Halloysite Formation Through In Situ Weathering of Volcanic Glass from Trachytic Pumices, Vico's Volcano, Italy

Clay Minerals ◽  
1988 ◽  
Vol 23 (4) ◽  
pp. 423-437 ◽  
Author(s):  
P. Quantin ◽  
J. Gautheyrou ◽  
P. Lorenzoni
Keyword(s):  
Pyroclastic Flow ◽  
Microprobe Analysis ◽  
Volcanic Glass ◽  
Detailed Structure ◽  
Brown Soil ◽  
Mineralogical Properties ◽  
Mineralogical Characteristics ◽  
Tetrahedral Substitution ◽  
In Situ Weathering

AbstractThe weathering of a trachytic pumice within a pyroclastic flow underlying an andic-brown soil on the volcano Vico has been studied. The main mineral formed is a spherical 10 Å halloysite which has been shown by SEM and in situ microprobe analysis to have formed directly from the glass. The major mineralogical characteristics as determined by XRD, IR, DTA, TEM and microdiffraction are typical of 10 Å halloysite. However, some minor mineralogical properties and the high Fe and K contents, suggest that it is an interstratification of 74% halloysite and 26% illite-smectite. The calculated formula of the hypothetical 2:1 minerals reveals an Fe- and K-rich clay, with high tetrahedral substitution, like an Fe-rich vermiculite, but the detailed structure of this mineral remains uncertain.

scholarly journals GENESIS AND PHYSICAL CHARACTERISTICS OF THE NEOGENE RED BEDS FROM THE CEDARHILS OF THESSALONIKI, MACEDONIA , GREECE

2018 ◽  
Vol 36 (2) ◽  
pp. 708 ◽  
Author(s):  
A. Tsirambides
Keyword(s):  
Clay Minerals ◽  
Urban Forest ◽  
Clay Fraction ◽  
Eastern Mediterranean Region ◽  
Physical Characteristics ◽  
Coarse Grained ◽  
Red Beds ◽  
Primary Minerals ◽  
In Situ Weathering

The genesis and the physical characteristics of the Neogene red beds of the cedar hills surrounding Thessaloniki are studied in this paper. The peri-urban forest, which covers these hills, has a 3,022 ha area. The topographic relief is smooth and is divided in eight small drainage basins, tapped through small creeks. The elevation of the surrounding hills varies between 85 and 560 m. The dominant land slopes vary between 20 and 55%. All the samples are coarse grained, poorly sorted and friable and present earthy lustre and red colour because of the extensive presence of iron oxides. Angular to sub-angular rock fragments derived from the metamorphic bedrock are very common. Petrographically, the studied red beds belong to the clayey sands. The extended presence (41-66%) of coarse silt and sand size grains (>20 pm) in the samples suggests a mild intensity of in situ weathering of the bedrock. X-ray diffraction analysis of the coarsest fractions 250-20 pm and 20-2 μιτι revealed in decreasing abundance the presence of quartz, feldspars, epidote, micas, chlorite, pyroxenes, amphiboles, and talc. These fractions contain the 2M polytype of mica, while in the fraction <2 pm the 1Μα polytype of illite predominates. In the clay fraction (<2 pm) illite, smectite, and chlorite predominate. The presence of mixed-layer minerals is limited, testifying the almost complete character of hydrolysis of the primary minerals. The formation of red beds took place on low relief land under alternating wet and dry seasons, which prevail in the eastern Mediterranean region since Neogene. The clay minerals are the in situ weathering products of the primary minerals of the greenschists, gneisses and gabbros predominating in the studied area. The extensive presence of clay size grains (11-26%) in the samples, their poor sorting, and their sub-angular morphology, indicate that the red beds are texturally immature. In addition, the abundance of feldspars and Fe-Mg minerals reflects mineralogical immaturity. The low relief and the long-lasting tectonic stability in the Thessaloniki district were essential for the significant thickness of the red beds. The oxygen isotope data of the <0.2 pm fraction (+18.2 to +18.8%o) confirm the pedogenic origin of the clay minerals present. The red beds studied present low plasticity with liquid limit (WÏ) 26.9 to 33.4% and plasticity index (lp) 9.1 to 17.3%. In addition, they have high consolidation index (lc) values (1.03 to 2.28). The swelling potential is low to medium and the activity varies between 0.5 and 1.0. The consolidation and induration degree of the samples analyzed is low, because of the great range of their mineralogical composition and the mild conditions of pressure and temperature to which they have been submitted. The studied red beds are not considered problematic for the foundation of various constructions on them.

