Pb Ages Research Articles

Monazite Beats Zircon Regarding Dating of Young Metamorphic Events—An Example From Polycyclic Granitic Gneiss of the Pohorje Mountains, Slovenia

ABSTRACTThe result of dating U–(Th)–Pb bearing minerals in metamorphic rocks frequently suffers from the interpretative relation of their growth to a specific metamorphic event. This problem occurs in the southern Pohorje Mountains. Therefore, granitic gneiss from this area was studied. Rims of zircon in these rocks gave U–Pb ages around 90 Ma interpreted as an indicator of Late Cretaceous metamorphism. However, in situ dating of monazite with LA–ICP–MS yielded Early Miocene U–Th–Pb ages consistent with contact metamorphism by magmas forming the Pohorje pluton. This is supported by geothermobarometry using compositions of garnet and muscovite in granitic gneiss. This method led to pressure–temperature conditions of 6.5 kbar and 625°C, in line with intrusion depths estimated for the southeastern part of the Pohorje pluton. Consequently, zircon was not suitable for dating the latest metamorphic event but monazite was. Furthermore, monazite dating suggests two main intrusion pulses of magmas differing by 2–3 Ma.

Neoproterozoic Tectonics of the Arabian-Nubian Shield: Insights from U–Pb Zircon Geochronology, Sr–Nd–Hf Isotopes, and Geochemistry of the Deki Amhare Complex Granitoids, Central Eritrea

The Deki Amhare complex is located in central Eritrea, within the Arabian–Nubian Shield (ANS). It consists of an inner core of monzogranite porphyry and diorite enclaves (MMEs), surrounded outwardly by granodiorite and quartz diorite. The zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Hf isotopic compositions of the Deki Amhare complex granitoids were used to discuss the Neoproterozoic tectonics of the ANS. The Late Tonian granodiorite and quartz diorite are metaluminous and calc-alkaline to slightly high-K calc-alkaline I-type plutons, with ages of 811.2 ± 4.8 Ma and 811.6 ± 5.7 Ma, respectively. They exhibit positive εHf(t) (7.6–9.5) and εNd(t) (3.9–4.7) values and relatively low (87Sr/86Sr)i ratios (0.70374–0.70463), indicating that they derived from the partial melting of a metasomatized mantle wedge during intra-oceanic subduction. The Ediacaran monzogranite porphyry and MMEs are subalkaline to alkaline A2-type granitoids with ages of 620.0 ± 4.3 Ma and 614.8 ± 3.9 Ma. These display positive εHf(t) (5.3–8.7) and εNd(t) (4.2–4.7) values, as well as low (87Sr/86Sr)i ratios (0.70310–0.70480), implying that they formed through crust–mantle magma mixing related to post-collisional slab break-off. Based on these data, three stages of regional tectonic evolution can be described: (1) from ~1200 Ma to ~875 Ma, the mafic oceanic crust was derived from depleted mantle during the opening of the Mozambique Ocean; (2) from ~875 Ma to ~630 Ma, intra-oceanic subduction and arc formation occurred with the development of I-type batholiths; and (3) from ~630 Ma to ~600 Ma, crustal and lithospheric reworking took place post-collision, leading to the formation of A2-type granitoids.

Geochemistry and Zircon U–Pb Chronology of Jinchanshan Gold-Hosted Granitoids, Inner Mongolia: Implications for Petrogenesis and Geodynamic Evolution

