Zircon Ages Research Articles

Paleoproterozoic Reworking of Archean Crust and Extreme Back‐Arc Metamorphism in the Enigmatic Southern Trans‐Hudson Orogen

AbstractThe crustal evolution of the southernmost ∼2000–1800 Ma Trans‐Hudson orogen (THO) is enigmatic due to burial by Phanerozoic sediments. We provide new insights through petrochronologic analysis of a paragneiss drill core sample. Detrital zircon age peaks at 2625, 2340, and 1880 Ma and Hf isotopes suggest Paleoproterozoic arc development proximal to Archean source(s). Phase equilibria modeling and ternary feldspar thermometry suggest peak conditions of ≥1 GPa, ≥900°C, the first recognition of extreme, ultra‐high temperature metamorphism in the THO. The largely isobaric P‐T path, rapid heating rate, and ∼20 Myr duration (1872–1850 Ma) of peak conditions suggest that this metamorphism occurred in a back‐arc tectonic setting. The sample records post‐peak (1850–1815 Ma) mid‐crustal residence, slow cooling, and exhumation. Further retrogression occurred during Proterozoic regional exhumation (1630–1470 Ma) and Phanerozoic (360–220 Ma) reheating and/or fluid influx. Evidence for Paleoproterozoic arc(s) supports geophysical data for Archean cratonic and Paleoproterozoic arc crust in this region.

Petrogenesis and tectonic implications of the Bloubergstrand basaltic andesites, Tygerberg Formation, Malmesbury Group, Pan-African Saldania Belt, southwestern Africa

Abstract The Bloubergstrand Member, consisting of mafic to intermediate tuffs and flows within the Tygerberg Formation of the Malmesbury Group, is a crucial but understudied component of the western Saldania Belt in southwestern Africa. With a U-Pb zircon age of 555 ± 5 Ma, these volcanic rocks provide valuable insights into the origins and, more broadly, the tectonic setting of the Saldania Belt during the final stages of Malmesbury Group sedimentation in the context of the construction of southwestern Gondwana at approximately 560 to 540 Ma. The Bloubergstrand Member amygdaloidal volcanic rocks vary from basaltic andesitic to andesitic and have experienced varying degrees of alteration. The volcanic rocks are enriched in the large ion lithophile elements (LILE) relative to the high field strength elements (HFSE). When normalised to primitive mantle values, they show enrichment in Cs, Rb, K and Pb and mild enrichment in Th, U, Zr and Hf, with the light rare earth elements (LREE) enriched relative to the heavy rare earth elements (HREE). They are depleted in Ba, Nb, Ta, Sr, Eu, P and Ti. εNd(t) values are mildly negative ranging from -3.60 to -2.39, and Nd TDM model ages range from 1.4 to 1.7 Ga. Initial 87Sr/86Sr ratios vary from 0.70478 to 0.70620, with one higher value of 0.72270, the latter likely due to extensive alteration. The Bloubergstrand Member volcanic rocks exhibit characteristics suggesting their origin from partial melting of lithospheric to transitional asthenospheric upper mantle, influenced by sediment-derived melts and variable degrees of crustal contamination. With continental arc basalt compositions and similarities to shoshonites, the samples reflect variable degrees of partial melting and source heterogeneities. Fractional crystallisation of pyroxenes, hornblende, and plagioclase contributes to compositional variability. Erupting in a continental arc margin, likely part of the Arachania block of the Kalahari craton, separated during the Tonian break-up of Rodinia, the volcanics were associated with the Marmora basin formed by eastward-directed subduction below the western Kaapvaal Craton margin. Extruded in a distal position relative to the Cuchilla Dionisio Arc in present-day southern Brazil and Uruguay, these volcanic rocks preceded the closure of the southern Marmora basin. The mantle melting, possibly a result of slab roll-back, break-off, ridge subduction, or a combination, served as a precursor to the lower crustal heating that generated the granitic magmas of the Cape Granite Suite.

