Статті в журналах: "Lower Gawler Range Volcanics"

1

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.

Повний текст джерела

Анотація:

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.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

GILES, C. "Petrogenesis of the Proterozoic Gawler Range Volcanics, South Australia." Precambrian Research 40-41 (October 1988): 407–27. http://dx.doi.org/10.1016/0301-9268(88)90078-2.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Morrow, Nicole, and Jocelyn McPhie. "Mingled silicic lavas in the Mesoproterozoic Gawler Range Volcanics, South Australia." Journal of Volcanology and Geothermal Research 96, no. 1-2 (February 2000): 1–13. http://dx.doi.org/10.1016/s0377-0273(99)00143-2.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Fraser, G. L., R. G. Skirrow, and A. R. Budd. "Geochronology of Mesoproterozoic gold mineralization in the Gawler Craton, and temporal links with the Gawler Range Volcanics." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A185. http://dx.doi.org/10.1016/j.gca.2006.06.371.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Kivior, Irena, Stephen Markham, Leslie Mellon, and David Boyd. "Mapping geology beneath volcanics using magnetic data." APPEA Journal 58, no. 2 (2018): 821. http://dx.doi.org/10.1071/aj17205.

Повний текст джерела

Анотація:

Volcanic layers within sedimentary basins cause significant problems for petroleum exploration because the attenuation of the seismic signal masks the underlying geology. A test study was conducted for the South Australia Government to map the thickness of volcanics and sub-volcanic geology over a large area in the Gawler Range Volcanics province. The area is covered by good quality magnetic data. The thickness of volcanics and basement configuration was unknown as there has only been a limited amount of drilling. The Automatic Curve Matching (ACM) method was applied to located magnetic data and detected magnetic sources within different rock units, providing their depth, location, geometry and magnetic susceptibility. The magnetic susceptibilities detected by ACM allowed the differentiation of the volcanics and the underlying basement. The base of volcanics and the depth to the top of basement was mapped along 75 km NS profiles, that were spaced 1 km apart over a distance of 220 km. The volcanic and basement magnetic susceptibilities and the magnetic source distribution pattern were used as key determinants to interpret the depth to the two interfaces. The results for each interface were gridded, and images of the base of volcanics and depth to basement were generated. The mapped volcanics thickness was validated by comparison with the results from drilling, with the volcanics thickness matching very well. After project completion, a passive seismic survey was conducted in part of the test area, indicating a base of volcanics of ~4 km, which further confirmed the results.

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Agangi, Andrea, Jocelyn McPhie, and Vadim S. Kamenetsky. "Magma chamber dynamics in a silicic LIP revealed by quartz: The Mesoproterozoic Gawler Range Volcanics." Lithos 126, no. 1-2 (September 2011): 68–83. http://dx.doi.org/10.1016/j.lithos.2011.06.005.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Pankhurst, M. J., B. F. Schaefer, P. G. Betts, N. Phillips, and M. Hand. "A mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan." Solid Earth Discussions 2, no. 2 (September 9, 2010): 251–74. http://dx.doi.org/10.5194/sed-2-251-2010.

Повний текст джерела

Анотація:

Abstract. Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950–1100 °C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (~1600 ppm Fluorine, ~400 ppm Chlorine). These depolymerised the magma such that temperature-composition-volatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Pankhurst, M. J., B. F. Schaefer, P. G. Betts, N. Phillips, and M. Hand. "A Mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan." Solid Earth 2, no. 1 (March 31, 2011): 25–33. http://dx.doi.org/10.5194/se-2-25-2011.

Повний текст джерела

Анотація:

Abstract. Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950–1100 °C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (~1600 ppm fluorine, ~400 ppm chlorine). These depolymerised the magma such that temperature-composition-volatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

McPhie, J., F. DellaPasqua, S. R. Allen, and M. A. Lackie. "Extreme effusive eruptions: Palaeoflow data on an extensive felsic lava in the Mesoproterozoic Gawler Range Volcanics." Journal of Volcanology and Geothermal Research 172, no. 1-2 (May 2008): 148–61. http://dx.doi.org/10.1016/j.jvolgeores.2006.11.011.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Chapman, N. D., M. Ferguson, S. J. Meffre, A. Stepanov, R. Maas, and K. J. Ehrig. "Pb-isotopic constraints on the source of A-type Suites: Insights from the Hiltaba Suite - Gawler Range Volcanics Magmatic Event, Gawler Craton, South Australia." Lithos 346-347 (November 2019): 105156. http://dx.doi.org/10.1016/j.lithos.2019.105156.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Ferguson, Matthew R. M., Kathy Ehrig, and Sebastien Meffre. "Insights into magma histories through silicate-oxide crystal clusters: Linking the Hiltaba Suite intrusive rocks to the Gawler Range Volcanics, Gawler Craton, South Australia." Precambrian Research 321 (February 2019): 103–22. http://dx.doi.org/10.1016/j.precamres.2018.11.015.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Allen, S. R., C. J. Simpson, J. McPhie, and S. J. Daly. "Stratigraphy, distribution and geochemistry of widespread felsic volcanic units in the Mesoproterozoic Gawler Range Volcanics, South Australia*." Australian Journal of Earth Sciences 50, no. 1 (February 2003): 97–112. http://dx.doi.org/10.1046/j.1440-0952.2003.00980.x.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

13

Creaser, Robert A. "Neodymium isotopic constraints for the origin of Mesoproterozoic felsic magmatism, Gawler Craton, South Australia." Canadian Journal of Earth Sciences 32, no. 4 (April 1, 1995): 460–71. http://dx.doi.org/10.1139/e95-039.

Повний текст джерела

Анотація:

Mesoproterozoic felsic magmatism of the Gawler Range Volcanics and Hiltaba Suite granites occurred at 1585–1595 Ma across much of the Gawler Craton, South Australia. Nd isotopic analysis of this felsic magmatism, combined with petrological and geochemical arguments, suggest derivation by partial melting of both Paleoproterozoic and Archean crust. The majority of samples analyzed have Nd isotopic and geochemical characteristics compatible with the involvement of Paleoproterozoic crust stabilized during the 1.85–1.71 Ga Kimban orogeny as sources for the Mesoproterozoic magmatism; others require derivation from sources dominated by Archean rocks. This cycle of Paleoproterozoic crustal stabilization followed by involvement of this crust Mesoproterozoic felsic magmatism is one previously documented from many parts of Mesoproterozoic Laurentia. On the basis of models proposing East Australia–Antarctica to be the conjugate landmass at the rifted margin of western North America, it appears that the voluminous magmatism of South Australia is another example of a typically Mesoproterozoic style of magmatism linked to Laurentia. This Mesoproterozoic magmatism appears temporally linked to regional high-temperature, low-pressure metamorphism of the region, and together with the presence of mantle-derived magmas, implicates the operation of large-scale tectono-thermal processes in the origin of felsic magmatism at 1590 Ma.

