Hf Isotopic Analyses Research Articles

Closure of the Paleo‐Asian Ocean in the Middle‐Late Triassic (Ladinian‐Carnian): Evidence From Provenance Analysis of Retroarc Sediments

AbstractA major current debate in Asian tectonics concerns the time of closure of the Paleo‐Asian Ocean (PAO) and the collision between the Central Asian arcs and the Tarim and North China cratons (NCC). This has led to much uncertainty about the reconstruction of proto‐Asia and tectonic configuration of northeast Pangea. Here we report Triassic provenance change in the foreland of the Alxa Block by field‐based zircon U‐Pb and Hf isotopic analysis. Nonmarine sediments, unconformable on or in fault contact, with the Alxa basement yield Precambrian and Paleozoic–Triassic detrital zircon ages with maximum depositional ages of Middle‐Late Triassic (∼244–224 Ma). Hf isotopic data indicate that Middle Triassic sandstones were sourced from the NCC basement and a continental arc, whereas Late Triassic sediments received an additional input from a juvenile arc. This provenance change in the foreland sedimentation indicates that the final closure of the PAO was in the Middle‐Late Triassic.

Insights into characterization and genesis of the Tieshanmiao banded iron formation deposit, China: Evidence from zircon U–Pb dating and geochemistry

The Tieshanmiao hosted by the metamorphosed Paleoproterozoic Upper Taihua Group, is a large-scale BIF–hosted Fe deposit in the southern margin of the North China Craton. The formation age, BIF type, depositional condition as well as the genesis of pyroxene–rich BIF is under heated debate. In this study, we present petrology, whole–rock geochemistry, zircon U–Pb geochronology and Lu–Hf isotope analyses on the Tieshanmiao Fe deposit. The Fe ore of the deposit can be divided into two sub-types, including banded pyroxene–magnetite quartzite (BMQ) and disseminated magnetite pyroxenite (DMP). The hanging wall rock pyroxene biotite gneiss yields an upper intercept age of 2406 ± 24 Ma, interpreted as the lower limited age for BIF deposition. The foot wall rock garnet–bearing biotite plagioclase gneiss yields a weighted mean 207Pb/206Pb age of 2739 ± 12 Ma, interpreted as its maximal depositional age. Lu-Hf isotope systematics indicates that pyroxene biotite gneiss is derived from the Paleoproterozoic mantle contaminated by the crust, and the provenance of garnet–bearing biotite plagioclase gneiss is derived from a Mesoarchean crust.The primary mineral assemblages of the pyroxene–rich Tieshanmiao Fe deposit are Fe–silicate, Ca/Mg–carbonate, ferrihydrite, and minor quartz. The BMQs have high and variable Y/Ho ratios (40–80), recording periodic alkaline hydrothermal injection that is progressively diluted by seawater, while the DMPs have low and constrained Y/Ho ratios, archiving well–supplied alkaline hydrothermal injection. We propose a REY (lanthanide elements and Y) modelling of multi–Fe sources for the Tieshanmiao BIF deposit. The BMQs are sourced from seawater and high–T hydrothermal fluid, while the DMPs are sourced from seawater, high–T hydrothermal fluids and one or several additional Fe fluxes (e.g. high-Fe dissolved riverine fluxes, low–T hydrothermal fluids or benthic Fe shuttles driven by dissimilatory iron reduction).The basic gneisses as metabasalts associated with the Tieshanmiao Fe deposit are characterized by high–Fe assay, variable LREE enrichment, relatively depletion in Nb, Ta, Zr, Ti, Y, and Th. The geochemistry of the basic gneisses shows affinities to both MORBs and volcanic–arc basalts, indicating a back–arc basin setting of the BIF deposition. It is most likely a Superior–type BIF–hosted Fe deposit, which is formed in a back–arc basin along the craton–side continental shelf.

Latest Mesoproterozoic provenance shift in the southwestern Yangtze Block, South China: Insights into tectonic evolution in the context of the supercontinent cycle

The Huili Group, one of the most representative late Mesoproterozoic strata in the Yangtze Block, bears key information for the tectonic history of the South China Block in the context of the supercontinent cycle. We present an integrated dataset involving field observation, petrology, detrital zircon U-Pb dating, and Hf isotope analyses for the Huili Group. Our new detrital zircon U-Pb ages, in combination with available magmatic age data, confirm that the Huili Group was mainly deposited at ca. 1.1–1.0 Ga. The lower Huili Group is characterized by subrounded to rounded detrital zircon grains with age intervals of 2.80–2.40 Ga (~21%), 2.34–1.72 Ga (~64%), and 1.68–1.19 Ga (~14%). In contrast, zircon grains from the upper Huili Group have variable morphologies and yield two pronounced age populations of 2.00–1.25 Ga (~50%; subrounded to rounded grains) and 1.2–1.0 Ga (~46%; euhedral to subhedral grains). The majority of zircon grains have εHf(t) values and depleted mantle two-stage (TDM2) model ages comparable to those of magmatic rocks or older sediments in the Yangtze Block. Multiple sources are suggested to have contributed older detrital zircon grains to the lower Huili Group, whereas the upper part received greater proportions of zircon grains with ages close to or equal to the depositional age from proximal magmatic sources. This observation indicates a drastic provenance shift most likely occurred within the Huili Group at ~1.04 Ga. Through reappraising our detrital zircon results and available geological datasets, we suggest that the terrigenous clastic and carbonate rocks of the lower-middle Huili Group were deposited on a passive continental margin, but the upper volcano-sedimentary sequences were formed in a back-arc extensional setting. We further propose that the Yangtze Block was spatially separated from (i.e., not yet part of) the Rodinia supercontinent during the sedimentation of the Huili Group, supporting that a global supercontinent did not exist yet in the late Mesoproterozoic.

