Zircon Petrochronology Research Articles

Zircon petrochronology and chemistry reveal the formation of the giant tungsten deposit at Dahutang in South China by multi-stage tungsten enrichments

Zircon petrochronology and chemistry reveal the formation of the giant tungsten deposit at Dahutang in South China by multi-stage tungsten enrichments

Multi-million-year magmatic and hydrothermal activity is key to the formation of supergiant to behemothian porphyry copper deposits

Understanding the primary controls on mineral deposit formation and size is essential for sourcing the metals required by our ever-growing economy. The tonnage of porphyry copper deposits ranges five orders of magnitude but the key mechanisms and processes that modulate the size of these deposits remain enigmatic. Here, we investigate the behemothian deposits of the Chuquicamata Intrusive Complex (CIC) in northern Chile employing high-precision U–Pb and Re–Os geochronology. We resolve a complex long-lived magmatic-hydrothermal activity that lasted over 3.3 Myr. High-precision zircon petrochronology data indicate two distinct porphyry emplacement episodes, separated by 0.5 Myr, with the younger generation closely tied to the main intervals of hydrothermal mineralization. High-precision Re–Os molybdenite dates reveal a prolonged hydrothermal mineralization interval (> 2.5 Myr) that progressively migrated southwards within the CIC and continued after the end of the (apparent) magmatic activity. We show that the rate of copper precipitation varies little in nature (0.025–0.10 Mt/kyr) and is independent of the size of the deposit. Consistent with evidence from smaller deposits, our findings provide unprecedented evidence that copper endowment in porphyry copper deposits positively correlates with the timescales of magmatic and hydrothermal activity. Supergiant to behemothian deposits require multi-million-year magmatic-hydrothermal activity, linking the largest porphyry copper systems to a simple metric – the duration of magmatic-hydrothermal activity.

Xenolith Petrochronology (San Luis Potosi, Mexico) Constrains Heat Sources for Cenozoic Ultrahigh‐Temperature Metamorphism in the Lower Crust

AbstractUltrahigh‐temperature (UHT; >900°C) metamorphism drives crustal differentiation and is widely recognized in the rock record, but its geodynamic causes are debated. Previous work on granulite‐facies metapelite xenoliths from San Luis Potosí, Mexico suggests the lower crust experienced a protracted UHT metamorphic event that coincided with the onset of regional extension. To determine the duration, conditions, and heat sources of UHT metamorphism recorded by these xenoliths, this study characterizes the major‐element, trace‐element, and U‐Pb isotopic systematics of quartz, rutile, feldspar, garnet, and zircon by in situ electron microprobe (EPMA) and laser‐ablation inductively coupled‐plasma mass spectrometry (LA‐ICP‐MS), and augments these data with detailed petrography, thermobarometry, phase equilibria modeling, and diffusion modeling. Thermobarometry and phase equilibria modeling suggest peak metamorphic conditions exceeded 0.7 GPa and 900°C. Zircon petrochronology confirms >15 Myr of UHT conditions since its onset at ∼30 Ma. A small population of zircon record elevated temperatures following transition from backarc compression to extension during the waning stages of orogenesis (60–37 Ma). Garnet preserves trace‐element zoning and mineral inclusions consistent with suprasolidus garnet growth and subsequent compositional modification by intracrystalline rare‐earth element diffusion during protracted heating, with diffusion chronometry timescales in agreement with zircon data, followed by fluid‐driven remobilization of trace elements along now‐healed fractures within ∼1 Myr of eruption. In sum, these data are most compatible with lithospheric mantle attenuation or removal as the dominant heat transport mechanism driving synextensional UHT metamorphism and crustal melting, which has bearing on models for crustal differentiation and formation of modern and ancient granulite terranes globally.

