On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

Here we present titanite U-Pb dates from two banded calc silicate gneisses (SSP18-1A and 1B) from western Maine. Mineral textures and compositions display multiple phases of metamorphism. The peak lower granulite facies assemblage is Di + Kfs + Pl + Ttn, with little to no calcite present. Late Czo + Tr replaces Di + Pl, suggesting an influx of XH2O > 0.90 fluids. Nearby metapelites show the transition from sillimanite-bearing to muscovite-bearing assemblages, indicating that fluid infiltration may be widespread. Compositional maps of clinopyroxene in SSP18-1B show fracturing and rehealing of early Fe-rich diopside with late Mg-rich diopside. Both samples exhibit overprinting of An-rich plagioclase by increasingly Ab-rich plagioclase. Titanite grains in both samples exhibit BSE textures and compositional variation consistent with multiple phases of growth and dissolution-reprecipitation reactions.Titanite trace element and U-Pb data were collected by LA-ICP-MS at the University of Maine using an ESI NWR193UC excimer laser ablation system coupled to an Agilent 8900 ICP-MS. Single spot ages range from 280 to 400 Ma with 12-20 Ma propagated 2SE. Four composition-date domains are identified in SSP18-1B: A. 400 &#177; 8 Ma (dark BSE cores), B. 372 &#177; 4 Ma (bright BSE cores), C. 342 &#177; 6 Ma (bright BSE cores, no Eu anomaly), and D. 302 &#177; 3 Ma (dark BSE rims, low LREE). Titanite Fe and Y concentrations increase with decreasing date, whereas Sr concentrations decrease. In clinopyroxene, Fe and Y decrease between high Fe-diopside and late Mg-diopside, placing the fracturing and rehealing events between 400 and 372 Ma. Strontium concentrations in titanite decrease between subsequent generations of plagioclase, diopside, and titanite, suggesting a continual fractionation of Sr from the reactive bulk composition. Low LREE in ca. 300 Ma titanite domains in both samples are consistent with the formation of texturally late allanite and clinozoisite, thus constraining the timing of the high XH2O fluid infiltration event. Zr-in-titanite temperatures for rims in the quartz-bearing SSP18-1B give a weighted mean T of 764 &#176;C at 4.5 GPa, consistent with the muscovite-absent sillimanite-bearing assemblage in garnet cores from metapelite samples. However, the 100-150 &#176;C lower Grt-Bt temperatures for metapelites are not consistent with peak metamorphic phase equilibria. Our data demonstrate the utility of linking titanite textures and trace element concentrations with those of other minerals to reveal past metamorphic and deformational events. Additionally, we show that titanite may reliably preserve U and Pb isotopic ratios, trace elements, and textures over subsequent high-T metamorphic events.

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Petrology, phase equilibria modelling, and in situ zircon and monazite geochronology of ultrahigh-temperature granulites from the khondalite belt of southern India

Lithos ◽

10.1016/j.lithos.2019.105195 ◽

2019 ◽

Vol 348-349 ◽

pp. 105195 ◽

Cited By ~ 2

Author(s):

Bing Yu ◽

M. Santosh ◽

Shan-Shan Li ◽

E. Shaji

Keyword(s):

Phase Equilibria ◽

Southern India ◽

Ultrahigh Temperature ◽

Khondalite Belt

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Hybrid phase equilibria modelling with conventional and trace element thermobarometry to assess the P–T evolution of UHT granulites: An example from the Highland Complex, Sri Lanka

Journal of Metamorphic Geology ◽

10.1111/jmg.12569 ◽

2020 ◽

Author(s):

Prasanna L. Dharmapriya ◽

Sanjeewa P. K. Malaviarachchi ◽

Andrea Galli ◽

Leo M. Kriegsman ◽

Yasuhito Osanai ◽

...

Keyword(s):

Sri Lanka ◽

Phase Equilibria ◽

Trace Element

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Effects of feeding ultrahigh-temperature (UHT)-treated infant formula with different protein concentrations or powdered formula, as compared with breast-feeding, on plasma amino acids, hematology, and trace element status

American Journal of Clinical Nutrition ◽

10.1093/ajcn/68.2.350 ◽

1998 ◽

Vol 68 (2) ◽

pp. 350-356 ◽

Cited By ~ 23

Author(s):

B Lönnerdal ◽

O Hernell

Keyword(s):

