbro cumulate mush by H2O derived from dehydration and the partial assimilation of metabasaltic xenoliths. In terms of their REE characteristics, melts from which the Noe-Nygaard Intrusion crystallized are within the compositional range of melts for other early Tertiary mafic/ultramafic complexes of East Greenland. However, they were generated at a greater mean melting pressure, and have less radiogenic strontium isotope ratios than the nearby Imilik mafic/ultramafic complex, supporting existing models for mantle heterogeneity at the time of continental break-up. The abundance of metabasaltic xenoliths in the Noe-Nygaard Intrusion provides further evidence for the lateral extent of the North Atlantic flood basalt province, which onshore has been mostly removed by glacial erosion south of 68° N in Greenland.
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Hogg, A. J., J. J. Fawcett, J. Gittins, and M. P. Gorton. "Cyclical variation in composition in continental tholeiites of East Greenland." Canadian Journal of Earth Sciences 26, no. 3 (March 1, 1989): 534–43. http://dx.doi.org/10.1139/e89-045.
Full textAbstract:
The Prinsen of Wales Bjerge (PWB), part of the Tertiary volcanic province of East Greenland, consists of tholeiitic basalts overlain by alkalic basalts that were erupted 100–150 km west of the original axis of continental rifting and active ocean-floor development during the creation of the North Atlantic Ocean. They have many features of continental flood basalts but are somewhat enriched in Fe and in Ti relative to Fe and have slightly lower Al2O3. They have slight enrichments in the light rare-earth elements (La/Yb = 3–4). A nunatak within the PWB displays four cycles of tholeiitic basalt, each about 50 m thick, which are defined by trace-element variations (Ni, Cr, Sr, Zr, and Zr/Y). In three of the four cycles the lowermost flows are the most highly differentiated, and successive flows are increasingly primitive. These changes are thought to be the result of frequent injection of primitive, mantle-derived tholeiitic magma into small crustal magma chambers that contain evolved tholeiitic magma. The resultant mixing and expulsion of hybrid magma produce flows of small volume (0.01–0.03 km3) that display increasingly primitive character upward within each cycle (increasing Mg# and decreasing content of incompatible elements). This process is expected to be more efficient in small reservoirs than in the very large magma chambers that have been invoked by previous exponents of the differentiation–replenishment hypothesis. We suggest that cyclical volcanism in areas well back from the line of active rifting may be more common than is realized and is controlled by the fractionation–magma-replenishment process operating in numerous small reservoirs in an extensively fractured continental crust.