Zircon Geochronology Research Articles

Constraints on the age of dome-and-keel structures in the Pilbara Craton through integrated garnet geochronology and microstructural analyses

The dome-and-keel granite-greenstone structures in the East Pilbara Terrane are commonly interpreted to result from a crustal overturn process that underpinned the growth and stabilization of continental crust on early Earth. We investigate the timing and timescales of this overturn process using integration of garnet and zircon geochronology with microstructural analyses. We use this integrated approach to provide insight into the evolution of dome-and-keel structures in the East Pilbara Terrane. Garnet Lu-Hf and Sm-Nd geochronology shows that two discrete periods of fabric development related to dome formation occurred between ∼ 3.42 to 3.39 Ga and 3.34 to 3.30 Ga. The older population of garnet is mechanically disaggregated, and we interpret that their growth is related to an early metamorphic event in the East Pilbara that occurred prior to the main phase of dome-and-keel formation. The younger population of garnet, between 3.34 and 3.30 Ga, include garnet with post-kinematic growth structures. By coupling these microstructures and garnet Lu-Hf ages, we show that the main phase of dome formation is dated by this younger event of garnet growth at about 3.34 and 3.30 Ga. The Sm-Nd ages of these garnets are systemically younger than the Lu-Hf ages, consistent with protracted cooling of the system after dome formation. Together, these data show that dome-and-keel structures in the East Pilbara formed quickly, perhaps in a few tens of million years.

Monazite and xenotime petrochronologic constraints on four Proterozoic tectonic episodes and ca. 1705 Ma age of the Uncompahgre Formation, southwestern Colorado, USA

Abstract The Proterozoic tectonic evolution of the southwestern USA remains incompletely understood due to limited constraints on the timing and conditions of the tectono-metamorphic phases and depositional age of metasedimentary successions. We integrated multi-scale compositional mapping, petrologic modeling, and in situ geochronology to constrain pressure-temperature-time paths from samples of Paleoproterozoic basement gneisses and overlying quartzites in southwestern Colorado, USA. Basement gneiss from the western Needle Mountains records metamorphic conditions of 600 °C at 0.75 GPa at 1764 ± 9 Ma and ~575 °C at 1741 ± 10 Ma. Gneiss sampled from drill core near Pagosa Springs, Colorado, records conditions of 700 °C at 1748 ± 9 Ma, 800 °C at 1.1 GPa at 1650 ± 40 Ma, 540 °C at 1570 ± 36 Ma, and 440 °C at 1424 ± 12 Ma. The Uncompahgre Formation was deposited at ca. 1705 Ma, as constrained by detrital monazite (1707 ± 8 Ma) and xenotime (1692 ± 40, 1725 ± 50 Ma), metamorphic xenotime (1650 ± 10 Ma), and published 40Ar/39Ar and detrital zircon data. Compositions of ca. 1705 Ma detrital monazite and xenotime are consistent with derivation from a garnet-bearing source in the Yavapai orogenic hinterland. The Vallecito Conglomerate and Uncompahgre Formation record macroscopic folding and greenschist-facies metamorphism at 1650 ± 10 Ma and temperatures of 270 °C to >570 °C at 1470–1400 Ma. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon geochronology yielded dates of 1775 ± 18 Ma from the Twilight Gneiss and 1696 ± 7 Ma from the Bakers Bridge Granite, supporting previous isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates. The Eolus Granite yielded a date of 1463 ± 6 Ma, which is older than previous 1.44–1.43 Ga ID-TIMS dates. The newly dated granite of Cataract Gulch is 1421 ± 12 Ma. In situ analysis of detrital and meta-morphic monazite and xenotime, igneous zircon, and quantitative thermobarometry, integrated with previously published constraints, indicate multiple tectonic episodes after the emplacement of 1800–1760 Ma arc-related rocks. The region experienced greenschist- to amphibolite-facies metamorphism (M1) from 1760 Ma to 1740 Ma, which was followed by the intrusion of granites at 1730–1695 Ma and deposition of the Uncompahgre Formation at ca. 1705 Ma, contemporaneous with the Yavapai orogeny. Metamorphism at 1680–1600 Ma was characterized by greenschist-facies conditions near Ouray, Colorado, and granulite-facies conditions near Pagosa Springs (M2) during the Mazatzal orogeny. From 1470 Ma to 1400 Ma, greenschist- to amphibolite-facies metamorphism (M3) and largely granitic plutonism occurred during the protracted Picuris orogeny. These results demonstrate the power of monazite and xenotime analyses to constrain depositional ages, provenance, and pressure-temperature-time (P-T-t) paths to resolve the compound orogenic history that is characteristic of most mountain belts.