Paleo - position of the South China Craton in the Rodinia Supercontinent: Evidence from the U - Pb age and Hf isotope of detrital zircon from the Nam Co Complex

To constrain the paleo - positions of the South China Cratons in the Rodinia Supercontinent during the Neoproterozoic, the in - situ U - Pb dating, and Hf isotope analysis of the detrital zircon from the Nam Co Complex, Song Ma Suture zone, northwestern Vietnam was performed. The U - Pb isotopic dating on detrital zircons shows that the Nam Co Complex demonstrates the major population (>50%) of around ~850 Ma while the minor population is scattered between ~1.2÷3.0 Ga. The Neoproterozoic age spectrum exhibits a large range of the εHf(t) from strongly negative to positive values ( - 17.418022÷ 14.600527), indicating that the source of the magma for this age range has been not only derived from reworking of the Archean basement rocks, but also generated from the juvenile material. The U - Pb age distribution patterns and Hf isotopic data of the detrital zircon in the Nam Co Complex are compatible with those of the South China Craton rather than those of the Indochina Craton. The data also indicate that sedimentary protoliths of the Nam Co Complex were deposited in a convergent - related basin along the southwestern margin of the South China Craton during the Neoproterozoic. Combined with the similarities of the detrital zircon age between western Cathaysia, Indochina, East Antarctica and East India, it is proved that the South China Craton was situated at the margin of the Rodinia Supercontinent and in close proximity to the Indochina, East Antarctica and East India.

Zircon U-Pb and Lu-Hf isotopes and geochemistry of granitoids in central Tibet: Bringing the missing Early Jurassic subduction events to light

Jurassic magmatic and metamorphic rocks in central Tibet are considered to record the subduction history of the Meso-Tethys Ocean (MTO) and have therefore attracted considerable research interest. However, Early–Middle Jurassic island arc magmatism has been reported only from the Amdo and Basu areas in the eastern section of central Tibet. In this paper, we report newly discovered Early–Middle Jurassic granitoids from Lhaguotso in the middle section of central Tibet and from Shiquanhe in the western section of central Tibet. Zircon U–Pb dating and whole-rock geochemical and zircon Lu–Hf isotope analyses were conducted on three groups of samples: plagiogranites from Lhaguotso (LG, 185–181 Ma); granodiorites from Shiquanhe (SGD, 184–183 Ma); and amphibole tonalites from Shiquanhe (SAT, 170 Ma). The three groups of samples are differentially enriched in Mg, Fe, and Ca. In addition, the samples show high SiO2 contents and Mg# values, enrichment in large-ion lithophile elements, and depletion in high-field-strength elements. Combining these characteristics with their differing Th, Ba, and rare earth element contents and Hf isotopic compositions, we suggest that the LG were formed by partial melting of a depleted mantle wedge metasomatized by slab-derived fluids, whereas the SGD and SAT were formed by interaction between subducted sediment melts and the overlying depleted mantle. On the basis of our new data in combination with previous results, we propose that a broad oceanic island arc system existed in the MTO during the Early–Middle Jurassic. Differential influence of ancient microcontinent materials or crust-derived sediment led this intra-oceanic island arc to exhibit clearly different magmatic responses in its eastern and western regions.

Detrital zircon U-Pb and Hf constraints on provenance and timing of deposition of the Mesoproterozoic to Cambrian sedimentary cover of the East European Craton, part II: Ukraine

