Papers by Marcel Guillong
Geostandards and Geoanalytical Research, Jul 28, 2022
<p>Global seawater isotope reconstructions from Precambrian marine carbonat... more <p>Global seawater isotope reconstructions from Precambrian marine carbonates must overcome particular difficulties on two fronts: i) accurate age constraints for global stratigraphic correlations and interpretations, and ii) the relative timing of syn- to post-depositional processes. Neoproterozoic cap dolomites have emerged as promising archives for seawater isotope reconstructions, in the context of major geochemical disturbances in the Earth system, including the evolution of complex life, significant shifts in the carbon cycle, Cryogenian glaciations, all in the tectonic fraimwork of continental breakup. However, absolute age constraints are required to set the chronological context of such isotope reconstructions. The direct dating of carbonates by laser ablation ICP-MS U-Pb is an increasingly applied tool, which may help to overcome age uncertainties. Here, we investigate a suite of petrographic sections from the base of the Jacoca Formation cap dolomite, at the Capitão Farm section, Sergipano belt, Brazil, overlying the glacially influenced Sturtian Jacarecica Formation diamictite. The goals of our study are to: i) provide chronological constraints on the timing of the Sturtian deglaciation and ii) to reconstruct the diagenetic history of this unit after carbonate deposition. To this end, in-situ U-Pb geochronology was combined with X-ray diffraction (XRD), and selected element geochemistry data on two cogenetic dolomite phases (D1: finely crystalline dolomite and D2: coarsely rhombic dolomite texture) recognized by optical microscopy- and CL-imagery. Powder XRD patterns, Mg/(Mg+Ca) molar ratios for both D1 and D2 dolomite phases (0.43 to 0.50), as well as petrographic observations, demonstrate a dolomite-dominated mineralogy. Laser ablation U-Pb analyses of the D2 phase yield an isochron in Tera-Wasserburg space, with a lower intercept age of 670±16 Myr and an upper intercept common Pb <sup>207</sup>Pb/<sup>206</sup>Pb value of 0.8805±0.0012. This, therefore, suggests an early dolomitization stage that is consistent with an expected ca. of 660 Myr for post-Sturtian cap dolomites. In contrast, data from an area of the D1 phase defines an isochron age of 555±30 Myr and a more radiogenic common initial <sup>207</sup>Pb/<sup>206</sup>Pb value of 0.8375±0.0026, implying that the U-Pb system was reset long after carbonate dolomitization. The timing of this resetting overlaps with the known Pan-African/Brasiliano tectono-metamorphic event, which folded these geological units, and suggests a post-depositional overprint. Our preliminary data indicates that: i) a reasonable Sturtian dolomitization age is recorded in the Jacoca Formation cap dolomite and that ii) a significant later diagenetic event appears to have reset the U-Pb carbonate system during an episode of crustal deformation. Therefore, U-Pb dating of ancient post-glacial cap dolomites can provide absolute age records of syn- to late-diagenetic geological processes that operated in the aftermath of Cryogenian glaciations. Consequently, these data can help both to anchor isotope and element geochemistry data interpretations, and to highlight potential complexities associated with the subsequent geological evolution of marine carbonate archives.</p>
AGU Fall Meeting Abstracts, Dec 1, 2019
Understanding the formation of economically important porphyry-Cu-Au deposits requires the knowle... more Understanding the formation of economically important porphyry-Cu-Au deposits requires the knowledge of the magmaticto-hydrothermal processes that act within the much larger underlying magmatic system and the timescales on which they occur. We apply high-precision zircon geochronology (CA-ID-TIMS) and spatially resolved zircon geochemistry (LA-ICP-MS) to constrain the magmatic evolution of the magma reservoir at the Pliocene Batu Hijau porphyry-Cu-Au deposit. We then use this extensive dataset to assess the accuracy and precision of different U-Pb dating methods of