Thinning and Heating of Laramide Continental Lower Crust Recorded by Zircon Petrochronology

AbstractZircon grains from the metasedimentary lower crust of the Rio Grande Rift, New Mexico, preserve a metamorphic record of the transition from Laramide compression to Eocene extension. Zircon U‐Pb isotopes and trace‐element concentrations from five two‐pyroxene metaigneous granulite xenoliths define discrete populations: older zircon cores (∼15–50 Ma) that are depleted in heavy rare‐earth elements (HREE) but Ti‐rich, and younger zircon rims (∼3–15 Ma) with elevated HREE and lower Ti concentrations. Coupled phase equilibria and garnet‐melt‐zircon trace‐element partitioning calculations show that the older zircon cores equilibrated in thick (>40 km), hot (800–900°C), garnet‐bearing lower crust during the cessation of compression at the end of the Laramide orogeny. Zircon rim domains equilibrated at lower pressures, consistent with >9 km of thinning of the lower crust. Thermal‐kinematic calculations show that these pressure‐temperature‐time constraints require thinning of the lithospheric mantle prior to and during regional Cenozoic extension. Convective erosion of the mantle lithosphere over tens of millions of years, possibly facilitated by dynamics of the Farallon slab, provides a mechanism to facilitate lower crustal heating and extension.

Paleozoic Episodic Magmatism in Western Tianshan: Insight Into Assembling the Northeastern Pangea

AbstractThe late‐stage union of Pangea was associated with the convergence of Siberia with Laurussia, but the exact timing remains unclear. The orogenic duration of the Kazakhstan block can provide geochronological constraints as it connects Siberia, Baltica, and Tarim. Zircon petrochronology offers a reliable approach for ascertaining the lifespan of an ancient orogen. In this study, we explore three phases of magmatism recorded in detrital zircons from late Paleozoic and Mesozoic sandstone‐siltstones in Western Tianshan, that is, 400–470 Ma, 320–380 Ma, and 280–320 Ma. Based on their age‐propagated Hf isotopes, melt SiO2 contents, and crustal thicknesses, our findings suggest that the southern limb of Kazakhstan underwent the early Paleozoic amalgamation of microcontinents with arcs, the late Paleozoic maturation of an Andean‐like continental arc, and the late Carboniferous collision of Kazakhstan with the Junggar oceanic basin and the Tarim craton. Such characteristics manifest the long‐term orogenic progression of Kazakhstan. Combining published timelines and paleolatitudes of major orogens and blocks, we propose that the Kazakhstan block welded northeastern Pangea along with the cessation of these orogenic activities around it. Consequently, by docking Kazakhstan with surrounding cratons, the fundamental configuration of Pangea could have been established in the late Carboniferous.

Zircon Petrochronology of Au-Rich Porphyry and Epithermal Deposits in the Golden Quadrilateral (Apuseni Mountains, Romania)

Abstract The Golden Quadrilateral of the Apuseni Mountains (Romania) represents the richest Au(-Cu-Te) porphyry and epithermal district of Europe and the Western Tethyan metallogenic belt. The Au(-Cu-Te) mineralization is associated with Neogene calc-alkaline magmatism along graben structures growing during the late stages of the Alpine-Carpathian orogeny. We use zircon petrochronology to study the time-space distribution, sources, composition, and timescales of the Au(-Cu-Te)-mineralizing magmatism and explore its link to regional tectonics. Our own and published U-Pb zircon ages document ore-forming magmatic activity between ~13.61 and 7.24 Ma. In combination with available paleomagnetic data, the new zircon ages corroborate the hypothesis that the magmatism in the Golden Quadrilateral evolved in a tectonic environment dominated by major (up to 70°) crustal block rotation. Hafnium isotope composition of Neogene zircon (εHf between –2 and 10) supports the predominant origin of the magmas from a heterogeneous lithospheric mantle, which may have been fertilized during an earlier Cretaceous subduction event and possibly by concurrent Miocene subduction. Xenocrystic zircon shows involvement of crustal sources resembling European continental basement. Fertility indicators, including Eu/Eu* and oxygen fugacity based on zircon composition, show no systematic correlation with the mineralizing events and/or age. High-precision (isotope dilution-thermal ionization mass spectrometry) U-Pb zircon geochronology demonstrates that the magmatic systems exposed at district scale evolved over less than ~100 k.y. and that durations of hydrothermal mineralization pulses were even shorter.