We present the U-Pb geochronology and Hf isotope analysis of detrital zircons from the Ediacaran/Cambrian sediments of Podillya and south Volyn in western Ukraine, supplemented by the bulk rock XRD mineralogy of the host rocks. Such a combined analytical approach allows for identifying the source areas supplying detritus to sediments and for constraining an age of deposition. Our provenance analysis is based on fourteen samples collected from six exposures, mostly in the valley of the Dniester river. 84 mudstone samples were also examined by the XRD method. U-Pb dating of detrital zircons yielded two sets of maximum depositional ages: 578–546 Ma and 547–523 Ma, for the Mohyliv-Podilsky and Kanyliv Series, respectively. This suggests that the Ediacaran-Cambrian boundary in Podillya coincides with a major erosional gap, with a major change in provenance, and the disappearance of the Ediacaran fauna at the base of the Kanyliv Series, with implications for the stratigraphy and paleogeography of the entire East European Platform. Zircon U-Pb age spectra from the lower part of the Mohyliv-Podilsky Series include a large quantity of 2.2 to 1.9 Ga grains that reveal predominantly negative to nearly chondritic ɛHf values, jointly suggesting detritus supply from the crystalline basement of Sarmatia. Both U-Pb and mineralogical data also indicate a major contribution of volcanic detritus from the Volyn flood basalts. The younger Nagoryany rocks yielded zircon age spectra with peaks at c. 1.80 and 1.49 Ga, implying a shift of the catchment area to Fennoscandia. Above an erosional gap, the zircon age spectra in the Kanyliv and Baltic Series are dominated by peaks at 560–535 Ma. These data and ɛHf values ranging from negative to chondritic and juvenile suggest, in line with the mineralogical data, detritus supply from a continental magmatic arc and collisional orogen. Thus, we interpret the Kanyliv Series as infill of an early Cambrian foreland basin that was established in front of the Scythides and Santacrucides orogens, overriding the SW margin of Baltica.

On the petrogenesis of Paleoarchean continental crust: U-Pb-Hf isotope and major-trace element constraints from the Bastar Craton, India

Combined geochronological and (isotope) geochemical investigations of tonalite-trondhjemite-granodiorite (TTG) suites, which dominate Archean cratons, provide constraints on the sources and petrogenetic processes that gave rise to the Earth's early continental crust. In situ U-Pb and bulk Lu-Hf analyses of single zircon grains from TTGs of the Paleoarchean Bastar Craton in central India date the emplacement of the igneous rock suite and trace the chemical evolution of its source rocks. Complementary whole rock Lu-Hf and major and trace element data constrain the petrogenesis of the TTGs. The rocks are variably enriched in fluid mobile elements, particularly K and Pb, and are characteristically depleted in heavy rare earth elements. Calculated initial Hf isotopic compositions of zircon and whole rocks cluster around the chondritic value at ca. 3.55 to 3.45 Ga. The high precision Hf-isotope data reveal a trend of increasing radiogenic 176Hf/177Hf with age, the slope of which implies a 176Lu/177Hf = 0.02, and thus derivation from a mafic protolith. Geochemical modeling indicates that the granitoids can be directly produced by melting of a hydrous basalt in the garnet stability field, followed by minor fractional crystallization. Variations in the modal abundance of garnet suggest the source rocks melted at different depths. Rocks with moderately to strongly depleted HREE patterns require >10% garnet in the residue, consistent with derivation from a garnet-amphibolite or garnet-pyroxenite source. Modeling of the Lu-Hf systematics further highlights the important role of melting as opposed to fractional crystallization for reproducing the primary chemical characteristics of TTGs.The global Hf-isotope record of Archean mantle-derived rocks is considerably more radiogenic than that of the bulk silicate Earth, providing unambiguous evidence that parts of the mantle were significantly depleted in incompatible elements since at least the early Archean. The differences between Hf isotopic compositions of the mafic (greenstone belts) and felsic (gneissic terranes) rocks can be accounted for by crustal residence times of several 100 million years for the protoliths of the felsic magmatic suites. Consequently, TTGs integrate the geologic history of their precursor(s), complicating their isotopic record. Therefore, the near-chondritic Hf isotopic composition of TTGs is not direct evidence for their derivation from a primitive mantle, but rather a consequence of their specific petrogenesis involving an aged, mafic precursor. This relationship introduces uncertainties into models of crustal growth and geodynamics that are based on the felsic record, especially where the whole rock context is absent. In contrast, high-precision Hf-isotope analyses of single zircon grains, combined with whole rock isotope and elemental constraints, can be used to reliably identify the sources and processes involved in the generation of Earth's oldest continental crust.

Geochronological Constraint on the Evolution of the Aktyuz Terrane, Kyrgyz North Tianshan, and the Fate of the Taldybulak Levoberezhny Gold Deposit

