Geochronological Data Research Articles

Two episodes of extension induced by slab rollback and root foundering in the Eastern Tianshan, southwestern Altaids: Insights from granites and intermediate dykes

The widespread Late Paleozoic-Early Mesozoic magmatism in the Eastern Tianshan provides critical insights into geodynamic evolution of the southern Altaids. In this study, we conduct an integrated study of field geology, petrology, U-Pb zircon geochronology and major-trace elemental and Sr–Nd–Hf isotopic geochemistry on the Late Carboniferous monzogranite and diorite dyke and the Late Triassic gabbroic diorite dyke in the central part of the Eastern Tianshan. Geochronological data indicate that the monzogranite, diorite dyke and gabbroic diorite dyke formed at ∼318 Ma, ∼317 Ma and ∼235 Ma, respectively. The Late Carboniferous monzogranite shows transitional characteristics between highly fractionated and A-type granites, with relatively high zircon saturation temperatures (800–836 °C). It was derived by partial melting of juvenile infracrustal rocks, followed by plagioclase-dominated fractional crystallization. The Late Carboniferous diorite dyke has high Al2O3 contents (mostly >17 wt%) and Ba/La ratios, indicating an origin from a hydrous lithospheric mantle source that had been metasomatized by slab-derived fluids. The Late Triassic gabbroic diorite dyke, with relatively high Mg# values (57–58) and Th contents (3.28–3.46 ppm), originated from a less hydrous lithospheric mantle source containing significant sediment-derived components. Our new results, combined with previous studies, reveal an end-Early Carboniferous to middle Late Carboniferous magmatic flare-up in the Dananhu arc. The magmatic flare-up occurred in a long E-W trending banded zone parallel to the strike of the arc and was accompanied by significant normal arc magmatism, which widely migrated to the south of the Dananhu arc in comparison to prior magmatism. These together with coeval extension-related volcanic, sedimentary, structural and metamorphic events in the Dananhu and adjacent areas were attributed to southward rollback of the subducted Kanguer oceanic slab. The long-time arc magmatism and regional crustal thickening before the Late Triassic led to the formation of an arclogite-bearing root beneath the Dananhu arc. The Late Triassic extension-related magmatism in the Dananhu arc, which was synchronous with or slightly younger than regional thickened crust-derived magmatism, was linked to the local root foundering of the long-lived Dananhu arc at the late stage of orogenesis. The episodic occurrence of geodynamic processes such as slab rollback, arc root foundering and ridge subduction/slab tearing, which were accompanied by massive input of juvenile materials into continental crust, contributed to multi-stage significant crustal growth in southern Altaids.

Tectonic architecture of the northern Dora-Maira Massif (Western Alps, Italy): field and geochronological data

High-pressure and ultra-high-pressure metamorphic terrains display an internal architecture consisting of a pile (or stack) of several coherent tectonic thrust sheets or units. Their identification is fundamental for understanding the scale and mechanisms active during subduction and exhumation of these crustal slices. This study investigates the geometry of the northern Dora-Maira Massif and the kinematics of the major tectonic boundaries, combining field and geochronological data. The tectonic stack of the northern Dora-Maira Massif comprises the following units. The lowermost unit (the Pinerolo Unit) is mainly characterized by Upper Carboniferous fluvio-lacustrine (meta-)sediments. The Pinerolo unit is overthrust by a pre-Carboniferous basement. The latter is subdivided in two tectonic units (the Chasteiran and Muret Units) with different Alpine metamorphism (ultra-high-pressure and high-pressure, respectively). The pre-Carboniferous basement of the Muret Unit is thicker than previously thought for two main reasons. Firstly, some paragneisses, traditionally assumed to be Carboniferous and/or Permian in age, display detrital zircon ages indicating a main source at about 600 Ma. Secondly, three samples of the Granero Orthogneiss, previously assumed to be a Permian intrusive body, have provided zircon U–Pb ages of 447 ± 1 Ma, 456 ± 2 Ma and 440 ± 2 Ma, indicating a late Ordovician or early Silurian age for the protoliths. The uppermost unit (the Serre Unit) comprises porphyritic (meta-) volcanic and volcaniclastic rocks dated to the Permian (271 ± 2 Ma), on top of which remnants of the Mesozoic cover is preserved. Detailed mapping of an area about 140 km2 shows that (i) the ultra-high pressure Chasteiran Unit is localized at the boundary between the Pinerolo and Muret Units, (ii) the Granero Orthogneiss may be considered as the mylonitic sole of the Muret Unit, characterized by a top-to-W sense of shear, and (iii) the contact between the Muret and Serre Units displays ductile-to brittle structures (La Fracho Shear Zone), indicating a top-to-the-NW displacement of the hangingwall with respect to the footwall. A final episode of brittle faulting, cutting across the nappe stack (the Trossieri Fault), indicates an extensional stage in the core of the Alpine belt, as previously documented in more external zones. This work provides a necessary and robust basis before an accurate discussion of processes acting during continental subduction of the Dora-Maira Massif may be understood.