Late Triassic to Early Jurassic anatectic magmatism in the Chiapas Massif Complex, southern Mexico: New evidence for the onset and mode of crustal extension in western equatorial Pangea

During the Triassic, continental breakup started in western equatorial Pangea, while active continental margins developed along North and South America’s Pacific borders. Besides many uncertainties about how peri-Gondwanan terrains of Mexico evolved during and after Pangea’s amalgamation, the apparent absence of Late Triassic magmatism has been an enigmatic feature of Mexico’s geology. Here, we present the first documented occurrences of Late Triassic igneous rocks and a coeval high-grade metamorphic event in southern Mexico, as well as evidence for subsequent Early Jurassic ductile deformation and magmatism. Samples come from the Chiapas Massif Complex (CMC), a crystalline basement of the southern Maya Block. Field evidence suggests that garnet-bearing leucogranitic stocks intruded a former structural boundary between different Precambrian-Paleozoic basement units. High-precision Sm-Nd garnet-whole-rock ages (ID-TIMS partial dissolution techniques) and U-Pb geochronology on zircon rims (LA-ICPMS) revealed Norian igneous crystallization ages for the leucogranites (∼221–213 Ma). Isotope and geochemical data indicate that these granites originated from crustal reworking by anatexis. A garnet-bearing leucosome from a migmatite yielded a slightly younger Sm-Nd age (∼204 Ma), indicating cooling soon after the peak conditions of the anatectic event. Additionally, monazite from a mylonitized leucogranite yielded an Early Jurassic U-Pb age (∼179 Ma), indicating ductile deformation. Nearly coeval zircon ages from an undeformed pink granite and a nearby volcaniclastic sequence (∼184–189 Ma) further imply contrasting erosion levels during the Early Jurassic. The new data support models for regional stretching of eastern and southern Mexico, where crustal extension during the gravitational collapse of a collisional orogen in paleo-northern Mexico led to continental rifting and the breakup of Pangea. In the CMC, crustal extension is reflected by Norian anatectic crustal melts and migmatites, as well as Early Jurassic plutonic and extrusive magmatism that are localized in certain fault-bounded blocks with different erosion levels compared to adjacent blocks.

Plume-lithosphere interaction in the Comei Large Igneous Province: Evidence from two types of mafic dykes in Gyangze, south Tibet, China

Two suites of mafic dykes, T1193-A and T1194-A, outcrop in Gyangze area, southeast Tibet. They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze, T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al. (2016), indicating coeval formation time. Taking all the four diabase dykes into consideration, two different types, OIB-type and weak enriched-type, can be summarized. The “OIB-type” samples, including T1193-A and T0907 dykes, show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces (LIP), suggesting that they represent melts directly generated from the Kerguelen mantle plume. The “weak enriched-type ” samples, including T1194-A and T0902 dykes, have REEs and trace element patterns showing within-plate affinity but have obvious Nb-Ta-Ti negative anomalies. They show uniform lower εNd(t) values (–6––2) and higher 87Sr/86Sr(t) values (0.706–0.709) independent of their MgO variation, indicating one enriched mantle source. Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya, these “weak enriched-type” samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle (SCLM) in different proportions. These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction. This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.©2024 China Geology Editorial Office.

Late Cryogenian and early Ediacaran rare-metal rich granites in the Eastern Desert of Egypt: constraints from zircon ages and whole-rock Sr- and Nd- and feldspar Pb-isotopic compositions

Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian–Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U–Pb ages and O-isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96‰ and yielded ages of 628–633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7–678.9 Ma with δ 18 O V-SMOW c . 5.95‰. All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics. Supplementary material : Details of analytical details and supplementary tables and figures are available at https://doi.org/10.6084/m9.figshare.c.6949402

Spatiotemporal distribution of magmatism and crustal inheritance within an extensional–rotational environment: an updated geochronology of the Miocene and Quaternary magmatism of the South Apuseni Mountains

