Imaging of growth banding of minerals using 2-stage sectioning: application to accessory zircon

Long-dormant volcanoes (quiescence time is several 100&#8217;s to 10&#8217;s thousand years between eruptions) pose a particular hazard, since the long repose time decreases the awareness and there is mostly a lack of monitoring. The Haramul Mic, a pancake-shaped flat dacitic lava dome is part of the Ciomadul Volcanic Complex in eastern-central Europe (Romania) and serves as an excellent example of such volcanoes. The Haramul Mic lava dome is the earliest product of the Young Ciomadul Eruption Period (YCEP), when the activity recrudesced in the area after about 200.000 years quiescence time. Eruption age of the dome determined by (U-Th)/He dating on zircon gave 154 +/- 16 ka that is in agreement with the youngest zircon U-Th outer rim date (142 +18/-16 ka). In the YCEP zircon crystallization dates record typically long, up to 350-400 kyr lifetime of the magmatic plumbing system, in case of &#160;Haramul Mic the oldest zircon core is 306 +/- 37 ka old.The 880.7 m high lava dome covers an area of 1.1 km2 and has a volume of ~0.15 km3. It is composed of crystal-rich homogeneous high-K dacite. The average crystal content is 35-40% and consists of plagioclase, amphibole, biotite and accessory zircon, apatite, titanite and Fe-Ti oxides. The groundmass is mainly built up by perlitic glass with some microlites. The dacite includes mafic enclaves having plagioclase and amphibole besides a large amount of biotite crystals, that eventuates K-rich, shoshonitic bulk composition. The dacite contains abundant felsic crystal clots which comprise plagioclase, amphibole, biotite and interstitial vesicular glass.Amphiboles are relatively homogeneous in chemical composition. They are low-Al hornblendes suggesting 700-800 oC crystallization condition at 200-300 MPa compared with experimental data. Al-in-hornblende geobarometer and amphibole-plagioclase geothermometer calculations give results reproducing these temperature and pressure ranges. Although the Kis-Haram dacite is fairly rich in 25-45 anorthite mol% plagioclase, no negative Eu anomaly can be observed in the bulk rock and the glass. Similarities between Fish Canyon Tuff and Kis-Haram rocks can be strikingly noted regarding the major and trace element contents of mineral phases, glass and bulk rock that all refer to a wet oxidised calc-alkaline magmatic system. The relatively small volume Kis-Haram lava dome represents a rejuvenated low-temperature granodioritic crystal mush having similar features as the large volume silicic eruption of Fish Canyon Tuff. Their recorded almost similarly long zircon crystallization intervals give an interesting aspect with regard to the thermal evolution of the magmatic system and eruption volumes.This research was financed by the Hungarian National Research, Development and Innovation Fund (NKFIH) within No. K116528 project and was supported by the &#218;NKP-19-1 New National Excellence Program of the Ministry for Innovation and Technology.

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Age constraints for rare felsic mantle xenoliths from Elie Ness, Scottish Midland Valley

10.5194/egusphere-egu2020-20848 ◽

2020 ◽

Author(s):

Eszter Badenszki ◽

J. Stephen Daly ◽

Martin J. Whitehouse ◽

Brian G. J. Upton

Keyword(s):