Magma flux variations triggering shallow-level emplacement of the Takidani pluton (Japan): Insights into the volcanic-plutonic connection

Defining the physico-chemical evolution of felsic magmatic reservoirs in the middle-upper continental crust is crucial for understanding the connection between granitic plutons and silicic volcanic rocks and for research on the trigger mechanisms of volcanic eruptions. In this study, we investigate the formation and evolution of the Hotaka-Takidani volcano-plutonic complex (Japan) using a comprehensive approach that integrates zircon petrochronology with phase-equilibria and thermal modelling. The Takidani pluton is a Pleistocene tilted zoned intrusion of granodiorite-granite composition associated with at least two large caldera-forming eruptions. We have investigated the three uppermost units of the pluton and the oldest and more voluminous Nyukawa eruption, which deposited more than 400 km3 (DRE, dense rock equivalent) of crystal-rich dacitic ignimbrite. Amphibole thermobarometry, U-Pb zircon dates and geochemical data indicate that the Takidani pluton and the Nyukawa dacite were sequentially sourced from a 10–12 km-thick long-lived magmatic reservoir in the middle crust. Thermal evolution of the reservoir led to the extraction of the Nyukawa magma, followed by brief storage in the upper crust and eruption at ca. 1.706 ± 0.091 Ma. For two of the units of the pluton, we combine high-spatial resolution zircon U-Pb geochronology with zircon chemical data. Applying the Ti-in-zircon thermometer, we observe that magma within the reservoir was stored at a relatively constant temperature of ca. 700 °C for 300 kyr and subsequently, starting from 1.4 Ma, the temperature increased progressively reaching 820–850 °C at 1.1 Ma. This temperature shift is inconsistent with a constant magma flux and suggests an increase of the magma injection rate into the reservoir. Using the distribution of zircon ages and thermal simulations, we determined that the reservoir was built by a fairly low average magma flux of ca. 6 × 10−6 km3*km−2*yr−1, shifting to a magma supply rate which is three to four times higher during the last 300 ka of zircon crystallisation. This increase in magma flux caused the final emplacement of the Takidani magma in the upper crust, where it rapidly crystallized. The integration of geochronological data with phase-equilibria and thermo-chemical modelling demonstrates that multiple melt extraction events occurred during the evolution of the Hotaka-Takidani magmatic system. Only the first one triggered a major eruption, while subsequent events resulted in the emplacement of the Takidani pluton in the shallow crust.

The metamorphic footprint of western Laurentia preserved in subducted rocks from southern Australia

AbstractPolymetamorphic metapelitic rocks in central‐west Tasmania, southern Australia, contain high‐pressure mineral assemblages that formed during Cambrian‐aged subduction and relict garnet with published Lu–Hf ages of c. 1285–1240 Ma. These garnet ages, along with published detrital zircon data from throughout western Tasmania and western North America, have been used to propose the presence of Mesoproterozoic Laurentian crust in western Tasmania. In this study, we combine zircon petrochronology with compositional information from the inclusion assemblages in relict garnet to extract Mesoproterozoic pressure–temperature data from subduction‐overprinted rocks, which effectively constitute an interpreted remnant of Laurentian crust now residing in central‐west Tasmania. The new data suggest Mesoproterozoic metamorphism involved two stages. The first event is recorded by c. 1480–1235 Ma zircon that formed in a garnet‐absent, plagioclase‐present, high‐thermal gradient environment at pressures no greater than ~5–5.5 kbar. The second event recorded by c. 1285–1240 Ma relict garnet was characterized by the development of a moderate‐pressure kyanite–plagioclase–biotite‐bearing mineral assemblage, which formed at ~8.5 kbar and ~590–680°C. These pressure–temperature constraints are attributed to extension within a deep basin system associated with the cryptic East Kootenay Orogeny in North America, which coincides with the final stages of c. 1450–1370 Ma upper Belt‐Purcell Basin sedimentation. Taking into account new detrital zircon U–Pb–Hf isotopic data from central‐west Tasmania in this study and existing zircon provenance data from throughout western Tasmania and the Belt‐Purcell Basin, our results strengthen the hypothesis of a Laurentian footprint that potentially encompasses much of western Tasmania and relates to both Nuna and Rodinian tectonism.