Extension-related magmatism with arc-like features was active in the South Apuseni Mountains, Romania during the Neogene and Quaternary. The current chronological framework is primarily restricted to K–Ar dates. We present here new laser ablation inductively coupled plasma mass spectrometry U–Pb zircon age data for 20 subvolcanic and volcanic rocks from eight different Cenozoic volcanic–intrusive complexes and from Jurassic and Cretaceous lava flows. Our results support magmatic ages between c. 14 and c. 7 Ma, with Uroi, an alkaline intrusion, occurring significantly later at c. 1.5 Ma. Revising the timeline for the South Apuseni Mountains palaeomagnetic rotations shows that most of the clockwise vertical-axis rotation of these mountains (54.4° ± 10.7°) took place between c. 14 and 11 Ma, the age interval when the majority of the magmas were emplaced. Xenocrystic zircon dates show differences in the age populations between individual volcanic–intrusive complexes. A Permo-Triassic population is almost ubiquitous, indicating that basement Permo-Triassic igneous rocks are more widespread than previously thought, or that they were significantly involved in the generation of Neogene magmas. However, other observed age populations, such as Triassic or Paleogene, have no clear correspondence in the known geological record, indicating the presence of a cryptic component interacting with Neogene magmas. Supplementary material: Full analytical details and age calculations for the U–Pb age data collected during this study, rock samples and separated zircon fraction descriptions and the palaeomagnetic and age databases are available at https://doi.org/10.6084/m9.figshare.c.6951429

U-Pb ages of detrital zircons and composition of clastic sedimentary rocks from the southern periphery of the Siberian craton: Implications for the earliest Cambrian evolution of southern Siberia

Data on petrography, chemistry, and U-Pb ages of detrital zircons have been obtained for clastic sedimentary rocks within the Sayan regional stratigraphic stage from different parts of the southern Siberia craton, namely for the Ust’-Tagul (Biryusa zone, Sayan area), Shamanka (Irkut zone, Sayan area), Ushakovka and Kurtun (Baikal area) formations. The sedimentary strata share much similarity in lithofacial patterns, with gradual transition from continental to shallow-marine facies. The analyzed lithic sandstones have poorly to moderately sorted clastic grains, with large percentages of lithic fragments (16–37 %). The lithic sandstones from different formations were deposited in continental and deltaic settings as a result of clastic transport from different provenance lithologies. The clastic material for the Ust’-Tagul Fm. deposition came from the Precambrian rocks of the Siberian craton and the Neoproterozoic (870–940 Ma) units: either the Yenisei Ridge of the craton or the Arzybey terrane of the Central Asian Orogenic Belt (CAOB). For the Shamanka Fm., it was Ediacaran and Early Cambrian material from blocks and terranes of the northern CAOB. The clastic inputs for the Ushakovka and Kurtun Fms. deposition were from the Precambrian basement of the Siberian craton and the Neoproterozoic (550–920 Ma) North Transbaikalian group of CAOB terranes. The youngest detrital zircons have the earliest Cambrian ages (530–540 Ma). The clastic sedimentary rocks of the Sayan regional stratigraphic stage dispersed over the southern Siberian craton were deposited in the earliest Cambrian in separate disconnected sedimentary basins which resulted from Ediacaran accretionary-collisional events in southern Siberia.

Provenance of Detrital Rutiles from the Triassic–Jurassic Sandstones in Franz Josef Land (Barents Sea Region, Russian High Arctic): U-Pb Ages and Trace Element Geochemistry

Provenance study plays an important role in paleogeographic and tectonic reconstructions. Detrital zircons are commonly used to identify sediment provenance; however, a wide range of detrital zircon ages in clastic rock often represent a fingerprint of reworked older terrigenous successions rather than ages of magmatism and metamorphism in the provenance area. This study focuses on the provenance of detrital rutile grains in the Triassic–Jurassic sandstones from Franz Josef Land and shows the importance of multiproxy approaches for provenance studies. Trace element data demonstrate that most rutile grains were sourced from metapelitic rocks, with a subordinate population having a metamafic origin. The Zr-in-rutile thermometer and U-Pb geochronology suggest that detrital rutile grains were predominantly derived from rocks that underwent amphibolite facies metamorphism during the Paleozoic era, with a predominance of the Carboniferous–Permian ages. Therefore, we suggest that the provenance area for the studied sandstones on Franz Josef Land has a similar geological history to the Taimyr region and Severnaya Zemlya archipelago. We propose that this crustal domain extends across the Kara Sea and forms the basement to the north and east of FJL, representing a proximal provenance for the studied Mesozoic terrigenous rocks. This domain experienced both Middle–Late Ordovician and Carboniferous–Permian metamorphism. The comparison of U-Pb dating and the geochemistry of rutile, U-Th/He, and U-Pb dating of zircons showed that detrital rutiles are the powerful toll in provenance restoration and can give additional constrains when a provenance area locates within collisional-convergent settings.