Upper Mantle ◽

Solid Phase ◽

Mantle Xenoliths ◽

Solid Phase Reaction ◽

Phase Reaction ◽

Magma Intrusion ◽

Accessory Zircon ◽

Complex Source ◽

Age Constraints

EN-101, a rare albitite [Pl +Fe-Ti oxide +Ap +Zrn] xenolith from Elie Ness, Scottish Midland Valley, is hosted by a c. 290 Ma old alkali basaltic diatreme [1, 2].&#160; EN-101 is considered to belong to the Scottish &#8220;anorthoclasite suite&#8221; comprising xenoliths and megacrysts of various compositions which are interpreted as samples from the upper mantle &#8211; lower crust where they form (syenitic) vein or dyke-like bodies e.g., [3, 4, 5]. The &#8220;anorthoclasite suite&#8221; has been found in all Scottish terranes suggesting that the presumed dyke system must be extensive.Xenoliths of the &#8220;anorthoclasite suite&#8221; primarily consist of Na-rich and Ca-poor feldspar megacrysts, with generally high Na/K ratios [3] that are typically accompanied by accessory zircon, apatite, biotite, magnetite and Fe-rich pyroxene whereas garnet and corundum with Nb-rich oxides are only occasionally present [3, 4, 5]. Upton et al. [4, 5] argued that the parental melt of the &#8220;anorthoclasite suite&#8221; formed though small&#8211;fraction melting of metasomatized mantle and subsequent melt&#8211;solid phase reaction was also involved.&#160; Upton et al. [5] proposed that crystallization of the anorthoclasite suite samples occurred shortly prior to- or contemporaneously with their entrainment. However so far no in-situ dating has been carried out on these samples.Early attempts to date the anorthoclasite suite using zircon and feldspar megacrysts from Elie Ness suggested at least a two-stage formation mechanism, where zircon megacrysts yielded a U-Pb age of c. 318&#160;Ma, while euhedral feldspar xenocrysts are significantly younger and roughly coeval with the host volcanism yielding a K-Ar whole-rock age of c. 294 Ma [6].&#160; In this study we present the first in situ U-Pb dating of zircon, which yielded a concordia age of 328 &#177; 2 Ma (MSWD=0.19; n=12) for EN-101. Zircons &#949;Hf328 values range from +5.2 to +7.5 consistent with a mildly depleted source refreshed by metasomatism. These results may indicate that the proposed extensive syenitic veining within the Scottish upper mantle not only has a complex source [5], but is possibly the result of repeated episodes of magma intrusion.References:<ol><li>Gernon, T.M. et al. 2013 Bulletin of Volcanology. 75:1-20.</li> <li>Gernon, T.M. et al. 2016 Lithos. 264:70-85.</li> <li>Aspen, P. et al. 1990 European Journal of Mineralogy 2:503-17.</li> <li>Upton, B.G.J. et al. 1990 Journal of Petrology.40:935-56.</li> <li>Upton, B.G.J. et al. 2009 Mineral Mag. 73:943-56.</li> <li>Macintyre, R.M. et al. 1981 Transactions of the Royal Society of Edinburgh: Earth Sciences. 72:1-7.</li> </ol>

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Towards the analysis of coral skeletal density-banding using deep learning

SN Applied Sciences ◽

10.1007/s42452-021-04912-x ◽

2022 ◽

Vol 4 (2) ◽

Author(s):

Ainsley Rutterford ◽

Leonardo Bertini ◽

Erica J. Hendy ◽

Kenneth G. Johnson ◽

Rebecca Summerfield ◽

...

Keyword(s):

Neural Network ◽

Traditional Method ◽

Linear Extension ◽

Skeletal Growth ◽

Micro Computed Tomography ◽

Skeletal Density ◽

X Ray ◽

3D Space ◽

Density Banding ◽

Growth Banding

AbstractX-ray micro–computed tomography (µCT) is increasingly used to record the skeletal growth banding of corals. However, the wealth of data generated is time consuming to analyse for growth rates and colony age. Here we test an artificial intelligence (AI) approach to assist the expert identification of annual density boundaries in small colonies of massive Porites spanning decades. A convolutional neural network (CNN) was trained with µCT images combined with manually labelled ground truths to learn banding-related features. The CNN successfully predicted the position of density boundaries in independent images not used in training. Linear extension rates derived from CNN-based outputs and the traditional method were consistent. In the future, well-resolved 2D density boundaries from AI can be used to reconstruct density surfaces and enable studies focused on variations in rugosity and growth gradients across colony 3D space. We recommend the development of a community platform to share annotated images for AI.

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Annual internal growth banding and life history of the ocean quahog Arctica islandica (Mollusca: Bivalvia)

Marine Biology ◽

10.1007/bf00420964 ◽

1980 ◽

Vol 57 (1) ◽

pp. 25-34 ◽

Cited By ~ 106

Author(s):

I. Thompson ◽

D. S. Jones ◽

D. Dreibelbis

Keyword(s):

Life History ◽

Arctica Islandica ◽

History Of ◽

Growth Banding

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Annual growth banding in a cave stalagmite

Nature ◽

10.1038/364518a0 ◽

1993 ◽

Vol 364 (6437) ◽

pp. 518-520 ◽

Cited By ~ 167

Author(s):

Andy Baker ◽

Peter L. Smart ◽

R. Lawrence Edwards ◽

David A. Richards

Keyword(s):

Annual Growth ◽

Growth Banding

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Microscopic analysis of magmatic crystals - Part 2: A SEM study of the stability of accessory zircon under increasing metamorphic conditions

Microscopy Today ◽

10.1017/s1551929500061228 ◽

2007 ◽

Vol 15 (5) ◽

pp. 36-39

Author(s):

Robert Sturm

Keyword(s):

Physical Stability ◽

Microscopic Analysis ◽

Metamorphic Rocks ◽

High Grade ◽

Mineral Phase ◽

Accessory Zircon ◽

Operating Field ◽

Sem Study ◽

The Stability

This contribution is a continuation of a previously published work in Microscopy Today that described the microscopic analysis of magmatic crystal growth by the example of accessory zircon. Zircon does not only represent a remarkable mineral phase concerning its crystallization out of the magmatic melt, but has also other interesting characteristics, one of which is the rather high physical stability of zircon allowing a determination of the mineral—even in high-grade metamorphic rocks. The changes of zircon from low- to high-grade deformation are very noticable and therefore offer an interesting operating field for electron microscopy. Since crystal microscopy and its specific fascination cannot often be found in a microscopy magazine, it is assumed that the article would awake the interest of the readers.

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