Pb Dating Of Detrital Zircons Research Articles

Closing of the east Palaeo‐Tethys Ocean: Source–sink records from Middle Triassic sediments, Hainan Island, China

During the Late Palaeozoic to Early Mesozoic, the eastern segment of the Palaeo–Tethys Ocean closed, resulting in the collision and amalgamation of the South and North Hainan Islands. However, the exact location of the collision and amalgamation remains controversial. The main collision locations are the Baisha, Jiusuo–Lingshui and Changjiang–Qionghai faults. The U–Pb age of detrital zircons was used to determine the main source area of the Middle Triassic basin in the eastern part of Hainan Island and the closed position of the eastern section of the Palaeo‐Tethys Ocean. The U–Pb dating of detrital zircons revealed that the Middle Triassic Lingwen Formation contains four age groups: 235–258, 335–446, 766–986 and >1000 Ma. Notably, rock masses aged 248–252 Ma that were formed in a post‐orogenic tension setting have been identified in the western region of Hainan Island, whereas no igneous rocks from this period have been discovered in the eastern region. The detrital zircon samples from the Lingwen Formation revealed a peak at 249 ± 2 Ma U–Pb age, which is important evidence indicating that the Changjiang–Qionghai Fault is the product of collision between the southern and northern Hainan terranes. Affected by the bipolar subduction of the eastern segment of the Palaeo‐Tethys Ocean, the collision and amalgamation of the South and North Hainan terranes occurred, and experienced a post‐collision (extensional) process at ca. 249 ± 2 Ma.

The Source Areas of Terrigenous Deposits of the Laoeling–Grodekovo Terrane (Western Primorye): Evidence from Mineralogical and Geochemical Data and the Results of U–Pb Dating of Detrital Zircons

The Source Areas of Terrigenous Deposits of the Laoeling–Grodekovo Terrane (Western Primorye): Evidence from Mineralogical and Geochemical Data and the Results of U–Pb Dating of Detrital Zircons

EARLY CAMBRIAN DEPOSITS OF THE CONTINENTAL MARGIN (SOUTH OF TUVA, TEREGTIG FORMATION): RESULTS OF U–Pb DATING OF DETRITAL ZIRCONS AND Sr-CHEMOSTRATIGRAPHY

The sedimentation interval (530–520 Ma) of the Teregtig Formation deposits in southern Tuva is estimated based on U–Pb dating of detrital zircons from terrigenous deposits and Sr-chemostratigraphy of carbonate rocks. The main source area for clastic material, containing a large amount of detrital zircon grains, were rocks with an age of 580 Ma. The presence of a wide diversity of Precambrian detrital zircons indicates that sedimentation of the Teregtig Formation took place within a block of continental crust with a long evolutionary history. The presence of numerous chromites in their matrix indicates that the rocks of the Agardag ophiolite complex were also part of the eroded land during the accumulation of conglomerates of the Teregtig Formation.

A database of detrital zircon U–Pb ages in the North China Craton from the Paleoproterozoic to the early Palaeozoic

AbstractU–Pb dating of detrital zircon is widely used in geology to identify the source of sediments and constrain palaeogeography and tectonic history. We collected the detrital zircon from the Paleoproterozoic to early Palaeozoic strata to understand the North China Craton's geological chronological characteristics. After screening and sorting out data information, we managed and analysed 84 papers from 2006 to 2022. Three hundred seventy‐nine samples comprising 29,431 pieces of U–Pb ages of detrital zircons gathered from the Proterozoic to Ordovician sedimentary rocks in North China Craton (NCC). Detrital zircons within five areas in the NCC, i. e., Xuhuai Basin, Zhaertai‐Bayan Obo‐Huade Basin, Yanliao Basin, Xiong'er Basin and Alxa Block, are discussed in detail. Meanwhile, we collected 2,588 pieces of Lu‐Hf detrital zircon data in the study. This Database can be helpful in understanding and explaining the tectonic evolution of the NCC from the Paleoproterozoic to the Early Palaeozoic.