Jinchanshan is a medium-sized, granitoid-hosted gold deposit located in the Kalaqin area of Inner Mongolia. Mineralization predominantly occurs in the contact zone between biotite granites and quartz porphyry rocks, associated with the Jinchanshan minor intrusion, suggesting a genetic link to the granitoid-hosted gold deposit. In this study, the petrography, geochemistry, and LA-ICP-MS zircon U–Pb chronology of these two granitoid samples were studied. The results indicate that the zircon U–Pb age of the biotite granites is 127.9 ± 3.0 Ma, while that of the quartz porphyry is 121.4 ± 1.5 Ma, both dating back to the Early Cretaceous. The average SiO2 content of the granites is 66.64%, and the rocks have high total alkali (K2O + Na2O) content, averaging 9.13%. The average K2O content is 4.39%, with a K2O/Na2O ratio of 0.93. The quartz porphyry rocks are enriched in SiO2 (74.41%–76.85%) and have high Na2O + K2O content (8.67%–9.59%), but are low in MgO (0.03%–0.09%), CaO (0.44%–1.02 %), and TiO2 (0.08%–0.12%). Most samples of the biotite granite and the quartz porphyry rocks exhibit high-K peraluminous and medium-K calc-alkaline characteristics, respectively. Both rock types are enriched in Rb, Th, U, K, Zr, Hf, and Gd and relatively depleted in Ba, Sr, P, Ti, Nb, Ta, and Eu, with a pronounced negative Eu anomaly. The biotite granites show high ∑LREE/∑HREE ratios (6.1–6.9), while the quartz porphyry rocks exhibit lower ratios (2.0–4.2). Both granitoid types have elevated FeOT content and FeOT/(FeOT + MgO) ratios, indicating that the Jinchanshan granitoids are A-type granites. The zircon U–Pb ages, combined with the regional tectonic settings, suggest that these granitoids formed during large-scale metallogenic events in the Early Cretaceous, within the Yanshanian post-orogenic extensional tectonic regime. This is consistent with the lithospheric thinning and extensional processes in Eastern China during this period.

Late Ordovician Bentonites From the Southern Ordos Basin: Response to the Subduction of the Proto‐Tethys Ocean

ABSTRACTThe connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO2 (57.94–77.95 wt.%) and Al2O3 (9.21–14.33 wt.%), classifying them within the low‐potassium alkali basalt to medium‐potassium calc‐alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right‐dipping, with a more pronounced negative Eu anomaly (δEu = 0.48–0.67). The zircons in the bentonites yield two‐stage model ages ranging from 546 to 956 Ma, along with εHf(t) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto‐Tethys Ocean along the southern margin of the North China Block.

SOURCES OF MAGMAS OF PERMIAN GABBROS OF THE KHANGAI MOUNTAINS (Western Mongolia)

We present Sm–Nd and Rb–Sr isotope composition data on mafic–ultramafic massifs in the Khangai Mountains of Western Mongolia: Oortsog-Uul, Nomgon, and Yamaat-Uul. The U–Pb age of zircon and its Lu–Hf isotope and trace-element compositions were determined by LA–ICP–MS. New and previous geochronological data obtained by SIMS and LA–ICP–MS support the Permian age of the studied gabbros. The trace-element composition of zircon, characterized by strong HREE enrichment ((Lu/Gd)n > 7) and cerium positive (Ce/Ce* > 6.6) and europium negative (Eu/Eu* = 0.16–0.49) anomalies, indicates its magmatic genesis and the possibility of using isotope characteristics to assess the origin of mafic magmas. The formation of zircon from a residual mafic melt is inferred from the enrichment of zircon in U and Th with increasing Th/U, reflecting the accumulation of these highly incompatible elements in the residual melt, and from the crystallization temperature of zircon (810–880 °С). The geochemical characteristics of the rocks, their isotopic composition, the absence of xenogenic ancient zircons, and the lack of correlation between εNd(T) and major indices of crustal contamination indicate that crustal contamination did not influence the composition of the gabbros. Isotopic data on rocks and zircon indicate the involvement of two mantle sources in the formation of the mafic–ultramafic massifs of the Khangai Mountains: (a) depleted, predominant for the Nomgon and Yamaat-Uul massifs (εHf = 16.1–2.0; εNd = 4.5–0.0; and ISr = 0.70385–0.70537), and (b) enriched, predominant for the second phase of the Oortsog-Uul massif (εHf = 1.4–0.2; εNd = –3.6… –5.7; and ISr = 0.70704–0.70933).