Graphitization in Paleoproterozoic granulites from the Taihua Complex, North China Craton: Constraints from laser Raman spectroscopy, carbon isotopes and geochronology

The presence of graphite as a refractory form of solid carbon in high grade meta-sedimentary rocks serves as a valuable tool for identifying carbon sources and assessing the movement of carbon through the Earth's interior. In this study, we investigate the graphite formation processes from different lithologies (marbles, metapelites) from the Paleoproterozoic granulites in the southern margin of North China Craton. By utilizing a range of analytical techniques, including petrographic, mineral-chemical, laser Raman spectroscopic, carbon stable isotopic, and geochronological studies, we characterize the textural and isotopic variety of graphite and the timing of metamorphism associated with graphitization. The results suggest a progressive growth and graphitization of graphite during medium to high temperature metamorphic facies. The δ13C values of crystalline graphite in metapelites and marble range in −24.00‰ to −20.10‰, and − 22.50‰ to −21.60‰, respectively, both close to organic carbon averages. The calcite from the graphite-bearing marble shows δ13C values in the range of −2.90‰ to −2.80‰, which corresponds to marine carbonates. In contrast, graphite-bearing quartzo-feldspathic gneiss and diopside/augite-bearing marble show heavier isotopic values of −14.4‰ to −16.5‰, suggesting graphite precipitation from fluids of both organic and magmatic origin. The spectral and isotopic signatures of graphite in these rocks indicate a dominant biogenic signature with mixture of abiogenic carbon sources. Zircon UPb geochronology marks the timing of high-grade metamorphism at ca. 1.93 to 1.92 Ga, associated with graphite formation during subduction and accretion process associated with the final assembly of the North China Craton. We propose that crystalline graphite was formed during the continental collision-triggered medium to high temperature metamorphic event, consistent with a global graphite metallogenic event in the Paleoproterozoic.

High-Latitude Depositional Systems, Provenance, and Basinal Setting of the Late Cretaceous Cantwell Basin, Denali National Park and Preserve, Alaska: A Stratigraphic Framework for Paleontological and Paleoclimatic Studies

The Cantwell Formation of the central Alaska Range provides a robust archive of high-latitude, Late Cretaceous depositional systems and paleo-floral/faunal assemblages. Our stratigraphic analysis defines two mappable members. The lower member (1500–2000 m thick) represents vegetated alluvial fan and braided fluvial systems that transition up-section to fluvial–estuarine systems that drained into an inland continental seaway. The upper member (~2000 m thick) represents estuarine–marginal marine and lacustrine systems. Previous paleontological studies demonstrate that the Cantwell basin was populated by various dinosaurs, fishes, bivalves, birds, and marginal marine micro-organisms. Integration of new and published geologic mapping allows for reconstruction of depositional systems at the basin scale and provides additional paleogeographic context. The northern basin margin was defined by a previously unrecognized south-verging thrust belt, whereas the southern margin of the basin was defined by a north-verging thrust belt inboard of an active magmatic arc. Sediment sources interpreted from U-Pb detrital zircon geochronology included the coeval magmatic arc and older Cretaceous plutons, and Proterozoic–Mesozoic strata exhumed along the basin margins. Results of our study provide a depositional, stratigraphic, and structural framework that may serve as a guide for future paleontological and paleoclimatic investigations of Late Cretaceous Arctic environments of the Cantwell basin.

Lithospheric dripping triggered by slab break-off: A possible mechanism for Late Carboniferous magmatism in the eastern Central Asian Orogenic Belt

In this paper, we present zircon UPb dating, elemental geochemistry, and Sr–Nd–Hf isotopic compositions for Late Carboniferous intrusive rocks in the northern Great Xing'an Range, northeast China. We decipher the mechanisms which triggered lithospheric thinning under microblock-microblock collision and provide a new perspective on the Late Paleozoic evolution of the eastern Central Asian Orogenic Belt. Zircon UPb dating indicates that Jifeng gabbroic diorites and Xinlin granites were formed during a short time interval at 322–321 Ma, whereas the Xinlin gabbros were crystallized at 300 ± 2 Ma. The Jifeng gabbroic diorites exhibit typical arc characteristics, depleted in HFSEs and enriched in Pb and have positive εNd(t) (+1.88 to +2.00) and εHf(t) (+6.6 to +10.7) values, suggesting they originated from the partial melting of depleted lithospheric mantle modified by slab fluids. The Xinlin gabbros belong to alkaline series and are characterized by the enrichment in HFSEs with positive Nb and Ta anomalies and depleted NdHf isotopic compositions (zircon εHf(t) = +12.5 to +18.9, whole rock εNd(t) = +8.0 to +8.1). High Nb concentrations and low La/Nb (0.81–0.83) and La/Ta (12.50–14.61) ratios of the Xinlin gabbros indicate an origin from a depleted asthenospheric mantle. The Xinlin granites have high-K calc-alkaline compositions, belonging to I-type granites. These granites have positive εHf(t) values (+0.2 to +15.1) and juvenile two-stage model ages (1314–506 Ma) with low Sr and high Yb contents, indicating they were formed by the partial melting of a juvenile lower crust under low-pressure conditions. These data, together with the temporal and spatial distribution and the geochemistry characteristics of the Carboniferous igneous rocks in the Great Xing'an Range, suggest that the amalgamation between the Erguna–Xing'an and Songnen blocks occurred before the Late Carboniferous. The occurrence of asthenospheric mantle-derived mafic rocks indicates localized thinning process of lithosphere. Late Carboniferous magmatism on the Erguna–Xing'an Block attributed to dripping or piece removal of the lithosphere due to asthenospheric fluctuation triggered by slab break-off.