U–Pb detrital zircon ages from late Eocene to early Oligocene Pinghu formation of the East China Sea Shelf Basin: Inferences on synergistic effects between East Asia offshore sedimentation and major rivers supply

Our understanding of the late Eocene to early Oligocene provenance evolution of the East China Sea Shelf Basin has been limited, which hampers our study of the synergistic effects between East Asia offshore sedimentation and major rivers. To address this, we compared newly acquired detrital zircon chronological data from the East China Sea with published detrital U–Pb ages of major rivers in East Asia. Through this analysis, we have been able to reconstruct the provenance changes of sediments in the East China Sea during this crucial period. We have identified two large-scale and three small-scale denudation surfaces that developed in the Pinghu and lower Huagang Formations. These surfaces indicate that sediments were also derived from underlying strata and bedrock, particularly in the lower Pinghu and lower Huagang Formations. The newly acquired detrital zircon U–Pb age range was found to be roughly similar, ranging from 36.2 ± 0.7 to 2954.0 ± 30.3 Ma. The age peaks of the lower Pinghu Formation were more consistent, while the middle, upper Pinghu Formation, and lower Huagang Formation exhibited multiple age peaks. Comparing the compiled zircon U–Pb age peaks of the Chuanjiang segment of the upper Yangtze River with those of the East China Sea Shelf Basin, we found relative similarity. Additionally, the younger zircon grains with ages <500 Ma in the east Cathaysia catchment showed similarities with the East China Sea Shelf Basin. In terms of provenance contribution, the sediments of the lower Pinghu Formation were predominantly provided by the adjacent uplifts in the east Cathaysia catchment, with the Chuanjiang segment also playing a significant role. From the middle Pinghu Formation onwards, the provenance from the Chuanjiang segment became dominant, accounting for over 90 % of the sediments. However, this influence was limited to the northern part of the study area. This suggests a substantial increase in the Yangtze River catchment during this period, potentially related to the complete connection of the modern Yangtze River.

Provenance of Conglomerate and Sandstone from Early Permian Shoushangou Formation in Xi Ujimqin, Inner Mongolia: Implications for Understanding Paleo‐Asian Ocean Subduction

AbstractDuring the Late Carboniferous to Early Permian, a rift was formed by post‐collisional extension after ocean closure or an island arc‐related basin formed by Paleo‐Asian Ocean (PAO) subduction in the Xi Ujimqin area. Nevertheless, the closure time of the PAO is still under debate. Thus, to identify the origin of the PAO, the geochemistry and U‐Pb age of zircons were analyzed for the extra‐large deep marine, polymict clastic boulders and sandstones in the Shoushangou Formation within the basin. The analyses revealed magmatic activity and tectonic evolution. The conglomerates include megaclasts of granite (298.8 ± 9.1 Ma) and granodiorite porphyry (297.1 ± 3.1 Ma), which were deposited by muddy debris flow. Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I‐type granite, characterized by low Zr + Nb + Ce + Y and low Ga/Al values. The granitoid boulders were formed in island arc setting, indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction‐related granitoid in southern Xi Ujimqin. Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc‐related felsic rocks. Detrital zircon U‐Pb age cluster of 330‐280 Ma was obtained, indicating input from granite, ophiolite, Xilin Gol complex, and Carboniferous sources to the south. The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc. The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO. The backarc basin and intrusive rocks, in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol, confirm the presence of an Early Permian trench‐arc‐basin system in the region, represented by the Baolidao arc and Xi Ujimqin backarc basin. This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin.