Three Generations of the Basins of the Early Turkestan Ocean: Ediacaran–Silurian of the Southern and Middle Tien Shan

The results of U–Pb dating of detrital zircon from volcanoterrigenous Ediacaran–Silurian deposits, mainly from grauwacke turbidites, after accretion of which the “Caledonian” basement of the Paleozoic structure was formed in Kyzylkum and in the ridges of the Southwestern Tien Shan, including Northern Fergana, allowed us to clarify the age correlation and show the dynamics of the formation of this complex. It consists of deposits associated with the opening, filling and subsequent convergent development of three generations of oceanic basins, including the emergence and destruction of island arcs. The earliest of these basins was formed at the active volcanic margin of the eastern Rodinia/Gondwana, which included the Karakum-Tajik massif. Sandy turbidites (Besapan, etc.), whose age is not younger than the beginning of the Cambrian, were deposited here on top of siliceous (Taskazgan) Ediacaran sediments. The second generation is represented by Ordovician basins, in which radiolarian flints of the Lower Ordovician form the bathyal part of the sediments, and the main filling is turbidites of the middle Ordovician–Ruddan. The newly opened Silurian oceanic basins and their margins were filled with sediments of the third Caledonian generation, mainly graptolite aleuropelites and turbidites, starting from the end of the Llandovery. Incomplete preservation of the Ediacaran–Silurian sedimentary series is due to their partial absorption (tectonic erosion) during further subduction and collision, mainly already in the Carboniferous.

Composition and Age of Sources of the Lower–Middle Cambrian (?) Terrigenous Rocks from The Ernichny Formation in the Argun Massif, Eastern Part of the Central Asian Fold Belt

The paper presents the results of the mineralogical and geochemical studies of sandstones and siltstones of the Ernichny formation of the Argun series in the Argun continental massif, and the results of U–Pb (LA‑ICP-MS) dating for the detrital zircons from these rocks. It is established that the youngest detrital zircons from sandstone of the Ernichny Formation have age of 549–570 Ma. A maximum on the relative probability curve of zircon age corresponds to 566 Ma. These data determine the lower age limit of their accumulation on the border of the Ediacaran and Paleozoic age. According to the results of U–Pb dating of detrital zircon, the majority of detrital zircons from sandstones of Ernichny Formation are characterized by Neo- and Paleoproterozoic ages. The sources of zircons were Neo- and Paleoproterozoic igneous and metamorphic rocks that were widely developed within the Argun continental massif. In turn, the geochemical features of the terrigenous rocks of the Ernichny Formation, together with the presence of the poorly sorted and rounded clastic material in the studied samples, as well as the presence of interlayers of gravelstones, enabled us to establish that they were formed in a subduction-related setting.

The largest deflation basin in Asia reveals that the Miocene basin-filling sediments in the eastern Gobi Desert are an important dust source

Deflation is one of the most important exogenic forces in arid and semiarid regions. It not only shapes various wind erosion landforms but also releases a large amount of dust into the atmosphere. The Sunite Steppe in the eastern Gobi Desert is located in arid areas, where Neogene strata are widely distributed. However, the deflation process and its impact on landforms in this area are still unclear. We conducted comprehensive research on stratigraphy, sedimentology and geomorphology and found that there is a giant deflation basin (Sunite Deflation Basin) located to the west of the Otindag Sandy Land and to the east of the Tunggur Platform (Tamuqintala High Platform). With an area of over 8000 km2 and a volume of ∼393 km3, that deflation basin ranks second only to the Qattara Depression in North Africa and is much larger than Big Hollow in the United States; it is the second largest deflation basin in the world and the largest in Asia. Unlike the Qattara Depression (comma-like) and Big Hollow (rod-like), the Sunite Deflation Basin is shell-like in planform. The western edge of the basin is well defined with steep basin walls, indicating that the basin was developed on the ground represented by the Tunggur Platform. The basin bottom gradually becomes shallower from west to east, which is consistent with the prevailing westerly. Subordinate deflation basins, deflation mounds and blowouts are widely distributed in the Sunite Deflation Basin. The basement of the basin is mainly composed of Miocene alluvium and red clay, i.e., basin-filling sediments. The amount of dust (<20 μm) released from the basin that can be transported over long distances is preliminarily estimated to be as high as 216 km3. If all dust is deposited in the downwind loess area (∼37,200 km2) near Chifeng in Northeast China, the deposition thickness can reach ∼5.8 m. Nd isotope and U–Pb detrital zircon data suggest that the Miocene basin-filling sediments comprise aeolian deposits derived from the Gobi Desert and fluvial deposits derived from the Yinshan-Yanshan Orogenic Belt. The Sunite Deflation Basin must have begun forming after the deposition of basin-filling sediments (∼7.5 Ma) and most likely began to develop at ∼3.6 Ma as a result of the strengthened East Asian winter monsoon due to global cooling.