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Garner, A., and J. McPhie. "Partially melted lithic megablocks in the Yardea Dacite, Gawler Range Volcanics, Australia: implications for eruption and emplacement mechanisms." Bulletin of Volcanology 61, no. 6 (November 23, 1999): 396–410. http://dx.doi.org/10.1007/s004450050281.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Allen, S. R., and J. McPhie. "The Eucarro Rhyolite, Gawler Range Volcanics, South Australia: A >675 km3, compositionally zoned lava of Mesoproterozoic age." Geological Society of America Bulletin 114, no. 12 (December 2002): 1592–609. http://dx.doi.org/10.1130/0016-7606(2002)114<1592:tergrv>2.0.co;2.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

16

McPhie, Jocelyn, Fernando DellaPasqua, Sharon Allen, and Mark Lackie. "New constraints on source location and emplacement mechanisms of extensive felsic units in the Gawler Range Volcanics, South Australia." ASEG Extended Abstracts 2006, no. 1 (December 2006): 1–3. http://dx.doi.org/10.1071/aseg2006ab109.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Roache, M. W., S. R. Allen, and J. McPhie. "Surface and subsurface facies architecture of a small hydroexplosive, rhyolitic centre in the Mesoproterozoic Gawler Range Volcanics, South Australia." Journal of Volcanology and Geothermal Research 104, no. 1-4 (December 2000): 237–59. http://dx.doi.org/10.1016/s0377-0273(00)00208-0.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

18

Ferguson, Matthew R. M., Kathy Ehrig, Sebastien Meffre, and Sandrin Feig. "From magma to mush to lava: Crystal history of voluminous felsic lavas in the Gawler Range Volcanics, South Australia." Lithos 346-347 (November 2019): 105148. http://dx.doi.org/10.1016/j.lithos.2019.105148.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Allen, S. R., J. McPhie, G. Ferris, and C. Simpson. "Evolution and architecture of a large felsic Igneous Province in western Laurentia: The 1.6 Ga Gawler Range Volcanics, South Australia." Journal of Volcanology and Geothermal Research 172, no. 1-2 (May 2008): 132–47. http://dx.doi.org/10.1016/j.jvolgeores.2005.09.027.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Curtis, S., C. Wade, and A. Reid. "Sedimentary basin formation associated with a silicic large igneous province: stratigraphy and provenance of the Mesoproterozoic Roopena Basin, Gawler Range Volcanics." Australian Journal of Earth Sciences 65, no. 4 (May 3, 2018): 447–63. http://dx.doi.org/10.1080/08120099.2018.1460398.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Peucat, J. J., R. Capdevila, C. M. Fanning, R. P. Ménot, L. Pécora, and L. Testut. "1.60 Ga felsic volcanic blocks in the moraines of the Terre Adélie Craton, Antarctica: Comparisons with the Gawler Range Volcanics, South Australia." Australian Journal of Earth Sciences 49, no. 5 (October 2002): 831–45. http://dx.doi.org/10.1046/j.1440-0952.2002.00956.x.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Agangi, Andrea, Vadim S. Kamenetsky, and Jocelyn McPhie. "The role of fluorine in the concentration and transport of lithophile trace elements in felsic magmas: Insights from the Gawler Range Volcanics, South Australia." Chemical Geology 273, no. 3-4 (May 2010): 314–25. http://dx.doi.org/10.1016/j.chemgeo.2010.03.008.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Kamenetsky, V. S., N. Morrow, and J. McPhie. "Origin of high-Si dacite from rhyolitic melt: evidence from melt inclusions in mingled lavas of the 1.6 Ga Gawler Range Volcanics, South Australia." Mineralogy and Petrology 69, no. 3-4 (June 26, 2000): 183–95. http://dx.doi.org/10.1007/s007100070020.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Woodcock, N. H., and C. J. N. Fletcher. "Introduction to the Welsh Basin thematic issue." Geological Magazine 129, no. 5 (September 1992): 513–14. http://dx.doi.org/10.1017/s001675680002166x.

Повний текст джерела

Анотація:

The Welsh Basin was an area of enhanced Early Palaeozoic subsidence on the northwestern margin of the Eastern Avalonian microcontinent. It is bordered to the southeast by the Midland Platform and to the northwest by the smaller Irish Sea Platform (Fig. 1). The sedimentary rocks of the basin and its flanking platforms range from Lower Cambrian through Lower Devonian. The sequence is dominantly marine, with abundant volcanics in the Ordovician. A basinwide change to non-marine facies is preserved in the Lower Devonian, heralding basin inversion and the culminating Acadian (late Caledonian) Orogeny.

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Wade, Claire E., Anthony J. Reid, Michael T. D. Wingate, Elizabeth A. Jagodzinski, and Karin Barovich. "Geochemistry and geochronology of the c. 1585Ma Benagerie Volcanic Suite, southern Australia: Relationship to the Gawler Range Volcanics and implications for the petrogenesis of a Mesoproterozoic silicic large igneous province." Precambrian Research 206-207 (June 2012): 17–35. http://dx.doi.org/10.1016/j.precamres.2012.02.020.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Chauvel, C., N. T. Arndt, S. Kielinzcuk, and A. Thom. "Formation of Canadian 1.9 Ga old continental crust. I: Nd isotopic data." Canadian Journal of Earth Sciences 24, no. 3 (March 1, 1987): 396–406. http://dx.doi.org/10.1139/e87-042.

Повний текст джерела

Анотація:

A Nd isotopic study was carried out on 1.9−1.8 Ga rocks from two parts of the Trans-Hudson Orogen in northern Canada. The first part is the Reindeer Lake Zone in the Churchill Province in Saskatchewan, where a variety of volcanic, granitoid, and sedimentary rocks are preserved in several lithotectonic belts that border a reworked Archean craton to the northwest. The second area comprises the Ottawa and Belcher islands, in Hudson Bay, and the Fox River volcanics, in Manitoba. These form part of the Circum-Superior Belt, a band of basaltic volcanics and sedimentary rocks that overlies the Archean Superior craton.From U–Pb zircon ages, Pb–Pb ages, and Sm–Nd ages, Nd initial isotopic compositions were calculated for all analyzed samples. In the Saskatchewan terrains, we obtained a large range of εNd values, from +5 to −8. The highest values (+4 to +5) come from two volcanic-dominated belts (Flin Flon and Western la Ronge), lower values (~+2) characterize intervening sediment-dominated domains (Eastern La Ronge, Glennie Lake, and Kisseynew), and still lower values (−1 to −4) were found in migmatitic and granitoid belts adjacent to the reworked Archean craton in the northwest. Each lithotectonic belt has its own characteristic, restricted range of εNd values, and, with few exceptions, there is no correlation between εNd and rock type; i.e., in individual belts, volcanics, granites, and sediments have very similar εNd values.In the Circum-Superior Belt, three lava flows from the Ottawa Islands have εNd values ranging from +4.5 to 0, and samples from the Belcher Islands have values ranging from +3.5 to −9.These results are explained by mixing between mantle-derived rocks and variable amounts of Archean continental crustal rocks. Assuming that 1.9 Ga ago the mantle had an εNd value of +5 and Archean crust had an εNd value of −12, we calculate proportions of Archean crustal material in Trans-Hudson rocks ranging from ~2 to 35 %, increasing systematically toward the Archean platform. The mean Archean component is about 8%: this area of Proterozoic continental crust is clearly dominated by material derived directly from the mantle.The similarity between the εNd values of sediments, granites, and volcanics in the Trans-Hudson Orogen suggests that sedimentary processes played a dominant role in transporting Archean detritus from eroding Archean continental areas into basins, where it mixed with mantle-derived volcanic material and melted to form granitoids.

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Monjoie, Philippe, Henriette Lapierre, Artan Tashko, Georges H. Mascle, Aline Dechamp, Bardhyl Muceku, and Pierre Brunet. "Nature and origin of the Triassic volcanism in Albania and Othrys: a key to understanding the Neotethys opening?" Bulletin de la Société Géologique de France 179, no. 4 (July 1, 2008): 411–25. http://dx.doi.org/10.2113/gssgfbull.179.4.411.