Redefining timing, genesis and geodynamic setting of polymetallic skarn mineralization, Gangdese belt, Tibet, from LA–ICP–MS garnet U–Pb geochronology

Iron, Cu, Pb–Zn, and W–Mo skarn deposits occur in the Gangdese metallogenic belt, Tibet. A lack of precise age constraints for mineralization hinders understanding of the processes contributing to skarn mineralization, particularly identification of the causative intrusions. In this study, new garnet U–Pb geochronological data are provided for the Qiagong (Fe) and Jiaduobule (Fe–Cu) skarns. We place particular emphasis on skarn garnet mineralogy, using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS), to characterize garnet textures, compositions, and U–Pb isotope systematics. All garnets studied belong to the grossular-andradite series and display oscillatory compositional zoning (And100Gr0 to And20Gr80). Andradite-dominated garnet features a chondrite-normalized REE fractionation pattern exhibiting enrichment in LREE relative to HREE and a positive Eu anomaly, whereas grossular-dominated garnet displays relative LREE depletion and a marked flat HREE fractionation trend. Ore-forming elements, including Sn, W, As, and U, are detected at concentrations up to several hundreds of ppm in the same garnets. Concentrations of W and As are higher in andradite and correlate positively with one another. The correlation between U, Sn and the major oxide composition of garnet is insignificant, potentially resulting from the changing valence states of these elements under different redox conditions. Together with previously published and limited new data for the Gebunongba (Fe), Ri’a (Cu), and Hahaigang (W–Mo) skarns, the new garnet U–Pb age data indicate that the major Fe, Pb–Zn, and W–Mo mineralization event in the Gangdese metallogenic belt took place between 65 Ma and 50 Ma, with marked peaks at ∼ 65 Ma and ∼ 53 Ma. Partial melting of a crustal-dominated source due to the slab rollback (∼65 Ma) and break off (∼53 Ma) of Yarlug–Zangbo Tethyan Ocean and subsequent asthenosphere upwelling induced this regional event during the Paleogene to early Eocene. A less common but regionally widespread Cu (±Au) mineralization event in the same belt formed during the Late Cretaceous (∼85 Ma) and may have resulted from the coupled influence of the northward subduction of the Yarlug–Zangbo Tethyan Ocean and the southward subduction of the Bangong–Nujiang Tethyan Ocean. This contribution highlights the potential significance of the Late Cretaceous Cu(±Au) event and hence the prospectivity of the belt for both skarn and porphyry systems. More broadly, our findings carry implications for Neo-Tethyan metallogeny in the region extending from southwestern China to eastern Europe during the Late Cretaceous.

Archean crustal growth and reworking in the Superior Province, Canada: Insights from whole-rock geochemistry and Nd isotopic data of the La Grande, Nemiscau and Opatica subprovinces