Depositional environment and provenance of Early Carboniferous clastic sedimentary rocks at McIsaacs Point, Nova Scotia: implications for syntectonic basin development during the formation of Pangaea

Abstract Following the collision of Gondwana and Laurussia to form Pangaea, a large system of regional-scale strike-slip faults developed which resulted in the formation of transtensional syncollisional basins. One such basin, the Antigonish Basin, contains late Devonian fluvial, marine and lacustrine sedimentary rocks, including sandstone, conglomerate and shale. LA-ICP-MS U–Pb detrital zircon data from three samples from the lower and middle of the McIsaacs Point section have a strong Silurian–Devonian ( c. 440–380 Ma) population whereas the top of the section lacks these age populations and is instead dominated by Neoproterozoic ( c. 630–550 Ma) grains. Detritus was derived from a mix of local Avalonian and more distal Meguma terrane sources. Detrital zircon and field data show that sediments were deposited in a braided to meandering fluvial system transitional to a proximal braided stream environment followed by evolution to a more distal braided stream environment. As the basin evolved, the source of detritus shifted from a dominantly Meguma terrane source to a more local Avalonian source. This temporal evolution in provenance and depositional environment attests to the complex depositional processes associated with syntectonic basin evolution during the formation of Pangaea.

Provenance of the conglomerate and siliciclastic rocks from the Gadag Greenstone Belt, Western Dharwar Craton, India: Implications for understanding Neoarchean basin margin sedimentation

Petrographic, whole‐rock geochemical and geochronological analysis of polymictic conglomerate, associated siltstone and greywacke in the Neoarchean Gadag Greenstone Belt in the Western Dharwar Craton, India, provides new insights into sedimentary provenance and tectonic setting. The polymictic conglomerate contains granitic, gneissic, felsic and mafic volcanic, quartzite and banded ferruginous chert clasts within a quartzo‐feldspathic matrix. Framework grains in the siltstone and greywacke are quartz, feldspar with rock fragments, embedded in a chlorite‐dominant matrix. The chemical index of alteration values (~70) and A‐CN‐K plot for the rocks suggest a low‐to‐moderate degree of weathering. Rare earth element (REE) patterns show moderate fractionation (LaN/YbN ~ 12.31) with a weak negative europium anomaly (0.82). Enrichment in transition elements (Ni, Cr, Co, Sc) and depletion in high‐field‐strength elements, as well as relatively low La/Co (0.62), moderate to high Th/Yb (3.06), La/Th (5.16), La/Yb (17.5), and La/Sc (~2.37) ratios, suggest a mixed felsic‐mafic provenance. U–Pb dating of detrital zircon from the conglomerate and greywacke revealed major age peaks at ca. (3.2, 2.9, 2.8, 2.6, 2.5 Ga) and a maximum age of deposition of 2,508 ± 26 Ma, 2,493 ± 20 Ma, respectively. The above data suggest low to moderately weathered proximal sources for both conglomerate and greywacke, indicating that these two rock types were not deposited simultaneously, but rather separately. The association of these conglomerates and greywacke with continental arc‐related volcanics indicates the closing of an arc at the time of sedimentation. Complex provenance consisting of recycled and magmatic arc during basin closure confirm the notion of modern style plate tectonics operating during Neoarchaean.