Microstructure and Microtexture in Nb-Silicide Based Composites

1998 ◽  
Vol 4 (S2) ◽  
pp. 278-279
Author(s):  
B.P. Bewlay ◽  
J.A. Sutliff
Keyword(s):  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Czochralski Method ◽  
Phase Identification ◽  
Directionally Solidified ◽  
In Situ Composites ◽  
Back Scattering ◽  
Niobium Silicides ◽  
Microstructure And Microtexture

Directionally solidified in-situ composites based on niobium and niobium silicides, such as Nb5Si3 and Nb3Si, are presently under investigation as structural materials [1, 2], Alloying additions of elements such as Hf, Ti and Mo to these silicides are also being explored in order to increase strength and oxidation resistance. The present paper describes the effect of Hf, Mo and Ti additions on microstructure and microtexture of high temperature silcide-based in-situ composites.Alloys were prepared from high purity elements (>99.9%) using induction levitation melting in a segmented water-cooled copper crucible. The alloys were directionally solidified using the Czochralski method [2], Phase identification was performed using scanning electron microscopy, electron microprobe analysis (EMPA), and automated electron back scattering pattern (EBSP) analysis. Using EBSP, positive phase identification was accomplished by direct comparison of the location and character of the diffraction bands in the experimental pattern with those calculated from simulated patterns generated using the possible structure types.

scholarly journals In situ weathering of rocks or aeolian silt deposition: key parameters for verifying parent material and pedogenesis in the Opawskie Mountains—a case study from SW Poland

2019 ◽  
Vol 20 (1) ◽  
pp. 435-451 ◽  
Author(s):  
Aleksandra Loba ◽  
Marcin Sykuła ◽  
Jakub Kierczak ◽  
Beata Łabaz ◽  
Adam Bogacz ◽  
...  
Keyword(s):  
Parent Material ◽  
Sw Poland ◽  
In Situ Weathering

Wascana Creek Ash (Middle Pleistocene) in southern Saskatchewan: characterization, source, fission track age, palaeomagnetism and stratigraphic significance

1977 ◽  
Vol 14 (3) ◽  
pp. 357-374 ◽  
Author(s):  
J. A. Westgate ◽  
E. A. Christiansen ◽  
J. D. Boellstorff
Keyword(s):  
Mineral Assemblage ◽  
National Park ◽  
Fission Track ◽  
Volcanic Glass ◽  
The United States ◽  
Middle Pleistocene ◽  
Carbonate Content ◽  
Stratigraphic Position

Wascana Creek Ash, located close to Regina in Saskatchewan, is correlated with Pearlette ash, type O (classification of Izett et al. 1972) on the basis of its mineral assemblage, shard habit, composition of glass, titanomagnetite and chevkinite. Directions of magnetization and normal polarization of clay immediately below Wascana Creek ash further support this correlation, which is essentially confirmed by the fission track age of volcanic glass and zircon that show Wascana Creek Ash to be 0.6–0.7 Ma.Pearlette ash, type O, is derived from vents in Yellowstone National Park in Wyoming and Idaho, situated about 800 km southwest of Wascana Creek in Saskatchewan. Its air-fall tephra is widely distributed in the form of isolated lentils over the midcontinent region of the United States where stratigraphic relationships suggest a late Kansan, Yarmouth, or early Illinioan age.Wascana Creek Ash and its host clay occupy an intertill position; they rest directly on sandy till, interpreted as part of the Floral Formation, and are covered by till of the Battleford Formation. Thus, the Floral Formation in Saskatchewan may well be as old as the Kansan—that is, decidedly older than most current estimates, which favour an early Wisconsin age.The horizontal disposition and palaeomagnetic characteristics of the host clay, uniformity of carbonate content of the underlying till, and absence of local glaciotectonic features strongly suggest that the tephra and clay are in situ and not glacial erratics that have been transported as blocks from an older deposit. Furthermore, extensive reworking of the tephra from an older horizon is considered unlikely in view of minor detrital contamination, fresh glass, and conspicuous crop of glass-sheathed heavies. However, the stratigraphic position of Wascana Creek Ash should not be considered as firmly established for these observations of necessity pertain to just one locality; further occurrences must be found and studied before its stratigraphic position can be confidently defined.

scholarly journals A Study of Some Aspects of the Volcanic History of the Lake Taupo Area, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Paul C Froggatt
Keyword(s):  
New Zealand ◽  
Late Pleistocene ◽  
Pyroclastic Flow ◽  
Microprobe Analysis ◽  
Pyroclastic Flow Deposit ◽  
The Holocene ◽  
Volcanic History ◽  
Flow Deposit ◽  
History Of ◽  
Glass Shards