Geochemistry, U-Pb zircon geochronology, and Fe isotopes of the Shanzhuang banded iron formation in the North China Craton: Implications for genesis and depositional environment

The Shanzhuang banded iron formation (BIF) occurs in the Shancaoyu Formation, Taishan Group, in the western Shandong Province (WSP), eastern North China Craton (NCC). We constrained the Shanzhuang BIF depositional age of ∼2.50 Ga based on the zircon U-Pb dating of the leptynite interlayers and the cross-cutting metagranitoid. After deposition, the Shanzhuang BIF was subsequently metamorphosed into amphibolite facies at 2.50–2.45 Ga. According to different mineral assemblages, the Fe ores can be divided into three types: magnetite + quartz ± hornblende (type-1 ore), magnetite + quartz + hornblende + garnet ± hematite (type-2 ore), and quartz + hematite ± magnetite ± hornblende (type-3 ore). In the Post-Archean Australian Shale (PAAS)-normalized rare earth element and yttrium (REY) patterns, the three ore types show consistent flat REY curves. All ore types have moderate ƩREY concentrations (27.24–143 ppm), (La/Yb)N values of 0.29–2.31, significant positive Eu anomalies (1.05–3.47), slightly negative or positive Ce anomalies (0.87–1.26), slightly positive Y anomalies (1.16–1.48), and no apparent fractionation between light REEs (LREEs) and heavy REEs (HREEs), indicating mixing of hydrothermal fluid and seawater. The similar REY patterns and heavy Fe isotopes (0.47–1.02‰) of the three ore types suggest a certain amount of continental detritus was incorporated during the precipitation of the Fe phases in the Neoarchean-Paleoproterozoic oceans. The post-depositional metamorphism did not significantly affect the original REY geochemical signature of the BIF. The Shanzhuang BIF ores are not highly pure chemical sediments, but the type-1 ore is relatively pure and more representative of the original sedimentary composition. By contrast, the type-3 ore tends to have higher δ56Fe ratios (0.74–1.02‰) but lower δEu (1.27–1.97‰), implying substantial post-depositional hydrothermal alteration. The Shanzhuang Fe deposit is an Algoma-type BIF, and the surrounding rock consists of pyroclastic materials. Our model indicates that the Shanzhuang BIF was probably deposited in a redox stratified paleo-ocean environment.

Reconstructing the evolution of an ancient continental arc: Implications from the temporally-spatially related shoshonitic to calc-alkaline intrusive magmatism in the North China Craton

Coeval shoshonitic and calc-alkaline to high-K calc-alkaline rock series were discovered in the eastern North China Craton (NCC). Here, we report zircon and titanite UPb dating, zircon oxygen isotopic, whole-rock major and trace element and SmNd isotopic data for these rocks. Zircon and titanite UPb geochronology suggests that the coeval shoshonitic to calc-alkaline mantle-derived magmas from the Jinan terrane were emplaced at ∼2.5 Ga and recorded multi-phases of metamorphic imprints. The shoshonitic series in Group I show higher K2O, but in contrast, the calc-alkaline to high-K calc-alkaline series (Group II) are characterized by higher Na2O. The two groups have enriched light rare earth elements (LREE) and depleted/nearly flat heavy rare earth elements (HREE). They also show negative anomalies in some HFSE and positive anomalies in LILE. Therefore, the geochemical data, SmNd and O isotopes included, show that the Jinan shoshonitic to calc-alkaline magmas were generated by melting of the metasomatized mantle at an ancient continental arc. Distinct geochemical features possibly suggest different mantle source features (metasomatic agents). The elevated zircon δ18O values imply that the weathering was significant during the end of Archean. In addition, the crustal reworking or intra-crustal recycling process played an important role in the continental crust evolution. The low-δ18O magmas documented here possibly indicate high-temperature water-rock interaction that occurs between continental crust and meteoric water. This study represents an example of co-existed shoshonitic and calc-alkaline mantle-derived magma derived from the melting of metasomatized mantle above an ancient subduction zone. Similar coeval associations of shoshonitic to calc-alkaline mantle-derived rocks, in combination with high-P granulites and crust-derived granites, may be used to constrain the ancient subduction-collisional belts.