Повний текст джерела

Анотація:

AbstractTriassic volcanic rocks, stratigraphically associated with pelagic or reef limestones, are tectonically juxtaposed with Mesozoic ophiolites in the Tethyan realm. From the central (Dinarides, Hellenides) and eastern Mediterranean (Antalya, Troodos, Baër Bassit) to the Semail nappes (Oman), they occur either associated to the tectonic sole of the ophiolitic nappes or as a distinct tectonic pile intercalated between the ophiolites and other underthrust units. In the Dinaro-Hellenic belt, the Pelagonian units represent the lower plate, which is underthrust beneath the ophiolites. Middle to Late Triassic volcanic sequences are interpreted as the eastern flank of the Pelagonian platform and are therefore considered as a distal, deep-water part of the Pelagonian margin.The Triassic volcanics from Albania and Othrys are made up of basaltic pillowed and massive flows, associated locally with dolerites and trachytes. New elemental, Nd and Pb isotopic data allow to recognize four types of volcanic suites: (1) intra-oceanic alkaline and tholeiitic basalts, (2) intra-oceanic arc-tholeiites, (3) back-arc basin basalts, (4) calc-alkaline mafic to felsic rocks. Nd and Pb isotopic initial ratios suggest that the within-plate volcanic rocks were derived from an enriched oceanic island basalt type mantle source, devoid of any continental crustal component. The lower εNd value of the trachyte could be due to assimilation of oceanic altered crust or sediments in a shallow magma chamber. Island arc tholeiites and back-arc basin basalts have a similar wide range of εNd. The absence of Nb negative anomalies in the back-arc basin basalts suggests that the basin floored by these basalts was wide and mature. The high Th contents of the island arc tholeiites suggest that the arc volcanoes were located not far away from the continental margin.Albania and Othrys volcanics contrast with the Late Triassic volcanism from eastern Mediterranean (SW Cyprus, SW Turkey), which displays solely features of oceanic within plate suites. The presence of back-arc basin basalts associated with arc-related volcanics in Central Mediterranean indicates that they were close to a still active subduction during the Upper Triassic, while back-arc basins developed, associated with within-plate volcanism, leading to the NeoTethys opening.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Petterson, M. G. "The plutonic crust of Kohistan and volcanic crust of Kohistan–Ladakh, north Pakistan/India: lessons learned for deep and shallow arc processes." Geological Society, London, Special Publications 483, no. 1 (July 30, 2018): 123–64. http://dx.doi.org/10.1144/sp483.4.

Повний текст джерела

Анотація:

AbstractThe Kohistan–Ladakh terrane, northern Pakistan/India, offers a unique insight into whole-arc processes. This research review presents summaries of fundamental crustal genesis and evolution models. Earlier work focused on arc sequence definition. Later work focused on holistic petrogenesis. A new model emerges of an unusually thick (c. 55 km) arc with a c. 30 km-thick batholith. Volatile-rich, hornblende ± garnet ± sediment assimilation-controlled magmatism is predominant. The thick batholith has a complementary mafic–ultramafic residue. Kohistan crustal SiO2 contents are estimated at >56%. The new-Kohistan, silicic-crust model contrasts with previous lower SiO2 estimates (c. 51% SiO2 crust) and modern arcs that imply <35 km crustal thicknesses and arc batholith thicknesses of c. 7 km. A synthetic overview of Kohistan–Ladakh volcanic rocks presents a model of an older, cleaved/deformed Cretaceous volcanic system at least 800 km across strike. The Jaglot–Chalt–Dras–Shyok volcanics exhibit predominant tholeiitic-calc-alkaline signatures, with a range of arc-related facies/tectonic settings. A younger, post-collisional, Tertiary silicic volcanic system (the Shamran–Dir–Dras-2–Khardung volcanics) lie unconformably upon Cretaceous basement, and erupted within an intra-continental tectonic setting. Kohistan–Ladakh tectonic model controversies remain. In essence, isotope-focused researchers prefer later (Tertiary) collisions, whilst structural field-geology-orientated researchers prefer an older (Cretaceous) age for the Northern/Shyok Suture.

Стилі APA, Harvard, Vancouver, ISO та ін.

29

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.

Повний текст джерела

Анотація:

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.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Piasecki, S., L. M. Larsen, A. K. Pedersen, and G. K. Pedersen. "Palynostratigraphy of the Lower Tertiary volcanics and marine clastic sediments in the southern part of the West Greenland Basin: implications for the timing and duration of the volcanism." Rapport Grønlands Geologiske Undersøgelse 154 (January 1, 1992): 13–31. http://dx.doi.org/10.34194/rapggu.v154.8166.

Повний текст джерела

Анотація:

Volcanic rocks, forming hyaloclastites and subaqueous lava flows, were deposited intercalated with clastic sediments in a water-filled basin in West Greenland in the Early Tertiary. Three main stages of basin infilling occurred in the Disko-Nuussuaq area. The distribution of dinoflagellate cysts in the sediments shows that the basin was marine in the first stage and non-marine in the second stage of infilling. In the third stage the basin was displaced towards the south and was marginally marine. The dinoflagellate cysts form a typical mid-Paleocene assemblage which may be correlated with the calcareous nannoplankton (NP) zonation. The stratigraphically lowest investigated localities are coeval with the uppermost part of nannoplankton zone NP4, whereas the overlying localities within the marine basin (first stage) may be correlated with NP5-6. The localities from the non-marine second stage cannot be correlated with the NP zonation because they do not contain dinoflagellate cysts. Localities from the third stage are coeval with NP7-8. Younger volcanics are subaerially deposited. The total known range of the volcanics now falls within the NP3 to NP8 interval, giving a minimum duration for the main plateau-building stage of the volcanism of 4–6 million years. The subaerial basalts have previously been found to be mainly reversely magnetised, with one normally magnetised sequence which can now be stratigraphically correlated with NP4, and thereby identified as anomaly 27. The basalts in East Greenland started erupting during the NP9 zone, so that the volcanic activity in East Greenland largely succeeded that in West Greenland. In relation to the postulated mantle plume in the North Atlantic this means that the volcanic activity started in the peripheral part of the plume and only later switched to the central part.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Reid, Anthony. "The Olympic Cu-Au Province, Gawler Craton: A Review of the Lithospheric Architecture, Geodynamic Setting, Alteration Systems, Cover Successions and Prospectivity." Minerals 9, no. 6 (June 20, 2019): 371. http://dx.doi.org/10.3390/min9060371.

Повний текст джерела

Анотація:

The Olympic Cu-Au Province is a metallogenic province in South Australia that contains one of the world’s most significant Cu-Au-U resources in the Olympic Dam deposit. The Olympic Cu-Au Province also hosts a range of other iron oxide-copper-gold (IOCG) deposits including Prominent Hill and Carrapateena. This paper reviews the geology of the Olympic Cu-Au Province by investigating the lithospheric architecture, geodynamic setting and alteration systematics. In addition, since the province is almost entirely buried by post-mineral cover, the sedimentary cover sequences are also reviewed. The Olympic Cu-Au Province formed during the early Mesoproterozoic, ca. 1.6 Ga and is co-located with a fundamental lithospheric boundary in the eastern Gawler Craton. This metallogenic event was driven in part by melting of a fertile, metasomatized sub-continental lithospheric mantle during a major regional tectonothermal event. Fluid evolution and multiple fluid mixing resulted in alteration assemblages that range from albite, magnetite and other higher temperature minerals to lower temperature assemblages such as hematite, sericite and chlorite. IOCG mineralisation is associated with both high and low temperature assemblages, however, hematite-rich IOCGs are the most economically significant. Burial by Mesoproterzoic and Neoproterozoic-Cambrian sedimentary successions preserved the Olympic Cu-Au Province from erosion, while also providing a challenge for mineral exploration in the region. Mineral potential modelling identifies regions within the Olympic Cu-Au Province and adjacent Curnamona Province that have high prospects for future IOCG discoveries. Exploration success will rely on improvements in existing potential field and geochemical data, and be bolstered by new 3D magnetotelluric surveys. However, drilling remains the final method for discovery of new mineral resources.