The southeastern Superior Province contains Meso- to Neoarchean (2952–2677 Ma) tonalite-trondhjemite-granodiorite (TTG) suites, volcanic (2773–2703 Ma) and sedimentary (<2724 Ma) supracrustal sequences, and granitoid intrusions (2708–2598 Ma). The region is a key crustal cross-section for understanding the growth, evolution, and stabilization of Archean cratons. Whole-rock geochemistry and Nd isotopic analyses have been performed on TTG suites, volcanic assemblages and granitoid plutons of the La Grande, Nemiscau and Opatica subprovinces. These analyses, combined with existing structural and U-Pb geochronological data, have been used to investigate the extend of the basement within the three subprovinces, their interaction, and the degree of crustal reworking in the southeastern Superior Province.Nd isotope data and zircon inheritance indicate that the TTG suites were generated from: (i) an old crustal domain with Nd model ages at 3.5–3.2 Ga that may represent the southern extension of the Langelier Complex, (ii) a ca. 3.0 Ga domain with isotopically juvenile signatures, and (iii) the reworking of < 3.0 Ga Nd model age TTG suites from the Opatica subprovince. The Nd juvenile signatures of the mafic to ultramafic volcanism at ca. 2773–2756 and ca. 2723–2703 Ma suggest continuous or multiple mantle plume events beneath the southeastern Superior Province, whereas interlayered felsic volcanic rocks were formed from anatectic melting at high pressure. Subsequent magmatism was related to sanukitoid suites (2704–2693 Ma) emplacement that record mantle-TTG melt interactions. Based on a common tectonometamorphic evolution of the three subprovinces from ca. 2756 Ma, previous studies argued that the Mesoarchean TTG suites exposed in the La Grande and Opatica subprovinces represent a single crustal block. The sedimentary belts of the area were deposited in sagduction-type basins formed at ca. 2724–2706 Ma and, within less than 15–20 myr, were buried and metamorphosed up to granulite facies at 2697–2685 Ma during dip-slip-dominated D2. The burial and the following exhumation of these rocks from ca. 2677 Ma may be attributed to the delamination of lower crustal residues, favoring interaction between mantle and TTG melts, and the formation of sanukitoids and anatectic S-type granites. Nd signatures of the 2646–2598 Ma I-type granitic intrusions indicate extensively reworking of TTGs due to crustal thickening during the D3-D4 events.Our study suggests that the Archean tectonic regime recorded in the southeastern Superior Province is the result of mantle plume tectonics. We conclude that the La Grande-Opatica boundary does not represent a major suture zone but rather but rather a fossil boundary within an older extensively reworked crustal block over which the metasedimentary rocks of the Nemiscau and La Grande subprovinces were deposited.

Geodynamic Settings of Late Paleozoic–Early Mesozoic Granitoid Magmatism at the Arctic Continental Margins: Insights from New Geochronological and Geochemical Data from the Taimyr Peninsula

Despite significant progress in Arctic geological studies, a number of principal questions concerning the Paleozoic collisional events remain unanswered. Therefore, the Taimyr Peninsula, representing the only outcropped high Arctic region where magmatic complexes, formed by Hercynian collision between the Siberian Craton and the Kara Block, are well exposed, is crucially important. In this paper we report new geochemical and geochronological data for intrusions in the poorly studied northeastern part of the Taimyr Peninsula. The obtained results in combination with published data show that supra-subduction magmatism at the southern active margin of the Kara Block continued from ca. 345 to 285 Ma (Early Carboniferous to Early Permian), and was followed by a post-collisional magmatic pulse that affected the whole Taimyr across terrane boundaries at ca. 280 Ma in the Early Permian. After cessation of the post-collisional magmatism at ca. 265 Ma, the Taimyr experienced extension, and voluminous magmatic series associated with a Siberian mantle plume were formed between 251 and 228 Ma during the Triassic. The studied post-collisional and plume-related intrusions of the Northeastern Taimyr are generally classified as evolved high-K I-type granites with adakitic affinity. The latter is a regional feature because the majority of the analyzed plume-related granitoids are geochemically similar to high potassium continental adakites. It is suggested that the adakitic geochemical characteristics of the plume-related granitoids resulted from melting of hydrated mafic lower crustal protoliths and were controlled by the source lithology. Comparison of the new results with data available for adjacent areas allows for correlation of terranes on a regional scale and sheds light on the evolution of the Arctic continental margins in general. In the Early–Middle Paleozoic, the Kara Block was part of a continental terrane that formed at the northern edge of Baltica as a result of Neoproterozoic Timanian orogeny. In the Early Carboniferous, the southern margin of Kara turned into an active margin, while its inferred continuation in the eastern Uralian margin of Baltica remained a passive margin until the Early Permian. This discrepancy can be explained by dextral displacement of Kara relative to Baltica that took place in the Early Carboniferous and was later accommodated by the formation of the Taimyr collisional belt in the course of the Early Permian collision between Kara and Siberia. After collision, the Taimyr was incorporated into the northern Eurasian margin as an uplifted block that experienced surface erosion and supplied clastic material in surrounding basins.