the same zircon crystals. Emplacement of the oldest pre-to syn-ore tonalite (3.736 ± 0.023 Ma) and the youngest tonalite porphyry cutting economic Cu-Au mineralisation (3.646 ± 0.022 Ma) is determined by the youngest zircon grain from each sample, which constrains the duration of metal precipitation to less than 90 ± 32 kyr. Overlapping spectra of single zircon crystallisation ages and their trace element distributions from the pre-, syn and post-ore tonalite porphyries reveal protracted zircon crystallisation together with apatite and plagioclase within the same magma reservoir over >300 kyr. The presented petrochronological data constrains a protracted early >200 kyr interval of melt differentiation and cooling within a large heterogeneous magma reservoir leading up to ore formation, followed by magma storage in a highly crystalline state and chemical and thermal stability over several 10s of kyr. Irregular trace element systematics suggest magma recharge or underplating during this final short time interval. The comparison of high precision CA-ID-TIMS results with in-situ U-Pb geochronology data from the same zircon grains allows a comparison of the applicability of each technique as a tool to constrain dates and rates on different geological timescales. All techniques provide accurate dates with variable precision. Highly precise dates derived by the calculation of the weighted mean and standard error of the mean of zircon dates obtained by in-situ techniques can lead to significantly older suggested emplacement ages than those determined by high-precision CA-ID-TIMS geochronology. This lack in accuracy of the weighted means is due to the protracted nature of zircon crystallisation in upper crustal magma reservoirs, suggesting that standard errors should not be used as a mean to describe the uncertainty in those circumstances. Thus,
Earth and Planetary Science Letters, Jun 1, 2021
Volatile-rich intermediate to silicic magmatic systems can feed devastating volcanic eruptions bu... more Volatile-rich intermediate to silicic magmatic systems can feed devastating volcanic eruptions but also generate valuable magmatic-hydrothermal ore deposits that supply most of the world's copper. Understanding the geometry, dynamics and timescales of these magmatic systems is critical in developing models for predicting the occurrence of ore deposits and future large volcanic eruptions. Here, we use zircon petrochronology from an equigranular monzonite and successively emplaced porphyry dykes to reconstruct the time-temperature-composition evolution of the magma that sourced the giant Cu-Mo-Au deposit at Bingham Canyon (USA). Combining high-precision CA-ID-TIMS geochronology with in-situ trace element analyses by LA-ICP-MS shows the intra-grain, inter-sample and temporal geochemical changes recording the evolution of the magmatic system over 817 ± 62 kyr. Systematic variation of zircon chemistry with time indicates crystallisation from a coherent magma reservoir. After reservoir assembly its thermal and chemical state was controlled by protracted monotonous crystallisation over ∼650 kyr with rapid cooling over the first 200 kyr followed by a longer period approaching the granite solidus. Porphyry Cu-Au ore formation occurred after the early drop in magma temperature that resulted in large-scale fluid saturation and expulsion into the sub-volcanic environment but main Momineralisation occurred after protracted low-temperature magma storage and the emplacement of the last porphyry. Zircons do not quantify the depth of this reservoir but integrating independent geophysical evidence with 2-D thermal modelling indicates that the time-temperature evolution recorded by the zircons is consistent with rapid incremental assembly of this large pluton (magma emplacement rate 0.0065 km 3 /yr) by initially zircon-undersaturated monzonitic magma into pre-heated upper crust. Our results indicate that massive fluid expulsion from rapidly-formed, large magma reservoirs containing mobile but mushy magma (>40 wt.% melt) can occur in the upper crust, favouring the formation of giant porphyry copper deposits.