Zircon U–Pb age constraints on the provenance and response to tectonics: Lower Oligocene of the western Qiongdongnan Basin, South China Sea

Provenance changes and tectonic activity during the Early Oligocene in the Qiongdongnan Basin are responses to the evolution of the northwestern South China Sea. However, the provenance of the Lower Oligocene (Yacheng Formation) in the Qiongdongnan Basin is poorly understood owing to a lack of available borehole samples and poorly constrained stratigraphy. Here, combined with published data from wells of different part of the basin, we apply U–Pb dating of detrital zircons on samples nearby the western boundary fault of the basin to analyse the provenance of the Yacheng Formation and its regional tectonic implications. The zircon U–Pb age spectra of the sediments in three different members of Yacheng Formation show different features. A single U–Pb age peak at ca. 235 Ma occurs in the Third Member of the Yacheng Formation, whereas the U–Pb age spectra in the stratigraphically younger Second Yacheng Formation show different zircon U–Pb age spectra features: an age pattern has two major peaks at ca. 248 Ma and 441 Ma and lacks zircons younger than 200 Ma, and another pattern has two major peaks at ca. 95 Ma and 252 Ma. The Early Oligocene provenance evolution of the western Qiongdongnan Basin is reconstructed by comparing the zircon U–Pb age spectra of the sediments in the different samples to potential sources nearby. Abrupt changes in the U–Pb ages throughout the Lower Oligocene in the western Qiongdongnan Basin suggest that sediment supply in the Second Member of Yacheng Formation was dominated by rivers from western Hainan Island and Central Vietnam. By contrast, Hainan Island and local structural highs within the Qiongdongnan Basin were the main sources in the Third and First Members of the Yacheng Formation, respectively. The difference in the U–Pb age spectra between sediments in the Qiongdongnan Basin and the Red River implies that the time at which the Red River system entered the Qiongdongnan Basin was later than the Early Oligocene. Paleorivers sourced from Central Vietnam entered into the western Qiongdongnan Basin and did not reach the central or eastern part of the basin until ca. 31.5–29.9 Ma. An examination of the activity of the Red River Fault showed that the transition of provenance in the study area during the Early Oligocene could be a response to sinistral strike-slip motion along the Red River Fault.

The Manifestation Areas of the Intra-Visean Orogeny in the Eastern Zones of the Southern Urals According to the U–Pb Dating of Detrital Zircons from the Upper Visean Solnechnaya Formation

The Manifestation Areas of the Intra-Visean Orogeny in the Eastern Zones of the Southern Urals According to the U–Pb Dating of Detrital Zircons from the Upper Visean Solnechnaya Formation

HT–MP metamorphism in Central Qilian Block, NE Tibet Plateau: Implications on the tectonic evolution of the Qilian Orogen

The metamorphism of the Central Qilian Block in the northeastern Tibetan Plateau records a complete tectonic history of the Qilian Orogen. Here, results of structural measurements, geochronological data, and thermobarometry for metamorphic rocks in the Central Qilian Block were presented, which trace the tectonic evolution of the Qilian Orogen. New U–Pb dating of detrital zircon from one paragneiss shows a main age population between c. 1500 and c. 1250 Ma, with the youngest age of 1085 Ma. This unit was intruded by an orthogneiss which has a U–Pb weighted mean age of 920 ± 18 Ma. Together with c. 1200–1000 Ma ages from inherited zircon cores in amphibolites, these results indicate that the protoliths of the Huangyuan Group were formed during the Mesoproterozoic and Neoproterozoic. Rims of these zircons obtain tightly constrained and concordant ages ranging from c. 459 to c. 427 Ma, with a weighted mean age of c. 450 Ma. Phase equilibrium modelling and conventional thermobarometry jointly indicate high‐temperature/medium‐pressure HT–MP metamorphism along a clockwise pressure–temperature (P–T) path at c. 450 Ma, passing through prograde conditions of 7.8–8.0 kbar and 620–650°C to peak conditions of ~7 kbar and ~780–800°C. Together with documented widespread metamorphism, magmatism, and ductile shear belts, these new results reassert that the Central Qilian Block experienced a three‐stage tectono‐metamorphic evolution during the Early Palaeozoic and the HT–MP metamorphism of Huangyuan Group was developed by a continental collision geodynamic setting with coeval mafic and granitic magmatism.