Episodic magmatism of the Gongga batholith (eastern Tibet) revealed by detrital zircon U-Pb geochronology: Insights into phased Xianshuihe fault activity and plateau growth

Understanding the onset and episodes of magmatism is essential for comprehending tectonic history, crustal extension, and geodynamic processes. However, due to physical constraints, many places have remained unexplored, which makes it difficult to understand their geological evolution. Following thorough sedimentary provenance analysis, the chronology and periods of magmatism within a drainage area can be revealed through the detrital zircon U-Pb dating method. Here, we present detrital zircon U-Pb ages (n = 1429) obtained from sediments in modern rivers of the Gongga batholith in the eastern Tibetan Plateau. Our results reveal five major magmatic episodes since the early Mesozoic. Three episodes of magmatism occurred in the early to middle Mesozoic (ca. 230–200 Ma, ca. 200–180 Ma, and ca. 180–160 Ma), followed by a protracted period of magmatic quiescence. During the Cenozoic, there were two main periods of magmatism at ca. 50–25 Ma and ca. 25–5 Ma. This is consistent with bedrock geochronological data acquired previously. We propose that the Mesozoic magmatism was most likely caused by post-collisional extension after the closure of the Paleo-Tethys Ocean. The two Cenozoic magmatic episodes are coeval with the progressive intensification of Xianshuihe fault activity. Consequently, these episodes highlight two significant phases of plateau growth in the eastern Tibetan Plateau: the northward push of the Indian plate and “lateral extrusion,” which is consistent with the ongoing subduction of the Indian plate beneath the Eurasian plate.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Field geology, petrology and geochronology of pluton–dyke systems: emplacement conditions of the Trapecio and Ushuaia peninsula dyke swarms (Fuegian Andes) and their relations with tectonics

We report the field geology, petrography, and geochemical and geochronological data for two dyke swarms in the Fuegian Andes, with the aim of correlating them with known suites and improving our knowledge of the magmatism of the Late Cretaceous rear arc and its relations with ductile deformation. We provide keys for correlation based on the K 2 O content of amphiboles. The Trapecio dyke swarm is mildly alkaline and ferriferous, with a zircon U–Pb age of 75 Ma, and therefore belongs to the Fuegian potassic magmatism (78–68 Ma). The Ushuaia peninsula dyke swarm, also known as the Ushuaia Peninsula Andesites, is shown to be high-K, calc-alkaline and magnesian, with new radiometric ages of 87–86 Ma. Although the Ushuaia peninsula dyke swarm exhibits foliation associated with ductile deformation, the Trapecio dyke swarm is post-kinematic and reveals emplacement controlled by the slaty cleavage in the metapelite host. Field and geophysical evidence suggest both swarms overlie small upper crustal plutons that are mostly buried. The variable composition of the dykes suggests a protracted history of dyke injection, mostly fed from deeper reservoirs. Contact metamorphism around both pluton–dyke systems is very weak. By comparison with adjacent plutons, we argue that the main variables controlling the development of the aureole are the small magma volumes and low rates of injection. Supplementary material: Full analytical procedures (Online Resource 1); detailed petrography of the investigated Trapecio dyke swarm samples (Table S1 and Fig. S1) with geochemical data (Table S3 and Fig. S2) (Online Resource 2); extended petrography and photomicrographs (Fig. S3) of the Ushuaia Peninsula Andesite dyke swarm (Online Resource 3); mineral chemistry data (Table S2) and the results of zircon U–Pb and hornblende Ar–Ar age measurements and ratios (Tables S4–S8) (Online Resource 4), and thermobarometric results (Table S9) (Online Resource 5) are available at https://doi.org/10.6084/m9.figshare.c.7097733

A conceptual model for the evolution of a magmatic system based on U-Pb zircon studies on the devonian granites of Sierra de San Luis, Argentina