The Aktyuz Terrane in Kyrgyz North Tianshan is of particular interest due to the occurrence of high and ultrahigh pressure (HP–UHP) rocks and it containing the third largest gold deposit in Kyrgyz North Tianshan, i.e., Taldybulak Levoberezhny (abbreviated to Taldybulak Lev.). To constrain the ages of the host Kemin Complex and its auriferous monzogranite porphyry, detailed zircon U–Pb dating [by laser ablation inductively coupled plasma-mass spectrometry (LA-ICPMS) and secondary ion mass spectroscopy (SIMS)] and Lu–Hf isotopic analyses were carried out. The intensively altered auriferous monzogranite porphyry yielded two weighted mean ages of 444 ± 3 Ma (n = 14, mean squared weighted deviation (MSWD) = 0.49, by LA-ICPMS) and 440 ± 5 Ma (n = 8, MSWD = 0.82, by SIMS) that are indistinguishable within error ranges. Such ages are consistent with a previously reported sulfide Re–Os isochron age of 434 ± 18 Ma, supporting a Silurian porphyry gold mineralization. The granitic gneiss yielded a protolith age of 773 ± 7 Ma (n = 7, MSWD = 0.04) and two metamorphic ages of 514 ± 4 Ma (n = 8, MSWD = 0.09) and 483 ± 3 Ma (n = 11, MSWD = 0.04). Detrital zircons from one fuchsite schist sample yielded highly variable ages from 729 ± 13 Ma to 2,463 ± 30 Ma, with 12 data points weighted at 740 ± 5 Ma (MSWD = 0.95). The metamorphic overgrowth yielded a weighted mean age of 460 ± 4 Ma (n = 4, MSWD = 0.15). Detrital zircons in the migmatitic amphibolite are aged from 788 ± 7 Ma to 3,447 ± 32 Ma, with two major concentrations at 941 ± 7 Ma (n = 13, MSWD = 0.95) and 794 ± 5 Ma (n = 8, MSWD = 0.19). The metamorphic overgrowth yielded an average age of 555 ± 4 Ma (n = 8, MSWD = 0.65). The detrital and xenocryst zircons, and evolved εHf(t) values (−20.9 to −7.8) and old two-stage Hf model ages (1,367–3,159 Ma), revealed the presence of a Precambrian basement that may be dated back to the Archean Eon. The two metamorphic ages may correlate with oceanic subduction and continental collision, respectively.

Precambrian crustal evolution in Northern Indian Block: Evidence from detrital zircon U-Pb ages and Hf-isotopes

Integrated detrital zircon U–Pb and Lu–Hf isotope analyses were conducted on three siliciclastic sedimentary rock samples from the Vindhyan Supergroup in the Son Valley section of central India. These display two prominent 2.7–2.4 Ga and 1.9–1.5 Ga age groupings along with minor Paleoarchean-Mesoarchean (3.5–2.9 Ga) and late Mesoproterozoic (1.3–1.0 Ga) zircons. These 3.5–1.5 Ga detrital zircons match well with the exposed magmatic and metamorphic rock components within the Bundelkhand and Aravalli cratons of the Northern India Block. Zircon grains of >2.0 Ga mainly produce negative εHf(t) values suggestive of episodic recycling and reworking of old crust components in Northern India Block, whereas zircon grains in the age range of 2.0–1.4 Ga commonly produce positive εHf(t) values, indicating dominant juvenile crust growth in response to assembly and breakup of Columbia supercontinent. Contemporaneous mafic dykes (2.15–2.0 Ga and ca. 1.98 Ga) intruded into the Bundelkhand Igneous Complex present direct lithological evidence for juvenile crustal growth. Similar basement rock compositions and detrital zircon age distributions provide robust evidence that the Bundelkhand craton has possibly been combined with the Aravalli-Banded Gneiss Complex (ABGC) since Paleoproterozoic. 1.3–1.0 Ga old detrital zircons could have sourced from South China or the Central Indian Tectonic Zone or the Eastern Ghats or a pre-existing hidden terrane in India; their dominant negative εHf(t) values suggest reworking of old crustal components in Northern India Block in response to the assembly of Rodinia supercontinent.

Structure and spatial-temporal relationships of Eocene-Oligocene potassic magmatism linked to the Ailao Shan-Red River shear zone and post-collisional extension

Eocene potassic magmatic rocks are abundantly developed in the Jinshajiang–Ailaoshan tectono-magmatic belt that stretches from eastern Tibet over western Yunnan to Vietnam. This study reports results from adakite-like potassic rocks from the Ailaoshan-Red River shear zone (ASRR-SZ) investigated by geochemistry, Zircon U–Pb geochronology, electron microprobe, Lu–Hf isotopic and EBSD analysis. High SiO2 (68.95–72.38%), K2O (4.38–5.80%) and low MgO (0.29–0.51%), Y (5.58–14.19 ppm) and Yb (0.4–1.34 ppm) contents as well as high Sr/Y (70–285) and La/Yb (11.5–47.5) ratios show that these rocks belong to high-K calc-alkaline to shoshonitic adakite-like rocks. Zircon U–Pb ages reveal that the adakite-like potassic rocks with different deformation characteristics emplaced between 39 and 30 Ma. εHf values of magmatic zircons of these adakite-like rocks range from −2 to +6, and two-stage model ages TDM = 750–1500 Ma supports the interpretation of its formation by mixing and partial melting of enriched mantle-derived melt and magmas derived from thickened ancient crust. The potassic magmatic activity lowered the rheological strength of the lithosphere, which was one of the triggers of initiation of the ASRR-SZ. Temperature and pressure calculated by amphibole-plagioclase thermobarometry reveal average emplacement depths of ca. 18 km of granodiorites, indicating exhumation from nearly 18 km depth by apparent vertical movement of ASRR-SZ. In combination with the results of the Eocene potassic magmatism in the Jinshajiang–Ailaoshan tectono-magmatic belt, we suggest that the adakite-like potassic rocks were formed during the Eocene post-collisional extensional tectonic setting, which were closely related to the rollback and/or detachment of the Neo-Tethys oceanic slab.