<p>Rhyolitic pyroclastic eruptives from the Taupo area, New Zealand have been mapped as nine tephra formations of Holocene (0-10 kyr B.P.), and six of late Pleistocene age (20-c.50 kyr B.P.). Only the 10 younger tephras are dated by radiocarbon. All formations contain PLINIAN type airfall units but three, KAWAKAWA, WAIMIHIA and TAUPO also contain a major pyroclastic flow deposit (IGNIMBRIIE) unit. Dome extrusion can only be demonstrated for KARAPITI eruptive episode, but is inferred for the other Holocene episodes. TAUPO IGNIMBRITE is the product of the most recent eruption and is a particularly well preserved and extensive, unwelded pyroclastic flow deposit, up to 50m thick. Its variety of appearance is described in terms of three lithofacies; valley facies, fines depleted facies and veneer facies, each being formed by particular mechanisms within a pyroclastic flow. Abundant charred logs, lying prone within Taupo Ignimbrite, are radial about the source and attest to a radially outward moving mass dominated by laminar flow. Lake Taupo today covers most of the volcanic source area, preventing close examination and the identification of individual source vents. A vent for each Holocene tephra is inferred from isopachs, grainsize and lake bathymetry, but the vents so inferred show no spatial distribution with time. Nevertheless they are evenly spaced along a northeast trending line and lie on intersections with a northwest trending set of lineations, indicating deep, crustal, structural control on volcanism. Cumulative volume of airfall and ignimbrite material erupted in the Taupo area in the last 50 kyr has amounted to about 175 km3 of magma. Eruptions have proceeded in a step-wise manner, indicating the period to the next eruption is about 8 kyr. By the same approach, the next eruption from the Okataina area, 50 km to the north of Taupo is expected in less than 400 years. Whole rock and mineral chemistry clearly distinguishes between the Holocene and the late Pleistocene tephras, but within each group variations are subtle and no trends with time are apparent. None of the formations exhibit evidence for a chemically zoned magma body, but some data, especially pyroxene phenocryst chemistry, suggests magma inhomogeneities of mafic elements. The Holocene tephra were probably all erupted from the same magma chamber in which crystallisation was the dominant process but convection, crystal element diffusion and chamber replenishment were all probably operative. Results obtained by electron microprobe analysis of glass shards are critically dependent on the beam diameter and current used. By standardising these at 10 microns and 8 nanoamps respectively, comparable major element analyses on glass shards from numerous tephras ranging in age from 20 kyr to 600 kyr were obtained. The stratigraphic relationships between sets of samples (located mainly distal from source) and the close chemical similarity of some samples enabled a comprehensive tephrostratigraphy to be established. In particular, MT. CURL TEPHRA has a glass chemistry quite different from other stratigraphically separate tephras, establishing correlation of Mt. Curl Tephra to Whakamaru Ignimbrite. Likewise, other ignimbrite formations can be correlated to widespread airfall tephras, so establishing an absolute ignimbrite stratigraphy. Microprobe analysis of glass shards provides a method for indirectly determining the amount of hydration. For dated samples from a known weathering environment, the parameters controlling hydration can be quantified. For glass of uniform chemistry, shard size and porosity, ground temperature and groundwater movements are the most important parameters. No shards in the 63-250 micron size range have been found with more than 9% water, suggesting once this maximum is reached, glass rapidly alters to secondary products. Detailed knowledge of the volcanic history of the Taupo area, particularly since 50 kyrs B.P. allows the volcanic hazards of the region to be assessed. Fifteen major eruptions in 50 kyr gives a frequency of 1 in 3300 years, but the timing of individual events is not evenly spread throughout that time. Monitoring for volcanic Precursory events (not being undertaken at present) is essential to gauge the present and short-term future volcanic activity of the Taupo Volcanic Zone.</p>

scholarly journals A Study of Some Aspects of the Volcanic History of the Lake Taupo Area, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Paul C Froggatt
Keyword(s):  
New Zealand ◽  
Late Pleistocene ◽  
Pyroclastic Flow ◽  
Microprobe Analysis ◽  
Pyroclastic Flow Deposit ◽  
The Holocene ◽  
Volcanic History ◽  
Flow Deposit ◽  
History Of ◽  
Glass Shards