Evolution and fertility of magmas associated with iron oxide-apatite (IOA) deposits, Coastal Cordillera, Northern Chile: A zircon petrochronology perspective

Iron oxide-apatite (IOA) deposits in the Coastal Cordillera of northern Chile are spatially associated with Late Jurassic to Early Cretaceous intrusive rocks of intermediate composition. To constrain the magmatic conditions and identify possible ore fertility indicators, we used simultaneous LA-ICP-MS U–Pb dating and trace element geochemistry of zircon crystals from intrusions related to IOA deposits in the El Algarrobo district. These data are contrasted against the geochemistry and ages of zircons from granitoids spatially related to Cretaceous porphyry Cu–Mo ± Au east of the El Algarrobo district. Our data show that intrusive rocks related to IOA deposits in the El Algarrobo district formed during a ∼5 Myr period (128–123 Ma) and were associated with water-poor (Eu/Eu* < 0.3) and relatively reduced (ΔFMQ from −1.5 to +1.1) intrusions, which could explain the sulfur-poor nature of IOA deposits. In contrast, intrusive rocks associated with porphyry-type mineralization east of El Algarrobo formed between 97 and 95 Ma and exhibit higher water content (Eu/Eu* up to 0.7) and oxidizing conditions (ΔFMQ from 0.0 to +2.2). We interpret these contrasting signatures as reflecting a change in the geodynamic setting at 123–122 Ma—from extensional to compressional conditions—that led to higher residence times of magmas at deep crustal levels, resulting in an increase in their H2O content through episodic magma (and volatile) replenishment. Based on our zircon data, we propose potential IOA fertility indicators characterized by (Eu/Eu*)/(Dy/Yb)N ratios <3 and relatively reduced conditions, i.e., ΔFMQ < +1. The relation of reduced magmas with IOA deposits supports the hypothesis that it was the result of the crystallization of large amounts of igneous magnetite related to ore genesis. Reduced magmas in arc settings are uncommon, and hence, the proposed IOA fertility indicators are a promising exploration tool that needs further testing in IOA–IOCG districts.

Garnet and zircon petrochronology reveal coherent subduction and exhumation of eclogites and associated schists in the Changning–Menglian orogenic belt, southeast Tibet

Determining whether high-grade metamorphic eclogites and surrounding metasediments underwent a shared subduction-exhumation cycle or distinct metamorphic paths before their juxtaposition at shallow levels is crucial for deciphering metamorphic processes in orogenic belts. Constructing pressure-temperature-time (P–T-t) paths for both rocks is the most straightforward approach. However, current time constraints overwhelmingly rely on dating accessory mineral like zircon, rutile, and monazite, which may only record a portion of the entire metamorphic history. Here we present an integrated petrochronological analysis using garnet Lu–Hf and Sm–Nd, and zircon U–Pb on two eclogites and their surrounding micaschists from the Changning–Menglian orogenic belt in southeast Tibet. Pseudosection modelling and conventional thermobarometers suggest a clockwise P–T path for the eclogites, from ∼1.4 GPa/∼520 °C to ∼2.5 GPa/∼600 °C, followed by decompression to <∼0.7 GPa, and peak conditions of 2.0–2.2 GPa/570–620 °C for the micaschists. Lu–Hf dating for eclogites yields ages of ca. 238–241 Ma, indistinguishable from the Sm–Nd dates of ca. 239 Ma. However, the Lu–Hf ages for micaschists (ca. 249–251 Ma) are older than the corresponding Sm–Nd dates (ca. 240 Ma). The well-preserved growth zoning in garnet indicates a short growth period in eclogites and at least ∼10 Myr in micaschists, bracketing the timing of protracted the two distinct zircon growth phases at around 238 Ma and 250 Ma. The similarity in peak metamorphic conditions and the consistent high-pressure metamorphic ages suggest a coherent subduction and exhumation process for both eclogites and micaschists. The Lu–Hf ages of the micaschists constrain the subduction of the Lancang Group dates back to ca. 250 Ma. The narrow temporal gap between the initiation of subduction and the age of the protoliths implies a rapid shift from the formation of the protoliths to the subduction of oceanic slabs and the scraped-off sediments to depths exceeding 80 km during the Triassic—a hypothesis that warrants further exploration.

