Constraining the timing and character of crustal melting in the Adirondack Mountains using multi-scale compositional mapping and in-situ monazite geochronology

2019 ◽  
Vol 104 (11) ◽  
pp. 1585-1602 ◽  
Author(s):  
Michael L. Williams ◽  
Timothy Grover ◽  
Michael J. Jercinovic ◽  
Sean P. Regan ◽  
Claire R. Pless ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Bulk Composition ◽  
Previous History ◽  
Melting Reaction ◽  
Tectonic History ◽  
Three Samples ◽  
Accessory Phase ◽  
Close Proximity ◽  
Orogenic Belts

Abstract Migmatites are common in the hinterland of orogenic belts. The timing and mechanism (in situ vs. external, P-T conditions, reactions, etc.) of melting are important for understanding crustal rheology, tectonic history, and orogenic processes. The Adirondack Highlands has been used as an analog for mid/deep crustal continental collisional tectonism. Migmatites are abundant, and previous workers have interpreted melting during several different events, but questions remain about the timing, tectonic setting, and even the number of melting events. We use multiscale compositional mapping combined with in situ geochronology and geochemistry of monazite to constrain the nature, timing, and character of melting reaction(s) in one locality from the eastern Adirondack Highlands. Three gray migmatitic gneisses, studied here, come from close proximity and are very similar in microscopic and macroscopic (outcrop) appearance. Each of the rocks is interpreted to have undergone biotite dehydration melting (i.e., Bt + Pl + Als + Qz = Grt + Kfs + melt). Full-section compositional maps show the location of reactants and products of the melting reaction, especially prograde and retrograde biotite, peritectic K-feldspar, and leucosome, in addition to all monazite and zircon in context. In addition, the maps provide constraints on kinematics during melting and a context for interpretation of accessory phase composition and geochronology. More so than zircon, monazite serves as a monitor of melting and melt loss. The growth of garnet during melting leaves monazite depleted in Y and HREEs while melt loss from the system leaves monazite depleted in U. Results show that in all three localities, partial melting occurred during at ca. 1160–1150 Ma (Shawinigan orogeny), but the samples show high variability in the location and degree of removal of the melt phase, from near complete to segregated into layers to dispersed. All three localities experienced a second high-T event at ca. 1050 Ma, but only the third (non-segregated) sample experienced further melting. Thus, in addition to bulk composition, the fertility for melting is an important function of the previous history and the degree of mobility of earlier melt and fluids. Monazite is also a sensitive monitor of retrogression; garnet breakdown leads to increased Y and HREE in monazite. Results here suggest that all three samples remained at depth between the two melting events but were rapidly exhumed after the second event.

Crustal anatexis and its relation to the exhumation of collisional orogenic belts, with particular reference to the Himalaya

2002 ◽  
Vol 66 (1) ◽  
pp. 53-91 ◽  
Author(s):  
A. G. Whittington ◽  
P. J. Treloar
Keyword(s):  
Volume Fraction ◽  
Thermal Conditions ◽  
Western Himalaya ◽  
Crustal Anatexis ◽  
Accessory Phase ◽  
Small Volume Fraction ◽  
Active Processes ◽  
Metamorphic Terranes ◽  
Orogenic Belts

AbstractWe review the causes, mechanisms and consequences of crustal anatexis during the exhumation of metamorphic terranes, from a petrological perspective. During both prograde and retrograde metamorphism, limited influx of free hydrous fluids may result in small volumes of very hydrous melts, which cannot ascend far (if at all) before reaching their solidus. If thermal conditions for dehydration melting are attained in fertile micaceous crustal layers, much larger volumes of water-undersaturated granitic magmas may result, especially where limited external fluid influx raises water activities above those that may be buffered by dehydrating hydrous phases. Magmas have specific trace element characteristics depending on the reaction which formed them which, combined with accessory phase thermometry, may enable the (P-T) conditions of melting to be ascertained. Small volume-fraction magmas will typically remain as in situ migmatites unless their extraction is assisted by deformation. In turn, deformation will be focused in weaker partially molten zones, so that water-undersaturated magmas may often be mobilized. Once segregated, their ascent is limited by the rate of dyke propagation, and they may reach shallow levels (<2 kbar) before crystallizing. The complex interplay between deformation and melting is exemplified by the Miocene evolution of the central Himalaya, where thrust and normal faulting, melting and exhumation were all simultaneously active processes which were linked by feedback relations. In the Nanga Parbat Massif of the western Himalaya, rapid post-Miocene denudation and vigorous fluid flux enabled rocks to experience more than one episode of melting simultaneously, at different levels of the same exhuming crustal section.