<p>Rhyolitic pyroclastic eruptives from the Taupo area, New Zealand have been mapped as nine tephra formations of Holocene (0-10 kyr B.P.), and six of late Pleistocene age (20-c.50 kyr B.P.). Only the 10 younger tephras are dated by radiocarbon. All formations contain PLINIAN type airfall units but three, KAWAKAWA, WAIMIHIA and TAUPO also contain a major pyroclastic flow deposit (IGNIMBRIIE) unit. Dome extrusion can only be demonstrated for KARAPITI eruptive episode, but is inferred for the other Holocene episodes. TAUPO IGNIMBRITE is the product of the most recent eruption and is a particularly well preserved and extensive, unwelded pyroclastic flow deposit, up to 50m thick. Its variety of appearance is described in terms of three lithofacies; valley facies, fines depleted facies and veneer facies, each being formed by particular mechanisms within a pyroclastic flow. Abundant charred logs, lying prone within Taupo Ignimbrite, are radial about the source and attest to a radially outward moving mass dominated by laminar flow. Lake Taupo today covers most of the volcanic source area, preventing close examination and the identification of individual source vents. A vent for each Holocene tephra is inferred from isopachs, grainsize and lake bathymetry, but the vents so inferred show no spatial distribution with time. Nevertheless they are evenly spaced along a northeast trending line and lie on intersections with a northwest trending set of lineations, indicating deep, crustal, structural control on volcanism. Cumulative volume of airfall and ignimbrite material erupted in the Taupo area in the last 50 kyr has amounted to about 175 km3 of magma. Eruptions have proceeded in a step-wise manner, indicating the period to the next eruption is about 8 kyr. By the same approach, the next eruption from the Okataina area, 50 km to the north of Taupo is expected in less than 400 years. Whole rock and mineral chemistry clearly distinguishes between the Holocene and the late Pleistocene tephras, but within each group variations are subtle and no trends with time are apparent. None of the formations exhibit evidence for a chemically zoned magma body, but some data, especially pyroxene phenocryst chemistry, suggests magma inhomogeneities of mafic elements. The Holocene tephra were probably all erupted from the same magma chamber in which crystallisation was the dominant process but convection, crystal element diffusion and chamber replenishment were all probably operative. Results obtained by electron microprobe analysis of glass shards are critically dependent on the beam diameter and current used. By standardising these at 10 microns and 8 nanoamps respectively, comparable major element analyses on glass shards from numerous tephras ranging in age from 20 kyr to 600 kyr were obtained. The stratigraphic relationships between sets of samples (located mainly distal from source) and the close chemical similarity of some samples enabled a comprehensive tephrostratigraphy to be established. In particular, MT. CURL TEPHRA has a glass chemistry quite different from other stratigraphically separate tephras, establishing correlation of Mt. Curl Tephra to Whakamaru Ignimbrite. Likewise, other ignimbrite formations can be correlated to widespread airfall tephras, so establishing an absolute ignimbrite stratigraphy. Microprobe analysis of glass shards provides a method for indirectly determining the amount of hydration. For dated samples from a known weathering environment, the parameters controlling hydration can be quantified. For glass of uniform chemistry, shard size and porosity, ground temperature and groundwater movements are the most important parameters. No shards in the 63-250 micron size range have been found with more than 9% water, suggesting once this maximum is reached, glass rapidly alters to secondary products. Detailed knowledge of the volcanic history of the Taupo area, particularly since 50 kyrs B.P. allows the volcanic hazards of the region to be assessed. Fifteen major eruptions in 50 kyr gives a frequency of 1 in 3300 years, but the timing of individual events is not evenly spread throughout that time. Monitoring for volcanic Precursory events (not being undertaken at present) is essential to gauge the present and short-term future volcanic activity of the Taupo Volcanic Zone.</p>

Ion microprobe analysis—a review of geological applications

1989 ◽  
Vol 53 (369) ◽  
pp. 3-24 ◽  
Author(s):  
S. J. B. Reed
Keyword(s):  
Microprobe Analysis ◽  
Ion Beam ◽  
Isotopic Analysis ◽  
Specimen Preparation ◽  
Ion Microprobe ◽  
Spatially Resolved ◽  
Secondary Ions ◽  
Focussed Ion Beam ◽  
Isotope Studies

AbstractIn ion microprobe analysis the specimen is bombarded with a focussed ion beam a few µm in diameter and the secondary ions produced are accelerated into the entrance slit of a mass spectrometer. An outline of the salient features of the instrument is given here, together with an account of the methods used for quantitative elemental and isotopic analysis.The major part of this paper consists of a comprehensive account of the geological applications of ion microprobe analysis. These include elemental analysis, especially for trace elements (down to sub-ppm levels in many cases) and light elements (H-F) which are beyond the scope of the electron microprobe. The other main area of geological interest is isotopic analysis, where the ion microprobe has the advantage over conventional mass spectrometry of being capable of in situ analysis of selected points on polished sections, obviating the need for laborious specimen preparation, and enabling spatially-resolved data to be obtained, with a resolution of a few µm. The ion microprobe has been especially successful in U-Pb zircon dating and the study of isotope anomalies in meteorites. Other significant applications include diffusion and stable isotope studies.

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