Early Neoproterozoic Granite‐Gneisses of the Junggar Alataw (Southeastern Kazakhstan): Age, Petrogenesis and Tectonic Implications

AbstractThe combined petrographic, petrological, geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane. It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt. The U‐Pb single‐grain zircon ages indicate that granite‐gneisses formed from the same source and crystallised in the early Neoproterozoic ca. 930–920 Ma. The chemical composition of gneisses corresponds to A2‐type granites. The whole‐rock Nd isotopic characteristics (εNd(t) = –4.9 to –1.0 and TNd(DM‐2st) = 1.9 to 1.7 Ga) indicate the involvement of Paleoproterozoic crustal rocks in magma generation. Early Neoproterozoic ca. 930–920 Ma A‐type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within‐plate magmatism adjacent to the collisional belt or a local extension setting in back‐arc areas of the continental arc.

U-Pb zircon ages and petrogeochemistry and tectonic implications of gabbro and granite in southwest Lahad Datu area of Sabah, Malaysia

U-Pb zircon ages and petrogeochemistry and tectonic implications of gabbro and granite in southwest Lahad Datu area of Sabah, Malaysia

Late Neoproterozoic tectonic evolution of the northern Tarim block: New insights from integrated detrital zircon and rutile geochronology and trace element geochemistry

In the Neoproterozoic era, the breakup of the Rodinia supercontinent had a profound impact on different aspects of Earth; yet, the precise driving mechanism behind this event has been a source of ongoing controversy. The Tarim block, as a crucial component, presents an opportunity to gain valuable insights into the breakup process through its tectonic-sedimentary evolution history and dynamic background. However, the comprehension of basin evolution is limited due to the presence of an ambiguous prototype basin during the late Neoproterozoic and its intricate interconnections with surrounding blocks. In this contribution, we integrate detailed field observations, U-Pb dating of detrital zircon and rutile, and trace element analysis of detrital rutile to elucidate the source-to-sink relationships and the tectonic setting of Ediacaran sedimentary strata in the Aksu area (northern Tarim block, China). Detrital zircon age spectra exhibit consistent distributions with ages between ∼850 and ∼600 Ma and between ∼2100 and ∼1800 Ma. Rutile age groups however exhibit an abrupt transition between the lower member of the Sugatbrak Formation and the succeeding upper member to the Qigebrak Formation in the basin, with ages between ∼1800 and ∼900 Ma and nearly identical to those between ∼2100 and ∼1800 Ma. Calculated Zr-in-rutile temperatures and Cr-Nb compositions imply that the majority of the detrital rutiles were sourced from amphibolite facies metapelites, with an abrupt transition from amphibolitic schist to amphibolite-granulite facies for the ∼1800 Ma group grains. Provenance tracing shows that the detrital sediments of the lower Sugatbrak Formation are sourced from both the Central Tianshan and the Tarim blocks, and that the overlying strata have a single source in the Tarim block. A corresponding change from syn-rift detrital facies to a shallow-marine environment in on a passive continental margin is suggested in terms of depositional setting. In light of prior published evidence from petrology, geochronology and paleomagnetism, we propose that the Neoproterozoic northern Tarim margin was affected by a protracted subduction zone retreat. Associated back-arc spreading eventually was responsible for the opening of the southern Tianshan Ocean and rifting of the Central Tianshan block from the Tarim block in the late Ediacaran. This development ultimately prevented detrital material from the Central Tianshan block from reaching the northern Tarim depocenters as the latter evolved into a passive continental margin.