Constraints of in-situ elemental compositions and U–Pb ages of cassiterite on the origin of the Cretaceous Gejiu and Dulong tin deposits, SW China: Implications for the linkage of tin belts in SE Asia

The western Yunnan tin belts in SW China and the southern Myanmar tin belt in SE Asia are traditionally thought to be part of the SE Asian tin metallogenic province. However, the tectonic setting of the Youjiang tin belt in SW China and its genetic relationship to the other tin belts are poorly documented. In this belt, the giant Gejiu and Dulong tin deposits are typical of skarn-type deposits and both contain contact and distal skarn orebodies. Tin ores of distal orebodies in these two deposits are composed of cassiterite, sulfide and calcite. In both deposits, most cassiterite grains from these ores are rich in Fe and W and depleted in Nb and Ta. They have 238U/206Pb ages between 81.4 and 84.1 Ma, similar to hosting granitic plutons. Two generations of cassiterite with distinctly different microtextures and trace elemental compositions can be recognized. The first generation (Cst-I) is compositionally and texturally homogeneous, but the second generation (Cst-II) displays distinctly oscillatory zoning. Cst-II contains Nb, W, and U lower, and Fe, Ta, Zr and chalcophile elements (Ga, Ge, In, and Sb) higher than Cst-I. These textural and compositional variations reflect the potential involvement of meteoric water in the magmatic-hydrothermal system. In this system, ore-forming fluids were evolved to more alkaline and oxidized to facilitate the precipitation of cassiterite. Our study indicates that these two deposits in the Youjiang tin belt have mineralization styles similar to those in the adjacent western Yunnan and southern Myanmar tin belts and all these tin belts belong to the SE Asian metallogenic provinces. A westward-younging trend of tin mineralization in these three belts can be explained by the rollback of the subducted Neo-Tethyan oceanic slab. This setting is different from the one related to the subduction of the Paleo-Pacific plate.

Erratum to: U–Pb (ID-TIMS) Age of Perovskite from Kimberlites of the Manchary Pipe (Khompu-May Kimberlite Field, Central Yakutia)

Erratum to: U–Pb (ID-TIMS) Age of Perovskite from Kimberlites of the Manchary Pipe (Khompu-May Kimberlite Field, Central Yakutia)

Petrogenesis and tectonic setting of granitic pegmatites in the Beishan orogenic Belt, Northwest China: Evidence from geology, geochronology and geochemistry

The Weiboshan (Li-, Cs- and Ta-enriched) LCT-type Nb–Ta deposit located in Ejin Banner, Inner Mongolia, represents a newly discovered pegmatite-type rare metal deposit of significant interest. In this paper, we describe the petrography and present new mineralogical and whole-rock geochemical data and zircon U–Pb ages of ore-related granitic pegmatites in this deposit. Pegmatite dikes can be divided into three distinct zones on the basis of their contents: the K-feldspar graphic granite pegmatite zone (Kf), microcline graphic granite pegmatite zone (Mic), and albite–muscovite granite pegmatite zone (Ab). The pegmatite dikes and associated mineralization formed during the Mesozoic. Granite pegmatites in various zones display distinctive geochemical features characterized by high silicon contents, substantial alkali enrichment, and relatively low iron, calcium, and magnesium levels. These pegmatites are classified as peraluminous or quasialuminous and exhibit low total rare earth element concentrations. Notably, these pegmatites are enriched in large ion lithophile elements (LILEs), such as Rb, K, and U, but depleted in high field strength elements (HFSEs), such as P and Ti. The progression from the Kf to Mic to Ab zones signifies the thorough evolution of the granitic magma, where the late-stage near-hydrothermal system assumed a crucial role in the mineralization of rare metals during magma differentiation. The Weiboshan pegmatites, which exhibit syncollisional attributes, are A-type granites formed through crustal partial melting induced by decompression. This process occurred against the background of postorogenic extension driven by asthenospheric mantle upwelling resulting from lithospheric delamination due to crustal collision and thickening.

Petrogenesis and tectonic implication of the Triassic monzogranite from the central segment of the East Kunlun Orogen, NW China