A geometallurgical characterization study of the Crystalkop Reef at the Great Noligwa Mine, Klerksdorp Goldfield, South Africa

2017 ◽  
Vol 120 (3) ◽  
pp. 303-322
Author(s):  
D. Pienaar ◽  
B.M. Guy ◽  
C. Pienaar ◽  
K.S. Viljoen
Keyword(s):  
South Africa ◽  
Treatment Plant ◽  
Processing Parameters ◽  
Processing Plant ◽  
Small Contribution ◽  
Gold Cyanide ◽  
Three Samples ◽  
Characterization Study ◽  
Different Sources

Abstract Mineralogical and textural variability of ores from different sources commonly leads to processing inefficiencies, particularly when a processing plant is designed to treat ore from a single source (i.e. ore of a relatively uniform composition). The bulk of the Witwatersrand ore in the Klerksdorp goldfield, processed at the AngloGold Ashanti Great Noligwa treatment plant, is derived from the Vaal Reef (>90%), with a comparatively small contribution obtained from the Crystalkop Reef (or C-Reef). Despite the uneven contribution, it is of critical importance to ensure that the processing parameters are optimized for the treatment of both the Vaal and C-Reefs. This paper serves to document the results of a geometallurgical study of the C-Reef at the Great Noligwa gold mine in the Klerksdorp goldfield of South Africa, with the primary aim of assessing the suitability of the processing parameters that are in use at the Great Noligwa plant. The paper also draws comparisons between the C-Reef and the Vaal Reef A-facies (Vaal Reef) and attempts to explain minor differences in the recovery of gold and uranium from these two sources. Three samples of the C-Reef were collected in-situ from the underground operations at Great Noligwa mine for mineralogical analyses and metallurgical tests. Laboratory-scale leach tests for gold (cyanide) and uranium (sulphuric acid) were carried out using dissolution conditions similar to that in use at the Great Noligwa plant, followed by further diagnostic leaching in the case of gold. The gold in the ore was found to be readily leachable with recoveries ranging from 95% to 97% (as opposed to 89% to 93% for the Vaal Reef). Additional recoveries were achieved in the presence of excess cyanide (96% to 98%). The recovery of uranium varied between 72% and 76% (as opposed to 30% to 64% for the Vaal Reef), which is substantially higher than predicted, given the amount of brannerite in the ore, which is generally regarded as refractory. Thus, the higher uranium recoveries from the C-Reef imply that a proportion of the uranium was recovered by the partial dissolution of brannerite. As the Vaal Reef contain high amounts of chlorite (3% to 8%), which is an important acid consumer, it is considered likely that this could have reduced the effectiveness of the H2SO4 leach in the case of the ore of the Vaal Reef. Since the gold and uranium recoveries from the C-Reef were higher than the recoveries from the Vaal Reef, the results demonstrate that the processing parameters used for treatment of the Vaal Reef are equally suited to the treatment of the C-Reef. Moreover, small processing modifications, such as increased milling and leach retention times, may well increase the recovery of gold (particularly when e.g. coarse gold, or unexposed gold, is present).

scholarly journals Memory Effect on a LDH/zeolite A Composite: An XRD In Situ Study

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2102
Author(s):  
Breno G. P. Bezerra ◽  
Lindiane Bieseki ◽  
Mariele I. S. de Mello ◽  
Djalma R. da Silva ◽  
Cristiane B. Rodella ◽  
...  
Keyword(s):  
Memory Effect ◽  
Inert Atmosphere ◽  
Effect Study ◽  
Physical Mixture ◽  
Zeolite A ◽  
Three Samples ◽  
In Situ Experiments ◽  
Double Hydroxide ◽  
Rehydration Process

In this memory effect study, hydrotalcite-type compounds in the lamellar double hydroxide-like (LDH)/zeolite A composite material were analyzed using X-Ray Diffration XRD) in situ experiments. Three samples were analyzed: Al,Mg-LDH, Al,Mg-LDH/ZA composite, and a physical mixture (50/50 wt%) of zeolite A and Al,Mg-LDH. The Al,Mg-LDH sample was treated at 500 °C in an O2 atmosphere and subsequently rehydrated. The Al,Mg-LDH/ZA composites had three treatments: one was performed at 300 °C in a He atmosphere, and two treatments were performed with an O2 atmosphere at 300 and 500 °C. In the physical mixture, two treatments were carried out under O2 flow at 500 °C and under He flow at 300 °C. Both went through the rehydration process. All samples were also analyzed by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The results show that the LDH phase in the Al,Mg-LDH/ZA compounds has memory effects, and thus, the compound can be calcined and rehydrated. For the LDH in the composite, the best heat treatment system is a temperature of 300 °C in an inert atmosphere.

scholarly journals X-Ray Fluorescence Analysis of a Gold Ibex and other Artifacts from Akrotiri