Amino Acids ◽

Trace Element ◽

Infant Formula ◽

Breast Feeding ◽

Plasma Amino Acids ◽

Trace Element Status ◽

Ultrahigh Temperature

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The South Qôroq Centre nepheline syenites, South Greenland. Petrology, felsic mineralogy and petrogenesis

Bulletin Grønlands Geologiske Undersøgelse ◽

10.34194/bullggu.v118.6660 ◽

1976 ◽

Vol 118 ◽

pp. 1-55

Author(s):

D Stephenson

Keyword(s):

Phase Equilibria ◽

Trace Element ◽

Experimental System ◽

Alkali Feldspar ◽

Continuous Series ◽

Small Range ◽

The South ◽

Outward Diffusion ◽

Co Precipitation ◽

Ring Dyke

The South Qoroq Centre is one of four high-level, major intrusive centres comprising the Igaliko Nepheline Syenite Complex. Three elliptical stocks of foyaite were emplaced in fairly rapid succession by ring fracture and block subsidence, followed by a partial ring· dyke of augite syenite. Inward-dipping microsyenite sheets appear to be associated with the ring-dyke; and four earlier, satellitic stocks occur around the periphery of the centre. Petrographic and mineralogical data show that the intrusions become successively less differentiated with time. Felsic mineral phases (alkali feldspar, nepheline and sodalite) constitute over 80% of most rocks from the centre. Electron-microprobe analyses demonstrate the major role of felsics in the fractionation of the magma and, together with estimates of feldspar structural state from 2V measurements, give indications of the history and conditions of crystallisation. Nepheline compositions fall within a small range of decreasing Si content, but are outside the Morozewicz-Buerger convergence field and are not affected by sub-solidus alkali exchange. Feldspars form a continuous series from Or1Ab67An32 to a K-enriched alkali feldspar Or72Ab28An0. From comparison with other rock suites, this extended feldspar trend seems to be associated with the co-precipitation of nepheline, and increasing peralkalinity of the magma. Major and trace element analyses of the rocks, made by X-ray fluorescence, give variation trends which may be interpreted mainly in terms of fractionation of feldspar and the ferromagnesian phases. In particular, trace element distributions are highly characteristic of fractional crystallisation series, but may not be compatible with fractional melting. Analyses of rocks with co-existing felsic phases compare favourably with phase equilibria in the experimental system Q-ne-ks at 1kb. It is suggested that the centre evolved from an underlying differentiated magma chamber, formed by crystal fractionation and accumulation. Successively lower portions of the chamber were tapped, producing batches of fractionated magma. Later stages of crystallisation were influenced by a build-up in volatiles consisting of H2O, CO2, Cl and F, and post-emplacement differentiation was implemented mainly by outward diffusion of these volatiles together with alkalis under a thermal diffusion gradient. Temperatures of crystallisation deduced from the nepheline geothermometer (Hamilton, 1961) and from phase equilibria in the Ab-Or-H2O system are in reasonable agreement. Assuming a PH2O of about 1 kb, the foyaite feldspars crystallised at about 850°C and augite syenite feldspars slightly higher. Nephelines commenced crystallisation within the range 900-850°C but stabilised at 775-700°C irrespective of rock-type. Physico-chemical conditions during recrystallisation attributable to the later Igdlerfigssalik Centre are inferred from textural, geochemical and mineralogical changes. The recrystallised rocks provide evidence for the behaviour of trace elements during the initial stages of remelting under hydrous conditions in an open system.

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Phase equilibria testing of a multiple pulse mechanism for origin of mafic–ultramafic intrusions: a case example of the Shiant Isles Main Sill, NW Scotland

Geological Magazine ◽

10.1017/s0016756809006499 ◽

2009 ◽

Vol 146 (6) ◽

pp. 851-875 ◽

Cited By ~ 15

Author(s):

RAIS LATYPOV ◽

SOFYA CHISTYAKOVA

Keyword(s):