Dating corona formation in high-grade rocks: integrated garnet and zircon petrochronology of granulite-facies rocks in the North China Craton

Dating corona formation in high-grade rocks: integrated garnet and zircon petrochronology of granulite-facies rocks in the North China Craton

Pressure–temperature–time path of ultrahigh-pressure metamorphic terranes constrained by zircon petrochronology: A case study of orthogneisses from the northern Sulu belt, China

Reconstruction of pressure–temperature–time (P–T–t) path of volumetrically-dominant orthogneisses in deeply subducted continental crusts is challenging due to their simple amphibolite-facies mineral assemblages. To provide new insights into this issue, a detailed study of mineral inclusions, trace elements and U-Pb ages within robust zircon containers, together with titanite U-Pb dating and petrology were conducted on ultrahigh-pressure (UHP) orthogneisses from the northern Sulu belt. The following P–T–t conditions of three metamorphic stages were constrained: (i) cathodoluminescence (CL)-grey zircon cores (ca. 238–237 Ma) with flat heavy rare earth element (HREE) patterns include garnet, phengite and omphacite that yield estimated P–T conditions of 2.3–2.8 GPa/730–800 °C, corresponding to prograde high-pressure (HP) metamorphism before the UHP peak. (ii) CL-dark zircon mantles (ca. 224 Ma) contain multiphase solid inclusions of plagioclase + K-feldspar + quartz and show extremely low Th/U ratios (≤0.08) and negative Eu anomalies, demonstrating their crystallization from hydrous melt at 2.0–1.8 GPa/890–820 °C during HP eclogite-facies exhumation. In addition, titanite grains are characterized by high LREE contents (1939–5239 ppm), Th/U ratios (0.37–0.81) and crystallization temperatures (830–801 °C), suggesting their peritectic origin. The lower intercept age (220 ± 4 Ma) of titanite is broadly consistent with the ages of the zircon mantles, indicating that they both crystallized from the melt at the same stage. (iii) CL-bright zircon rims (ca. 212–211 Ma) preserve low-pressure mineral inclusions of plagioclase, K-feldspar and quartz, and they show low Th/U ratios (0.03–0.12) and steep HREE patterns with negative Eu anomalies, witnessing amphibolite-facies overprinting at 1.0–0.8 GPa/610–550 °C. Combined with the metamorphic peak conditions of 3.2 GPa/840 °C at ca. 232 Ma constrained by previous studies from the same area, the P–T–t path of the northern Sulu UHP belt is reconstructed. The data reflects two-stage exhumation of this terrane, including an early-stage (5.8 km/m.y.) and a later-stage slower (3.1 km/m.y.) exhumation processes. The faster exhumation during early decompression was probably enhanced by extensive melting activity recorded by the CL-dark zircon mantles from the orthogneisses.

Age of the magma chamber and its physicochemical state under Elbrus Greater Caucasus, Russia using zircon petrochronology and modeling insights

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 for future activity of Elbrus calling for much-needed seismic imaging. Similar zircon records worldwide require continuous intrusive activity by magmatic accretion of silicic magmas generated at depths, and that zircon ages do not reflect eruption ages but predate them by ~ 103 to 105 years reflecting protracted dissolution–crystallization histories.