A post-collisional batholith from Southern Iberia rooted in the Earth's mantle: Los Pedroches batholith

The Los Pedroches batholith (SW Spain) is one of the most salient igneous alignments of the Iberian massif. The batholith is considered one of the best examples of post-collisional batholiths of Iberia and is dominated by a biotite granodiorite that was emplaced in the shallow crust postdating the main deformation phases of the Variscan orogeny. In the Quintana de la Serena area, to the northwest of the batholith, granodiorites were partially emplaced into dacites characterized by the presence of abundant orthopyroxene. The quality of outcrops and abundant quarries in the area, together whit the near absence of local crustal contamination, make this zone an ideal location for petrogenetic studies about the origin of granodiorite magmas and their related microgranular enclaves. We present in this paper new SRHRIMPII-based zircon geochronology data that indicate orthopyroxene-bearing subvolcanic rocks emplaced and cooled at the age of 310 ± 2 Ma, slightly earlier than the intrusion and cooling of the massive granodiorites (307 ± 1 Ma and 306.6 ± 0.7 Ma) and their related mafic microgranular enclaves (307.8 ± 0.8 Ma). Whole rock geochemistry demonstrates that the three groups of rocks, dacites, granodiorites and mafic microgranular enclaves, define a coherent geochemical trend indicating that they are cogenetic and related by fractionation of a common parental magma. This study proves the role played by intermediate magmas of sanukitoid affinity in the generation of the most abundant and massive granodiorite rocks that form large post-collisional batholiths in Iberia.

Magma evolution and growth process of the Ushikiri-yama granodiorite body a member of the Cretaceous Northern Kyushu batholith, SW Japan: Implication for the crustal forming and growth of the initial Cretaceous plutonic activity in northern Kyushu along the East Asian active continental margin

The ascending and emplacement processes of granitoid magma combined with magma genesis are essential in intrusive rocks of various scales. This study is performed to reconstruct and re-evaluate the formation of the Ushikiri-yama granodiorite body, a small-scale plutonic body in the Northern Kyushu batholith. The Ushikiri-yama granodiorite occurs as a laccolith, which can be classified into the south and north bodies. Both bodies are situated along the low-angle rigidity boundary of the host rocks between crystalline limestone and pelitic-psammitic metamorphic rocks. Magmatic foliation and lineation reveal that the granodiorite magma extends to the south and north from the central region of the Ushikiri-yama granodiorite to form a laccolith. The zircon UPb dating of the south and north bodies presents ages of 112.1 ± 0.8 and 110.8 ± 0.6 Ma, respectively, which indicates that the granodiorite magmas are active at different pulses. These ages correspond to the initial stage of the Northern Kyushu batholith. The Ushikiri-yama granodiorite magma ascends from the source region through the same conduit with at least two pulses and is located at the shallow crustal level, utilizing the low-angle rigidity boundary to form a small-scale laccolith as a pioneering magmatic activity of the Northern Kyushu batholith. As the northern region of Southwest Japan and the southern region of the Korean Peninsula during the Cretaceous are assumed to be situated within the extensional setting due to slab roll-back, the results of this study provide new insights into the complicated batholith formation processes and crustal evolution under the extensional regime.

Sediment provenance and dispersal in the early Eocene Dongying Depression, Bohai Bay Basin, Eastern China: Evidence from detrital zircon geochronology, geochemistry and petrology