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Brück, Peter M., Kenneth T. Higgs, Nadia Maziane-Serraj, and Michel Vanguestaine. "New palynological data from the Leinster Lower Palaeozoic massif, southeastern Ireland." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 3-4 (2000): 509–14. http://dx.doi.org/10.1017/s026359330000835x.

Повний текст джерела

Анотація:

ABSTRACTIn southeastern Ireland, the tectonic evolution of the northwestern Avalonian margin is rather poorly understood and only partially constrained. This is because the stratigraphy comprises in the main unfossiliferous turbidites. Nevertheless, some authors have attempted to define ‘terranes’ and ‘tracts’ in the region, aided by several significant Caledonoid-trending structural breaks that can be determined in the field. Palynological work was carried out in the early 1970s and established a range of ages from approximately mid Cambrian to late Silurian, although much of the succession proved barren. In the current study, the Lower Palaeozoic sequences W of the Leinster Granite and in the Slievenamon Inlier to the S have been palynologically re-investigated. Previous work proposed an unbroken succession from lower Ordovician Ribband Group turbidites and volcanics younging westwards conformably into upper Silurian Kilcullen Group sediments. The new study clearly shows that the Ordovician palynomorphs in the older part of the Kilcullen Group are reworked. In fact, there exists a major stratigraphical break between the Ribband Group dated as early Ordovician, Arenig, and the Kilcullen Group which is entirely Silurian, late Llandovery to early Wenlock in age. This major break has a minimum strike length of 150 km and is most likely much longer, extending some hundreds of kilometres SW to Dingle and possibly equating with a similar discontinuity in the Isle of Man to the NE. This break would thus appear to be a major feature within the succession of the northwestern Avalonian margin.

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Guilbaud, Marie-Noëlle, Claus Siebe, Christine Rasoazanamparany, Elisabeth Widom, Sergio Salinas, and Renato Castro Govea. "Petrographic, Geochemical and Isotopic (Sr–Nd–Pb–Os) Study of Plio-Quaternary Volcanics and the Tertiary Basement in the Jorullo-Tacámbaro Area, Michoacán-Guanajuato Volcanic Field, Mexico." Journal of Petrology 60, no. 12 (December 1, 2019): 2317–38. http://dx.doi.org/10.1093/petrology/egaa006.

Повний текст джерела

Анотація:

Abstract The origin of the large diversity of rock types erupted along the subduction-related Trans-Mexican Volcanic Belt (TMVB) remains highly debated. In particular, several hypotheses have been proposed to explain the contemporary eruption of calc-alkaline and alkaline magmas along the belt. The Michoacán-Guanajuato Volcanic Field (MGVF) is an atypical, vast region of monogenetic activity located in the western-central part of the TMVB. Here we present new petrographic, geochemical, and isotopic (Sr–Nd–Pb–Os) data on recent volcanics in the Jorullo-Tacámbaro area that is the closest to the oceanic trench. TMVB-related volcanics in this area are Plio-Quaternary (<5 Ma) and mainly form a calc-alkaline series from basalts to dacites, with rare (<5 vol. %) alkaline rocks that range from trachybasalts to trachydacites, and transitional samples. Crystal textures are consistent with rapid crystallization at shallow depth and processes of mixing of similar magma batches (magma recharge). All of the samples exhibit an arc-type trace element pattern. Alkaline and transitional magmas have higher Na2O and K2O, lower Al2O3, and higher concentrations in incompatible elements (e.g. Sr, K, Ba, Th, Ce, P) compared to calc-alkaline rocks. Calc-alkaline rocks are similar isotopically to transitional and alkaline samples, except for a few low 87Sr/86Sr samples. Sr, Nd and Pb isotopes do not correlate with MgO or 187Os/188Os, indicating that they were not significantly influenced by crustal contamination. Isotopic and trace-element systematics suggest that the Tacámbaro magmas are produced by melting of a mantle wedge fluxed by fluids derived from a mixture of subducted sediments and altered oceanic crust. Alkaline and transitional magmas can be derived from a lower degree of partial melting of a similar source to that of the calc-alkaline rocks, whereas the few low 87Sr/86Sr calc-alkaline rocks require a lower proportion of fluid derived from oceanic sediments and crust. Volcanism at the trenchward edge of the MGVF was thus driven purely by subduction during the last 5 Ma, hence discarding slab rollback in this sector of the TMVB.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Wellman, Charles H. "Spore assemblages from the Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Rhynie outlier, Scotland." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 2 (June 2006): 167–211. http://dx.doi.org/10.1017/s0263593300001449.

Повний текст джерела

Анотація:

ABSTRACTSince the late 1980s an extensive programme of trenching/borehole drilling has been undertaken in order to study the Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Rhynie outlier in the Grampian Highlands of Scotland. The boreholes have provided new information on the stratigraphical succession and geological structure of the Rhynie outlier, both of which were hitherto poorly understood due to the paucity of good surface exposure and the complex geological relationships of the deposits. One hundred and eighteen palynological samples were collected, representing much of the stratigraphical sequence of the inlier, of which 106 were productive. Productive samples yield assemblages of well preserved palynomorphs, dominated by spores and phytodebris, but also containing arthropod cuticle and rare freshwater algal remains. The spore assemblages are systematically described and two new genera and six new species proposed. They are similar throughout the sequence and the spores belong to the polygonalis–emsiensis Spore Assemblage Biozone of Richardson & McGregor (1986) and the PoW Oppel Zone (possibly Su Interval Zone) of Streel et al. (1987), indicating an early (but not earliest) Pragian–?earliest Emsian age range, that may possibly be restricted to latest Pragian–?earliest Emsian. The palynomorph assemblages contain only terrestrial forms, supporting sedimentological interpretation of the deposits as ‘Lower Old Red Sandstone’ fluviatile and lacustrine deposits, with occasional extrusive volcanics and volcaniclastic sediments intercalated. The palynomorphs are of variable thermal maturity (within and between samples), probably reflecting differential heating associated with the complex volcanic/hydrothermal system. The new palynological data provide, for the first time, a reliable biostratigraphical age for the deposits, and suggest that they accumulated relatively rapidly. Spore biostratigraphy and thermal maturity studies facilitate correlation of the tectonically complex deposits, and shed light on other aspects of the geological history of the outlier. The palynomorph assemblages also aid interpretation of the biota of the Rhynie basin, including the exceptionally preserved biotas of the Rhynie and Windyfield cherts.

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Landing, Ed, Susan C. Johnson, and Gerd Geyer. "Faunas and Cambrian volcanism on the Avalonian marginal platform, southern New Brunswick." Journal of Paleontology 82, no. 5 (September 2008): 884–905. http://dx.doi.org/10.1666/07-007.1.