The Triassic granitoids in the East Kunlun Orogenic Belt (EKOB) are crucial for understanding the tectonic evolution of the Paleo-Tethys Ocean. This study presents zircon U–Pb ages, Lu–Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotope compositions from monzogranite plutons in the central segment of EKOB to constrain their petrogenesis and tectonic evolution. These monzogranites are dominant composed of mineral assemblages of K-feldspars, plagioclase, minor biotite and accessory minerals. U–Pb dating of zircons from the Xinle South (XLS), Nanshankou (NSK) and Changgou South (CGS) plutons yield ages of 251 Ma, 232 Ma and 221 Ma, respectively. The studied monzogranites have relatively high SiO2 and Al2O3, but have low contents of TiO2, Fe2O3T, MgO relative to the coeval granodiorites. These monzogranites are classified as fractionated I-type granites, ranging from calc-alkaline to high-K calc-alkaline compositions. Their negative εNd(t) values (−4.2 to −6.3) and zircon εHf(t) values (−6.1 to −9.3) suggest that magma generation occurred through partial melting of ancient lower crust, followed by extensive fractional crystallization. Integrating our new data with regional geological evidence, we propose that the Early Triassic XLS monzogranite emplaced in a localized extensional environment linked to the northward subduction of the Paleo-Tethys oceanic plate. In contrast, during the post-collisional extensional phase of the Late Triassic, the formation of the NSK and CGS monzogranite plutons was directly influenced by asthenospheric upwelling, lower crust delamination, and subsequent continental rifting.

Sedimentary provenance supports a mid-paleozoic tectonic connection between the Junggar and Altai terranes in central Asia

The provenance of Precambrian detritus in the Junggar and Altai terranes provides crucial constraints on the peri-Siberian accretionary tectonic evolution in the middle Paleozoic. The Precambrian detrital zircons have no coeval magmatic equivalents in the Junggar terrane but show U–Pb age spectra and εHf(t) values comparable to those in the Altai terrane. The correlations suggest that the old detrital materials in the Junggar and Altai terranes were most likely derived from the Siberia craton and adjacent Tuva-Mongolian microcontinent. Paleozoic zircons in the Junggar terrane display a εHf(t) pattern from large spread to dominantly positive values at ca. 420–410 Ma. Such an abrupt change points to an accretionary tectonic transition from an advancing to retreating mode during mid-Paleozoic time, synchronous with similar tectonic switch occurring in the Altai terrane. Taking into account the temporal and spatial relations in sedimentation, tectonism and arc magmatism, we propose that the Junggar terrane had once collided onto the peri-Siberian Altai terrane to receive abundant old detritus from the Siberian continent in the Silurian–early Devonian. They were subsequently separated at ca. 420–410 Ma, possibly due to the slab rollback of the subducting Paleo-Asian Ocean (PAO) plate. These results constrain an Early Paleozoic tectono-paleogeographic boundary of the CAOB along the North Tianshan–Solonker suture zone, and also imply a long-lived PAO subduction was responsible for the Neoproterozoic to Paleozoic accretionary orogenesis at the margins of southern Siberia, eastern Kazakhstan, and northern Gondwana.

Detrital Zircons From Lower Palaeozoic Metamorphic Complexes and Silurian–Devonian Strata in the South Kitakami Belt, Northeast Japan: Implications for the Northern Extension of the Terra Australis Orogen in Northeast Gondwana

ABSTRACTTo reconstruct the detailed location of proto‐Japan around northeastern Gondwana during the early Palaeozoic, this article presents detrital zircon U–Pb age spectra for lower Palaeozoic metamorphic complexes and Silurian–Devonian strata from the western margin of the South Kitakami belt in northeast Japan. Psammitic and siliceous schists have youngest age peaks ranging from the Ordovician (479–458 Ma) to early Silurian (ca. 439 Ma). Sandstones have youngest age peaks varying from the early Silurian (ca. 435 Ma) to Late Devonian (370–360 Ma). The U–Pb age spectra exhibit major peaks at 510–500, 480–470, and 450–440 Ma. Excluding the Upper Devonian sandstones, significant age peaks occur at 650–550 and 1300–900 Ma. These data can be interpreted as a Pacific Gondwana signature, indicating a tectonic association with the Terra Australis Orogen that developed along the northeastern Gondwanan margin and Paleo‐Pacific Ocean, extending from eastern Australia (i.e., the Thomson, Lachlan, and Delamerian orogens) to Antarctica (i.e., the Ross Orogen). In northeast Asia, the Pacific Gondwana detrital zircons and 480–470 Ma zircons occur in the Bainaimiao arc belt along the northern margin of the North China Craton and in the Jiangyu continental arc in the Jilin area. The magmatic arcs of proto‐Japan and these regions were part of the Terra Australis Orogen during the Ordovician–early Silurian. A decrease in the proportion of Pacific Gondwana detrital zircons in Upper Devonian strata may be due to multistage trench retreat, such as that recognized in the Tasmanides in eastern Australia, which corresponds to the northern Terra Australis Orogen.