Comprehensive provenance studies of syn-rift basin fills are required to better understand possible sources of clastic detritus and sediment routing systems. The Eocene fill of the Bohai Bay Basin in eastern China represents a syn-rift succession, where subsurface datasets permit investigation of sediment sources and sinks. New detrital zircon U–Pb samples (441 detrital zircon grains) from six wells were combined with elemental geochemical analysis of siliciclastic sediment, sandstone petrography and palynology to investigate depositional ages and provenance. This study demonstrates the importance of integrating geochronometry, geochemistry, petrology and palynology datasets to fully unravel syn-rift sediment provenance and routing. Zircons of the Dongying Depression were derived principally from an active continental margin island-arc setting characterized by felsic acid magmas, and subordinately from a recycled orogenic belt. The Shicun and Binnan faults controlled the relationship between sediment routing systems and source areas, explaining spatial differences of provenance signals in the depression. The routing system around the Shicun fault is characterized by a dominance of late Paleozoic and Paleoproterozoic zircons and subordinate Mesozoic zircons. In contrast, increased Mesozoic zircons in samples from south of the Binnan fault provide evidence of Mesozoic magmatism in this area. The early Eocene sediments record the signal of early Cretaceous magmatism in the North China Craton, but lack a record of substantial syn-depositional magmatic activity since the Paleogene in the Dongying Depression. Zircons from early Cretaceous strata and pre-existing zircons from the Xing-Meng Orogenic Belt and Inner Mongolia paleo-uplift were transported to the Yanshan and Luxi areas together. These sediments entered the Dongying Depression in the early Eocene, following a period of recycling. In addition, a Precambrian basement signal indicates possible denudation of Neoarchean to Proterozoic rocks in the Luxi uplift and from the Binnan fault footwall. Overall, the provenance signals of the basin reflect zircon recycling from an Early Cretaceous succession, denudation of ancient magmatic rock masses and the absence of syn-sedimentary magmatism.

Provenance variation of the Cambrian-Ordovician sedimentary rocks across South China and implication for its paleogeography in East Gondwana

The tectonic nature of the Early Paleozoic Kwangsian event in the South China Block (SCB) and the paleogeographic position of the SCB in East Gondwana remain enigmatic. Clastic rocks contain significant clues for their detritus provenances, paleogeographic reconstruction and tectonic setting. This study presents detailed detrital zircon UPb geochronology and Hf isotope analyses for the Cambrian sandstones in the SCB, as well as summarizing previously-published data of other Cambrian-Ordovician sedimentary rocks. All the Cambrian-Ordovician sedimentary samples can be subdivided into three groups: the ZD-CL (between Zhenghe-Dapu and Chenzhou-Linwu faults), CL-AL (between Chenzhou-Linwu and Anhua-Luocheng faults) and AL-West (west of Anhua-Luocheng Fault) zones. These three subgroup samples have similar detrital zircon age spectra, cumulative proportion curves and εHf(t) values. Their detrital zircon age spectra are characterized by one prominent age-peak at ∼953 Ma and three subordinate age-peaks at ∼2500 Ma, ∼788 Ma and ∼ 529 Ma. Such signatures argue against provenance variation throughout the SCB during the Early Paleozoic, suggesting an intra-continental affinity for the Kwangsian event in the SCB. The Cambrian-Ordovician sedimentary samples in the SCB have similar detrital zircon age spectra and cumulative proportion curves to those in Australia, Qiangtang and Himalaya. The detrital zircons of ∼953 Ma and ∼ 529 Ma age-clusters in the SCB have similar εHf(t) values to those in Australia and Qiangtang. These features imply that the SCB was located at the nexus between Australia and India during the Cambrian-Ordovician, receiving sediment detritus both from India and Australia.

Rheological behavior of amphibolite facies migmatites during orogenesis: A case study from the North Qinling Belt, China

The rheological behavior of amphibolite-facies migmatites are key to understanding the evolution of middle–lower crust during orogenesis. The amphibolite-facies metamorphosed migmatites from the North Qinling Terrane are investigated to elucidate high temperature melt-present deformation and shear localization. The metatexite (plagioclase amphibolite and biotite plagiogneiss), diatexites, and deformed residuum (mylonitic amphibolite and layered amphibolite) are well-preserved in outcrops. The SW dipping and E-W striking foliation, and ptygmatic, asymmetrical folds indicate compressional deformation with top-to-the-WNW shearing. Zircon UPb geochronology indicates that crustal anatexis mainly occurred at ca. 400–386 Ma, associated with the collision between the North and South China Blocks. The occurrence of peritectic amphibole, the estimated anatectic conditions of 2.32–4.29 kbar and 595–691 °C and variation of mineral major compositions jointly demonstrate incongruent water-present melting reactions, which involved biotite- or amphibole-breakdown, while the deformation temperature is constrained at 605–644 °C. In the plagioclase amphibolite, the amphibole is dominated by (100)[001] dislocation slip, while plagioclase doesn't display a clear fabric. In the biotite plagiogneiss, plagioclase is dominated by strain-induced (010)[100] slip and quartz shows prism <a > slip. Rheological processes (brittle fracturing, melt(fluid)-assisted partial mylonitization and layering process) indicate that melt migration has an effect on the residuum. The formation of amphibole type-II fabric is controlled by cataclastic flow and rigid rotation during progressive deformation process and dissolution-precipitation processes lead to further weakening and strain localization.