Phase Equilibria ◽

Fractional Crystallization ◽

Single Case ◽

Bulk Composition ◽

Single Pulse ◽

Olivine Phenocryst ◽

Relative Volume ◽

Compositional Profile ◽

Magma Pulses ◽

Large Pulse

AbstractIn this paper we examine the role of multiple emplacement of sills into partly solidified rocks (an intrusive mechanism ‘liquid into solid’) as a possible explanation for some textural and compositional ‘anomalies’ of single-cyclic mafic intrusions. As a case study we used the Shiant Isles Main Sill that is widely regarded as a classical example of a multiple, picrite–picrodolerite–crinanite alkaline sill. This sill is currently interpreted as having been formed by several olivine phenocryst-rich pulses of magma, which were successively emplaced into their almost solidified predecessors. Such an intrusive mechanism is a random process in which many parameters vary independently and unpredictably. Among them are: the number, relative volume and bulk composition of magma pulses, and their place, sequence and timing of emplacement, as well as modal abundance, phase composition and distribution of intratelluric phenocrysts in magmas upon emplacement. In terms of these variables, one can envisage countless different profiles through alkaline sills produced from only three randomly intruded magma pulses of picritic, picrodoleritic and crinanitic composition. Such multiple sills can readily be distinguished from simple ones formed from a single pulse of magma by anomalous compositional profiles with several prominent breaks in crystallization and compositional sequences. The compositional profile of the Shiant Isles Main Sill is remarkably similar to an M-shaped profile expected from fractional crystallization of a single pulse of olivine-saturated magma along a crystallization path Ol+Sp+L (picrite), Ol+Pl±Sp+L (picrodolerite = troctolite), Ol+Pl+Cpx+L (crinanite). The probability of the accidental formation of such a compositional profile by multiple intrusion ‘liquid into solid’ is exceedingly small, even for the single case of the Shiant Isles Main Sill. The probability approaches zero when considering that exactly the same sequence of intrusive events must have been repeated in about 20 neighbouring alkaline sills with similar compositional profiles. This can only be achieved by some universally operating differentiation process. The best candidate for this is the classical fractional crystallization of magma constrained by liquidus phase equilibria. This suggests that the Shiant Isles Main Sill can be best interpreted and modelled as a simple sill that crystallized from one large pulse of magma, with possible involvement of minor refilling events. Further progress in our knowledge of intrachamber magma fractionation processes will probably enable us to interpret many ‘anomalous’ textural and compositional features of mafic–ultramafic intrusions in the frame of a single magma pulse model.

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Geological, Mineralogical and Textural Impacts on the Distribution of Environmentally Toxic Trace Elements in Seafloor Massive Sulfide Occurrences

Minerals ◽

10.3390/min9030162 ◽

2019 ◽

Vol 9 (3) ◽

pp. 162 ◽

Cited By ~ 4

Author(s):

Emily Fallon ◽

Matthias Frische ◽

Sven Petersen ◽

Richard Brooker ◽

Thomas Scott

Keyword(s):

Trace Elements ◽

Trace Element ◽

Current Knowledge ◽

Trace Element Distribution ◽

Potentially Toxic Metals ◽

Potential Toxicity ◽

Toxic Trace Elements ◽

Oxidation Rates ◽

Wide Range ◽

Tectonic Settings

With mining of seafloor massive sulfides (SMS) coming closer to reality, it is vital that we have a good understanding of the geochemistry of these occurrences and the potential toxicity impact associated with mining them. In this study, SMS samples from seven hydrothermal fields from various tectonic settings were investigated by in-situ microanalysis (electron microprobe (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)) to highlight the distribution of potentially-toxic trace elements (Cu, Zn, Pb, Mn, Cd, As, Sb, Co, Ni, Bi, Ag and Hg) within the deposits, their minerals and textures. We demonstrate that a combination of mineralogy, trace element composition and texture characterisation of SMS from various geotectonic settings, when considered along with our current knowledge of oxidation rates and galvanic coupling, can be used to predict potential toxicity of deposit types and individual samples and highlight which may be of environmental concern. Although we cannot quantify toxicity, we observe that arc-related sulfide deposits have a high potential toxicity when compared with deposits from other tectonic settings based on their genetic association of a wide range of potentially toxic metals (As, Sb, Pb, Hg, Ag and Bi) that are incorporated into more reactive sulfosalts, galena and Fe-rich sphalerite. Thus, deposits such as these require special care when considered as mining targets. In contrast, the exclusive concern of ultra-mafic deposits is Cu, present in abundant, albeit less reactive chalcopyrite, but largely barren of other metals such as As, Pb, Sb, Cd and Hg. Whilst geological setting does dictate metal endowment, ultimately mineralogy is the largest control of trace element distribution and subsequent potential toxicity. Deposits containing abundant pyrrhotite (high-temperature deposits) and Fe-rich sphalerite (ubiquitous to all SMS deposits) as well as deposits with abundant colloform textures also pose a higher risk. This type of study can be combined with “bulk lethal toxicity” assessments and used throughout the stages of a mining project to help guide prospecting and legislation, focus exploitation and minimise environmental impact.

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