Detrital zircon U–Pb geochronology of the trench-fill sandstone on the Cretaceous Shimanto accretionary complex in SW Japan: Implications for provenance and igneous activity in the eastern edge of East Asia

Cretaceous igneous rocks are widely distributed in the East Asian margin, and their formation is due to the large-scale migration of igneous activity areas from the continental interior to near the subduction margin. Detrital zircon U–Pb ages of trench-fill sandstones of the Shimanto accretionary complex in the Akaishi Mountains of southwest Japan can provide information on eroded igneous rocks, and their location at the eastern edge of East Asia makes them essential for better understanding the intensity and migration of the igneous activity. As a result of the dating, the Cretaceous zircons in the trench-fill sandstones were found to increase dramatically in the middle Cretaceous and to be abundant in the Late Cretaceous. In addition, these large amounts of Cretaceous zircons were found to be derived from igneous rocks such as the Abukuma Granites and Ryoke Granites distributed in the proto-Japan arc. These results indicate that migration of igneous activity from the continental side reached the eastern edge of East Asia in the middle Cretaceous and that large-scale igneous activity continued to occur in the eastern edge of East Asia until the Late Cretaceous. Thus, the detrital zircon age spectra in trench-fill sediments provide a clear picture of the degree of igneous activity in the source area and migration of the igneous activity on active continental margins.

Hf Isotopes and Detrital Zircon Geochronology of the Silasia Formation, Midyan Terrane, Northwestern Arabian Shield: An Investigation of the Provenance History

ABSTRACTU–Pb ages and Hf isotopic data from detrital zircon of the Silasia Formation in the Midyan Terrane record evidence for the provenance and tectonic evolution of the northern Arabian Shield. Given that the youngest acknowledged age of these detritus sediments is 735 ± 13 Ma, it is likely that the Silasia Formation was deposited during the closure of the Mozambique Ocean. The U–Pb ages define a major Mesoproterozoic peak, with two minor peaks of Neoproterozoic and Archean age. Combined with zircon Hf isotopic compositions, the sedimentary detritus of the Silasia Formation was mainly derived from source rocks formed during the Grenville Orogeny during the assembly of Rodinia, with a minor contribution from Archean and Paleoproterozoic crustal material, in addition to a limited arc‐basement supply related to the early Mozambique Ocean. The youngest Concordia age of 735 ± 13 Ma with highly variable εHf(t) values (11 to −35) indicates a complex mixture of sources from juvenile to extremely ancient. The Concordia ages at 1113 ± 11 and 1046 ± 10 Ma have positive hafnium isotope signatures (up to +10.45) that are consistent with juvenile source rocks formed during the Grenville Orogeny. Several detrital zircons with ages of 2622 ± 22 Ma and 2690 ± 7 Ma are similar to those reported in Yemen, whereas 1818 ± 19 Ma, 2071 ± 8 Ma and 2001 ± 19 Ma Paleoproterozoic ages are similar to dated outcrops in the Khida terrane in the eastern Arabian Shield.

The large Rupelian Rhodope Massif eruptions as the source of airfall tuffs in SE, S and Central Europe: 40Ar/39Ar and U–Pb age constraints

The large Rupelian Rhodope Massif eruptions as the source of airfall tuffs in SE, S and Central Europe: 40Ar/39Ar and U–Pb age constraints

Integration of new zircon U–Pb ages with biostratigraphy to establish a high-precision age model of the Miocene Nakayama Formation on Sado Island in Central Japan