Paleo-Pacific subduction in Southeast Vietnam: Evidence from Late Cretaceous intrusive rocks in the Dalat zone

The Dalat zone in Southeast Vietnam forms a key component of the Paleo-Pacific subduction system, which stretches from the Coastal South China to West Borneo. Petrology, zircon UPb geochronology and in-situ LuHf isotopes, and whole-rock geochemical analyses for gabbros and granitoids in this zone might define details of its role in the Pacific subduction. The gabbros in this region yield an age of ca. 93 Ma, and are enriched in large-ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) with remarkable negative anomalies in NbTa and Ti, similar to the Cretaceous mafic rocks in the Coastal South China. Their initial 87Sr/86Sr ratios range from 0.70531 to 0.70615, εNd(t) values range from −0.8 to +1.4, (206Pb/204Pb)i ratios range from 18.58 to 18.67 and zircon in-situ εHf(t) values range from +0.4 to +9.7. These characteristics suggest that the gabbros originated from a mantle wedge that had modified by sediment-derived melts. The granitoids found in the Deoca, Dinhquan, Ankroet (Cana) suits of the Dalat zone formed at 103–93 Ma. They exhibit significant variations in major oxide content (SiO2 = 58.84–78.61 wt%; MgO = 0.04–2.66 wt%), classifying them as high-K calc-alkaline I-type granites. In comparison with coeval gabbros, the granitoids show similar whole-rock Sr-Nd-Pb and zircon in-situ LuHf isotopic compositions, arguing for a juvenile crust with arc-like geochemical affinities. The Cretaceous igneous rocks in the Dalat zone of Southeast Vietnam give collectively two age-clusters of ca. 122–112 Ma and ca. 108–75 Ma, resembling those in the Coastal South China and West Borneo. Consequently, these rocks are considered the part of the Cretaceous Paleo-Pacific subduction system, providing a connection between South China in the north and West Borneo in the south.

Coastal response to global warming during the Paleocene-Eocene Thermal Maximum

Global warming during the Paleocene-Eocene Thermal Maximum (PETM) is hypothesized to have had a profound effect on the paleohydrologic cycle, including enhanced seasonality and increased water and sediment discharge. Although the PETM may represent the closest geologic analog for future global climate changes, the effects of this event on ancient coastal systems are poorly understood. We examined drill core from two locations in eastern Texas that preserve a record of tidally influenced deltaic sedimentation associated with the paleo-Colorado River that drained up to 2 × 106 km2 of central North America, approximately two-thirds of the area of the modern Mississippi River catchment. In these cores, the development of a regionally extensive sand-rich unit (the Carrizo Formation) at the onset of the PETM is identified from a negative carbon isotope excursion and supported by detrital zircon UPb geochronology and pollen occurrence data. The basal Carrizo Formation indicates that the onset of the PETM was characterized by an increase in the delivery of coarser-grained sediments and progradation of the coastline, which occurred despite rising sea level. Using a mass-balance framework for equilibrium deltaic systems, we estimate that sediment delivery to the coastline increased by ca. 46% (2-σ: 13% to 167%). Our findings of enhanced sediment delivery to the coast are consistent with proxy climatic and sedimentologic data indicating heightened precipitation seasonality in the interior of North America during the PETM. Thus, the effects of a regional change in climate forced by greenhouse events were transmitted downstream by large river systems to produce shifts in coastal sediment supply, progradation, and coastline evolution.

A comparison of fast pulse and conventional LA-ICP-MS detrital zircon geochronology: A large n detrital zircon study from the Centralian Superbasin, northwestern Australia

Over ten thousand detrital zircon U–Pb analyses on thirty four samples were undertaken using a fast pulse laser ablation protocol from the Neoprotoerozoic rocks of the largely unexposed Yeneena and northwestern Officer Basins in Western Australia. In addition, conventional laser ablation detrital zircon U–Pb geochronology was carried out on three of the samples. A comparison of the two datasets demonstrated that no statistical significant difference was observed in the detrital zircon spectra between the two techniques.The results of the detrital zircon analyses reveal that after an intial pulse of material dominated by Archean detritus the sediment are dominated by Mesoproterozic sources. This indicates that there is little variation in source materials within and between the identified formations. The major age peaks coincide with magmatic rock ages from within Australia. The results indicate that either the Palaeoproterozoic and Mesoproterozoic terranes remained sources throughout the deposition of the Yeneena and northwestern Officer Basins during the Neoproterozoic, or that recycling of zircons occurred within a quasi-closed system for the duration of sedimentation. The remaining 10 % of grains are difficult to reconcile with magmatic suites of any significant volume within Australia. However, when considering the broader palaeogeographic context at the time the sediments are inferred to have been deposited, rocks from Dronning Maud Land and the Kalahari Craton can supply grains of appropriate ages and are consistent with the known paleocurrent directions.This work demonstrates that there is no significant disadvantage in the application of the fast pulse technique when applied to the collection of U–Pb detrital zircon datasets for the purpose of detrital zircon fingerprinting. However, there is a large upside related to the significant amount of data that can be collected for a given amount of time compared to other more conventional techniques.