2019 ◽  
Vol 11 ◽  
Author(s):  
A. G. Karydas ◽  
T. Pantazis ◽  
C. Doumas ◽  
A. Vlachopoulos ◽  
P. Nomikos ◽  
...  
Keyword(s):  
Bulk Composition ◽  
Fluorescence Analysis ◽  
Wall Painting ◽  
Inorganic Elements ◽  
X Ray ◽  
Wide Range ◽  
Soldering Technology ◽  
Excavation Area

In-situ X-ray fluorescence analysis (XRF) of ancient artifacts from the excavation area was performed using a novel X-ray instrumentation, composed of a portable silicon PIN thermoelectrically cooled X-ray detector, a miniature X-ray source, and portable data acquisition devices. The main objective of the analyses in Akrotiri was to explore the potential of the technique to provide answers to a wide range of archaeometric questions regarding the bulk composition of metal alloys, especially of gold, the characterization of corrosion products in bronze artifacts, identification of inorganic elements which are fingerprints of the minerals used in wall-painting pigments, and of the painting materials and techniques used for the decoration of clay vase surfaces. Among the analysed artifacts are a unique gold ibex, a bronze dagger and blade, various pigments from the wall paintings of room 3 in Xeste 3, decoration pigments from rosettes of faience, a bichrome jug, and other clay vases. The results of the in-situ XRF survey, primarily those of the bulk composition and soldering technology of the gold ibex, are discussed and compared with literature.

Analyses of Eutectoid Phase Transformations in Nb–SilicideIn SituComposites

2004 ◽  
Vol 10 (4) ◽  
pp. 470-480 ◽  
Author(s):  
B.P. Bewlay ◽  
S.D. Sitzman ◽  
L.N. Brewer ◽  
M.R. Jackson
Keyword(s):  
Crystal Structure ◽  
Phase Transformation ◽  
High Temperature ◽  
Room Temperature ◽  
Bulk Composition ◽  
High Strength ◽  
Eutectoid Decomposition ◽  
Quaternary Alloys ◽  
Temperature Fracture

Nb–silicide in situ composites have great potential for high-temperature turbine applications. Nb–silicide composites consist of a ductile Nb-based solid solution together with high-strength silicides, such as Nb5Si3and Nb3Si. With the appropriate addition of alloying elements, such as Ti, Hf, Cr, and Al, it is possible to achieve a promising balance of room-temperature fracture toughness, high-temperature creep performance, and oxidation resistance. In Nb–silicide composites generated from metal-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. At high Ti concentrations, Nb3Si is stabilized to room temperature, and the eutectoid decomposition is suppressed. However, the effect of both Ti and Hf additions in quaternary alloys has not been investigated previously. The present article describes the discovery of a low-temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3possesses the hP16 crystal structure, as opposed to the tI32 crystal structure observed in binary Nb5Si3. The Ti and Hf concentrations were adjusted over the ranges of 21 to 33 (at.%) and 7.5 to 33 (at.%) to understand the effect of bulk composition on the phases present and the eutectoid phase transformation.

Evaluating the temperature dependence of bedrock hillslope erosion in the Mont Blanc massif using in situ cosmogenic 3He-10Be-14C

2021 ◽  
Author(s):  
Donovan P. Dennis ◽  
Dirk Scherler ◽  
Samuel Niedermann ◽  
Kristina Hippe ◽  
Hella Wittmann ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Erosion Rates ◽  
Close Proximity ◽  
Order Of Magnitude ◽  
Stochastic Events ◽  
Exposure Ages ◽  
Alpine Environments ◽  
Magnitude Difference ◽  
Mont Blanc Massif