Повний текст джерела

Анотація:

The Cambrian inlier at Beaver Harbour, southern New Brunswick, is now confidently referred to the marginal platform of the late Proterozoic–Early Paleozoic Avalon microcontinent. The sub-trilobitic Lower Cambrian Chapel Island and Random Formations are unconformably overlain by the mafic volcanic-dominated Wade's Lane Formation (new). Late Early Cambrian trilobites and small shelly taxa in the lowest Wade's Lane demonstrate a long Random–Wade's Lane hiatus (middle Terreneuvian–early Branchian). Latest Early–middle Middle Cambrian pyroclastic volcanism produced a volcanic edifice at Beaver Harbour that is one of three known volcanic centers that extended 550 km along the northwest margin of Avalon. Middle Middle Cambrian sea-level rise, probably in theParadoxides eteminicusChron, mantled the extinct volcanics with gray-green mudstone and limestone of the Fossil Brook Member. Black, dysoxic mudstone of the upper Manuels River Formation (upper Middle Cambrian,P. davidisZone) is the youngest Cambrian unit in the Beaver Harbour inlier.Lapworthella cornu(Wiman, 1903) emend., a senior synonym of the genotypeL. nigra(Cobbold, 1921),Hyolithellus sinuosusCobbold, 1921, and probablyAcrothyra seraMatthew, 1902a, range through the ca. 8 m.y. of the trilobite-bearing upper Lower Cambrian, andH. sinuosusandA. serapersist into the middle Middle Cambrian.Lapworthella cornuandH. sinuosusreplaced the tropical taxaL. schodackensis(Lochman, 1956) andH. micansBillings, 1872, in cool-water Avalon.

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Pujol, J., and S. Smithson. "Seismic wave attenuation in volcanic rocks from VSP experiments." GEOPHYSICS 56, no. 9 (September 1991): 1441–55. http://dx.doi.org/10.1190/1.1443164.

Повний текст джерела

Анотація:

Seismic wave attenuation in the Columbia Plateau basalts and Snake River Plain volcanics was analyzed using vertical seismic profiling (VSP) data. The computation of attenuation coefficients is based on fitting a straight line to the logarithm of amplitude ratios computed for fixed values of frequency and variable depth. This approach does not require any assumptions on the dependence of Q on frequency. For the Columbia Plateau basalts, the attenuation coefficients obtained from the field data are smaller than those computed from the synthetic VSP generated using the sonic and density logs, indicating that the observed attenuation is related to scattering effects and is substantially larger than the intrinsic attenuation of basalt. Therefore, it is concluded that only a lower bound for Q can be established, in agreement with recent findings by other authors. The effective attenuation of seismic energy in basalts (about [Formula: see text] for the peak frequency) is comparable to the effective attenuation observed in sedimentary rocks (between [Formula: see text] and [Formula: see text]). Results from two VSPs recorded in the Snake River Plain volcanics using air gun and vibrator sources show some frequency‐dependent effects. The depth range analyzed covers two different lithologic units (rhyolitic rocks with interbedded volcanic sediments above more homogeneous rhyodacitic rocks). The air gun energy (with a peak frequency near 15 Hz) clearly detects a difference in the attenuating properties of the two types of rocks. The vibrator energy, on the other hand, also detects this difference, but only for the lower frequencies. For frequencies near the peak frequency (31 Hz), attenuation is almost the same in the two units. The difference in attenuation for the two types of rocks is real and cannot be explained as processing artifacts, because it can be observed for both sources by analyzing the amplitude decay in the time domain. The peak‐frequency attenuation coefficients for the lower section are [Formula: see text] and [Formula: see text] for the vibrator and air gun sources, respectively. For the upper section, the corresponding values are [Formula: see text] and [Formula: see text]. The difference in attenuation implied by the last two coefficients is probably not real, because the decay of energy in the time domain for the two sources is much closer to each other. The Columbia Plateau and Snake River Plain VSPs show that the poor quality of reflection data commonly associated with volcanic rocks cannot be explained by unusually high attenuation.

Стилі APA, Harvard, Vancouver, ISO та ін.

37

Xu, Zhitao, Jinggui Sun, Xiaolong Liang, Zhikai Xu, and Xiaolei Chu. "Geochronology, Geochemistry, and Pb–Hf Isotopic Composition of Mineralization-Related Magmatic Rocks in the Erdaohezi Pb–Zn Polymetallic Deposit, Great Xing’an Range, Northeast China." Minerals 10, no. 3 (March 18, 2020): 274. http://dx.doi.org/10.3390/min10030274.

Повний текст джерела

Анотація:

Late Mesozoic intermediate–felsic volcanics and hypabyssal intrusions are common across the western slope of the Great Xing’an Range (GXAR). Spatiotemporally, these hypabyssal intrusions are closely associated with epithermal Pb–Zn polymetallic deposits. However, few studies have investigated the petrogenesis, contributions and constraints of these Pb–Zn polymetallic mineralization-related intrusions. Therefore, we examine the representative Erdaohezi deposit and show that these mineralization-related hypabyssal intrusions are composed of quartz porphyry and andesite porphyry with concordant zircon U–Pb ages of 160.3 ± 1.4 Ma and 133.9 ± 0.9 Ma, respectively. These intrusions are peraluminous and high-K calc-alkaline or shoshonitic with high Na2O + K2O contents, enrichment in large ion lithophile elements (LILEs; e.g., Rb, Th, and U), and depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), similar to continental arc intrusions. The zircon εHf(t) values range from 3.1 to 8.0, and the 176Hf/177Hf values range from 0.282780 to 0.282886, with Hf-based Mesoproterozoic TDM2 ages. No differences exist in the Pb isotope ratios among the quartz porphyry, andesite porphyry and ore body sulfide minerals. Detailed elemental and isotopic data imply that the quartz porphyry originated from a mixture of lower crust and newly underplated basaltic crust, while the andesite porphyry formed from the partial melting of Mesoproterozoic lower crust with the minor input of mantle materials. Furthermore, a magmatic–hydrothermal origin is favored for the Pb–Zn polymetallic mineralization in the Erdaohezi deposit. Integrating new and published tectonic evolution data, we suggest that the polymetallic mineralization-related magmatism in the Erdaohezi deposit occurred in a back-arc extensional environment at ~133 Ma in response to the rollback of the Paleo-Pacific Plate.

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Martinez, Amancay, Adrian Gallardo, Laura Giambiagi, and Laura Tobares. "The Choiyoi Group in the Cordón del Plata range, western Argentina: structure, petrography and geochemistry." Earth Sciences Research Journal 24, no. 2 (April 1, 2020): 121–32. http://dx.doi.org/10.15446/esrj.v24n2.79515.

Повний текст джерела

Анотація:

The Choiyoi Group from the Permo-Triassic, is one of the most conspicuous volcano-sedimentary suites of southern South America, considered critical to understand the geological evolution of the western margins of Gondwana. In this regard, petrography, geochemistry, and structural data were examined to better elucidate the physical character and emplacement conditions of the unit in the Cordon del Plata range, within the Frontal Cordillera of Mendoza, Argentina. The site is representative of the magmatism and deformation through different Andean cycles. Results of the study indicate three lithological facies of increasing acidity upwards. Mafic units consist of basalts, andesite and andesitic breccias at the base of the sequence. Felsic rocks such as rhyodacites, granites and welded tuffs are predominant above. The fault zone of La Polcura – La Manga is the most prominent structural feature in the region, which presumably controlled the emplacement of breccias and ignimbrites within the middle and upper members. These compositional variations suggest a magma evolution from subduction to a rifting environment after the San Rafael orogeny in the Late Palaeozoic. In this line, the Lower Choiyoi was observed to overlie the San Rafael structures indicating thus, that compression ceased before the volcanic extrusion. Geochemistry data indicate that mafic rocks are mostly high-potassium, calc-alkaline volcanics derived from the mantle wedge above the subduction zone. In contrast, the felsic rocks range from high-potassium rhyolites to shoshonites, typically depleted in Eu. This indicate partial melting of a lithospheric mantle in an average to thin crust.