Timescales of ultra-high temperature metamorphism and crustal differentiation: Zircon petrochronology from granulite xenoliths of the Variscan French Massif Central

Lower crustal ultra-high temperature (UHT) metamorphism and the resulting production and transfer of granitic magmas represent key processes of intracrustal differentiation. The timescales of these phenomena are debated, due to the complexity of the granulite zircon U-Pb record and because direct links between granulites and granites are difficult to establish. To address these issues, we present the results of zircon petrochronology (coupled U-Pb dating, trace element and Lu-Hf isotopic analyses) for lower crustal felsic and mafic granulite xenoliths from the Variscan eastern French Massif Central and compare them with data from well-characterized mid-/upper crustal migmatites and granites. The felsic and mafic granulites represent pre-Variscan meta-sedimentary and meta-igneous mafic rocks, respectively; which experienced Variscan UHT peak metamorphism at 940–970°C and 8 ± 2 kbar. Zircons from the felsic granulites show U-Pb dates spreading over ∼50 Myr between ∼315 and ∼265 Ma, correlated to Ti-in-zircon temperatures decreasing from 940–970°C to 800°C and REE contents consistent with growth in equilibrium with garnet at (U)HT conditions. This is best explained by continuous crystallization of zircon upon cooling from the thermal peak owing to decreasing Zr solubility of residual melt, despite significant prograde melt loss. Zircons from the mafic granulite only record the last stage of this time-temperature evolution (295–265 Ma; 800–900°C) due to later zircon saturation. Upper crustal granite emplacement started at 340 Ma and culminated at the age of the lower crustal thermal peak of 313 ± 3 Ma (defined by the highest-temperature zircons from felsic granulites), reflecting melt extraction along the ∼27 Myr prograde path of the lower crust. In turn, the crystallization ages of mid-crustal migmatites (315–300 Ma) and the lower crustal granulites (315–265 Ma) are consistent with slow cooling in the presence of melt. These results provide a direct assessment of the timescales of melt production and residence at the crustal scale; and validate the granulite-granite connection in the framework of the melt loss theory in migmatitic systems.

Magma evolution in a complex geodynamic setting, South Harghita volcanic area, East-Central Europe: Constraints from magma compositions and zircon petrochronology

Magma evolution in a complex geodynamic setting, South Harghita volcanic area, East-Central Europe: Constraints from magma compositions and zircon petrochronology

Evidence of Vertical Slab Tearing in the Late Triassic Qinling Orogen (Central China) From Multiproxy Geochemical and Isotopic Imaging

AbstractThe process of slab tearing profoundly affects interchanges of material and energy between the lithosphere and asthenosphere and has been invoked as a trigger of magmatism in modern and ancient subduction‐collision systems. Horizontal slab tears may occur after continental collision and subsequent slab break‐off, whereas vertical slab tears may occur in response to along‐strike variations in rollback velocity, thereby ripping the subducting lithosphere. Previous studies have documented tearing of subducting slabs in modern convergent settings using geophysical methods, but in ancient collisional belts, where these methods cannot be applied, detection of slab tearing is more difficult, particularly if the oceanic plate was fully subducted and the geological evidence for subduction is limited. Here, we employ multiproxy element‐isotope imaging, as well as zircon petrochronology and whole‐rock geochemistry, to assess evidence of vertical tearing of the Mianlue slab in the Triassic Qinling Orogen in central China. Our results show evidence of anomalous, inferred tear‐related magmatism east of 107°E, at 225–210 Ma. Vertical tearing of the northward subducting Mianlue slab is recorded by geochemically anomalous igneous rocks, and the recognition of N–S to NE–SW trending boundaries defined by Sr‐Nd‐Hf isotopes, elemental ratios (Nb/Ta, and Ca/Al), Mg#, and reduced crustal thickness between 107° and 108°E. The inferred vertical tear may have been driven by slab rollback of the Mianlue slab at 225–210 Ma. The results show that multiproxy element‐isotope imaging (e.g., of εNd(t), εHf(t), (87Sr/86Sr)i, Nb/Ta, Mg#, and Ca/Al) can be used to reconstruct the evolution of fossil subduction systems.