The Sr, Nd, Pb and Hf isotopes and crystallization conditions of the middle Eocene Dağdibi Pluton in the eastern Sakarya Zone, Turkey

AbstractMagmatic activity in the Sakarya Zone, an important segment of the Alpine orogenic belt, continues intermittently from the middle Carboniferous to Miocene. In this study, we provide geochronological and geochemical data from the Dağdibi Pluton in the eastern Sakarya Zone to present some inferences on the source region and petrogenesis of the middle Eocene magmatism. U–Pb zircon geochronology from two granodiorite samples gives middle Eocene ages of 44.75 ± 0.92 and 45.01 ± 0.59 Ma. The pluton is mainly composed of K-feldspar, plagioclase, quartz, Mg-hornblende/actinolite, Fe–Ti oxides and small amounts of biotite, and secondary chlorite and epidote. Parental magma of the intrusive rocks has a high-K calc-alkaline affinity with metaluminous character. The oxygen fugacity values vary between −18 and −17. The rocks show slightly radiogenic 87Sr/86Sr(i) (0.704845–0.705726) ratios and ϵNdi values between −0.96 and +0.52. Pb–Pb isotope ratios are typical for those of the lower continental crust. ϵHf(i) values of the zircons range from 0.14 to 10.26. The geochemical and isotopic features of the pluton point to a parental magma derived from a depleted mantle that was metasomatized by fluids during previous subduction events. The volumetric abundances of the rock types are decreased as the silica content increase, implying that the fractional crystallization is the most important process during the formation of the present compositional range of the pluton. Amphibole, plagioclase and Fe–Ti oxides are the fractionated phases while K-feldspar is largely accumulated. In the light of the data presented above, slab breakoff is regarded as the geodynamic process responsible for the formation of the Dağdibi Pluton in the middle Eocene.

One billion years of tectonism at the Paleoproterozoic interface of North and South Australia

The Mount Woods Domain, in the northeastern Gawler Craton, occupies a tectonically important location in Proterozoic Australia, yet there is very little published U–Pb geochronology data from this region to underpin tectonic models. New LA-ICP-MS U–Pb monazite and detrital zircon geochronology reveal Archean to Paleoproterozoic basement in the central Mount Woods Domain, comprising metasedimentary rocks and garnet-bearing granite with protolith ages of c. 2550–2400 Ma and metasedimentary rocks deposited after c. 1855 Ma. The southern Mount Woods Domain contains younger metasedimentary sequences deposited after 1750 Ma. Metamorphic monazite and zircon geochronology combined with phase equilibria modelling show the rocks of the central Mount Woods Domain were metamorphosed to granulite facies between 1700 and 1670 Ma, reaching pressure and temperature conditions of 4.8–5.3 kbar and 800–840 °C. Monazite geochronology from samples located along major shear zones and in the westernmost Mount Woods Domain record amphibolite facies metamorphism and reworking at 1570–1550 Ma, with a further phase of shear zone activity along the northern margin of the Mount Woods Domain at c. 1480 Ma. Laser ablation inductively coupled plasma triple quadrupole mass spectrometry (LA-ICP-QQQ-MS) Rb–Sr biotite ages from across the Mount Woods Domain range between 1480 and 1390 Ma. The protracted geological history in the Mount Woods Domain from c. 2500–1400 Ma provides a piercing point linking different regions of Proterozoic Australia and western Laurentia during the tenure of the Nuna supercontinent.

Detrital Zircon Geochronology of the Volyn-Orsha Sedimentary Basin in Western Ukraine: Implications for the Meso-Neoproterozoic History of Baltica and Possible Link to Amazonia and the Grenvillian—Sveconorwegian—Sunsas Orogenic Belts

We used LA-ICP-MS U-Pb data for detrital zircon to constrain the Maximum Depositional Age (MDA) and provenance of clastic sedimentary rocks of the Volyn-Orsha sedimentary basin, which filled an elongated (~625 × 250 km) depression in SW Baltica and attained ~900 m in thickness. Eighty-six zircons out of one hundred and three yielded concordant dates, with most of them (86%) falling in the time interval between 1655 ± 3 and 1044 ± 16 Ma and clustering in two peaks at ca. 1630 and 1230 Ma. The remaining zircons yielded dates older than 1800 Ma. The MDA is defined by a tight group of three zircons with a weighted mean age of 1079 ± 8 Ma. This age corresponds to the time of a ~90° clockwise rotation of Baltica and the formation of the Grenvillian—Sveconorwegian—Sunsas orogenic belts. Subsidence was facilitated by the presence of eclogites derived from subducted oceanic crust. The sediments of the Orsha sub-basin in the northeastern part of the basin were derived from the local crystalline basement, whereas the sediments in the Volyn sub-basin, extending to the margin of Baltica, were transported from the orogen between Laurentia, Baltica and Amazonia.