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Asudeh, I., D. A. Forsyth, R. Stephenson, A. Embry, H. R. Jackson, and D. White. "Crustal structure of the Canadian polar margin: results of the 1985 seismic refraction survey." Canadian Journal of Earth Sciences 26, no. 5 (May 1, 1989): 853–66. http://dx.doi.org/10.1139/e89-069.

Повний текст джерела

Анотація:

The 1985 refraction survey based on Ice Island covered a northern transition zone along the Canadian polar margin north of Axel Heiberg Island. The refraction survey included a 60 km line along the inner shelf, a 180 km parallel line along the outer shelf, and a 60 km connecting line. Shotpoints offset from the line ends recorded upper mantle observations to a distance of 240 km.Along the inner shelf, the upper 700 m, with an interval velocity of 3.7 km/s, is interpreted as Tertiary–Cretaceous strata. The underlying 4 km thick layer has a starting velocity of 5 km/s and a gradient of 0.2 s−1. It is thought to consist of mainly deformed lower Paleozoic strata capped by upper Paleozoic – Triassic clastics and carbonates and (or) Cretaceous volcanics. Sequentially, the lower unit, with a starting velocity of 5.8 km/s, most likely consists of Proterozoic – lower Paleozoic rocks.Beneath the offshore line, up to 5 km of strata with a starting velocity of 2.2 km/s and a gradient of 0.5 s−1 probably represents Tertiary–Cretaceous elastics. The underlying material with a starting velocity of 4.5 km/s and a gradient of 0.1 s−1 is interpreted as a sedimentary succession of either Cretaceous–Tertiary elastics or upper Paleozoic to Cretaceous strata. Beneath this section, a probable Proterozoic – lower Paleozoic lower crustal layer with a starting velocity of 6.2 km/s extends to about 25 km. Apparent upper mantle velocities in the 8.0–8.2 km/s range are observed.Beneath the transitional onshore–offshore line, a Neogene sedimentary basin is interpreted as being floored by faulted blocks of probably deformed Proterozoic to lower Paleozoic rocks on the landward side and possibly Cretaceous to lower Tertiary rocks on the seaward side.

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Savov, Sava, Christo Dabovski, and Kiril Budurov. "New data on the stratigraphy of the Tethyan Triassic in the Strandzha Mts., SE Bulgaria." Geologica Balcanica 25, no. 5-6 (December 30, 1995): 33–42. http://dx.doi.org/10.52321/geolbalc.25.5-6.33.

Повний текст джерела

Анотація:

Data newly obtained by the authors together with already published evidence allow for a new analysis of the Triassic stratigraphy in the Strandzha Mountains. The Triassic in the Strandzha Mountains is referred with certainty to the Tethyan type of evolution. Its zonal stratigraphy is being detailized on the basis of conodont fauna, and the section is reconstructed and correlated with the other sections in Bulgaria. The numerous lithostratigraphic units already introduced have been created mainly due to secondary features as different degree of metamorphism and of tectonic reworking. They are now generalized into four formal units (Formations), and namely (from bottom to top): the basal Stravnitsa Formation built up of metagravelites, metapsammites and interbedded fine-pebble conglomerates; the Zaberska Formation (with two members, Gramatikovo and Kaziyskidol Members, respectively), built up of flyschoid alternation of shales, phyllites, metasiltstones, metapsammites, and marmorized limestones as well as of basic volcanics and ore bodies, within the age range from upper parts of the Spathian to lowermost parts of the Aegean Substage of the Anisian Stage; Kondolovo Formation built up of limestones and marmorized limestones, with Anisian (Pelsonian and Illyrian Substages) and Ladinian (Fassanian and lower and middle parts of the Longobardian Substage) age; and (at the top) the Lipacka Formation built up of flyschoid interbedding of limestones, slates and sandstones within the range upper parts of the Ladinian (Upper Longobardian Substage) – Norian (Lacian and parts of the Alaunian Substage).

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Sajid, Muhammad, Muhammad Yaseen, Muhammad Zeeshan Ullah, and Ghulam Murtaza. "Textural Implications in Assessment of Physico-Mechanical behaviour of Metavolcanic Rocks from Dir Upper, north western Pakistan." International Journal of Economic and Environmental Geology 11, no. 3 (December 4, 2020): 1–10. http://dx.doi.org/10.46660/ijeeg.vol11.iss3.2020.469.

Повний текст джерела

Анотація:

The Dir-Utror meta-volcanics from the south western portion of the Kohistan arc in northern Pakistan areanalyzed in term of their petrography, physico-mechanical properties. Field observations and petrography show thecollected representative samples to be fine-grained meta-andesites (FMA), coarse-grained meta-andesites (CMA) andagglomerate (AG). The relationship between petrography and physico-mechanical properties has been investigatedwhich inferred the grain size to be the major factor, alongside grains’ shape, arrangement and size distribution as wellas degree of mineral alteration significantly affecting the mechanical behavior of rocks. The CMA yield more strength(98 MPa) than FMA (93 MPa) due to its lesser degree of mineral alteration, inequigranular texture, lack of preferredmineral alignment, relatively low porosity and water absorption. The lower strength of agglomerate (57 MPa)corresponds to abundance of soft minerals (calcite), exotic rock fragments and coarse-grained texture. Based onphysico-mechanical properties including specific gravity, bulk density, aggregate impact value, Los Angeles abrasionvalue and unconfined compressive strength (UCS), these rocks fall within permissible range to be utilized for multipleengineering purposes including dimension stones and foundation materials for other civil structures. However,petrographic investigations reveal excessive amount of reactive silica in these rocks making them prone to alkali-silicareactivity in concrete works with ordinary Portland cement (OPC). Hence these rocks are not recommended for use assole aggregate material or low-alkali cement is recommended, if used.

Стилі APA, Harvard, Vancouver, ISO та ін.

42

Sutthirat, C., S. Saminpanya, G. T. R. Droop, C. M. B. Henderson, and D. A. C. Manning. "Clinopyroxene-corundum assemblages from alkali basalt and alluvium, eastern Thailand: constraints on the origin of Thai rubies." Mineralogical Magazine 65, no. 2 (April 2001): 277–95. http://dx.doi.org/10.1180/002646101550253.