Identifying sources of non-unique detrital age distributions through integrated provenance analysis: An example from the Paleozoic Central Colorado Trough

AbstractTo address the longstanding issue of provenance interpretation of non-unique detrital zircon age populations, we integrated zircon U-Pb, rare earth element (REE), and εHf(t) data from upper Paleozoic strata in the northern Central Colorado Trough and Cambrian intrusions with petrography, paleocurrent data, and structural and stratigraphic observations. This data set indicates that Cambrian sediment was shed by multiple local sources instead of distant sources hundreds of kilometers away, and it reveals a detailed history of tectonic drainage reorganization in the northern Central Colorado Trough during Ancestral Rocky Mountain deformation. During the Early–Middle Pennsylvanian, Cambrian detrital zircons were a minor constituent of northern Central Colorado Trough sediment. However, during the Late Pennsylvanian–early Permian, westward advancement of the adjacent Apishapa Uplift deformation front precipitated drainage reorganization, which resulted in an episode of dominant Cambrian detrital zircon sourcing. Paleocurrent and petrographic data indicate that the source of Cambrian detritus was shed by an igneous rock body that was ≤15 km northeast of the depocenter, which has since been eroded away or mantled by Tertiary volcanic rocks. The addition of zircon petrochronology to the data set applied here was critical in confirming this hidden source of detritus and elucidating the compositional characteristics of that igneous rock. Zircon εHf(t) provided a regional provenance indicator of a western Laurentian affinity, and REE composition aided in discriminating possible local sources of Cambrian zircon. Furthermore, this work serves as a case study of a dominant Cambrian detrital zircon signature sourced from outside of the wellknown Amarillo-Wichita Uplift, and it has implications for the interpretation of such detrital spectra in the context of a direct-from-basement source or the recycling of Cambrian zircon-dominated rocks. In summary, we demonstrate the utility of this multi-provenance proxy approach in interpreting a complex structural history of a dynamic hinterland and concomitant drainage reorganization through an in-depth investigation into the basin record.

Incipient collision of the Rae and Slave cratons at ca. 1.95 Ga

AbstractIncipient collision between the Rae and Slave cratons represents a critical initial stage in the final assembly of the composite Laurentian craton. However, the timing and kinematics of this event remain poorly constrained. Here, we integrate phase equilibria modeling and Lu-Hf garnet and U-Pb monazite and zircon petrochronology to precisely date the timing of peak metamorphism along the Great Slave Lake shear zone, the central segment of the western Rae cratonic margin that was the locus of terminal Rae-Slave collision. Zircon and monazite U-Pb ages broadly constrain prograde-to-peak metamorphism to 1933–1913 Ma, whereas the timing of upperamphibolite facies peak metamorphism (0.8–1.0 GPa and 750–800 °C) is best constrained by two garnet Lu-Hf ages of 1931 ± 12 and 1917 ± 6 Ma. Our results highlight the inherent strengths and limitations of garnet, monazite, and zircon petrochronology in the context of dating Paleoproterozoic-aged metamorphism. Based on the timing of crustal thickening constrained by Lu-Hf garnet geochronology, we posit that the Slave craton first collided with the western Rae margin at ca. 1950 Ma. Taken together with prior constraints on the timing of metamorphism elsewhere along the western Rae margin, we propose incipient collision was followed by the northwards zippering of the margins and the eventual ~500 km of dextral translation of the Slave craton along the Great Slave Lake shear zone.

Multi‐mineral petrochronology on a high‐pressure mafic granulite reveals short‐lived high‐temperature metamorphism in the North China Craton