&lt;p&gt;The erosion of cold bedrock hillslopes in alpine environments depends not only on rates of frost weathering and accumulated rock damage, but additionally on the removal of the weathered material from the bedrock surface. In the Mont Blanc massif, steep bedrock faces with exposure ages sometimes much older than 50,000 years sit in close proximity to actively-eroding rockwalls, suggesting a more complex relationship between temperature and erosion rates than encompassed by the proposed &amp;#8220;frost-cracking window.&amp;#8221; Stochastic events like rockfalls and rock avalanches, despite their rarity, contribute a non-trivial proportion of the total sediment budget in alpine permafrost regions, adding to the contribution from background &amp;#8220;steady-state&amp;#8221; erosion. Employing a methodology based on the combination of in-situ cosmogenic nuclides &lt;sup&gt;3&lt;/sup&gt;He -&lt;sup&gt;10&lt;/sup&gt;Be-&lt;sup&gt;14&lt;/sup&gt;C, we test the temperature-dependence of high-alpine erosion while taking into account erosional stochasticity.&lt;/p&gt;&lt;p&gt;From cosmogenic &lt;sup&gt;10&lt;/sup&gt;Be concentrations of amalgamated samples collected on the Aiguille du Midi (3842 m a.s.l.) in the Mont Blanc massif, we find an order of magnitude difference in erosion rate across the peak&amp;#8217;s surface. Our preliminary measured erosion rates, ranging between appx. 0.03 mm yr&lt;sup&gt;-1&lt;/sup&gt; and 1.0 mm yr&lt;sup&gt;-1&lt;/sup&gt;, correlate neither with modern temperature measurements from borehole thermistors, nor with our current estimates of bedrock cosmogenic &lt;sup&gt;3&lt;/sup&gt;He-derived paleotemperatures. The corresponding cosmogenic &lt;sup&gt;14&lt;/sup&gt;C/&lt;sup&gt;10&lt;/sup&gt;Be ratios (between 1.70 and 4.0) for these erosion rates indicate that our measurements are not biased by recent stochastic rockfall events. Our current results therefore suggest that on geomorphic timescales, bedrock hillslope erosion rates are not set solely by rates of frost-cracking, but rather by the combined effects of frost-cracking and permafrost thaw-induced rockfalls. These insights are relevant both for short-term monitoring of alpine permafrost and associated geohazards under a warming climate, as well as studies of proposed &amp;#8220;buzzsaws&amp;#8221; operating on glacial-interglacial timescales.&lt;/p&gt;

Comparison of Primary and Metastatic Malignant Melanoma of the Esophagus: Clinicopathologic Review of 10 Cases

2008 ◽  
Vol 132 (10) ◽  
pp. 1623-1629 ◽  
Author(s):  
Amy A. Sanchez ◽  
Tsung-Teh Wu ◽  
Victor G. Prieto ◽  
Asif Rashid ◽  
Stanley R. Hamilton ◽  
...  
Keyword(s):  
Metastatic Melanoma ◽  
Cell Morphology ◽  
Growth Phase ◽  
Cutaneous Melanoma ◽  
Radial Growth ◽  
Spindle Cell ◽  
Previous History ◽  
Depth Of Invasion ◽  
History Of

Abstract Context.—Primary esophageal melanoma (PEM) is a rare disease and is difficult to distinguish from other esophageal malignancies and from metastatic melanoma. Objective.—To develop diagnostic criteria for PEM, we compared the clinicopathologic features of 5 PEMs and 5 metastatic melanomas to esophagus. Design.—Ten cases of esophageal melanoma, including 4 surgically resected specimens, 2 autopsy cases, and 4 cases reported on mucosal biopsies, were reviewed. The histologic parameters used in this study were well-characterized features for cutaneous melanoma, including junctional component (in situ melanoma), radial growth phase, modified Breslow thickness, depth of invasion, lymphovascular invasion, satellitosis, predominant type of cytology, and regional lymph node metastasis. Clinical and follow-up information was obtained by reviewing patients' medical records. Results.—Previous history of cutaneous melanoma was present in all 5 cases of metastatic esophageal melanoma but was not present in the 5 patients with PEMs. In situ melanoma and/or radial growth phase were identified in all 5 PEMs but were not present in any of the metastatic cases. Among the 4 resected and 2 autopsy cases, melanocytosis and mixed epithelioid and spindle cell morphology was present in 2 (50%) of 4 PEMs but was not present in 2 (40%) of the metastatic melanomas. Melanin pigment was detectable in all cases. Patients with PEM had better survival than those who had metastatic melanoma to esophagus (P = .03). Conclusions.—The presence of in situ melanoma, radial growth phase, melanocytosis, and mixed epithelioid and spindle cell morphology, in the context of no history of melanoma, distinguishes PEM from metastatic melanoma.

An unusual case of dysphagia

2018 ◽  
Vol 17 (3) ◽  
pp. 154-155
Author(s):  
Adam Williamson ◽  
◽  
Christopher Kelly ◽  
Keyword(s):  
Unusual Case ◽  
Previous History ◽  
Upper Respiratory Tract ◽  
Medical Unit ◽  
Solid Foods ◽  
Acute Medical Unit ◽  
History Of ◽  
Upper Respiratory ◽  
Ventriculo Peritoneal Shunt

A 51-year-old lady, with a background of an arachnoid cyst and ventriculo-peritoneal shunt in situ, presented to the Acute Medical Unit with a 2-day history of neck pain. She awoke from sleep with the pain and it persisted since. She had not been involved in any trauma, had no previous history of neck or back pain and her pain was not controlled with simple analgesia. She also complained of new odynophagia and high dysphagia, particularly to solid foods. There was no history of upper respiratory tract infection.

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