The Devonian accretionary orogen of the North Patagonian cordillera

The Andean basement of NW Patagonia contains remnants of a Devonian accretionary orogen that lasted for about 50 Ma. We present and review U-Pb geochronology, major and trace element geochemistry and O- and Hf-isotope analyses of zircon for Devonian igneous and metasedimentary rocks from the western edge of the North Patagonian Massif to the Pacific coast. Two contrasting magmatic domains are characterised. The Foreland Devonian Domain (FDD) of the North Patagonian Massif is dominated by subduction-related calcalkaline granite, granodiorite and tonalite emplaced in the interval c. 405–395 Ma and here named the San Martín arc. They are generally enriched in alkalis, light rare earth and Large Ion Lithophile elements, and have igneous zircon with δ18O mostly in the range +6 to +9‰ and ƐHft typically +3 to −5, indicating magmas that incorporated continental crustal material, possibly Mesoproterozoic. A younger (374 ± 3 Ma) body in this group has lower δ18O (down to +5‰) and Hf-isotope characteristics at the primitive end of this range. The Pacific Devonian Domain (PDD) lies on the western flank of the Andes and has uniformly primitive character. Granitic rocks here represent a more extended magmatic history (c. 395–355 Ma) and are mostly subalkaline tonalites with δ18O (<+6‰) that fall within or below the normal mantle field: with one exception their ɛHft values are > +4 and closer to Devonian depleted mantle composition. The PDD also has metabasalts of both N-MORB and E-MORB affinities, interbedded with Devonian turbidite metasandstones in which detrital zircon O- and Hf-isotope compositions and morphology indicate coetaneous derivation from the FDD arc. The results lead to a tectonic model involving continental arc, forearc rifting, Chaitenia oceanic arc and marginal basin formation, double arc subduction, and marginal basin closure in Mississippian times. This is recognisable as part of a more extensive Devonian accretion scenario along the SW Gondwana margin.

Emplacement ages and petrogenesis of intermediate‐acid intrusive rocks in the Lajishan region of the Central Qilian Belt, China: Constraints from zircon U–Pb ages, Hf isotopes, and whole‐rock geochemistry

As a major tectonic unit along the southwestern rim of the Central Qilian Belt, the Lajishan region plays an important role in the amalgamation of continental plates in the Qilian Orogenic Belt. In this study, zircon laser ablation inductively coupled plasma mass spectrometry for U–Pb dating and Hf isotope analysis, as well as geochemical analysis of intermediate‐acid intrusive rocks from the Lajishan area were conducted. Results show that formation ages of the intermediate‐acid intrusive rocks are 438–452 Ma. Whole‐rock geochemistry results show that the diorite and monzodiorite are metaluminous, low‐ to medium‐K series, and characterized by obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments. The εHf(t) values of zircons from monodiorite range from +2.71 to +10.59 and the two‐stage model ages range from 751 to 1,253 Ma. A large transversal span of εHf(t) values suggests that the source of depleted mantle was mixed with a small amount of older crustal material. The diorite and monzodiorite show a covariant relationship between εHf(t) values and Th/U ratios, which imply the existence of source heterogeneity. The diorites and monzodiorites were most likely produced in an arc setting. The granites are low K in composition and metaluminous to weakly peraluminous. In view of obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments, parent magmas of the granites are suggested to have formed with the participation of crustal source materials. The εHf(t) values of zircons from granite range from +5.82 to +8.90, and the two‐stage model ages range from 861 to 1,057 Ma, indicating that magmas of the granites were mainly derived from partial melting of depleted mantle or juvenile thickened lower crust. The granites were most likely produced in an arc setting and share a similar source with the diorite and monzodiorite. Correlation between major oxides and SiO2 show that during the formation of the three kinds of rocks, crystallization and differentiation both played important roles. Combined with published data from the Central Qilian Belt and its vicinity, our results conclude that the northward subduction of oceanic crust contributed to the formation of an Early Palaeozoic subduction–accretion system in the Lajishan region. This model reveals a tectonic–magmatic thermal event and provides important insights into the tectonic evolution process in the Qilian region, as well as the Central Orogenic Belt during the Early Palaeozoic.

Finding of Ca. 1.6 Ga Detrital Zircons from the Mesoproterozoic Dagushi Group, Northern Margin of the Yangtze Block

The middle Mesoproterozoic is a crucial time period for understanding the Precambrian tectonic evolutionary history of the northern Yangtze Block and its relationship with the supercontinent Columbia. The Dagushi Group (Gp) is one of the Mesoproterozoic strata rarely found at the northern margin of the Yangtze Block. U–Pb geochronology and Lu–Hf isotopic analyses of detrital zircons were analyzed for three metamorphic quartz sandstone samples collected from the Luohanling and Dangpuling formations of the Dagushi Gp. These metasandstones yielded major zircon populations at ~2.65 Ga and ~1.60 Ga, respectively. The ~1.60 Ga ages first discovered yield a narrow range of ɛHf(t) values from −1.8 to +1.8, which lie above the old crust evolutionary line of the Yangtze Block, suggesting the addition of mantle material. Trace element data indicate that ~1.60 Ga detrital zircons share a basic provenance, whereby they have low Hf/Th and high Nb/Yb ratios. Zircon discrimination diagrams suggest that the ~1.60 Ga detrital zircon source rocks formed in an intra-plate rifting environment. Dagushi Gp provenance studies indicate that the ~1.60 Ga detrital zircon was most likely sourced from the interior Yangtze Block. Thus, we suggest that the late Paleoproterozoic to early Mesoproterozoic continental break-up occurred at the northern margin of the Yangtze Block.