Detrital zircon U–Pb analysis constrain the depositional age and provenance of Cryogenian glacial successions of the Macaúbas group in the northeastern Araçuaí orogen, eastern Brazil

The precursor basin of the Araçuaí – West Congo Orogenic System (AWCO) formed a large gulf within the São Francisco – Congo Paleocontinent (SFCP), where the diamictite-bearing Macaúbas Group was deposited during the Neoproterozoic. However, the lack of robust age constraints on the Cryogenian glaciogenic successions prevents correlation to one or both of the Cryogenian Snowball Earth glaciations. The present study introduces new field data and new U–Pb detrital zircon data from diamictite-bearing units on the southern margin of the São Francisco Craton, in the northeastern Araçuaí Orogen. This region is much closer to possible Ediacaran-Cryogenian igneous rocks of the southern São Francisco craton than other regions previously studied for the Macaúbas Group, enhancing the probability of detecting detrital minerals from those rocks, if they were involved as source areas. In the studied region, the Macaúbas Group is composed of metadiamictite with sparse clasts and schistified metagraywacke with bulk mineralogy similar to the quartz-muscovite-feldspar matrix of the metadiamictites. U–Pb (LA-MC-ICP-MS) dating of 182 detrital zircon grains from the Lower Chapada Acauã Formation forming the syn-glacial sequence yielded main age peaks at 939 ± 3 Ma, 1409 ± 10 Ma, 1822 ± 8 Ma, 2044 ± 7 Ma, 2551 ± 9 Ma and 3103 ± 19 Ma. The youngest concordant zircon grain found in this study aged 753 ± 12 Ma. U–Pb (LA-MC-ICP-MS) dating of 104 zircon crystals from a granitic clast recovered from the diamictite exhibits highly discordant data plotting in distinct Discordia lines with upper intercept ages of 2.0 Ga, 2.5 Ga, 2.6 Ga and 3.2 Ga, indicating derivation from the adjacent cratonic basement. The U–Pb age spectra suggests important contribution from the Archean and Paleoproterozoic basement of the São Francisco – Congo paleocontinent and metamorphic complexes, from the Mesoproterozoic intrusive and volcanic rocks of São Francisco Craton, and from the Tonian Salto da Divisa Suite. Despite the relative abundance of Cryogenian zircon grains in the surrounding prospective source areas, the studied rocks lack this interval age. The glaciogenic events in the Macaúbas basin system probably did not sample rocks with these age intervals due to the general characteristics of this type of deposit or because the sources were not exposed. Thus, the lower diamictite-bearing units of the Macaúbas Group in the northeastern São Francisco craton were deposited after ca. 753 Ma, but their correlation to either the Sturtian or Marinoan global glaciations remain speculative.

U–Pb age constraints on the protolith, cooling and exhumation of a Variscan middle crust migmatite complex from the Central Iberian Zone: insights into the Variscan metamorphic evolution and Ediacaran palaeogeographic implications

