Geology topics

Urs Schaltegger

Publications and source records attributed to Urs Schaltegger.

4 recordsLinked to original sources

USGS2026

Trace element heterogeneity and crystallization history of the Plesovice zircon: Implications for its use as a U–Pb LA-ICP-MS reference material

Zircon crystals from Plešovice hyperpotassic granulite (HPG) have been widely used as a reference material for LA-ICP-MS dating. Detailed cathodoluminescence (CL) imaging and trace element analysis reveal a complex internal structure of Plešovice zircon linked to extreme chemical heterogeneity, which allows us to distinguish different zircon domains formed during its crystallization: (i) rare low-CL cores enriched in U, Nb, HREE and Y; (ii) dominant sector-zoned to oscillatory-zoned domains, and (iii) CL-bright rims poor in trace elements. Relic fine oscillatory zoned areas are chemically homogeneous, whereas coarsened and blurred areas, and CL-dark replacement domains, are heterogeneous. Based on these data we suggest a complex and protracted zircon evolution: (i) crystallization of metamorphic zircon in anatectic calc-alkaline granulite; (ii) magmatic zircon crystallization at high temperature and pressure in a dry ultrapotassic melt at presence of peritectic garnet; (iii) coupled zircon dissolution-precipitation processes triggered by percolating hydrous residual melt; and (iv) coarsening and replacement of the pre-existing zircon due to prolonged exposure to a reactive fluid/hydrous melt. New CA-ID-TIMS U Pb dates between 337.167 ± 0.080 and 337.840 ± 0.080 Ma confirm crystallization age for HPG zircon at around 337.4 Ma and suggest that previously published dates of 336.37 Ma were biased by non-mitigated lead loss. We thus confirm the U/Pb homogeneity of Plešovice reference zircon despite its chemical heterogeneity. We further discuss the implications of using the chemically extremely heterogeneous Plešovice reference zircon as primary or secondary standard for in-situ LA-ICP-MS geochronology, in particular for quantification of the chemical matrix-dependence of the relative sensitivity factor ( β ) of laser ablation.

Plešovice quarry↗

USGS2024

Using stochastic point pattern analysis to track regional orientations of magmatism during the transition to cenozoic extension and Rio Grande rifting, Southern Rocky Mountains

The southern Rocky Mountains in Colorado and northern New Mexico hosted intracontinental magmatism that developed during a tectonic transition from shortening (Laramide orogeny, ca. 75 to 40 Ma) through extension and rifting. We present a novel approach that uses stochastic weighted bootstrap simulations of a large set of new and historical geochronology data to better understand how regional anisotropies responsible for focusing magma emplacement evolved through time. This technique can detect subtle trends in directional distributions, including multi-modal orientations, and can be filtered from regional to local scales. Our results indicate that magmatism followed first the northeast trend of the Colorado mineral belt between 75 and 40 Ma and deviated afterward. These deviations vary depending on the scale of the analysis. At the smallest scale we evaluated (<75 km), the orientation of magmatism from 45 to 30 Ma rotated counter-clockwise before aligning with the north-south trend of the modern Rio Grande rift. Larger, regional-scale analyses indicate magma centers between 40 to 35 Ma and 25 to 20 Ma were dominantly oriented southwest-northeast, whereas magmatism between 35 and 25 Ma had north-south orientation. The large areal footprint of magmatism and shifting regional patterns suggest that ancient zones of weakness in the North American lithosphere accommodated magma flow at different moments in time, rather than controlled by a retreating interface of the Farallon and North American plates.

Tectonics↗

USGS2023

Tracing magmatic genesis and evolution through single zircon crystals from successive supereruptions from the Socorro Caldera Complex, USA

Large volume rhyolitic ignimbrite volcanism is a significant contributor to the evolving crust. The introduction of high-silica material into the upper crust, differentiation within the middle crust, and partial melting in the lower crust contributes to geochemical and isotopic evolution of the crust. Developing accurate models for the genetic evolution of these events is dependent upon geochronology to determine rates of magmatic processes as model constraints. We present new zircon high-precision CA-ID-TIMS U-Pb geochronology and MC-ICPMS Hf isotope geochemistry for four ignimbrites from the nested caldera complex near Socorro, New Mexico (USA), within the Mogollon-Datil volcanic field. In agreement with past 40 Ar- 39 Ar data, interpretations of new U-Pb data indicate eruptions from the Socorro caldera cluster were pulsed. These pulses were intermittently spaced, and a volcanic hiatus following the Hells Mesa Tuff at 33.442 ± 0.015 Ma was interrupted by four successive eruptions, beginning with the La Jencia Tuff at 29.158 ± 0.025 Ma and finishing with the South Canyon Tuff at 28.066 ± 0.021 Ma. Zircon age spectra became more protracted with each eruption, exhibiting age dispersions ranging from 0.347 Myr in the Hells Mesa Tuff to 4.502 Myr in the South Canyon Tuff. The increased dispersion is paralleled by an increase in the proportion of normally discordant grains, indicative of xenocryst incorporation. These protracted age spectra are not necessarily a function of thermal maturation in the middle to upper crust due to long-lived magma chambers. Rather, they are likely the result of increased melting of zircon-bearing lower crust due to deep thermal maturation from repeated juvenile magma injections based on the incorporation of zircon material at the melt source. In contrast, the Hf isotope record is volumetrically dominated by autocrystic zircon domains and becomes more radiogenic through time, recording juvenile replenishment of the lower crust during progressive melting. Together, these data record the protracted evolution of the lower crust sampled by ignimbrites, lend insight into that evolution, and emphasize the need for detailed interpretation of high-precision datasets to advance volcanic models.

Arizona, New Mexico↗

USGS2011

Lifetime of an ocean island volcano feeder zone: Constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40Ar/39Ar age determinations, Fuerteventura, Canary Islands

High-precision isotope dilution thermal ionization mass spectrometry (IDTIMS) UPb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40 Ar/ 39 Ar amphibole dating yielded ages from 21.9 0.6 to 21.8 0.3, identical within errors to the UPb ages, despite the expected 1% theoretical bias between 40 Ar/ 39 Ar and UPb dates. This overlap could result from ( i ) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40 Ar/ 39 Ar age uncertainties) from closure temperatures ( T c ) of zircon (699988C) to amphibole (500600C) ( ii ) lead loss affecting the youngest zircons or ( iii ) excess argon shifting the plateau ages towards older values. The combination of the 40 Ar/ 39 Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole T c is 0.8 Ma, suggesting PX1 lifetime of 520000 to 800000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 0.07/0.08/0.15 Ma and 21.58 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope 18 O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO 2 -rich carbonatite-derived fluids released during contact metamorphism.

Canary Islands↗