Variation in the analytical figure of merit for in situ Hf isotopic measurements by LA-MC-ICPMS in zircon standards at variable spatial resolutions.

Lu-Hf isotopic systematics is a powerful tool and gained importance as a geochemical tracer in geosciences. A multi-collector inductively coupled plasma mass spectrometer coupled with a laser ablation system has been used to perform zircon hafnium (Hf) isotopic analysis, and protocol is established for measurement of Hf isotopes. Toward this, two zircon standards, Z91500 and Plesovice, have been used for Hf isotopic measurements at four different spot sizes (50, 40, 25, and 20 μm). The isotopic data for ≥25 μm have an excellent agreement with published data, but for 20 μm, the results are erroneous and irrelevant to geological application. It has been observed that Hf beam intensity has a linear relation to the volume of the target (RM) ablated. 178 Hf/177 Hf ratio and ɛHf for both standards are comparable with the published recommended values. The present study indicates that 176 Lu/177 Hf ratio for Z91500 is more homogeneous than Plesovice zircon. The 176 Hf/177 Hf isotopic ratio for 50 and 25 μm shows an excellent agreement with the previously reported data. However, for 40-μm spot size, a slightly higher but negative offset of -123 and -105 ppm in 176 Hf/177 Hf ratio have been observed for Plesovice and 91500, respectively.

The detrital zircon U-Pb-Hf isotopes of the Triassic sediments in northern Pakistan: Implications for crustal evolution of the NW Indian continent

Detrital zircon analysis of the Triassic Kashala Formation of the Alpurai Group in Swat, Pakistan, west of Indus syntaxis, record Archean to Paleozoic ages. The U-Pb age spectra show distinctive age clusters at 3510–3100 Ma, 2700–2400 Ma, 1750–1500 Ma, 1350–750 Ma, 700–600 Ma and 580–470 Ma, with one youngest age of 229 Ma, suggesting secular and episodic continental growth. The prominent negative εHf(t) values indicate dominantly crustal reworking together with a minor contribution from a juvenile crust. The age pattern is similar to the detrital zircon from Tethyan Himalaya and South India, showing two major peaks at 926 Ma and 532 Ma, and corresponding to Greenville and Pan-African orogenies, respectively. The U-Pb age peaks between ca. 1750–1600 Ma and 900–750 Ma are correlated well with the peaks of detrital zircon from Precambrian and Ordovician rocks in the Hazara region. Detrital zircon analysis suggests proximal source areas. Based on combined U-Pb and Hf isotope analysis and grain morphology, Paleoproterozoic detrital zircon grains were derived from basement rocks of the Besham Complex, which is presently exposed in the Indus syntaxis. The zircon trace element geochemistry reveals mainly felsic and mafic igneous rocks of the continental crust, suggesting that proximal Proterozoic-Paleozoic intrusions in the Swat and Hazara regions as a possible source.

Evidence from the U–Pb–Hf signatures of detrital zircons for a Baltican provenance for basal Old Red Sandstone successions, northern Scottish Caledonides

The provenance of Devonian Old Red Sandstone (ORS) continental successions in the northern Scottish Caledonides is poorly known: were they derived locally or from more distal sources? The integration of U–Pb and Hf isotope analyses in detrital zircon crystals reduces potential ambiguities arising from non-unique age populations and yields information on the crustal evolution of the source terranes. Samples of basal ORS successions yield zircon U–Pb age groupings of c. 1800–1500 and c. 1200–900 Ma, with minor Neoarchean, Tonian, Ediacaran and Ordovician contributions. SW Baltica provides the best match for detrital zircon ages and Hf isotopic signatures and much of the &gt;900 Ma zircon population was probably recycled from Neoproterozoic successions. ε Hf ( t ) values in c. 1800–1000 Ma grains reflect the assembly of Nuna, the development of a long-lived retreating subduction system along its margin and Grenville collisional orogenesis. These basal ORS successions were probably deposited within the same regional fluvial system as coeval sedimentary rocks in the Midland Valley, draining an area of positive relief in SW Baltica where continental convergence continued through the Early Devonian. Supplementary material : Isotopic data, statistical comparison of selected samples and TIMA heavy mineral data are available at https://doi.org/10.6084/m9.figshare.c.5301780

Metallogenic chronology and tectonic setting of the Erdaohe Pb–Zn–Ag deposit in Inner Mongolia, NE China: Constraints from sphalerite Rb–Sr dating, zircon U–Pb dating, and Hf isotope analysis