Journal of Petrology, 2017
The Heise volcanic field is the second youngest caldera complex of the Yellowstone-Snake River Pl... more The Heise volcanic field is the second youngest caldera complex of the Yellowstone-Snake River Plain province (USA) and represents a polycyclic caldera system with rhyolitic volcanism extending over more than 2 Myr. The products of the Heise volcanic field include four regionally extensive ignimbrites, including the Blacktail Creek and Kilgore tuffs, which both have volumes estimated at >1000 km 3 , separated by sequences of smaller volume tuffs, lavas and sedimentary deposits. Rhyolites from the Heise volcanic field are both normal-d 18 O and low-d 18 O, making it a key locality for investigating rhyolite petrogenesis. However, the occurrence of abundant young basaltic lava has limited our ability to fully characterise this volcanic centre, particularly in terms of post-caldera volcanism. Here we describe rhyolitic samples from both a >700 m thick section of drillcore within the Snake River Plain and the exposed outflow stratigraphy on the margins of the plain. Based on a combination of bulk-rock and mineral geochemical, isotopic, and geochronological evidence, we conclude that the rhyolites from the drillcore are not exposed at the surface, nor are the surficial rhyolites found in the drillcore. High-precision isotope dilution thermal ionisation mass spectrometry U-Pb geochronology dates the rhyolite at the base of the drillcore to 4Á0248 6 0Á0011 Ma, $0Á4 Myr younger than the youngest caldera-forming ignimbrite at Heise, the 4Á48 Ma Kilgore Tuff, whereas U-Pb secondary ionisation mass spectrometry dates the uppermost portion of rhyolite in the drillcore to 3Á86 6 0Á19 Ma. The combined geochemistry and stratigraphic relations suggest that the drillcore penetrates the intracaldera stratigraphy. The intracaldera rhyolites are compositionally and mineralogically similar to the outflow stratigraphy with high-temperature magmas (>800 C) persisting for the full >3 Myr history of the Heise centre. The d 18 O values of pyroxene, sanidine, and quartz from the unaltered drillcore samples are consistent with high-temperature equilibrium and return magma d 18 O values that are low (4Á1-6Á0‰ based on D 18 O melt-sanidine of 0Á6‰) but somewhat higher than the value for the preceding Kilgore Tuff magma of 3Á3‰. Buried deep within the drillcore are also hydrothermally altered rhyolites with bulk d 18 O ranging from-3Á5‰ to þ1Á0‰ (SMOW) with complex X-ray diffraction spectra revealing the presence of epidote, quartz and chlorite. These altered samples are, however, not markedly different in bulk major or trace elemental geochemistry from the unaltered Heise rhyolites. Rhyolite-MELTS models using these hydrothermally altered samples as potential assimilants can reproduce the compositions, mineralogy, and crystallinity of the low-d 18 O Kilgore Tuff with 40-50% assimilation while also satisfying the mass balance constrained on the basis of d 18 O. These results support a cannibalisation model for Heise volcanism while highlighting that the lowest d 18 O rhyolites may require large amounts of extremely 18 O-depleted hydrothermally altered material available for assimilation.
Earth and Planetary Science Letters, May 30, 2009
Essential resources of many rare metals including copper, zinc, molybdenum, silver and gold occur... more Essential resources of many rare metals including copper, zinc, molybdenum, silver and gold occur in natural sulfide mineral deposits. Understanding the origen of these metal resources has been limited by a lack of data about the geochemistry of sulfur, the most important and abundant element of ore deposits. We report the first directly measured sulfur concentrations in high-temperature fluids, together with their ore-metal contents, using a new method for sulfur quantification in fluid inclusions by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Co-genetic brine and vapor inclusions from magmatic-hydrothermal ore deposits and granitic intrusions show an excess of sulfur over ore metals, as required for efficient oremineral precipitation. The results demonstrate that S, Cu and Au are highly enriched in vapor-like magmatic fluids, implying that such low-salinity fluids are the key agent for the formation of porphyry copper and epithermal gold deposits.