Detrital zircon age constraints on low-grade sedimentary successions of the eastern Circum-Rhodope Belt, Bulgaria

Detrital zircon age constraints on low-grade sedimentary successions of the eastern Circum-Rhodope Belt, Bulgaria

New age constraints for metasedimentary rocks in southern Finland

Metasedimentary rocks from nine sampling sites in southern Finland and an intermediate dyke in one of these sites were sampled for analysis of U–Pb zircon age and geochemical composition. The zircons of the metasedimentary rock samples yield 207Pb/206Pb dates ranging from 3281 to 1810 Ma. The nearly concordant dates from apparent detrital zircon cores indicate a prominent source with age around 2.1–2.0 Ga. The maximum depositional ages estimated for six of the metasedimentary rock samples span from 1.96 to 1.89 Ga. The data from zircon rims and overgrowths and metamorphic zircons in the metasedimentary rock samples indicate regional metamorphic events in the study area at least at ca. 1.89 and 1.84 Ga, and possibly also at ca. 1.87 Ga. The minimum age of the deposition (≤1.89 Ga) was estimated based on the ages of the regional metamorphism and the intrusive rocks. Some zircon rims and overgrowths yield ≥1.91 Ga 207Pb/206Pb dates, which are considered to possibly represent metamorphic events in the source areas.

Extensional tectonics of the Indian passive continental margin in the Middle and Late Jurassic: Constraints from detrital zircon ages in the eastern Tethyan Himalaya

Knowledge the initial extension in the Indian continent during the Jurassic is important for understanding the dynamics of its breakup from Eastern Gondwana. The absence of Jurassic magmatic activity in the eastern Tethyan Himalaya hinders the understanding of this process. We report a provenance and tectonic setting study on the Middle Jurassic Zhela and Late Jurassic Weimei Formations sandstone in Gyangze, eastern Tethyan Himalaya. Detrital zircons of Jurassic sediments indicate four major age peaks: ∼500 Ma, ∼820 Ma, ∼950 Ma, and ∼2450 Ma, which reflect the affinity between the Tethyan Himalaya and India. The differences between the crystallization age and depositional age of isolated detrital zircons from the Middle Jurassic Zhela and Late Jurassic Weimei Formations, indicate that they were formed in an extensional continental margin and deposited on the passive continental margin of India. Combined with regional geological information, our results show that extensional tectonics was dominant on the northern margin of the Indian continent during the Jurassic. The source-sink sedimentary system and the topography remained stable at this time. After the extension event in the Middle and Late Jurassic, the Kerguelen mantle plume commenced activity, indicating the transition from the lithospheric thinning process to active rifting. The mantle plume activity in the Early Cretaceous led to large-scale uplift in the southeast part of the Tethyan Himalaya, that ultimately led to the breakup of India from Eastern Gondwana.

Reconstruction of ancient drainage in the contact karst of the Harmanecká dolina Valley, Western Carpathians, based on mineralogical data from the allochthonous sediments and isobase geomorphometry

AbstractCaves are unique sedimentary archives that may record the evolution of the surrounding landscape. In this study, we applied combination of mineralogical data on allochthonous sediments with digital modelling of isobase surfaces to reconstruct the multi‐phased geomorphological development of the karst of the Harmanecká dolina Valley. The allochthonous cave sediments contain quartz and translucent heavy minerals (HMs) such as tourmaline, garnet, rutile, apatite, zircon, pyroxene, amphibole, staurolite, spinel, monazite, corundum, epidote, xenotime and florencite. Rounded shape and surface microtextures preserved on quartz and most HM grains point to predominantly a fluvial transport of detritus and its multiple recycling history. Pyroxene and amphibole are exceptions that denoted a very close source and the first‐cycle sedimentation from the adjacent volcanic Kremnické vrchy Mts. corresponding to obtained SHRIMP U–Pb detrital zircon ages of ~13.8–12.8 Ma. Heavy‐mineral geochemistry (e.g., zoned grossular‐rich garnet) and wide range of the Palaeozoic ages (Ordovician to Permian) confirms that the studied detritus sourced dominantly in the Western‐Carpathian crystalline basement rocks of the Veporic/Tatric tectonic units initially distributed by the palaeo‐Hron River and its tributaries from the east. Rare cummingtonite, remarkable tourmaline with omphacite inclusions and florencite point to the mixture of recycled sediments of Neogene Danube Basin formations containing also Austroalpine pre‐Neogene basement detritus, and confirm the original widespread distribution of the Neogene sediments currently eroded. Geomorphometric analyses of a LiDAR digital terrain model and derived isobase surface elevation models indicate the topographic development of wider area and support the findings about the transport direction of detritus. Presented multi‐method approach is suitable not only for the understanding of development of the surroundings of Harmanecká dolina Valley but also for the palaeogeographic and geomorphological reconstructions of similar karst and non‐karst areas.