• The Erdaohe deposit is a large-scale Pb-Zn-Ag deposit in the Great Hinggan Range. • The granite porphyry and the sphalerite in the deposit formed at 133.6Ma and 130.5Ma. • The mineralization was affected by the Mongolia-Okhotsk and Paleo-Pacific Ocean. • The discovery of the Erdaohe deposit shows a good exploration prospect in the region. The Erdaohe deposit is a recently discovered large-scale Pb–Zn–Ag deposit in the northern section of the Great Hinggan Range, Inner Mongolia, China. The ore bodies are mainly located in the skarnized contact zone between the granite-porphyry and calcareous wall rock, and in the fissures of the wall rock of the outer contact zone. Several vein-type ore bodies are located in the fissures of the distal volcanic strata, with obvious magmatic–structural ore-control characteristics. In this study, seven sphalerite samples from ores in the quartz–sulfide metallogenic stage yielded an Rb–Sr isochron age of 130.5 ± 1.9 Ma (MSWD = 1.6), with initial 87 Sr/ 86 Sr ratios of 0.70967 to 0.70994. LA-ICP-MS zircon U–Pb dating of the granite-porphyry samples yielded a concordant age of 133.6 ± 0.46 Ma (MSWD = 1.2). Combined with the previous studies, dating results and the field relation between the granite-porphyry and the ore body, it is considered that the granite-porphyry is genetically related to the mineralization of the deposit. The zircon ε Hf (t) values of the granite-porphyry ranged from 6.8 to 8.5, and the two-stage Hf model age (t DM2 ) ranged from 575 to 668 Ma, revealing that the granite-porphyry originated from the partial melting of the juvenile crust accreted from the depleted mantle during the end of the Neoproterozoic. Extensive magmatism during the Early Cretaceous was caused by lithospheric delamination after the closure of the Mongolia–Okhotsk Ocean and the back-arc extension induced by the subduction of the Paleo-Pacific Plate towards Eurasia; thus, the Erdaohe deposit was formed under this favorable metallogenic structure and material system. By comparing the metallogenic age, tectonic setting, and ore-forming resources, we propose that the formation of Erdaohe Pb–Zn–Ag deposit belongs to the same regional metallogenic event as the Pb–Zn–Ag deposits in the southern segment of the Great Hinggan Range, potentially indicating further exploration prospects for Pb–Zn–Ag deposit in the middle segment of the Great Hinggan Range.

Sana Granite, a post-collisional S-type magmatic suite of the Ribeira Belt (Rio de Janeiro, SE Brazil)

The postcollisional magmatism in the Ribeira Belt, a collisional Orogen developed through several episodes during the convergence of the Pan-African/Brasiliano Orogeny, was marked in the Eastern Terrane (Rio de Janeiro, SE Brazil) by intense granitic magmatism of Cambro-Ordovician age. This magmatism was previously divided into the Suruí and Nova Friburgo suites, both interpreted as I-type granites generated by the interactions of magmas with crustal and mantle origins. This paper presents a new contribution to the understanding of the Sana Granite. It is based on the analysis of field work, mineralogical and geochemical (elemental concentrations by Inductively Coupled Plasma Emission Spectrometer, ICP-ES, and Inductively Coupled Plasma Mass Spectrometry, ICP-MS) data, and U–Pb dating and Lu–Hf isotope analyses, by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) from the main body and one satellite of the Sana Granite. The results of this work show that the Sana Granite, previously grouped with the Nova Friburgo suite, presents petrographic, geochemical, and isotopic characteristics that do not match its initial petrogenetic interpretation. Data from this work show that the Sana Granite is composed of alkali feldspar granites, syenogranites and monzogranites. All these rocks are hololeucocratic to leucocratic, with small grains ranging from fine to coarse. They are silica-supersaturated, peraluminous, and mostly alkali-calcic rocks and plot at the limit between the ferrous and magnesian fields. Crystallization ages of 480 ± 6 million years (Ma) and 495 ± 4 Ma are obtained in the main body of the Sana Granite, while the ages obtained in the satellite body are 506 ± 10 Ma and 508 ± 5 Ma. The Hf isotope data indicate crustal sources, with depleted mantle model ages (TDM) varying between 2.22 and 1.69 Ga and εHf values ranging between −15.54 and − 6.54. The data set from this work suggests that Sana is an S-type granite formed by the partial melting of metasedimentary rocks from the dehydration of hydrous minerals, such as biotite and muscovite. This massif is composed of muscovite-bearing peraluminous granitoids (MPGs) associated with high-pressure collisional Orogens. Considering that the characteristics of the Sana Granite are incompatible with those of the Nova Friburgo suite, it is proposed to use the Sana suite to characterize S-type granites generated in the postcollisional stage of the Ribeira Belt.