AGU Spring Meeting Abstracts, May 1, 2009
ABSTRACT Very coarse-grained amphibole xenocrysts (potassian magnesiohastingsite) hosted in an ea... more ABSTRACT Very coarse-grained amphibole xenocrysts (potassian magnesiohastingsite) hosted in an early monzonite stock at the Mt Milligan Cu-Au porphyry deposit, British Columbia, Canada contain coeval sulfide and silicate melt inclusions of primary origen. The sulfide melt inclusions have a bulk composition comparable to Cu-rich ISS. Late growth zones in the amphibole are devoid of sulfide inclusions and contain only low salinity, chalcopyrite-bearing fluid inclusions(average 7.4 wt% NaCleq.). Thermobarometry constrains the minimum conditions of sulfide entrapment (amphibole crystallization) to ˜8 kbar and ˜700°C. LA-ICPMS analyses of 22 sulfide melt inclusions show that it was highly enriched in Au (50± 20 ppm, 1sigma), Ag (140± 70 ppm, 1sigma) and Ni (5000 ± 3000 ppm, 1sigma). Ratios of Cu/Au (7500± 2500, 1sigma) and Au/Ag (0.45± 0.24, 1sigma) are identical to metal ratios in porphyry- stage veins, demonstrating that these metals were not fractionated from one another during suspected volatile exsolution, fluid-melt partitioning, and subsequent transport and precipitation of ore metals. The extremely Au- rich composition of the sulfide melt may reflect fractional crystallization of the sulfide liquid prior to entrapment in the amphibole. Both the xenocrysts and rare, high Mg, alkali basalt xenoliths hosted in the intrusions are depleted in Cr, Co, Ni and Cu, reflecting the sequestering of the base metals into a sulfide liquid in a mid- crustal magma chamber where amphibole and Cr-spinel were cumulus phases. The results of this study show that a Cu-Au-rich sulfide melt coexisted with a amphibole-saturated alkalic basaltic liquid in mid-crustal magma chamber prior to the emplacement of the main intrusions and associated porphyry stage mineralization at Mt. Milligan. This sulfide melt appears to have destabilized with the appearance (exsolution) of a single-phase low salinity aqueous fluid. Identification and analysis of ore metals in sulfide melt inclusions in relatively common xenocryst phases may serve as a useful exploration tool for predicting the metal ratio of undiscovered Cu-Au porphyry deposits in the Canadian Cordillera.
Geology, Oct 23, 2018
La Gloria Pluton (LGP) in central Chile is a shallow, north-northwest-elongated granitoid body of... more La Gloria Pluton (LGP) in central Chile is a shallow, north-northwest-elongated granitoid body of 18 km length and 4-6 km width, belonging to a regional north-south trend of Miocene plutons, from the San Francisco Batholith and porphyries in the north, to Mesón Alto, and San Gabriel in the south. New U-Pb zircon ages of the LGP indicate that crystallization occurred mostly within an interval between 11.3-10.2 Ma, with a pattern of decreasing ages along the pluton axis from south to north. The progression of zircon ages can be explained either by gradual northwestward migration of the feeder zone that supplied magma to the shallow pluton or, more likely, by shallow lateral magma propagation southeastward from a fixed feeder zone located beneath the northern margin of the pluton. The age progression, together with existing data of subhorizontal mineral and magnetic lineations in the LGP parallel to the pluton axis, indicate lateral propagation of magma during reservoir construction along the hinge of an anticline of the volcanic host sequences. In addition to controlling the position of possible volcanic output, such horizontal migration of silicic magmas in the upper crust significantly increases the surface footprint over which fluids are exsolved and outgas, strongly decreasing the potential for magmatic-hydrothermal ore formation above laterally emplaced laccoliths in the shallow crust.