The Figueira de Castelo Rodrigo–Lumbrales Anatectic Complex (FCR-LAC) located in the Central Iberian Zone of the European Variscan Belt is delimited by two shear zones, which have been interpreted as constraining its exhumation. New U–Pb zircon and apatite ages for the migmatites allowed us to obtain a peak metamorphic age of the anatectic complex (316.8 ± 2.0 Ma), and to estimate fast cooling (7–54°C Ma –1 ) and fast exhumation (0.2–1.3 mm a −1 ) after a vertical displacement of c. 6–9 km. Our results show a similar zircon age distribution between migmatites and the Excomungada Formation from the host Ediacaran–Cambrian Douro–Beiras Supergroup. Although the existence of an inherited zircon population lasting c. 500 Ma, absent in the metasedimentary units, suggests the contribution of Ollo de Sapo magmatic rocks during the Lower–Middle Pennsylvanian melting events. Detrital zircon ages of the Pinhão Formation (Douro Group) have contrasting sources to units from the Beiras Group, which may indicate the presence of a barrier that prevented older detrital components from reaching the Douro basin. However, at odds with what has been postulated before, such a barrier must have been placed farther south of the FRC-LAC, and thus not coincident with the Juzbado–Penalva do Castelo shear zone. Supplementary material: A full description of the stratigraphy and lithologies (Supplementary 1 and 2, respectively); the analytical conditons of the LA-ICP-MS analyses (Supplementary Material 3); the U–Pb zircon and apatite data of the FCR-LAC migmatites and the U–Pb detrital zircon data of the DBSG (Supplementary Material 4) are available at https://doi.org/10.6084/m9.figshare.c.6002006

U–Pb geochronology of Upper Triassic – Lower Jurassic detrital sequences from SE margin of the South China Block: implications for Palaeo-Pacific subduction and tectonic evolution

AbstractWe performed U–Pb dating of detrital zircons and conducted petrological and whole-rock geochemical analyses to assess the provenance of the Upper Triassic – Lower Jurassic clastic rocks in the southeastern margin of the South China Block. Detrital zircon U–Pb ages are mainly classified into age groups of 2000–1700, 900–700, 490–390 and 280–210 Ma, consistent with derivation from the Jiangnan orogenic belt, Nanling Belt, as well as Wuyi and Yunkai domains. Lower Jurassic samples yield a special main age population of 200–190 Ma, and these detrital zircon grains have low Th/U and Nb/Hf ratios and high Th/Nb and Hf/Th ratios, showing they are derived from a continental magmatic arc. However, the cross-correlation and likeness coefficients of kernel density estimates of Upper Triassic and Lower Jurassic sandstones are 0.8608 and 0.8403, indicating that their populations are highly similar. Since the tectonic setting is the key factor in controlling the relationship between source and sink, the stable supply of identical provenance suggests that the tectonic setting did not significantly change during Late Triassic – Early Jurassic time. Sandstone petrography, regional facies distribution and the detrital zircon age patterns all reflect a consistent tectonic setting for the South China Block during Late Triassic – Early Jurassic time. The Palaeo-Pacific subduction therefore did not control the tectonic evolution of the South China Block until after the Early Jurassic Epoch.

A story of Devonian ocean plate stratigraphy hosted by the Ulaanbaatar accretionary complex, northern Mongolia: implications from geological, structural and U–Pb detrital zircon data

A story of Devonian ocean plate stratigraphy hosted by the Ulaanbaatar accretionary complex, northern Mongolia: implications from geological, structural and U–Pb detrital zircon data

Detrital zircon ages, provenance and tectonic evolution in the early Paleozoic of Tasmania and Waratah Bay, Victoria