The most common age constraint for the diatomaceous sediments is biostratigraphy of siliceous microfossils. Although biostratigraphy is a powerful tool to establish stratigraphy and correlate with sedimentary sequences in other sites, biostratigraphy generally includes uncertainties difficult to evaluate. In this study, we measured zircon U–Pb ages of eight tuff beds intercalated with diatomaceous mudstone of the Nakayama Formation on Sado Island in Central Japan and integrated the U–Pb ages with diatom and radiolarian biostratigraphy, whose ages and errors were re-evaluated by this study, to establish an age model precisely representing the sedimentary age. Two tuff beds in the upper and middle part of the formation offered zircon U–Pb ages of 6.7 ± 0.2 Ma and 10.87 ± 0.07 Ma, which are consistent with biostratigraphy, and provided a good example of effective integration of zircon U–Pb ages with the biostratigraphy. On the other hand, zircon U–Pb ages of the other six tuff beds in the lower part are around 12 Ma and not distinguishable from each other. In addition, older zircon grains in the 6 tuff beds are assembled in the interval from 30 to 20 Ma, which is consistent with the age of the volcanic basement rocks forming most part of Sado Island. Similarities in chemical compositions of glass shards and age distributions of zircon grains indicate that the volcaniclastic components in the tuff beds should originate from single or associated magmatic activities.

Tectonic evolution of the Early Paleozoic proto-East Asian continental margin: Inference from Paleozoic metamorphic rocks in the South Kitakami belt, northeast Japan

To constrain the incipient Pacific-type orogeny and tectonic processes in the Early Paleozoic proto-East Asian continental margin, the Motai–Matsugadaira–Yamagami (MMY) metamorphic rocks in the South Kitakami belt, northeast Japan were investigated. They are divided into two different types: amphibolite-facies rocks associated with serpentinite and blueschist-facies rocks associated with pelitic and psammitic schists. Three geochemical groups are identified from the MMY metamorphic rocks. Groups 1 and 2 resemble geochemical characteristics of mid-ocean ridge basalt and continental arc rocks, respectively. Group 3 exhibits considerable depletion of highly incompatible elements, which is caused by the high degree of partial melting of a hot mantle plume. The zircon U–Pb ages of Group 1 indicate that the protoliths experienced amphibolite-facies metamorphism soon after their formation in the Early Ordovician. Group 2 exhibits a coeval zircon U–Pb age with Group 1. The age distribution of detrital zircons in the MMY psammitic schists shows a peak of 500–400 Ma, the presence of Archean to Neoproterozoic zircons, and the youngest Late Devonian zircon. The following model is proposed for the tectonic evolution of the proto-East Asian continental margin: (1) the formation of an arc in the eastern margin of the South China craton in the Cambrian to Ordovician; (2) the subduction of a spreading axis and an oceanic plateau at the same time as the continental arc formation; (3) the consumption and subduction of arc materials by tectonic erosion; and (4) the formation of the Carboniferous accretionary complex and high-pressure metamorphic rocks under steady oceanic plate subduction. The proposed tectonic evolution model may also be applicable to equivalent Early Paleozoic rocks in southwest Japan.

Reconstructing the Zama (Mexico) discovery source to sink story, Part I; detrital zircon U–Pb and (U‐Th)/He provenance analysis and implications for sediment source terranes