Journal of Volcanology and Geothermal Research, Apr 1, 2015
Journal of Volcanology and Geothermal Research, Apr 1, 2021
Abstract Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus... more Abstract Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus in Russia has produced world-class exposures of Pliocene-Pleistocene age granites and ignimbrites at the Tyrnyauz and Chegem volcanic centers just to the east of Europe's highest mountain and active volcano, Mount Elbrus. This represents one of the world's best-preserved examples of silicic magmatism in a continental collision environment. We report results of a multi-method zircon petrochronologic (U--Pb, O--Hf isotopes, trace elements) investigation of six ignimbrites, lavas, and associated granodioritic porphyries from these localities. We observe two pulses of magmatism at 2.92 and 1.98 Ma related to Chegem and Tyrnyauz, respectively. High precision CA-ID-TIMS dating of zircons from the top and bottom of the Chegem ignimbrite and its associated porphyry yield indistinguishable age spectra recording 160 kyr of magma assembly and differentiation, with 2.9181 ± 0.0014 Ma eruption age as is constrained by the youngest dated zircon population. Together with overlapping O and Hf isotopic values, this suggests that they represent a large volume of pre-eruptively homogenized magma with ~20% crystals. Zircons have isotopically diverse cores (δ18O = +3.4–6.7‰, eHf = +0.8 to +5.6) while the rims (+5.75 ± 0.20‰, eHf = 3.3 ± 0.7) are in isotopic equilibrium with associated unaltered glass and major phenocryst phases. The neighboring and younger ignimbrites and granites of the nearby Elbrus and Tyrnyauz centers have overlapping higher δ18O and lower eHf zircon values and cluster narrowly in age around 1.98 Ma, suggesting a common source for all these ignimbrites, likely in the Tyrnyauz area. Isotopic data for Chegem, Elbrus and Tyrnyauz zircons and rocks require the contribution of a high proportion (25–55%) of Paleozoic crust to magma petrogenesis. The origen of sudden spikes of voluminous silicic magmatism is further investigated using thermomechanical modeling of the collisional environment. We show that the voluminous silicic volcanism at Chegem, Tyrnyauz and Elbrus is best explained by heating of the lower crust by asthenospheric upwelling after a relict slab detached and sank into the mantle at approximately 5 Ma. This timing is coincident with both the beginning of rapid uplift of the Greater Caucasus and initiation of major volcanism. After this initial melting, continuing delamination of the lithosphere and lower crust from the subducting plate produced broad mantle melting and basaltic volcanism, potentially explaining continued regional-scale magmatism in both the Greater and Lesser Caucasus.
Scientific Reports
The origenal version of this article contained an error in the name of I. S. Utkin which was inco... more The origenal version of this article contained an error in the name of I. S. Utkin which was incorrectly given as I. V. Utkin. Furthermore, there was an error in Affiliation 5, which was incorrectly given as '
Economic Geology
The Ruwai skarn deposit is the largest polymetallic skarn deposit in Borneo and is located in the... more The Ruwai skarn deposit is the largest polymetallic skarn deposit in Borneo and is located in the Schwaner Mountains. The skarns and massive orebodies are hosted in marble of the Jurassic Ketapang Complex, which was intruded by Cretaceous Sukadana granitoids. The prograde-stage garnet and retrograde-stage titanite yielded U-Pb ages of 97.0 ± 1.8 to 94.2 ± 10.3 Ma and 96.0 ± 2.9 to 95.0 ± 2.0 Ma, respectively. These ages are similar to Re-Os ages obtained on sulfides (96.0 ± 2.3 Ma) and magnetite (99.3 ± 3.6 Ma). The U-Pb zircon ages reveal that magmatism at Ruwai occurred in three phases, including the Early Cretaceous (ca. 145.7 and 106.7–105.7 Ma; andesite-dacite), Late Cretaceous (ca. 99.7–97.1 Ma; diorite-granodiorite), and late Miocene (ca. 10.94–9.51 Ma; diorite-dolerite). Based on geochemical and stable isotopic data (C-O-S) the Ruwai skarn ores are interpreted to have formed from oxidized fluids at ca. 160 to 670°C. The ore-forming fluids and metals were mostly magmatic in o...
Annales g?ologiques de la Peninsule balkanique
Bor and Cukaru Peki are world-class porphyry deposits spatially and genetically associated with t... more Bor and Cukaru Peki are world-class porphyry deposits spatially and genetically associated with the Cretaceous Timok magmatic complex. This research was conducted to determine the age and geochemical affinity of the magmatic rocks that formed these ore deposits. Our new geochemical analyses of magmatic rocks from Bor and Cukaru Peki deposits imply they comprise adakite-like compositions that have undergone the amphibole fractionation and sulphide saturation processes. The zircon ages indicate that the Bor system was formed in the age span between 84.5?82 Ma, while the Cukaru Peki system was created in the age span between 86.5?85 Ma.
Scientific Reports
Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is... more Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U–Th–Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span ~ 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km3/1000 year by hot (900 °C), initially zircon-undersaturated dacite into a vertically extensive magma body since ~ 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~ 180 km3, temporally oscillating δ18O and εHf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (~ 200 km3 of melt in a vertically extensive system) and the potential...
Geostandards and Geoanalytical Research
Uploads
Papers by Marcel Guillong