Crustal thickness variation of the Dabie orogenic belt: Insights from detrital zircon evidence and geological significance

The Dabie orogenic belt is characterized by widely distributed Mesozoic ultrahigh-pressure metamorphic rocks. Together with the Qinling orogenic belt, it constitutes one of the most important collisional orogens in eastern Asia. Because of intense continental subduction and collision during the Mesozoic and subsequent denudation, it remains controversial whether pre-Mesozoic convergent events happened in the region of the Dabie orogenic belt. In this study, we reconstruct the crustal thickness variation of the Dabie orogenic belt based on detrital zircon data. Results reveal three stages of crustal thickening at ca. 900-800 Ma, ca. 530-400 Ma, and ca. 250-210 Ma that are likely associated with three major convergent events that happened between the North and South China Blocks since the Neoproterozoic. The first thickening stage is possibly related to long-term subduction-accretion-collision processes along the northern margin of the South China Block. The second one corresponds to early Paleozoic ocean closure and the arc-continent collision that happened between the North and South China Blocks. The third one is a most significant thickening that represents the final collision between the North and South China Blocks during the Mesozoic. The turning point (ca. 210 Ma) of the crustal thickness curve represents the cessation of ultradeep subduction and constrains the completion of Mesozoic continental collision. Late Archean crustal thinning may be related to the onset of plate tectonics. Overall, the fluctuations of crustal thickness and detrital zircon age populations from sediments of the Dabie orogenic belt suggest interaction among Chinese continental blocks is consistent with the evolution of global supercontinent cycles.

Marinoan glaciation in the Indian subcontinent - Anatomy and global implications

Detailed sedimentological analysis of the Pokaran Boulder Bed, representing the most basal unit of the Neoproterozoic-Lower Cambrian Marwar Supergroup, clearly indicates its glacial origin. The glacial sediments are interpreted as an ice-contact submarine fan deposit. Based on the detrital and inherited zircon population of the Marwar Supergroup sediments and interlayered pyroclastic deposits, a Marinoan cryochron of the Cryogenian Period is envisaged for the Pokaran Boulder Bed. The well-preserved Ediacaran elements in the post-glacial sedimentary succession also support a Cryogenian to Early Cambrian age of the Marwar Supergroup. The glacial deposition at the base of the Marwar Supergroup strengthens the regional correlation between the studied sediments with the Lesser Himalayan Blaini-Krol-Tal sediments and the Haqf Supergroup of Oman. The available zircon ages and paleomagnetic data of the Malani Igneous suite, along with the Marinoan glacial deposits, detrital zircon ages, and Ediacaran fossil elements of the Marwar Supergroup add significant information to the Neoproterozoic Earth history.

Local Singularity Spectrum: An Innovative Graphical Approach for Analyzing Detrital Zircon Geochronology Data in Provenance Analysis

Detrital zircon geochronology plays a crucial role in provenance analysis, serving as one of the fundamental strategies. The age spectrum of detrital zircons collected from the sedimentary unit of interest is often compared or correlated with that of potential source terranes. However, biases in the age data can arise due to factors related to detrital sampling, analysis techniques, and nonlinear geological mechanisms. The current study reviewed two sets of detrital zircon datasets established in 2011 and 2021 to discuss the origins of the Tibetan Plateau. These datasets collected from different media effectively demonstrate a progressive understanding of provenance affinity among the main terranes on the Tibetan Plateau. This highlights issues regarding weak and unclear temporal connections identified through analyzing the age spectrum for provenance analysis. Within this context, a local singularity analysis approach is currently employed to address issues associated with unclear and weak provenance information by characterizing local variations in nonlinear behaviors and enhancing detection sensitivity towards subtle anomalies. This new graphical approach effectively quantifies temporal variations in detrital zircon age populations and enhances identification of weak provenance information that may not be readily apparent on conventional age spectra.