Повний текст джерела

Анотація:

AbstractAn inclusion of corundum (ruby) was found in a clinopyroxene xenocryst in alkali basalt from the late-Cenozoic Chanthaburi-Trat volcanics of eastern Thailand. The clinopyroxene is fairly sodic, highly aluminous and magnesian (0.12–0.14 Na, 0.31–0.33 AlIV and 0.36–0.40 AlVI per 6(O), and Mg/(Mg+Fe2+) > 0.9)) and is chemically similar to clinopyroxene inclusions in rubies from nearby alluvial gem deposits, suggesting a common origin for the two types of occurrence. Sapphirine (Mg/(Mg+Fe2+) = 0.91–0.94) and garnet (py56–67alm11–18grs18–23) also occur as inclusions in alluvial rubies. Thermodynamic calculation of the equilibrium 2 di + 2 crn = 2 cats + en constrains the temperatures of clinopyroxene + corundum crystallization to between 800 and 1150 ± 100°C. Use of other equilibria as stability limits places the pressures of crystallization between 10 and 25 kbar, implying depths of between 35 and 88 km. The most Fe-rich clinopyroxene crystallized at a pressure in the lower part of the range. The pyropic garnet inclusions in corundum crystallized at pressures of >18 kbar (i.e. at depths > ~63 km).The xenocrystic clinopyroxene could have coexisted in equilibrium with garnet of similar composition to the observed inclusions at the deduced temperatures of crystallization. The rubies probably crystallized in rocks of mafic composition, i.e. garnet-clinopyroxenites or garnet-pyriclasites, within the upper mantle.

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Hart, S. R., J. S. Steinhart, and T. J. Smith. "Terrestrial heat flow in Lake Superior." Canadian Journal of Earth Sciences 31, no. 4 (April 1, 1994): 698–708. http://dx.doi.org/10.1139/e94-062.

Повний текст джерела

Анотація:

Using oceanographic heat-flow techniques, 162 measurements of heat flow were made in Lake Superior during the summers of 1966 and 1967. These data are of high quality, with precisions with respect to intercomparisons typically in the 3–5% range. The data define two very clear features. One is a trough of low heat-flow values, which runs continuously for 650 km along the northern edge of the lake, with values ranging between 0.46 and 0.98 heat-flow units (HFU) (19.2–41.0 mW/m2). This feature correlates with surface exposure of Keweenawan mafic volcanics; it is believed to delineate a major crustal separation associated with the Midcontinent Rift and is filled to crustal thicknesses with mafic intrusives and extrusives. This feature has not been imaged with the seismic reflection profiling of GLIMPCE. The other heat-flow feature is an arcuate ridge of high heat-flow values (1.0–1.45 HFU; 41.8–60.7 mW/m2), parallel to and south of the heat-flow trough. The highest areas of this ridge correspond to areas of thick rift-filling Keweenawan sediments. The high heat flow is modulated to lower values in areas where the thick sediments overlie highly thinned crust now containing large thicknesses of mafic volcanic rock. The heat-flow features show very good correlation with the magnetic anomaly map of Lake Superior, but only spotty correlation with the Bouguer gravity anomaly features.

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Moffat, I. W., R. M. Bustin, and G. E. Rouse. "Biochronology of selected Bowser Basin strata; tectonic significance." Canadian Journal of Earth Sciences 25, no. 10 (October 1, 1988): 1571–78. http://dx.doi.org/10.1139/e88-150.

Повний текст джерела

Анотація:

Recent evaluation and reinterpretation of fossil floral and faunal data more clearly define the ages of strata exposed in the Groundhog Coalfield and the surrounding Bowser Basin of north-central British Columbia. In the Groundhog Coalfield, Bowser Lake Group strata consist of an overall coarsening-upwards cycle divisible into four informal stratigraphic units, which are, from oldest to youngest, the Jackson, Currier, McEvoy, and Devils Claw units. The section has an unconformable relationship with underlying Bajocian Spatsizi marine shales, volcanics, and arenaceous sediments. Marine macrofossils indicate a Callovian to Oxfordian age for the Jackson unit. The fossil plant succession present in the overlying Currier unit indicates Late Jurassic affinities. Recent unpublished palynologic data from lower McEvoy rocks in the northern Groundhog Coalfield suggest a Barremian age. The palynoassemblage present in the lower Devils Claw unit in the central part of the Groundhog Coalfield suggests a late middle Albian age.Rocks of the Sustut Group have an angular unconformable relationship with underlying Bowser Lake Group strata near the eastern margin of the Bowser Basin. The palynoassemblage present in Sustut Group rocks from the southern Sustut Basin suggests a Campanian to Maastrichtian age range, in contrast to a probable late Albian to Campanian age range for the northern Sustut Basin and a middle to late Albian age from Sustut Group outliers present within the northern Bowser Basin. Within the Groundhog Coalfield, Devils Claw strata have a conformable or paraconformable relationship with underlying Bowser Lake Group strata.Regional discrepancy in the age and geometry of the sub-Sustut unconformity is attributed to a time-transgressive unconformity that resulted from cratonward advance of an isostatically induced peripheral bulge. Age and contact relationships suggest that deformation in the Bowser Basin and surrounding Sustut Basin must have spanned the time period that corresponds to a second uplift pulse of the Columbian orogen (Aptian to early Cenomanian) and the uplift pulse related to the Laramide orogen (Campanian to Maastrichtian).

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Garzione, Carmala N., P. Jonathan Patchett, Gerald M. Ross, and JoAnne Nelson. "Provenance of Paleozoic sedimentary rocks in the Canadian Cordilleran miogeocline: a Nd isotopic study." Canadian Journal of Earth Sciences 34, no. 12 (December 1, 1997): 1603–18. http://dx.doi.org/10.1139/e17-129.

Повний текст джерела

Анотація:

Nd isotopes and trace elements in sedimentary rocks of the Yukon, the Northwest Territories, and northern British Columbia are used to examine the source of sediments in the Canadian Cordilleran miogeocline. Previous Nd isotope studies in southern Alberta demonstrated that strata of Neoproterozoic to Late Ordovician age were derived from Archean and Proterozoic Canadian Shield sources, whereas by the Late Devonian, a shift of 6 εNd units to younger crustal sources (εNd (T) = −6 to −9) had occurred. In this study, we found that the shift to younger crustal Nd isotopic signatures in the Yukon and Northwest Territories occurred much earlier than in southern Alberta. Cambrian and older strata have εNd(T) values of −10.0 to −21.1, consistent with derivation from Canadian Shield sources. Lower Ordovician through Permian strata in the Yukon and Northwest Territories, including the Innuitian-derived Imperial Assemblage, have εNd(T) values of −5 to −11.4. In northern British Columbia, the shift to a younger source reflects a wider range of εNd(T) values, from -−8.7 to −14.6 in Middle Ordovician through Middle Devonian strata, suggesting continued input from Canadian Shield sources. By the Middle Devonian, a complete shift to younger crustal signatures (εNd(T) = −5.9 to −10.5) had occurred in northern British Columbia. Several sources for the more juvenile sediments include (1) a mixture of locally erupted volcanic rocks with Canadian Shield sources, (2) a Grenville source, and (3) an Innuitian source. We propose that Ordovician to Lower Devonian strata were derived from a mixture of locally erupted, juvenile volcanics and pre-Cambrian Canadian Shield sources, and post-Middle Devonian strata were sourced from the Innuitian orogen in the Canadian Arctic.

Стилі APA, Harvard, Vancouver, ISO та ін.

46

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.

Повний текст джерела

Анотація:

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.

Стилі APA, Harvard, Vancouver, ISO та ін.

47

Eros, James M., Markes E. Johnson, and David H. Backus. "Rocky shores and development of the Pliocene-Pleistocene Arroyo Blanco Basin on Isla Carmen in the Gulf of California, Mexico." Canadian Journal of Earth Sciences 43, no. 8 (August 1, 2006): 1149–64. http://dx.doi.org/10.1139/e06-019.