AbstractAccurately defining the peak ages and timescales of high‐temperature metamorphism is fundamental to unravelling tectonic dynamics. However, metamorphic constraints are frequently hampered by a large spread of zircon U–Pb ages without explicit textural relationships. Integrated garnet and zircon petrochronology may clarify ambiguous ages retrieved from ancient high‐temperature metamorphic rocks. There is a long‐standing debate on the interpretation of the spread of zircon ages from c. 2.5–1.8 Ga for the granulites of the North China Craton. In order to clarify the timing and duration of (ultra)high‐temperature metamorphism in the North China Craton, we investigated a mafic granulite and the adjoining gneiss from the Yinshan Block of the North China Craton using zircon and titanite U–Pb geochronology combined with garnet Lu–Hf and Sm–Nd geochronology. Pseudosection modelling and conventional thermobarometric calculations constrain the peak metamorphic conditions to be ~1.0 GPa and ~850°C. The near‐complete lack of major‐element zoning in garnet, aside from ~2 μm diffusion profiles at crystal rims, suggests complete re‐equilibration at peak temperatures followed by fast cooling from high temperatures. The Lu–Hf garnet age of 1870 ± 4 Ma and Sm–Nd age of 1870 ± 7 Ma, determined on the same garnet fractions, are indistinguishable from the zircon U–Pb age of 1866 ± 11 Ma obtained from zircon that grew contemporaneously with garnet, evidenced by the chemical equilibrium of coexisting garnet and zircon, and are additionally consistent with a titanite U–Pb age of 1876 ± 7 Ma. We interpret this close agreement of ages, within uncertainty, coupled to the existence of flat Sm–Nd–Hf profiles in garnet that also has well‐preserved Lu zoning, to reflect a short‐lived high‐temperature metamorphic event that was terminated by rapid exhumation and cooling. The short‐lived (&lt;4 Myr) high‐temperature metamorphism may be generated in the lowermost parts of the crust through magmatic underplating/intraplating during extension that follows collision of the Ordos and the Yinshan Blocks.

Zircon petrochronology reveals the moderately juvenile signature of a diatexite from the boundary zone between the Brasília and Ribeira orogens (SE Brazil): Relict of a Tonian arc?

Unraveling the tectonic evolution of Precambrian high-grade rocks is often challenging owing to widespread metamorphic overprint under high to ultra-high temperature conditions. In this scenario, isotopic systems-based investigations constitute an important tool to obtain the time constrains of formation and evolution of rocks.We present a petrochronological investigation using U–Pb and Lu–Hf data of zircon grains extracted from a biotite-bearing granitic leucosome from a diatexite found in the boundary zone between the Brasília and Ribeira orogens, SE Brazil. Clusters of 176Hf/177Hf(t) ratio values characterize two distinct zircon data groups, suggesting at least two different crystallization stages. 176Hf/177Hf(t) ratios from group 1 range from 0.28230 to 0.28247 with εHf (t) between +7.54 and −1.55, representing a moderately juvenile to evolved magma. This group constrains a time interval of ca. 890-540 Ma, and the ancient zircon core (890 Ma) could potentially record the minimum age for the magmatic crystallization of a moderately juvenile protolith, with ϵHf (890) ranging from +8.66 to +0.36. Excluding this ancient zircon (since it is the only date older than 800 Ma), the oldest grain provides a minimum crystallization age of ca. 797 Ma, with ϵHf (797) between +6.73 and -1.61. Group 2, exhibiting 176Hf/177Hf(t) ratios from 0.28214 to 0.28225and negative εHf(t) values (−3.35 to −7.53), represents xenocrysts of crustal origin from the protolith or an influx of allochthonous crustal melt during high-grade metamorphism. The age spreading from ca. 890 Ma to ca. 540 Ma along the concordia is consistent with a Pb-loss scenario, with cores locally providing younger ages than rims. This is also consistent with prolonged metamorphism, as newly crystallized domains also present a spread of ages. Our data indicate that the leucosome is the metamorphic product of a moderately juvenile rock. When placed in the regional context, the biotite-bearing granitic leucosome may represent the relic of a magmatic arc, now located in the boundary zone between the Brasília and Ribeira orogens. Its moderately juvenile signature suggests the following tectonic setting interpretations: (i) an intra-oceanic subduction setting similar to modern island arcs or an early stage of continental subduction, formed at ca. 890–800 Ma and, thus could be potentially correlated with juvenile magmatic arcs found in both Brasília (Mara Rosa – Arenópolis arc system) and Ribeira (Serra da Prata – Rio Negro arc system) orogens, suggestive of a large ocean realm to the south of the São Francisco paleocontinental block in Tonian time; and (ii) the most primitive relic of an early stage of the continental magmatic arc installed on the active margin of the Paranapanema paleocontinent.