Jurassic evolution of the Qaidam Basin in western China: Constrained by stratigraphic succession, detrital zircon U-Pb geochronology and Hf isotope analysis

The formation and evolution of an intracontinental basin triggered via the subduction or collision of plates at continental margins can record intracontinental tectonic processes. As a typical intracontinental basin during the Jurassic, the Qaidam Basin in western China records how this extensional basin formed and evolved in response to distant subduction or collisional processes and tectonism caused by stresses transmitted from distant convergent plate margins. The Jurassic evolution of the Qaidam Basin, in terms of basin-filling architecture, sediment dispersal pattern and basin properties, remains speculative; hence, these uncertainties need to be revisited. An integrated study of the stratigraphic succession, conglomerates, U-Pb geochronology, and Hf isotopes of detrital zircons was adopted to elucidate the Jurassic evolutionary process of the Qaidam Basin. The results show that a discrete Jurassic terrestrial succession characterized by alluvial fan, braided stream, braided river delta, and lacustrine deposits developed on the western and northern margins of the Qaidam Basin. The stratigraphic succession, U-Pb age dating, and Hf isotope analysis, along with the reconstructed provenance results, suggest small-scale distribution of Lower Jurassic sediments deposited via autochthonous sedimentation on the western margin of the basin, with material mainly originating from the Altyn Tagh Range. Lower Jurassic sediments in the western segment of the northern basin were shed from the Qilian Range (especially the South Qilian) and Eastern Kunlun Range. And coeval sediments in the eastern segment of the northern basin were originated from the Quanji massif. During the Middle-Late Jurassic, the primary source areas were the Qilian Range and Eastern Kunlun Range, which fed material to the whole basin. The Jurassic sedimentary environment in the Qaidam Basin evolved from a series of small-scale, scattered, and rift-related depressions distributed on the western and northern margins during the Early Jurassic to a larger, extensive, and unified depression occupying the whole basin in the Middle Jurassic. The Altyn Tagh Range rose to a certain extent during the Early Jurassic but lacked large-scale strike-slip tectonism throughout the Jurassic. At that time, the North Qaidam tectonic belt had not yet been uplifted and did not shed material into the basin during the Jurassic. The Qaidam Basin experienced intracontinental extensional tectonism with a northeast-southwest trend throughout the Jurassic in response to far-field effects driven by the sequential northward or northeastward amalgamation of blocks to the southern margin of the Qaidam Block and successive accretion of the Qiangtang Block and Lhasa Block onto the southern Eurasian margin during the Late Triassic−Early Jurassic and Late Jurassic−Early Cretaceous, respectively.

Petrogenesis and tectonic implications of Early Paleozoic granitoids in the Qiaerlong district of the West Kunlun orogenic belt: constraints from petrology, geochronology, and Sr-Nd-Hf isotope geochemistry

ABSTRACT The West Kunlun orogenic belt (WKOB) is a complex orogenic belt that preserves the evidence of Early Palaeozoic and Late Palaeozoic orogenic events, with the former resulting from the closure of the Proto-Tethys Ocean. To better reveal the relationships between Early Palaeozoic granitoids in the WKOB and the tectonic evolution of the Proto-Tethys Ocean, we analysed the rocks of Akedala pluton, which is exposed within the Qiaerlong basin, and compared the results with contemporaneous magmatic rocks elsewhere in the WKOB. Integrated petrology, geochronology, and Sr–Nd–Hf isotope analyses of the rocks revealed the following: (1) The Akedala pluton is mainly composed of metaluminous–peraluminous I-type quartz monzonite and monzogranite; U–Pb dating of zircon indicates that quartz monzonite and monzogranite components is emplaced at 473–479 Ma and 462 Ma, respectively. (2) Both of them were enriched in large-ion lithophile elements and light rare earth elements and depleted in high field strength elements with negative Nb, Ta, Zr, P and Ti anomalies, indicating that they formed in a subduction zone environment. (3) Quartz monzonites were enriched in MgO concentrations (>3.10 wt.%), and show variable whole rock Sr-Nd isotopic ratios ((87Sr/86Sr)i = 0.7042–0.7058, εNd(t) = – 0.4 to +1.1), and had positive zircon εHf(t) (+0.0 to +6.8) values, which suggests they are derived from a mixed source of juvenile crust and older lower crust. (4) Monzogranites were characterized by high Sr (461–804 ppm) and low Y (2.00–3.68 ppm) and Yb (0.19–0.31 ppm) contents with high Sr/Y (164–325) and (La/Yb)N (12.6–46.7) ratios, indicating an adakitic affinity; they had relatively homogeneous whole rock (87Sr/86Sr)i (0.7044–0.7045) and positive εNd(t) (+2.0 to +2.9) and positive zircon εHf(t) (+1.1 to +4.3) values with low MgO, Cr, Ni and Nb contexts, suggesting that they were mainly generated from partial melting of thickened lower crust. Comparative analysis of these results with other Early Palaeozoic arc magmas in the WKOB shows that the Akedala pluton was formed due to the southward subduction of the Proto-Tethys Ocean. Divergent bidirectional subduction of the Proto-Tethys Ocean was initiated in the Early Cambrian, continued through the Middle Ordovician, and ended in the Early Silurian, due to terminal collision between the Tarim block and the West Kunlun terrane, which created the Early Palaeozoic orogenic belt.