AbstractThe Zama discovery was identified off the coast of Tabasco, Mexico, in the Sureste Basin of the Gulf of Mexico and is hosted in a three‐way closure in the Upper Miocene. This study conducted a detailed detrital zircon (DZ) U–Pb and (U‐Th)/He provenance analyses on samples from sandstone reservoirs in the Zama‐3 and Zama‐2ST1 wells. A total of 22 sandstone samples (11 from each well) were collected for DZ U–Pb and (U‐Th)/He dating from different reservoir zones, testing the hypothesis that different zones were whether originally derived from varied sedimentary source terranes and associated transport pathways to the Zama mini‐basin depositional site. Additional objectives include determination of maximum depositional ages, reconstruction of paleofluvial systems, and exploring the temporal evolution of the drainage region and hinterland tectonics. The DZ U–Pb age spectra from both Zama wells have remarkably homogenous DZ signatures with very similar DZ age modes and modal percentages, displaying dominant Permian/Chiapas Batholith (ca. 35%–45%), Mesoproterozoic/Oaxaquian (ca. 20%–35%), Early Palaeozoic/Acatlán (ca. 8%–20%), and Cenozoic magmatic arc (ca. 15%–25%) age modes, as well as some subsidiary (<5%) early Proterozoic/Archean and Early Cretaceous DZ age components, linked to recycled lower Palaeozoic strata and the Guerrero Terrane and Alisitos arc, respectively. Despite differences in paleocurrent directions, deduced from image logs, there are no systematic differences in DZ spectra, indicating a consistent sediment provenance and no changes in source area. All Zama samples analysed in the study are characterized by abundant syn‐depositional Late Miocene DZ grains, clustering between 8.6 and 10.2 Ma, corroborating a Tortonian (Late Miocene) depositional age, and yield rapid sediment accumulation rates of ca. 200 m in <1.4 Ma (13 m/Myr). Doubled zircon U–Pb and (U‐Th)/He age pairs are indicative of recycling of early Mesozoic rift strata and Paleogene and younger Chiapas basement. These new DZ U–Pb and (U‐Th)/He data have a nearly invariant Tortonian sediment provenance that is similar to the modern Grijalva River flowing generally northward out of the Chiapas highlands. The paleo‐Grijalva drainage, providing sediment to the Late Miocene Zama mini‐basin, was likely drastically larger than the present catchment as it involved 10 Ma plutonic sources that were subsequently downfaulted along the Pacific coast in the latest Miocene. Importantly, DZ U–Pb age components are consistent with Oaxaquia, early Acatlán, and Guerrero/Alisitos signatures and point to sourcing from the Chortis block during its tectonic eastward translation. Such a scenario would allow for a substantially larger Miocene paleo‐drainage that would have encompassed both Chiapas and portions of Chortis. The Miocene tectonic translation of Chortis and erosion of a large and tectonically active hinterland would also reconcile the dramatically larger Middle to Late Miocene sediment supply, funnelling a large influx of sediment into the southern Gulf of Mexico. Rapid Late Miocene sediment accumulation in the salt‐defined Zama mini‐basin must have involved sustained sediment flux via the paleo‐Grijalva drainage and was likely facilitated and focused by continued salt deflation due to sediment loading, as described in Part II. Thus, our work provides new scientific insights into one of the largest hydrocarbon discoveries in Mexico in recent years.

Scheelite as a microtextural and geochemical tracer of multistage ore-forming processes in skarn mineralization: A case study from the giant Xintianling W deposit, South China

The Xintianling deposit is one of the largest skarn-type scheelite deposit in China. Recent discoveries of quartz-vein-type scheelite mineralization within the deposit have raised questions about its origin and the evolution of ore-forming fluids, hindering a comprehensive understanding of the ore-forming process. We investigate the microtextures, trace elements, and oxygen isotope compositions of scheelite from different stages in both skarn-type and quartz-vein-type W mineralizations. Combined with apatite geochemistry and U–Pb dating, we determine the timing of quartz-vein-type mineralization and the evolution of magmatic-hydrothermal system. Based on detailed petrological observation, three types (seven subtypes) of scheelite and two types of apatite are identified. The Mo contents and Eu/Eu* ratios of scheelite, along with the Ce/Ce* ratios of apatite indicate the oxygen fugacity of fluids during the skarn metallogenic episode is generally higher than that during the quartz-vein metallogenic episode. Furthermore, the Y/Ho ratios and REE patterns of scheelite indicate the presence of at least three significant stages of fluid influx and fluid-rock interactions throughout entire ore-forming process. The O isotope compositions of scheelite in the quartz-vein-type metallogenic episode reveal that the ore-forming fluids are originated from a magmatic source, and meteoric water was mixed into the system, leading to the precipitation of the latest stage of scheelite. The apatites closely coexist with scheelite, from the early and the late stages of quartz-vein metallogenic episode, yield consistent U–Pb ages within error of 160.4 ± 2.4 Ma and 158.4 ± 1.3 Ma, respectively, indicating a close genetic link between quartz-vein-type W mineralization and the fine-grained porphyritic biotite granite. Our study highlights the significance of pulsed fluid exsolution and the combined effects of multiple mechanisms, including fluid-rock interaction, fluid mixing, and physicochemical condition changes, in the formation of large W deposits.