ABSTRACT It is widely acknowledged that thermal models clearly demonstrate that crustal magma bodies should solidify rapidly upon emplacement. Small plutons can cool below the solidus in thousands of years, while even large plutons require hundreds of thousands of years, but not more than a million years. However, recent U-Pb zircon geochronological data contradict these results, strongly suggesting that magmatic systems are often characterized by protracted events. Therefore, a conceptual framework that reconciles thermal models and the geochronology data is necessary. The Devonian foreland magmatism of the Sierra de San Luis is made up of two distinctive suites, the Monzonite suite (<65 wt.% SiO2) and the Granite suite (>65 wt.% SiO2), both emplaced at ca. 3.7 kbar. Classification of the studied Devonian granitoids is debatable because they have a hybrid I- to A-type granite signature. Based on a robust geochronological U-Pb zircon dataset we corroborate the development of a protracted magmatic activity with three major crystallization events for this Devonian magmatism: 391 ± 1, 384 ± 1, and 379 ± 2 Ma. Considering these geochronological data, we postulate the presence of a deep mush reservoir, where a prolonged magmatic activity, permitted the prolonged crystallization of antecrysts (ca. 395–384 Ma). Migration of the parental magma from the mush reservoir zone occurred near the time of emplacement and culminated in the formation of an ephemeral magma chamber located at shallow levels, where zircon autocrysts crystallized (ca. 379 Ma). Age spectra reported within individual samples support the idea of a massive migration of magma when conditions were favourable (e.g. thermally matured crust). Individual crystallization ages recorded by monazites hosted in two-mica granites are comparable to those obtained from zircons, supporting the presence of a long-lasting hot source. Additional geochronological data indicate that a later thermal event (ca. 353 Ma) could have partially affected some areas of the Devonian magmatic zircons promoting Pb loss, with subsequent partial resetting of the isotopic clock.

Neogene to modern foreland basin development in the Sub-Andean zone of southern Bolivia and northern Argentina, 21−23°S

The Sub-Andean retroarc region is a unique example of an active continental-scale retroarc foreland basin system. Heavily targeted for hydrocarbon exploration, the region hosts a large volume of subsurface data coupled to surface studies dedicated to refining its evolution in time and space. This paper presents a regional correlation of stratigraphic markers from seismic reflection and well logs across the Sub-Andean foothills at 23−21°S in southern Bolivia and northern Argentina, which reveals the contrasting along-strike history of Mesozoic to Cenozoic tectonics that preceded the foreland basin setting. Supported by published geochronological data and new zircon U-Pb maximum depositional ages, we describe the depositional transition from pre-Andean to Andean stratigraphy and discrete episodes of foreland basin subsidence and shortening. Based on interpreted stratigraphic breaks, we define the extent and stepwise evolution of this foreland basin, which was characterized by the progressive eastward migration of foreland basin depozones. Based on restored thickness profiles, we present flexural models of basin subsidence for the Sub-Andean foothills region. The modeling of discrete episodes of foreland basin subsidence refines the widely accepted bimodal elastic strength in the foreland basin at 21−23°S, which is weaker in the western ranges (∼20 km effective elastic thickness) and stronger eastward (&amp;gt;40 km). Modeling results also reveal minimum values of subsidence rates (up to 1.2 mm/yr) in the sequential foredeep depozones and suggest that the modeled tectonic load migration—as constrained by the record of syntectonic strata—probably increased over time through the incorporation of Sub-Andean rocks into the orogenic wedge.

Reassessing the timing of high-strain deformation in the Strangways Metamorphic Complex, Central Australia, by in situ mica Rb–Sr and titanite U–Pb geochronology

Dating the timing of deformation within shear zones is critical to quantifying orogenic processes and developing time-resolved regional tectonic frameworks. Such work requires the integration of detailed microstructural analysis with in situ geochronology to quantify when deformation mechanisms were active at the micro-scale. The Proterozoic, granulite-facies Strangways Metamorphic Complex was exhumed during the Devonian to Carboniferous intracontinental Alice Springs Orogeny. New microstructural observations, quartz c -axis orientation analyses, mica chemistry, Ti-in-biotite thermometry, in situ mica Rb–Sr and titanite U–Pb geochronology outline a detailed history of ductile shearing across the complex. Movement along the north boundary shear zone of Strangways Metamorphic Complex appears to have initiated c. 382 Ma, preceding peak metamorphism in the area during the Alice Springs Orogeny. Widespread reverse-sense ductile shearing occurred within the Strangways Metamorphic Complex between c. 365 and 355 Ma, and correlates with rapid cooling of the region. Late-stage ductile deformation is recorded at c. 335 Ma, likely reflecting the terminal exhumation of the Strangways Metamorphic Complex. Finally, the new in situ muscovite and biotite Rb–Sr data collected herein permit comparison with previous two-point mica Rb–Sr isochrons and 40 Ar– 39 Ar dates from the same specimens. In the rocks analysed, the biotite Rb–Sr system returned dates similar to the previous 40 Ar– 39 Ar white mica dates, perhaps indicating a similar effective closure temperature. Supplementary material: Test results and previous geochronology data from the Alice Springs Orogeny are available in tabular form at https://osf.io/yjp24/?view_only=0bf5bec9f5c94a1aa4fb413320ec24e8

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.