Повний текст джерела

Анотація:

Arroyo Blanco Basin on Isla Carmen preserves a 157 m thick, nearly complete record of Pliocene–Pleistocene history in the Gulf of California. Examples of rocky-shore geomorphology occur on all margins of this trapezoidal-shaped, 3.3 km2 basin. A shoreline is developed in low relief on Miocene andesite from the Comondú Group at the rear of the basin parallel to the long axis of the island. Two end walls trace normal faults that stayed active during the life of the basin and maintained steep rocky shores. The basin is 64% filled by calcarudite and calcarenite derived from crushed rhodolith debris. Other facies include shell beds and stringers of andesite conglomerate that define a 4°–6° ramp. The ramp expanded onshore through Pliocene time, based on a succession of overlapping range zones for 22 macrofossils typical of Lower through Upper Pliocene strata in the Gulf of California. The unconformity exposed 1 km inland at the rear of the basin is between Miocene volcanics and Pleistocene cap rock at an elevation of 170 m above sea level. Whole rhodoliths encrusted on andesite pebbles occur above this unconformity. Presumably, the older Miocene-Pliocene unconformity is buried beneath the ramp. Four marine terraces with sea cliffs notched in Pliocene limestone occur at elevations of 68, 58, 37, and 12 m. The 12 m terrace is associated regionally with the last interglacial epoch between 120 000 and 135 000 years ago. Juxtaposition of ramp and terrace features in the same exhumed basin supports a long history of gradual Pliocene subsidence followed by episodic Pleistocene uplift.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Borissova, Irina, and Gabriel Nelson. "Petroleum potential of the offshore southern Carnarvon Basin—insights from new Geoscience Australia data." APPEA Journal 51, no. 2 (2011): 746. http://dx.doi.org/10.1071/aj10126.

Повний текст джерела

Анотація:

In 2008–9, under the Offshore Energy Security Program, Geoscience Australia (GA) acquired 650 km of seismic data, more than 3,000 km of gravity and magnetic data, and, dredge samples in the southern Carnarvon Basin. This area comprises the Paleozoic Bernier Platform and southern part of the Mesozoic Exmouth Sub-basin. The new seismic and potential field data provide a new insight into the structure and sediment thickness of the deepwater southernmost part of the Exmouth Sub-basin. Mesozoic depocentres correspond to a linear gravity low, in water depths between 1,000–2,000 m and contain between 2–3 sec (TWT) of sediments. They form a string of en-echelon northeast-southwest oriented depressions bounded by shallow-dipping faults. Seismic data indicates that these depocentres extend south to at least 24°S, where they become more shallow and overprinted by volcanics. Potential plays in this part of the Exmouth Sub-basin may include fluvio-deltaic Triassic sandstone and Lower–Middle Jurassic claystone source rocks sealed by the regional Early Cretaceous Muderong shale. On the adjoining Bernier Platform, minor oil shows in the Silurian and Devonian intervals at Pendock–1a indicate the presence of a Paleozoic petroleum system. Ordovician fluvio-deltaic sandstones sealed by the Silurian age marine shales, Devonian reef complexes and Miocene inversion anticlines are identified as potential plays. Long-distance migration may contribute to the formation of additional plays close to the boundary between the two provinces. With a range of both Mesozoic and Paleozoic plays, this under-explored region may have a significant hydrocarbon potential.

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Perepelov, Alexander, Mikhail Kuzmin, Svetlana Tsypukova, Yuri Shcherbakov, Sergey Dril, Alexey Didenko, Enkhbat Dalai-Erdene, Mikhail Puzankov, and Alexander Zhgilev. "Late Cenozoic Uguumur and Bod-Uul Volcanic Centers in Northern Mongolia: Mineralogy, Geochemistry, and Magma Sources." Minerals 10, no. 7 (July 8, 2020): 612. http://dx.doi.org/10.3390/min10070612.

Повний текст джерела

Анотація:

The paper presents new data on mineralogy, geochemistry, and Sr-Nd-Pb isotope systematics of Late Cenozoic eruption products of Uguumur and Bod-Uul volcanoes in the Tesiingol field of Northern Mongolia, with implications for the magma generation conditions, magma sources, and geodynamic causes of volcanism. The lavas and pyroclastics of the two volcanic centers are composed of basanite, phonotephrite, basaltic trachyandesite, and trachyandesite, which enclose spinel and garnet peridotite and garnet-bearing pyroxenite xenoliths; megacrysts of Na-sanidine, Ca-Na pyroxene, ilmenite, and almandine-grossular-pyrope garnets; and carbonate phases. The rocks are enriched in LILE and HFSE, show strongly fractioned REE spectra, and are relatively depleted in U and Th. The low contents of U and Th in Late Cenozoic volcanics from Northern and Central Mongolia represent the composition of a magma source. The presence of carbonate phases in subliquidus minerals and mantle rocks indicates that carbon-bearing fluids were important agents in metasomatism of subcontinental lithospheric mantle. The silicate-carbonate melts were apparently released from eclogitizied slabs during the Paleo-Asian and Mongol-Okhotsk subduction. The parent alkali-basaltic magma may be derived as a result from partial melting of Grt-bearing pyroxenite or eclogite-like material or carobantized peridotite. The sources of alkali-basaltic magmas from the Northern and Central Mongolia plot different isotope trends corresponding to two different provinces. The isotope signatures of megacrysts are similar to those of studied volcanic centers rocks. The P-T conditions inferred for the crystallization of pyroxene and garnet megacrysts correspond to a depth range from the Grt-Sp phase transition to the lower crust. Late Cenozoic volcanism in Northern and Central Mongolia may be a response to stress propagation and gravity instability in the mantle associated with the India-Asia collision.

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Bean, J. M., and R. D. B. Whalley. "Native grasslands on non-arable slopes of the Garrawillie Creek sub-catchment, Western Liverpool Plains, New South Wales." Rangeland Journal 23, no. 2 (2001): 119. http://dx.doi.org/10.1071/rj01001.

Повний текст джерела

Анотація:

NSW Government vegetation legislation over the past five years has highlighted the need for a deeper understanding of native grasslands in NSW. The present study looked at such native grasslands on non-arable slopes in the Garrawillie Creek sub-catchment at the western margin of the Liverpool Plains. Sixteen sampling sites were selected on two contrasting rock types and aspects. Species composition and frequency scores were determined at each site using eight concentric nested subquadrats. Cluster analysis revealed seven grassland associations, each designated by a distinctive native grass species. Associated prominent grass species and forbs with 100% fidelity were listed for each grassland association. Within any one association there was a range in condition of the grassland, measured according to the number of perennials + natives relative to the number of annuals + exotics at any individual site. The seven grassland associations were interpreted as states in a state and transition model, in which rock type, aspect and possibly microtopography were important factors determining the states. With some but not all states, management overrode the underlying factors such that transitions occurred across rock type and aspect boundaries. The Sporobulus creber and Eriochloa pseudoacrotricha grasslands were restricted to lighter textured soils on scree slopes of the phonolite lava domes. On the heavy textured soils of the basaltic rocks of the Garrawilla Volcanics, the Bothriochloa spp. grassland maintained a characteristic high level of perennials, even where located within a few metres of land cultivated for at least 30 years. In contrast the Austrostipa aristiglumis grassland, found at lower altitudes on heavy textured soils, displayed low inertia and stability with natives:exotics and perennials:annuals ratios, at the site sampled, close to 1:1. The Eriochloa pseudoacrotricha and Aristida ramosa grasslands were limited to NW slopes.

Стилі APA, Harvard, Vancouver, ISO та ін.

Статті в журналах з теми "Lower Gawler Range Volcanics"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями