Zircon Ages Research Articles

Disputed tectonic setting for the late Silurian–early Carboniferous development of the northern New England Orogen: detrital zircon ages suggest a continental margin arc association

Devonian successions in the Calliope and Yarrol provinces of the northern New England Orogen in central to northern Queensland have a lithological assemblage and depositional environments indicative of a close association with a subduction-related volcanic arc. These rocks have been interpreted as related to island arc and backarc settings based on geochemical characteristics of magmatic rocks. We present new detrital zircon ages from the Devonian to lower Carboniferous successions of the Calliope and Yarrol province successions. Most samples have no or relatively few zircon grains extracted except for samples of quartz-rich sandstone in the Middle Devonian Erebus beds of Hunter Island, located 160 km north-northwest of Rockhampton and another sample in the Rockhampton district. The samples with abundant zircon, and some with less common zircon, have prominent peaks of mid Cambrian to Ordovician ages and are consistent with derivation from the northern Thomson Orogen where igneous rocks of this age are documented in the Charters Towers Province. These data indicate a connection between the Devonian arc-flank deposits of the northern New England Orogen and the Thomson Orogen, which had previously been well established for Carboniferous deep-marine sandstones of the subduction complex (e.g. Shoalwater Formation). These results favour an east-facing continental margin arc setting in the Devonian contra to intra-oceanic island arc settings previously proposed. Detrital zircon age spectra from sampled early Carboniferous units of northern New England Orogen association indicate a pulse of felsic magmatism of that age.

Permian tectonic evolution of the proto-Japan and East Asia: Insights from detrital zircon geochronology and crystal morphology

Combination analyses of detrital zircon ages and morphology from Permian sandstones in Japan provide evidence of orogenic evolution caused by collision in East Asia and reveal their paleogeographic setting. This study compares published and newly measured data from Permian fore-arc accretionary complexes (Akiyoshi Belt) and back-arc basin deposits (Maizuru Belt) in the Inner Zone of Southwest Japan. The fore-arc deposits and lower part of the back-arc deposits consist mainly of approximately 300–250 Ma zircon grains that are close to the depositional ages and are generally angular to subangular. These sediments formed around the Late Paleozoic volcanic arc isolated from the older continental crust, and their source rocks were exposed immediately prior to their erosion and transport and were transported directly to the depositional site in a relatively short time. In contrast, upper part of the back-arc deposits generally contains approximately 2,700–1,800 and 500–250 Ma zircon grains, which are commonly older than their depositional ages and are rounded. These grains were supplied from multiple sources, such as the Paleozoic volcanic arc and Precambrian continental block, and were affected by long-distance transport and a strong abrasion effect during transport. Comprehensive detrital zircon data emphasize that the oceanic arc–back-arc basin–continental margin system formed along the eastern margin of East Asia, and that the volcanic arc collided with the eastern margin of the Sino-Korean Block during the Permian. The variation in detrital zircon ages and shapes of back-arc deposits provides a constraint for modeling the East Asian Permian collision. Detritus derived from continental crust was captured by a back-arc basin and blocked by the uplift zone of the volcanic arc. However, a small amount of detritus originating from the continental crust was supplied to the fore-arc.

Geochronology, geochemistry, and geological evolution of the Troiseck-Floning and Rosskogel nappes (Eastern Alps): unraveling parallels between the Eastern Alps and Western Carpathians

The Troiseck-Floning and Rosskogel nappes are part of the Austroalpine Unit in the eastern part of the Eastern Alps. The nappes are in tectonic contact and comprise Permian to Mesozoic lower greenschist facies metamorphic metasediments, but only the Troiseck-Floning Nappe consists of a pre-Permian crystalline basement (Troiseck Complex) as well. LA-ICP-MS U–Pb zircon ages, Rb–Sr biotite ages and geochemical data unravel the geological evolution of these tectonic units from Neoproterozoic to Mesozoic times. Detrital U–Pb zircon analyses from siliciclastic metasediments of the Troiseck Complex indicate a late Ediacaran to early Cambrian deposition age of the volcanoclastic sequence. The age distribution correlates with a position along the northeastern Gondwana margin. A late Cambrian crystallization age (502.4 ± 6.8 Ma) of granitic intrusions together with evidence for Late Cambrian/Ordovician magmatism and metamorphism indicate a position at an active plate margin. Polyphase overprinting during the Variscan orogeny is recorded by Late Devonian/early Carboniferous pegmatite dikes (~ 353 Ma) that formed after an early Variscan event, while Pennsylvanian ages of overgrowth rims and inherited grains (~ 320 Ma) are evidence for late Variscan metamorphism. Rhyolitic to andesitic volcanic rocks from the Troiseck-Floning and Rosskogel nappes (271–264 Ma) concomitant with intrusions of porphyric granitoids now transformed to augen gneiss (271 Ma) yield evidence for Permian rift-related magmatism that is widely reported from the Eastern Alps and Western Carpathians. Rb–Sr biotite ages (75–74 Ma) indicate Late Cretaceous cooling below c. 300 °C. This relates to Late Cretaceous exhumation of the Troiseck-Floning Nappe following an Eo-Alpine metamorphic overprint at lower greenschist-facies metamorphic conditions. Based on the similar lithostratigraphy, analogous geological evolution and structure, the Troiseck-Floning Nappe represents the lateral extension of the Seckau Nappe. The new dataset also allows for correlations with other basement complexes that occur in the Western Carpathians.

The El Gigante Metamorphic Complex: A missing block with a Grenville-age basement in the Western Sierras Pampeanas, Argentina

The southwestern paleo-margin of Gondwana is interpreted as an accretionary margin that was active from the late Neoproterozoic to the late Paleozoic. The basement of this paleo-margin is widely exposed in the central-western part of Argentina (Sierras Pampeanas area), where a protracted evolution from the Mesoproterozoic to the late Paleozoic is recorded. Part of this evolution is preserved in the El Gigante Metamorphic Complex (Sierra de El Gigante; Western Sierras Pampeanas), a small rotated block within the Valle Fértil Lineament fault zone that separates the Western and Eastern Sierras Pampeanas. The complex is composed of medium-grade meta-siliciclastic and meta-carbonate rocks and medium- to high-grade meta-igneous rocks, affected by tight to isoclinal folds and a pervasive east–west foliation resulting from the Famatinian orogeny (broadly late Cambrian to early Devonian). Later events include localized ductile shear zones. The isotopic and geochronological data from El Gigante Metamorphic Complex reveal at least three distinct lithological assemblages: (1) metamorphosed felsic igneous rocks of ca. 1.11 Ga, i.e., late Mesoproterozoic, (2) a Neoproterozoic metasedimentary succession composed of quartzites and mica-schists, (3) possibly mid- to late-Cambrian marble and graphite-schist. The Grenvillian assemblage (1) was part of a large reworked Paleoproterozoic continental block called MARA (acronym of Maz-Arequipa-Río Apa) and was the basement over which the Neoproterozoic and Cambrian sedimentary successions were deposited. Based on U-Pb zircon ages, lithological similarities and Sr-isotope data, the three lithological assemblages of the El Gigante Metamorphic Complex can be correlated with similar ones in the nearby geologically better-known Sierra de Pie de Palo. The Neoproterozoic and the Cambrian metasedimentary successions are respectively equivalent to the Difunta Correa Metasedimentary Sequence and the Nikizanga-Caucete Groups, which are recognized throughout the Sierras Pampeanas, east and west of the Valle Fértil Lineament.

1.88 Ga granitoids at Sorsakoski, Central Finland: A-type magmatism within the Raahe-Ladoga suture zone

Four quartz monzonite – granite intrusions forming the Sorsakoski granite lithodeme, are found within the Raahe-Ladoga suture zone in Central Finland. The prevailing potassium feldspar megacrystic quartz monzonites and granites form a bimodal association with diorites and gabbros. The granitoids are mainly calc-alkaline, ferroan, per- to metaluminous, and have high Zr and REE contents. Dominant mafic minerals are biotite and hornblende, clinopyroxene and orthopyroxene are locally present. The mafic units display effects of fractionation of clinopyroxene. In our interpretation, these intrusions were emplaced during regional late stages of deformation and post-crystallisation deformation partitioned into major shear zones leaving bulk of the intrusions relatively undeformed. Based on one new (1876 ± 6 Ma) and one pre-existing (1882 ± 5 Ma) U-Pb zircon age determination, the crystallisation age of the granitoids can be assumed at ca. 1880 Ma. Based on mineralogy, petrography, geochemistry, bimodal nature of magmatism and age, we correlate these intrusions to the A-type rocks of the previously described Saarijärvi suite. This shows that the syn-orogenic A-type magmatism extended eastwards beyond the Central Finland Granitoid Complex.

Geochemical and detrital zircon U[sbnd]Pb geochronology of the qigequan formation in the yuejin 2 area: Implications for tectonics and uranium sources

The Yuejin 2 mining area lies within the Mangya region, situated on the northwestern periphery of the Qaidam Basin. Recently discovered, it harbors a medium-sized uranium deposit within the basin. Nonetheless, investigations into the sedimentary provenance and paleoclimate of the Neogene Qigequan Formation in this locale have been sparse. This study delves into a meticulous examination of petrogeochemical attributes and the detrital zircon UPb geochronology of sandstones from the Qigequan Formation within the mining area, aiming to discern their origins and tectonic context. By scrutinizing the trace and rare earth element signatures of the rocks, we discern that the lower strata of the Qigequan Formation primarily originate from felsic sedimentary sources, indicative of a continental island arc tectonic. Detrital zircon ages from the Qigequan Formation manifest primarily in three distinct periods: 169–292 Ma, 327–505 Ma, and > 670 Ma, corresponding with geological ages documented in the Altyn Tagh and East Kunlun Mountains orogenic belts. Predominantly, the Altyn Tagh orogenic belt and the Qimantag Mountains in the eastern Kunlun Mountains serve as the principal source of the Qigequan Formation. The chemical weathering index (CIA*) is 70.54, suggesting a moderate level of chemical weathering within the source region. Additionally, the angular morphology of the detrital zircon implies proximity between the source area and the basin. During the late sedimentary epoch of the Qigequan Formation, rapid uplift of the Altyn Tagh led to a notable rise in temperature within the Yuejin 2 area, transitioning from a reducing to an oxidizing environment. Surface water enriched with uranium and eroded source rocks gradually infiltrated the sand bodies of the lower Qigequan Formation. Interaction with reducing agents facilitated the enrichment and formation of ore. Paleoclimatic shifts instigated the oxidation–reduction sequence necessary for uranium mineralization. Favorable conditions, characterized by oxygen-rich paleo-water, facilitated the activation, migration, and re-enrichment of uranium. Moreover, the Himalayan movement acted as a driving force and a pivotal factor in creating the conducive conditions imperative for large-scale uranium mineralization in the area.

Detrital zircon ages and proposed provenance of the Koegas Subgroup of the Ghaap Group, and overlying Makganyene Formation, of the Postmasburg Group, Transvaal Supergroup

Abstract The late Archaean to early Palaeoproterozoic strata of the Transvaal Supergroup of southern Africa is renowned for hosting geological units that preserve some the Earth’s most significant geological events. The glaciogenic Makganyene Formation is one such significant unit, given that it has been associated with the Snowball Earth Event. The maximum age of deposition of this formation, and subsequent timing of this event, has come into question, mostly because of concordant detrital zircon ages as young as ~2.2 Ga reported by Beukes et al. (2013). These ages are younger than the recently revised ca. 2.43 Ga baddeleyite age inferred for the overlying Ongeluk Formation and subsequently led to a significant revision of a long-held correlation between the upper Postmasburg- and Pretoria groups of the respective sub-basins of the Transvaal Supergroup. The primary objective of this study is to investigate the mode of occurrence of the ~2.2 Ga zircons in the Makganyene Formation as well as selected formations of the underlying Koegas Subgroup. Here, we report a total of 183 near concordant U-Pb zircon ages for the Koegas Subgroup (Pannetjie- and Naragas formations) and 967 such ages for the Makganyene Formation, extracted from seventeen samples from across the outcrop area for these units. Sensitive High Resolution Ion MicroProbe (SHRIMP) as well as three different Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) techniques were used for U-Pb age measurements. We assessed the quality of the respective data sets and possible shortcomings of the techniques to constrain the maximum age of deposition of the units and to infer possible source areas for the detritus. In contrast to zircon ages determined for the Koegas Subgroup, zircons younger than ~2.4 Ga are a prominent feature of the Makganyene Formation. Upon careful consideration of each data set, we concluded that these so-called young grains have likely suffered significant Pb-loss and that a possible overcorrection for common Pb during data reduction could not be ruled out. Although the age distribution generated using the respective techniques were comparable, none of the four techniques were successful in shedding light on the reliability of the ~2.2 Ga ages. The maximum age of deposition of the Makganyene Formation could not be constrained with confidence and therefore the revised correlation between the Postmasburg- and Pretoria groups is not contested. The detrital zircon age distribution of the Koegas-Makganyene succession was however found to be remarkably similar, with a major ~2.5 Ga age fraction and subordinate fractions at ~2.65 to ~2.9 Ga and older than ~3.0 Ga. The major ~2.5 Ga zircon age fraction points towards a prominent, likely orogenic source of detritus. We assign the origin of the major ~2.5 Ga and older zircon age fractions to a Rae-type craton, which we proposed to have been attached to the north of the Vaalbara Craton at time of deposition of these units and consider a tectono-magmatic event characteristically associated with this family of cratons as the possible cause of alteration and Pb-loss in zircon grains dated at ~2.2 Ga.

U-Pb detrital zircon age determination and provenance of the lower Karoo succession from the Karoo Research Initiative (KARIN) borehole KWV-1, Eastern Cape Province, South Africa

Abstract In recent years, the maximum age of sedimentation and possible sources of detritus to the sedimentary successions of the Karoo Supergroup has received a lot of interest, with various authors presenting age data from across the main Karoo Basin (MKB). Our paper aims to contribute to this ever-growing geochronological database as we report weighted mean ages for the youngest zircons as well as detrital zircon age distributions for the lower Karoo Supergroup succession sampled from the Centre of Excellence for Integrated Mineral and Energy Resource Analysis (CIMERA)-Karoo Research Initiative (KARIN) drill core KWV-1. A total of 880 near concordant zircon ages were determined using Laser Ablation Quadrupole Inductively Coupled Plasma Mass Spectrometry (LA-Q-ICP-MS) from fifteen samples representing the Dwyka Group, the Collingham-, Ripon-, Fort Brown- and Waterford formations of the Ecca Group and the Koonap Formation of the Beaufort Group as intersected by this ~2 352 m deep research borehole drilled in the southeastern sector of the basin. The weighted mean ages for the youngest zircons calculated for the formations of the Ecca- and Beaufort groups compares with findings reported by other authors and with the ages reported for tuffaceous layers associated with these units. The weighted mean ages for the youngest zircons of the Dwyka Group reflect the age of the youngest source area and do not aid in constraining the maximum age of deposition. A significant change in detrital zircon age distribution was noted between the Dwyka Group and the overlying formations of the Ecca and Beaufort groups, which we interpret as a change in provenance. The major Meso-to Neoproterozoic detrital zircon age fractions present in the Dwyka Group are attributed to source areas located towards the north and northeast of the MKB, in line with regional ice flow directions. A significant late Carboniferous to Permian detrital zircon age fraction is however observed throughout the formations of the Ecca- and Beaufort groups, with a lesser fraction of older zircon ages. The prevailing youngest age fraction reflects ages associated with magmatic source areas in the Gondwanide Orogeny located towards the south of the MKB at the time of deposition, while the recycling of deformed sedimentary strata of the Cape Supergroup contained in the Cape Fold Belt is considered the source of older detritus. The source of detritus to the MKB remained unchanged during the deposition of the respective formations of the Ecca- and Beaufort groups, despite changes in the depositional environment brough on by regional tectonics.

Retrieving meaningful information from detrital zircon in Palaeoproterozoic sedimentary rocks: Provenance, timing of deposition, metamorphism and alteration of zircon in sandstones of the Pretoria Group in the Transvaal Basin, South Africa

Abstract The Palaeoproterozoic sandstones and quartzites of the Pretoria Group (Transvaal Supergroup) in the Transvaal Basin of South Africa are important markers for regional correlations and dating of events of global importance (e.g., the Great Oxidation Event). The succession has few independent age markers, and much of the discussion about the time of deposition and the source of material of these rocks has been based on data from detrital zircon suites. The clastic sedimentary rocks of the Pretoria Group contain detrital zircon grains ranging from the Mesoarchaean to ages that are near-contemporaneous to, and even younger than the overlying and crosscutting igneous rocks of the Bushveld Complex. We show that the U-Pb age and Lu-Hf isotope distributions of the detrital zircon population in the Pretoria Group are the result of three different types of processes, acting successively: (1) Crystallisation in the igneous or metamorphic protosource rock (i.e., the rock where the zircon originally crystallised), (2) Metamorphic and hydrothermal resetting of the U-Pb chronometer induced by emplacement and crystallisation of the 2 055 Ma Bushveld Complex, and (3) Late, low-temperature processes (e.g., weathering). Critical age markers of maximum ages of deposition obtained after excluding effects of (2) and (3) are the 2 200 Ma Magaliesberg Formation (outside of the Bushveld aureole) and the 2 080 to 2 100 Ma Lakenvalei Formation. The Leeuwpoort Formation is a worst-case example, containing both young (<2 200 Ma) unmodified detrital zircon and hydrothermally altered zircon in the same age range. The two can only be distinguished from trace element analyses. Age distributions of Archaean and early Palaeoproterozoic zircon age fractions overlap with detrital zircon age suites in lower (i.e., pre-Timeball Hill Formation) parts of the Transvaal Supergroup, suggesting recycling within the basin or from the basin margin. Overlaps in 2 200 to 2 350 Ma zircon ages with those of volcanogenic zircon in the Timeball Hill Formation again suggest recycling. The origin of 2 080 to 2 150 Ma zircon is uncertain, but neither poorly constrained sources in the Kaapvaal Craton (e.g., Okwa Basement Complex) nor recycling of volcanogenic material from post-Magaliesberg formations can be ruled out.

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.

Investigation of rock genesis and geodynamic significance based on Sr–Yb granite classification and geochemical characteristics: A case study from Guangxi, China

The intrusive bodies in the study area are categorized into two intrusive units, γπK2 and ηoπK2, based on rock structure characteristics and intrusive contact relationships. The primary lithologies are granite porphyry and quartz monzonite porphyry. Through LA-ICP-MS zircon U–Pb dating, the weighted mean ages of zircon ^206Pb/^238U for these two units were determined to be 84.09 ± 0.86 Ma and 86.10 ± 0.76 Ma, respectively. According to geochemical characteristics and Sr–Yb granite classification, the quartz monzonite porphyry is classified as Zhejiang-Fujian type granite, and the granite porphyry as Nanling type granite. The study explores the geodynamic significance of granites in the area based on Sr–Yb granite classification, identifying the lower crust metamorphic facies as amphibolite facies. The source rocks are primarily basic granulites and felsic granulites, reflecting a thermally active lower crust with poorly developed fluids. Additionally, Sr–Yb granite classification aids in determining the crustal thickness of the lower crust, which is crucial for understanding continental geological evolution. This paper discusses the optimal locations and conditions for mineralizing fluid precipitation, noting that tungsten-tin mineralization is associated with Nanling type granites and that the mineralization process generally occurs later than the diagenetic process under conditions of low pressure and low oxygen fugacity. Tungsten-tin prospecting should focus on areas where the surrounding rock temperature ranges from 300 to 500 °C, with particular attention to the contact zones of sedimentary rocks or near structural fault zones.

Recently Identified Mesoproterozoic Strata in South‐Central Idaho Document Late‐Stage Rifting of the Nuna Supercontinent in Western Laurentia

AbstractSedimentary basins are valuable archives of tectonic processes involved in continental rifting. The northern Rocky Mountains preserve the Belt Supergroup, one of the most complete records of Mesoproterozoic strata on Earth; however, debate remains about its tectonic origin. We investigated a recently identified package of Mesoproterozoic strata at Leaton Gulch near Challis, Idaho, using a combination of traditional and newer sedimentological tools. Results suggest that the Leaton Gulch stratigraphic section was deposited in a fluvial setting ca. 1,380–1,317 Ma, spanning the poorly documented interval between late Belt Supergroup deposition at ∼1,370 Ma and recently characterized Deer Trail Group strata that are less than 1,300 Ma. Detrital zircon age distributions from Leaton Gulch demonstrate a similar provenance signature to Missoula Group rocks of the upper Belt Supergroup; however, Leaton Gulch strata are up to ∼70 Ma younger than most prior age constraints on Belt Supergroup rocks. Regional metabentonites (interpreted as metamorphosed reworked tuffs) found within Leaton Gulch and Missoula Group strata show dominantly radiogenic εHf(t), with a range of −8 to +15, interpreted as a mix of primary mantle and remelted metasedimentary sources. Zircon trace element data of the metabentonite from Leaton Gulch suggest a 1,450–1,300 Ma geochemically consistent and moderate–high silica melt source. Collectively, the strata of Leaton Gulch record basin sedimentation during a critical window of Mesoproterozoic time. We speculate that sedimentation during late‐stage Belt Supergroup deposition thickened and stepped westward, abandoning the main Belt basin, culminating with breakup of the Nuna Supercontinent.

Towards an astrochronological framework for the lower Paleoproterozoic Kuruman and Brockman Iron Formations

Abstract Recent evidence for astronomical-induced cycles in banded iron formations (BIFs) hints at the intriguing possibility of developing astrochronological, i.e. precise time-stratigraphic, frameworks for the earliest Proterozoic as also reconstructed for parts of the Mesozoic and Paleozoic. The Kuruman Iron Formation (IF) (Griqualand West Basin, South Africa) and Dales Gorge Member of the Brockman IF (Hamersley Basin, Western Australia) are of special interest in this regard, given their inferred temporal overlap at ca. 2.47 Ga and similar long-period orbital eccentricity imprint. This suggests that these two BIFs may be correlated on the basis of their large-scale cycle patterns and using additional radio-isotopic age constraints. To examine the possibility of establishing such a framework, we generated and analysed several high-resolution proxy records from both drill-core and outcrop, combined with high-precision U-Pb dating of zircon from interbedded shale horizons. Time-series analysis of these records yields a variety of spectral peaks, of which a prominent ~5 m and ~16 m cycle can be linked to the basic stratigraphic alternations and bundling as observed in the field. New and revised 207Pb/206Pb ages calculated from the U-Pb data of the Dales Gorge Member and Kuruman IF, respectively, indicate a comparable average sedimentation rate of 10 to 12 m/Myr for both units. Based on this depositional rate, we attribute the ~5 m cycle to the long (~405 kyr) orbital eccentricity cycle. More tentatively, we interpret the ~16 m cycle as the very long (presently ~2.4-Myr) eccentricity cycle, having a reduced period of ~1.3 Myr due to chaotic behaviour in the solar system. Other identified cycles (~560 kyr, ~700 kyr and ~1.8 Myr) can be explained in terms of weaker orbital eccentricity components and/or as harmonics and combination tones of these cycles resulting from nonlinear responses. An initial attempt to establish cyclostratigraphic correlations between the Kuruman IF and Dales Gorge Member solely based on their characteristic cycle patterns proved unsuccessful, which may be due to a difference in the recording of the astronomical signal between different depositional environments. Next, we used the zircon ages to first constrain correlations at the scale of the ~16 m cycle, followed by a correlation of the basic ~5 m cycles. The resultant framework remains problematic and debatable at the individual ~405 kyr cycle-level, but provides a starting point for future studies. Particularly, our findings highlight the need for further investigations into how Milankovitch forcing influenced BIF sedimentation and paleoenvironmental conditions at a time when the Earth and solar system behaved fundamentally different from today.

Reinterpretation of the post-26 ka Taupō Rhyolitic Magmatic System (New Zealand) as Deep and Vertically Extensive Based on Isotope Thermometry and Measured and Modeled Zircon Destinies

Abstract Taupō volcanic zone, the site of the 26 ka Oruanui supereruption, produced ~70 km3 of new rhyolites since 11 ka, culminating in 50 km3 Taupō eruption 1.8 ka. Major phenocrysts decrease from 4 to 1 vol%, and Oruanui and post-Oruanui ignimbrites all have identical high-δ18Omelt values of 7.39 ± 0.1‰ and lack low-δ18O values despite overlapping calderas. The Δ’17O values are −0.07‰, lower than the mantle and indicate source contamination of high-δ18O, low-Δ’17O metasediments, and limited interaction with high-Δ’17O hydrothermally altered crust. Previously published U-Th-Pb zircon ages demonstrate their diversity spanning 104–105 years for each unit. Zircon crystal size distribution shows a decrease in abundance and the mean size, and some units lack small (<~10 um) zircons suggesting that zircons were both growing and dissolving in the coexisting magma generation areas. Isotope thermometry indicates heating of the system from ~812 ± 35°C to 874 ± 36°C past zircon saturation in 1.8 ka eruption. We advocate that a deep vertically continuous and laterally discontinuous silicic magma system at the base of the Taupō rift, rather than a shallow batholith or an evolving mush, drives volcanism at Taupō. To explain the post-Oruanui magma production, rift-base silicic magma origin and moderate (~2 km3/1000 years) rhyodacitic magma flux from a growing and heating liquid magma body creates a sufficient solution for the most recent magmatism.

Provenance history of the eastern Pearl River Mouth Basin: Implications for the evolution of the South China margin

Abstract The provenance history of the Pearl River Mouth Basin is of great significance for understanding how the South China margin evolved from a Mesozoic Andean-type subduction margin into the present-day rifted passive margin. However, the long-term provenance history of continental margin basins in the northern South China Sea is poorly understood. Newly identified Mesozoic–Cenozoic successions from the Lufeng Sag in the eastern Pearl River Mouth Basin provide valuable records of the provenance history and related evolution of the South China margin. Here, we trace the provenance of the eastern Pearl River Mouth Basin using U-Pb ages of zircon and ZTR values (proportions of zircon, tourmaline, and rutile in all transparent heavy minerals) of heavy minerals, and determine the tectonic setting and crustal thickness using trace element ratios and Eu anomalies in zircon. The results show that from the middle Eocene strata—which have a U-Pb age spectrum similar to strata of the Upper Cretaceous—to the Miocene strata, the proportion of Mesozoic age populations gradually increases, while the proportion of Paleozoic age populations decreases. In addition, following the middle Eocene high values, the ZTR values decreased during the late Eocene and then increased during the early Oligocene. Based on the variations in zircon age populations and ZTR values, the middle Eocene sediment is interpreted to have been recycled from Upper Cretaceous to middle Eocene successions, followed by an early Oligocene provenance change from intrabasinal to extrabasinal sources. Moreover, the zircon trace element ratios and Eu anomalies indicate that a widespread Mesozoic continental magmatic arc formed before ca. 90 Ma along the South China margin, and the crust simultaneously thickened during this time. In accordance with the provenance history, the evolution of the South China margin is divided into three tectonic phases: the Paleo-Pacific, Proto-South China Sea, and South China Sea. During the transition from the Paleo-Pacific to the Proto-South China Sea tectonic phase, sediment was recycled from Upper Cretaceous to middle Eocene successions in the eastern Pearl River Mouth Basin. During the transition from the Proto-South China Sea to the South China Sea tectonic phases, the provenance changed from intrabasinal to extrabasinal sources.

Early Ordovician to Early Permian tectonic evolution of the northern Western Kunlun Orogen (NW China): Insights from the Omixia Complex and surrounding rocks

The Palaeozoic tectonic evolution of the Western Kunlun Orogen plays an important role in deciphering the Tethyan tectonic evolution. This study provides new geochronology, geochemistry and Lu–Hf isotopic data of igneous rocks from the Omixia Complex in the eastern section of the northern Western Kunlun, as well as detrital zircon ages from turbidites and meta‐sediments north of it. From the Omixia Complex, the determined ages of five ultramafic–mafic rock samples are approximately 470, 456, 429, 401 and 382 Ma. Two samples of acidic rocks from the same complex yielded ages of approximately 438 and 378 Ma. One pegmatitic plagiogranite sample exhibits feature of accretionary arc granites, while other samples show geochemical characteristics of island arc tholeiite and E‐MORB. Additionally, four turbidite matrix and two limestone samples, with a major peak around ca. 480–500 Ma, have the youngest zircon ages ranging from ca. 481 to 387 Ma, paralleling the age range of igneous rocks in the ophiolitic mélange. The εHf(t) values of these samples reveal a broad spectrum of crustal and mantle processes. The youngest zircon ages of five meta‐sedimentary rock samples north of the Omixia Complex range from ca. 581 to 535 Ma, with peak ages concentrated around ca. 0.9–1.0 Ga. Their provenance characteristics differ from the turbidite matrix in the southern Omixia Complex and from the meta‐sediments in the northern Tiklik terrane with peak ages of ca. 0.8 Ga. A younger limestone sample yielded youngest zircon age of ca. 294 Ma, which is unconformably overlain the Omixia Complex and surrounding older rocks. Based on these new results, combined with previous data, we propose a new tectonic model for the eastern section of the northern Western Kunlun Orogen, suggesting a continuous evolution process of multi‐terrane subduction–accretion collage from the Early Ordovician to the Middle Devonian in the Paleo‐Tethys Ocean, which evolved into an Andean‐type active margin in the Early Permian, contributing to the substantial continental growth of the southern Tarim Craton.

Petrogenesis, geochronology, and tectonic setting of the Calymmian 1.45–1.50 Ga basic magmatism in the Southern Ribeira Belt, Brazil: evidence of intracontinental rifting and Columbia break-up

ABSTRACT We present new petrographic, whole-rock geochemistry, and SHRIMP U – Pb zircon geochronological data of metabasic rocks interlayered as sills in the metasedimentary units of the Perau and Betara formations, Votuverava Group, Southern Ribeira Belt, Brazil. These formations overlie ~ 1.8 Ga Paleoproterozoic metagranitoids that represent basement inliers from the Paranapanema Craton. Petrography and whole-rock geochemistry allow the recognition of four groups, ranging from primitive to evolved compositions: i) cumulatic metadolerites (G1), ii) isotropic metadolerites (G2), iii) ortho-amphibolites (G3); and iv) ferroan ortho-amphibolites (G4). They exhibit tholeiitic subalkali basaltic composition, near-flat REE patterns, and signatures between N- and E-MORB. Fractional crystallization under low fO2 conditions is the main petrogenetic process controlling the magmatic evolution, as observed by Ti/V and Cr/Y ratio and tholeiitic trends. Crustal contamination signatures are observed through negative Nb anomaly, Th/Nb-Ti/V proxies trends, LILE enrichment, and, also, assimilated xenocryst zircons aged ~ 2.2 Ga. REE and trace element systematics indicate that the basic magmas were generated by ~ 20–10% partial melting of a model asthenospheric mantle source within spinel facies. TiO2/Yb-Nb/Yb and Nb/Yb-Zr/Yb ratio proxies and P-MORB metabasic rocks, previously described in the literature within the Votuverava Group, suggest a plume-influenced melt. A new SHRIMP U – Pb zircon age of 1448 ± 11 Ma was determined for an ortho-amphibolite sample (G3 group). We propose an intracontinental tectonic setting for the genesis of the metadolerites whitin the Perau and Betara formations, suggesting that this extensional event is associated with the Paranapanema Craton rifting. Furthermore, the genesis of the studied metabasic rocks could be associated with a regional extensional event during Calymmian times (~1.5–1.45 Ga), which generated basic magmatism in several other cratons, such as the Congo, São Francisco, Siberian, Laurentian, and China cratons, linked to the break-up of the Columbia Supercontinent.

Provenance of the late Jurassic to Cenomanian sedimentary succession of the Araripe Basin (NE Brazil) and implication for the geodynamic evolution of Western Gondwana

The separation of Gondwana was controlled by preexisting Proterozoic structures and by the development of rift aborted basins, of which the Araripe Basin (NE Brazil) is one of the best examples. Previous studies have focused on the presence and provenance of Aptian–Albian shallow-marine incursions in the Araripe Basin but to date, little attention has been given to its paleodrainage evolution during sedimentation stages. Understanding the paleodrainage evolution is crucial for determining sediment sources and how topographic changes relate to the geodynamic development of the northern part of South America during the fragmentation of Gondwana, and this study investigates the provenance of Mesozoic rift and post-rift sedimentary rocks in the Araripe Basin using a multi-proxy dataset comprising major and trace element concentrations, Sm–Nd isotopic composition, and detrital zircon U–Pb ages. The low Eu/Eu* ratios (0.3–0.9) and high Th/Sc ratios (>0.64) in the most of analyzed samples suggest a felsic and silicic source. The εNd(0) values (−12.3 to −23.7) and TDM ages (1.68 to 2.55 Ga) of analyzed samples suggest overall ancient crustal sources. The presence of oval and elongated zircon grains suggests a major contribution of first-cycle transport sediments. The presence of 2.3–1.8 Ga and 0.63–0.58 Ga U–Pb zircon ages further indicates the dominant contribution of the Borborema Province influenced by the Brasiliano cycle (650–520 Ma). The low contribution of Tonian (∼940 Ma) zircons to the U–Pb zircon age distribution of the rift-beginning stage sample associated with published paleocurrent direction suggests sources located in the northern and northwestern terranes of the Borborema Province. The increase of Tonian (0.9–1.0 Ga) zircon grains during the rift stage suggests a provenance change with a dominant source in the eastern terranes during the rift stage. During the post-rift I stage, the decrease of 1.2–0.72 Ga zircon ages suggests a change in the source areas, with the paleodrainage coming from northern Borborema Province, similar to that of the rift-beginning stage. The samples of the post-rift II stage exhibit dominant contributions of Paleoproterozoic and Neoproterozoic U–Pb ages related to the Albian to Cenomanian uplift of the Borborema plateau during the opening of Equatorial Atlantic Ocean. Together with previous published studies, these findings highlight the significant role played by the post-rift continental uplift to the paleodrainage of the northern part of South America.

Timing and Evolution of Gold Mineralization in the Maljavr Occurrence (NW Russia), NE Part of the Fennoscandian Shield

Gold occurrence Maljavr is the first Archean conglomerate-hosted gold mineralization found in the Fennoscandian Shield. Gold-mineralized metasomatic rocks form a set of lenses within a 10 m thick linear zone, conformable to the bedding of host conglomerates. The lenses are up to 10 m long and up to 1 m thick and they clearly exhibit three alteration envelopes: the rock in the central part consists of garnet and quartz or garnet-only; biotite, garnet, and quartz make the intermediate biotite–garnet envelope; hornblende, hedenbergite, and quartz are the principal rock-forming minerals in the outer zone of the lenses. All metasomatic rocks contain sulfide mineralization up to 15–20 vol.% and up to 0.6 g/t Au. The main ore mineral is pyrrhotite, and the minor minerals are arsenopyrite, chalcopyrite, pentlandite, löllingite, and troilite. The age of zircon from biotite gneiss in the zone of alteration is 2664 ± 18 Ma, this is considered as the time of formation of lenses of metasomatic rocks. Biotite gneiss-conglomerate and metasomatic rocks were later intruded by tourmaline granite pegmatite 2508 ± 7 Ma. The injection of pegmatite caused re-crystallization of sulfides (mainly arsenopyrite and löllingite) and redistribution of gold. Visible gold in association with Bi minerals native bismuth, ehrigite, maldonite, bismuthinite, joseite-B, and hedleyite was found in inclusions in recrystallized arsenopyrite and löllingite. Au content in the rocks with recrystallized arsenopyrite and löllingite is >1 g/t, up to 30 g/t in hand samples. The 2508 Ma pegmatite is interpreted as synchronous with formation of gold mineralization in its present form. The linkage of gold mineralization with pegmatite and geochemical association Au-As-Se-Te-Bi in the mineralized rocks agree with characteristics of intrusion-related gold deposits worldwide. Biotite gneiss–metaconglomerate, hosting the mineralized altered rocks, was the probable primary source of arsenic and gold for mineralization.

The Trans-Crustal Evolution of Miocene Magmatism Parental to Epithermal Mineralization in the Sierra Madre del Sur, Southern Mexico

Abstract Arc-related volcanism results from the interplay of magmatic processes occurring in trans-crustal systems that consolidate over time in a given location. Trans-crustal systems comprise extensive networks of magma reservoirs and conduits at different depths, wherein melts cyclically differentiate and segregate before reaching the surface. The study of these systems provides valuable insights into crustal-scale phenomena, such as the evolution of the continental crust and the formation of metallogenic regions. In this study, we address the trans-crustal magmatic evolution of lower Miocene magmatism parental to several intermediate-sulfidation epithermal deposits in the eastern Sierra Madre del Sur igneous province, southern Mexico. Using a multi-methodological approach, we document changes over ca. 1.1 Myr in the magmatic system that fed andesitic-to-felsic volcanism in this region. We employ whole-rock REE ratios and λ parameters—which are used to quantify the shape of a REE pattern—to track the involvement of pressure-sensitive minerals in the deep-crustal magmatic evolution. The andesitic rocks consist of lava flows, porphyries, and dikes that collectively show REE patterns suggestive of control by fractionated or residual (i.e. in crustal melting) amphibole and/or clinopyroxene. In contrast, the felsic rocks consist of rhyolitic–dacitic ignimbrites, domes, and dikes that show contrasting REE patterns suggestive of control by plagioclase, clinopyroxene, amphibole, and/or garnet. The distinct pressure-sensitive mineral assemblages in the andesitic and felsic rocks indicate that the locus of deep-crustal magma evolution varied within the middle–lower crust. These magmas were episodically injected into ephemeral shallow crustal reservoirs (shortly?) before being erupted, inducing a progressive thermomechanical maturation of the middle–upper crust. Meanwhile, low degrees of crustal assimilation occurred as recorded by Mesozoic inherited zircon ages and Sr–Nd–Pb radiogenic isotopes. An extensive middle–lower crustal magma evolution has been linked to the formation of porphyry Cu deposits (i.e. ‘fertile’ magmatism). Given that intermediate-sulfidation epithermal deposits may be genetically linked with porphyry Cu deposits, the documented processes could have contributed to the formation of epithermal deposits in the region. However, magmatic fertility proxies resemble those from infertile magmas worldwide. Since these proxies have been exclusively applied to porphyry-type deposits, our results highlight the importance of developing new geochemical exploration tools applicable to a wider range of ore deposits.