Petrogenesis of late triassic high-silica granites in the North Qiangtang terrane, central Tibetan Plateau

Although high-silica granites can provide unique insights into the maturity of the continental crust and rare metal enrichment, the origin of high-silica granitic magmatism remains uncertain. In this paper, we present an integrated study of zircon U-Pb geochronology and trace elements, whole-rock geochemistry, and Sr-Nd isotopes for two typical high-silica granites (namely, the Longbao granitic porphyry and the Yushu granite) found in the North Qiangtang terrane, central Tibetan Plateau. Zircon geochronological data indicate that these high-silica granites crystallized at 217–214 Ma. All the samples from the Longbao granitic porphyry and the Yushu granite exhibited high SiO2, low MgO, depletion of Ba, Nb, Sr, P, and Ti, and enrichment of Th and U. They exhibited relatively high (87Sr/86Sr)i ratios of 0.7120–0.7136 and low εNd(t) values of −8.58 ∼ −7.58; together with their old ages according to the two-stage Nd model (1.6–1.7 Ga), these features indicate the involvement of crustal materials. Geochemical and isotopic variation indicated that the high-silica granites studied were mainly produced by the dehydration melting of a muscovite (Ms)-bearing source, and that the Triassic turbidites might be a good candidate for the magma source. Combining this evidence with new regional studies, it can be concluded that partial melting of Triassic turbidites induced by slab roll-back might be the key factor controlling the origin of Late Triassic magmatism in the North Qiangtang terrane.

Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

U-Pb geochronology by isotope dilution−thermal ionization mass spectrometry (ID-TIMS) has the potential to be the most precise and accurate of the deep time chronometers, especially when applied to high-U minerals such as zircon. Continued analytical improvements have made this technique capable of regularly achieving better than 0.1% precision and accuracy of dates from commonly occurring high-U minerals across a wide range of geological ages and settings. To help maximize the long-term utility of published results, we present and discuss some recommendations for reporting ID-TIMS U-Pb geochronological data and associated metadata in accordance with accepted principles of data management. Further, given that the accuracy of reported ages typically depends on the interpretation applied to a set of individual dates, we discuss strategies for data interpretation. We anticipate that this paper will serve as an instructive guide for geologists who are publishing ID-TIMS U-Pb data, for laboratories generating the data, the wider geoscience community who use such data, and also editors of journals who wish to be informed about community standards. Combined, our recommendations should increase the utility, veracity, versatility, and “half-life” of ID-TIMS U-Pb geochronological data.

Is the Yermak Plateau a continental fragment from North America? Constraints from Cretaceous and early Eocene magmatic events

The Yermak Plateau (YP) north of Svalbard is a prominent bathymetric feature in the Eurasia Basin of the Arctic Ocean, forming the northwesternmost margin of the Eurasian plate. Seismic data indicate that the YP comprises continental basement; however, little is known about its geology. New petrographic, geochemical, Sr–Nd isotopic, and Ar–Ar geochronological data were obtained on rock fragments, which were previously recovered from basement highs of the northeastern and southwestern YP and are dominantly of magmatic origin. These new data combined with available literature data, and comparisons with volcanic and sedimentary rocks from onshore and offshore areas adjacent to the YP indicate that the northeastern YP and the southwestern YP are different regarding their geological evolution. The southwestern YP comprises an alkaline basaltic suite for which an Ar–Ar biotite age of 51 Ma was previously reported. The suite was formed in a continental extensional regime offshore northern Svalbard. Associated sedimentary rocks (sandstone, several limestones) show petrographic similarity with rocks of the Devonian Old Red Sandstone on Svalbard. From the northeastern YP, in contrast, we recovered mildly alkaline basaltic rocks with mid-Cretaceous Ar–Ar ages (102 ± 3 and 98 ± 3 Ma). The rocks show certain geochemical characteristics (partial enrichments of P, Ba, and Eu), which overlap with similar-aged Cretaceous basaltic rocks from northern Ellesmere Island of Canada and North Greenland. We suggest that the northeastern YP is a continental fragment derived from the North American plate, which was separated from the conjugate Morris Jesup Rise and juxtaposed to the geologically distinct southwestern YP by the propagation of the Gakkel Ridge spreading center since the early Oligocene.Graphical