Detrital Zircon LA-ICP-MS U-Pb Ages of the North Liaohe Group from the Lianshanguan Area, NE China: Implications for the Tectonic Evolution of the Paleoproterozoic Jiao-Liao-Ji Belt

The Liaohe Group, which is a significant lithostratigraphic unit within the Paleoproterozoic Jiao-Liao-Ji Belt situated between the Longgang and Liaonan-Nangrim blocks, comprises the Langzishan, Li’eryu, Gaojiayu, Dashiqiao, and Gaixian formations, which are characterized mainly by a clastic-rich sequence with an interlayered bimodal-volcanic sequence, carbonate-rich sequence, and (meta-)pelite-rich sequence. Currently, the tectonic background and evolution of the Liaohe Group remain contentious. Based on the study of detrital zircon geochronology and the zircon trace element characteristics in the Langzishan and Li’eryu formations in the North Liaohe Group in the Lianshanguan area, NE China, this paper reveals the formations’ provenances, depositional ages, and relationships with Paleoproterozoic granitoids (the Liao-Ji granites). The present results, in conjunction with previous studies, indicate that the depositional age of the Langzishan Formation is 2136 Ma and that of the Li’eryu Formation is 1974 Ma. The provenances of the Langzishan Formation and the Li’eryu Formation are mainly characterized by Neoarchean-to-early-Paleoproterozoic basement rocks (~2.6–2.4 Ga) and the Liao-Ji granites (~2.2–2.0 Ga), respectively. Moreover, the coeval mafic and metasedimentary rocks of the Liaohe Group exhibit characteristics of an extensional environment, which is represented by the tectonic setting of a back-arc basin. Notably, the Upper Langzishan Formation records a prominent shift in sedimentary environment from a passive continental margin to an active continental margin. In terms of the tectonic evolution of the North Liaohe Group and the Jiao-Liao-Ji Belt, our proposed model suggests that the Archean basement rocks in the northern part of the continental block, along with a limited contribution from the Paleoproterozoic Liao-Ji granites, served as the primary sources for the Langzishan Formation. Subsequently, the rapid deposition of the Li’eryu Formation was influenced by intense magmatism and subsequent erosion of the subduction-related magmatic arc (the Liao-Ji granites) within a back-arc basin environment. Lastly, the deposition of clastic materials from the Longgang blocks and the Liao-Ji granites resulted in the formation of the Gaojiayu, Dashiqiao, and Gaixian formations.

Sedimentary response to the early Silurian (Rhuddanian-Aeronian) post-glacial transgression and Kwangsian Orogeny in the Upper Yangtze region, South China

Unlike the lowermost Silurian ‘hot’ shales deposited in many other regions of the world, the early Silurian (Rhuddanian-Aeronian) succession in South China exhibits a distinctive lithofacies transition from organic-rich black siliceous mudstone in the early Rhuddanian, to interlaminated siltstone and mudstone with relatively low total organic carbon content in the late Rhuddanian, and finally to organic-lean argillaceous mudstone or calcareous mudstone in the late Aeronian. The interlaminated siltstone and mudstone interval has been the subject of a long-standing dispute over its nature, whether it belongs to turbidite or contourite. In this study, we employed a range of approaches, including petrographic analyses, UPb dating of detrital zircons, and measurements of paleocurrent directions to generate a dataset that reveals: (1) four typical fine-grained facies developed within the interlaminated siltstone and mudstone interval, (2) detrital zircon UPb ages yielding a wide age range from Archean (∼2.50 Ga) to early Paleozoic (0.42 Ga), with a predominant peak of ca. 447 Ma based on 516 detrital zircon UPb analyses, and (3) paleocurrent directions indicate the presence of current circulation in the Upper Yangtze region. The results of this study demonstrated that the detritus of the interlaminated siltstone and mudstone interval originated from concurrent explosive volcanic eruptions along the southeastern margin of the South China Craton. It was deposited and reworked by bottom currents under the background of the early Silurian post-glacial transgression. We suggest that the occurrence of the interlaminated siltstone and mudstone interval is indicative of a far-field sedimentary response to the onset and progradation of the Kwangsian Orogeny in the Upper Yangtze region.