The provenance of the upper Cambrian to Upper Ordovician sedimentary rocks of Tasmania and Waratah Bay in southern Victoria provides information about the complex and dynamic tectonic environment present during their deposition. This paper uses U–Pb detrital zircon data to constrain stratigraphic comparisons and tectonic reconstructions of these rock sequences. Multivariate statistics are used to investigate the similarity between the U–Pb ages and quantify the disparity among different samples from various locations. In western and central Tasmania, the Tyennan region supplied most detrital zircons during the late Cambrian and Early Ordovician. The overlying Middle Ordovician Pioneer Sandstone records a switch in provenance with zircons derived from the Mount Read Volcanics (MRV) mixed with zircons similar to those from continental-derived Paleozoic sedimentary rocks deposited throughout east Gondwana. The Middle to Upper Ordovician Gordon Group in western and central Tasmania lacks detrital zircons younger than 1.2 Ga, which indicates a return to a local provenance from Precambrian rocks. In southern Tasmania, the switch to zircons derived from the MRV and east Gondwana-like sources occurred earlier within the Cambrian Deadmans Bay Formation, which is dominated by the east Gondwana Paleozoic zircon age signature. In the East Tasmania Terrane, Ordovician sedimentary rocks from Lefroy have detrital zircon populations dominated by Neoproterozoic and earliest Paleozoic sources similar to the Ordovician sedimentary rocks in the Lachlan Orogen. In southern Victoria, the Bear Gully Chert from Waratah Bay exhibit both Tyennan and distal Gondwana detrital sources. The switching of detrital zircon sources in the west Tasmanian sedimentary sequences implies the docking of Tasmania with mainland Australia during the Cambrian Tyennan Orogeny. The arrival of the distal zircons into these basins occurred at different times in the different areas, reflecting a complex local topography and paleogeography. Key Points Paleozoic sedimentary rocks in Tasmanian exhibit multisource detrital U–Pb age signatures that change over time, implying tectonic activity during their deposition. Paleozoic sedimentary rocks in northeastern Tasmania show Gondwana-wide detrital signatures similar to Lachlan Orogen. The Ordovician Bear Gully Chert at Waratah Bay in southern Victoria shows mixed Tasmanian and distal Gondwana detrital populations. The change in detrital zircon signature in western Tasmania suggests that VanDieland docked with the Australian continent during the Cambrian Tyennan Orogeny.

Structure and Geodynamic Evolution of the Maksyutov Metamorphic Complex (Southern Urals): Structural Analysis and Results of U–Pb Dating of Detrital Zircons

Structure and Geodynamic Evolution of the Maksyutov Metamorphic Complex (Southern Urals): Structural Analysis and Results of U–Pb Dating of Detrital Zircons

Igneous genesis of the Bayan Obo REE–Nb–Fe deposit: New petrographical and structural evidence from the H1–H9 cross-section and deep-drilling exploration

Rare earth elements (REEs) are a focus of global attention because of their unique properties and high-tech applications. Bayan Obo is the world's largest REE deposit and is hosted in the Paleoproterozoic Bayan Obo Group, Inner Mongolia. The REE resources are concentrated in unit H8, “dolomite marble.” However, whether unit H8 has an igneous or sedimentary origin is debated, and relationships among units H1–H9 are unclear, hindering our understanding of the formation of such a giant REE deposit. It was previously assumed that the unit H8 orebody is located in both limbs of the Bayan syncline and unit H9 in the core, which also needs to be confirmed because it is a guide for ore exploration. Field observations and petrographic studies of units H1–H9 were undertaken to re-evaluate the petrology and structure of the Bayan Obo Group. It was found that some units (e.g., H5–H7) are missing from the studied cross-section, with the two sides of unit H9, across the hinge of the so-called syncline, not being directly comparable. Unit H8 displays petrological, mineralogical, and whole-rock REE geochemical characteristics distinct from those of the other units investigated, suggesting they are of different origin. Moreover, deep-drilling exploration indicates major differences between the two limbs of the orebodies in terms of thickness, occurrence, and spatial distribution. The East orebody has a steep dip angle of 70°–80° and continuously extends to depth without reduction of angle, suggesting the syncline is probably nonexistent. These results, combined with the reported intrusion relationship of unit H8 with surrounding rock and in situ isotopic studies previously reported, indicate that the orebody is a carbonatitic igneous conduit rather than being of sedimentary origin. SHRIMP U–Pb dating of detrital zircons from the units H2–H9 yielded ages of 2574 ± 25 to 132 ± 2 Ma, overlapping the ages of units H1–H9 and the main REE mineralization periods reported previously. These protracted and complicated ages of the orebody likely represent fluid-aided resetting ages.

Provenance Change in Cretaceous–Paleogene Fore-arc in Western Hokkaido: U–Pb Dating of Detrital Zircons from the Yezo Group

Provenance Change in Cretaceous–Paleogene Fore-arc in Western Hokkaido: U–Pb Dating of Detrital Zircons from the Yezo Group