A Greenland-wide empirical reconstruction of paleo ice sheet retreat informed by ice extent markers: PaleoGrIS version 1.0

Abstract. The Greenland Ice Sheet is a large contributor to global sea level rise, and current mass losses are projected to accelerate. However, model projections of future ice sheet evolution are limited by the fact that the ice sheet is not in equilibrium with present-day climate but is still adjusting to past changes that occurred over thousands of years. While the influence of such committed adjustments on future ice sheet evolution remains unquantified, it could be addressed by calibrating numerical ice sheet models over larger timescales and, importantly, against empirical data on ice margin positions. To enable such paleo data–model interactions, we need Greenland-wide empirical reconstructions of past ice sheet extent that combine geomorphological and geochronological evidence. Despite an increasing number of field studies producing new chronologies, such a reconstruction is currently lacking in Greenland. Furthermore, a time slice reconstruction can help to (i) answer open questions regarding the rate and pattern of ice margin evolution in Greenland since the glacial maximum, (ii) develop a standardised record of empirical data, and (iii) identify new sites for future field campaigns. Based on these motivations, we here present PaleoGrIS 1.0, a new Greenland-wide isochrone reconstruction of ice sheet extent evolution through the Late Glacial and early- to mid-Holocene informed by both geomorphological and geochronological markers. Our isochrones have a temporal resolution of 500 years and span ∼ 7.5 kyr from approximately 14 to 6.5 kyr BP. We describe the resulting reconstruction of the shrinking ice sheet and conduct a series of ice-sheet-wide and regional analyses to quantify retreat rates, areal extent change, and their variability across space and time. During the Late Glacial and early- to mid-Holocene, we find the Greenland Ice Sheet has lost about one-third of its areal extent (0.89 million km2). Between ∼ 14 and ∼ 8.5 kyr BP, it experienced a near-constant rate of areal extent loss of 170 ± 27 km2 yr−1. We find that the ice-sheet-scale pattern of margin retreat is well correlated to atmospheric and oceanic temperature variations, which implies a high sensitivity of the ice sheet to deglacial warming. However, during the Holocene, we observe inertia in the ice sheet system that likely caused a centennial- to millennial-scale time lag in ice extent response. At the regional scale, we observe highly heterogeneous deglacial responses in ice extent evident in both the magnitude and rate of retreat. We hypothesise that non-climatic factors, such as the asymmetrical nature of continental shelves and onshore bed topographies, play important roles in determining the regional- to valley-scale dynamics. PaleoGrIS 1.0 is an open-access database designed to be used by both the empirical and numerical modelling communities. It should prove a useful basis for improved future versions of the reconstruction when new geomorphological and geochronological data become available.

On the Rhodopean protoliths and their Middle Jurassic to Early Cretaceous evolution. A review

The Rhodope Massif represents a large high-grade metamorphic complex situated in the Balkan Peninsula, straddling the border between Bulgaria and Greece. Geological studies carried out during the last thirty years clearly established that the complex is composed of three major lithotectonic units characterized by differing protolith ages and Alpine thermotectonic evolution. The Rhodope Massif consists of Upper and Lower terranes representing continental fragments composed mainly of pre-Mesozoic magmatic rocks and covered by Early Mesozoic sedimentary sequences. These two entities are separated by an Intermediate Terrane comprising a Jurassic magmatic arc and its host rocks tectonically intercalated with Jurassic ophiolitic fragments together with the Early Mesozoic sediments. Detailed analyses of the previously published geochronological data revealed that the three main tectonic terranes were juxtaposed in the Late Jurassic–Early Cretaceous during the continental collision and northward subduction of the Lower and Intermediate terranes. These rocks experienced Middle Jurassic to Early Cretaceous high-pressure metamorphism, followed by high-temperature one accompanied by anatexis. At that time, the Upper Terrane was metamorphosed and deformed only partially. Being part of the European margin, this terrane represented an upper continental plate during the subduction, and therefore is not considered as a part of the Alpine Rhodope metamorphic complex. It is important to note that, although most of the present-day fabric and major tectonic zones in the Rhodope metamorphic complex are younger than Early Cretaceous, and therefore they postdate the geological evolution discussed in this study, they often reactivate the old boundaries between the main terranes and units.