Synchronous felsic volcanism and carbonate sedimentation as a setting for VMS deposits localization at the Salair terrane, NE Central Asian Orogenic Belt

The Salair terrane located in the northern part of the Central Asian Orogenic Belt (CAOB) contains many epithermal deposits including volcanogenic massive sulphide (VMS) deposits. The host rocks mainly consist of felsic volcanic rocks such as lavas, volcanic breccias and tuffs that associated with thick strata of carbonates. In this study, we present zircon U–Pb ages, whole rock geochemistry, and Nd isotope data from the volcanic rocks, and results of geochemical and isotope (Sr, C, O) studies of carbonates to constrain their age and petrogenesis, and to characterize the tectonic setting. Zircon U–Pb dating reveals that the ore-bearing felsic lavas have age of 519.3 ± 1.9 Ma, while the felsic tuffs have age of 516.0 ± 0.9 Ma. These volcanic rocks are characterized by high SiO2 and Na2O contents, enrichment in light rare-earth elements, remarkable negative Eu anomalies, and pronounced depletion in Nb, Ta, P, and Ti. They have depleted ɛNd(t) values ranging from +4.9 to +6.3, and young two-stage Nd model ages (from 0.82 to 0.64 Ga). The felsic volcanic rocks from the Salair terrane are interpreted as highly evolved I-type magmatic rocks that might be produced by high degree partial melting of juvenile lower crust without a significant contribution of ancient crust and without crustal reworking.Felsic volcanism was accompanied by the formation of thick strata of carbonates. These carbonates are marine limestones with Mg/Ca ratios less than 0.007, δ18O(SMOW) values from 17.1 to 23.8 ‰ and δ13C(PDB) values between –0.9 and +0.9. Their Sr isotope composition varies in a narrow range within 0.70844–0.70859 that interpreted as representing proxy for coeval seawater. These values are consistent with depositional ages of 520–510 Ma and confirms the synchronicity of the formation of carbonates and felsic volcanism. Based on the regional geology and geochemistry, the ore-host rocks of the Salair terrane were formed in the back-arc setting where the marine transgression occurred as a result of graben subsidence. It is important for better understanding epithermal deposits in the northern CAOB and might provide new insights about prospecting the VMS deposits in similar tectonic settings.

A rapid transition from subduction to Barrovian metamorphism: geochronology of mafic–ultramafic relicts of oceanic crust in the Central Alps, Switzerland

Relicts of subducted oceanic lithosphere provide key information for the tectonic reconstructions of convergent margins. In the Central Alps, such relicts occur as isolated mafic–ultramafic lenses within the migmatites of the southern Adula nappe and Cima-Lunga unit. Analysis of the major-, minor-, and accessory minerals of these ophiolitic relicts, combined with zircon and rutile U–Pb ages and zircon oxygen isotopes, allows the reconstruction of different stages of their complex evolution. The mafic–ultramafic suite in Valle di Moleno consists of chlorite-harzburgites associated with metarodingites and retrogressed eclogites. Relic omphacite and kyanite in retrogressed eclogites provide evidence for subduction-related metamorphism. Increasing XPrp in the garnet mantle towards the rim documents heating during high-pressure metamorphism up to 800–850 °C. Polyphase inclusions and chemical zoning in garnet suggest fluid-assisted melting during high-pressure metamorphism dated at 31.0 ± 0.9 Ma. In Val Cama, chlorite-harzburgites, metarodingites and calcsilicate-metasediments occur. Detrital zircon ages in the metasediment suggest a Mesozoic deposition. The metarodingite-metaperidotite-metasediment association and the low δ18O signatures of zircon (δ18O 3.0–3.7‰), inherited from seafloor metasomatism of the protoliths, show that the rocks are derived from former altered oceanic crust. Amphibolite facies metamorphism related to the Central Alps Barrovian evolution in Val Cama occurred at 28.8 ± 1.5 Ma. The combined data from Moleno and Cama indicate a rapid transition (~ 2 Ma) from subduction to collisional metamorphism with corresponding exhumation rates of 3–6 cm/year. Fast exhumation tectonics may have been favored by slab break-off or slab extraction. U–Pb dating of rutile from both localities yields ages of ~ 20 Ma, suggesting that these rocks remained at amphibolite-facies conditions for about 10 Ma and underwent a second fast exhumation of 3 cm/year associated with vertical movements along the Insubric line.