Revisiting the depositional age and provenance characteristics of metasedimentary rocks from the basement units in the Central Pontides (N Turkey): New constraints for tectonic evolution of the southern Black Sea region

The pre-Jurassic tectonic evolution of the Central Pontides in northern Turkey is still poorly understood due to the lack of detailed geochemical and geochronological data from the basement units. Therefore, this study reports for the first time combined whole rock geochemistry, trace element data and U-Pb ages for detrital zircons, and Ar-Ar geochronological data from the metasedimentary rocks of the Devrekani Massif, Geme Complex, and the Serveçay Unit to better understand their provenance, depositional age characteristics, and tectonic evolutions. The detrital zircon U-Pb data of metasedimentary units from the Devrekani Massif, Geme Complex, and the Serveçay Unit yield ca. 191, 185 and 298 Ma maximum depositional ages (youngest age peaks), respectively. The Devrekani Massif is dominated by Permo-Carboniferous-aged detrital zircons (67 %), whereas Neoproterozoic and Devonian-aged detrital zircons are more common in the Geme Complex (47 %) and the Serveçay Unit (53 %). These distinct age distributions clearly indicate that the Devrekani Massif may has been deposited in a dissimilar location compared to the Geme Complex and the Serveçay Unit. Furthermore, in contrast to the Devrekani Massif, the source area of the metasedimentary rocks from the Geme Complex is comparable with that of the Serveçay Unit. Lastly, the obtained detrital zircon U-Pb and mica Ar-Ar ages suggest that the Devrekani Massif and the Geme Complex were deposited and metamorphosed during the Early and Middle Jurassic, respectively. The Serveçay Unit was deposited and metamorphosed in the Permian.

Cretaceous to early Paleogene sediment provenance transition from continental to magmatic arc systems in the Northwestern Pacific Region

Unraveling the Paleo-Kuril Arc's origins is key to understanding northwest Pacific tectonics. The Paleo-Kuril Arc is viewed as an intraoceanic arc from trench subduction between the Izanagi and Pacific Plates. Alternatively, several studies suggest the Paleo-Kuril Arc as a continental magmatic arc, hypothesizing the existence of a mid-oceanic ridge and Paleogene subduction, placing the Paleo-Kuril Arc near the Okhotsk Block's southern edge. This study clarifies these hypotheses, previously clouded by limited geochronological data on deposits in the Paleo-Kuril Arc. We conducted U–Pb dating to examine the origins of detrital zircons from the Cretaceous–Paleogene Tokoro and Nemuro Belts of the Paleo-Kuril Arc. Cluster analysis, merging new and existing data, identified two unique detrital zircon age clusters. The abundance of Precambrian zircons in Cretaceous–Paleocene Paleo-Kuril Arc sandstones (Type 1 Cluster) suggests a continental magmatic origin, supporting the ridge subduction model. However, an early Eocene shift to a consistent local volcanic source (Type 2 Cluster) highlights a significant provenance change. This geochronological evidence, indicating a separation from continental sources, calls for further research to decode the simultaneous development of sediment sources in different geological belts, potentially tied to the ridge subduction event.

Multi-proxy paleoenvironmental data from Paulina Marsh inform human-environmental dynamics in the Northern Great Basin U.S.A.

Understanding the dynamics between climate change and human adaptive strategies is a longstanding question driving paleoecological and archaeological research in North America's Great Basin. We present multiproxy data from five sediment cores retrieved from Paulina Marsh in the Fort Rock Basin, Oregon, an area renowned for its archaeology but lacking the paleoenvironmental data needed to fully contextualize those records. Radiocarbon, pollen, particle size, elemental, and charcoal analyses of one core, and geochronological data from four additional cores, reveal fluctuating vegetation communities, hydrologic conditions, and fire histories during the Early and Late Holocene that are consistent with models proposed to explain changing settlement-subsistence patterns in the region. There was likely an emergent marsh or meadow and an absence of Juniperus at the core site during the Early Holocene. Middle Holocene deposits are not present due to a geologic unconformity, perhaps because of channel migration and climatic aridity. Late Holocene sediments record a more mesic meandering stream system between ∼3900 and 2200 years ago, followed by an increase in xeric-adapted vegetation in the last 2000 years. The lack of Juniperus pollen in the Early Holocene sediments inform ongoing debates about Juniperus spread in the Great Basin. These data represent the first Early Holocene pollen record from the Fort Rock Basin and are one of few lowland vegetation histories of this age in the region. This study contributes to our understanding of past ecology in semi-arid environments, provides new context for archaeological interpretations, and establishes a framework for future work in the region.