Sm-Nd Data Research Articles

Characteristics of antimony mineralization in the Yangla polymetallic deposit, northwestern Yunnan, SW China: Insights from calcite Sm-Nd dating and C-O-Sr isotopes

Calcite is the main gangue mineral in antimony (Sb) deposits, and its compositions can reflect the physicochemical conditions of Sb mineralization. The Yangla is the largest Sb deposit (10 kt Sb @ 14.87 %) in the Jinshajiang suture zone (SW China), and the lode-type Sb orebodies are stratabound or developed along NE-trending fracture zones in marble. To constrain the time of Sb mineralization and establish any genetic link with the local magmatism and wallrocks, we performed calcite Sm-Nd dating and bulk C-O and in-situ Sr isotope analyses. The results show that the Sb mineralization (∼155 Ma) was considerably younger than the Cu-Pb-Zn mineralization (∼230 Ma), skarn alteration (∼234 Ma), and granitoid emplacement (∼230 Ma) at Yangla, but much older than the local W mineralization (∼30 Ma). The initial 87Sr/86Sr ratio of calcite (0.71972–0.72208) is much higher than that of the Triassic granodiorite (0.71149– 0.71990) and Carboniferous basalt (0.70562–0.70995), suggesting mixed source of calcite from the ore fluids and Devonian wallrocks. The ore-related calcite has δ13CPDB (−4.53 to − 2.33 ‰) and δ18OSMOW (+14.98 to + 16.30 ‰) values that fall between the granite and marine carbonate isotopic fields. This suggests that the ore-forming fluid may be related to the low-temperature alteration of granites and marine carbonate dissolution. Simulated precipitation temperature calculation for the ore-related calcite yielded 200–150 °C, and the calcite C-O isotopes suggest that fluid mixing, fluid-rock interactions, and CO2 degassing may have precipitated the stibnite in the fracture zones under low-temperature conditions. Our new geochemical results and published data suggest that the Yangla polymetallic mineralization was multiphase, comprising the Indosinian Cu-Pb-Zn (∼230 Ma), Yanshanian Sb (∼155 Ma), and Himalayan W-Sb (∼30 Ma) metallogenic events.

A ~957 Ma Metamorphism in the Mesoarchaean Hindoli Group Supracrustal Rocks from the Jahazpur Shear Zone, East Rajasthan (India): Constraints from Sm-Nd Dating and Phase Equilibria Modeling

ABSTRACT A petrological-chronological investigation of the Hindoli Group of rocks within the Jahazpur Shear Zone in the eastern segment of the Aravalli Delhi Fold Belt (ADFB), NW India, has been conducted. We infer two stages of deformation (D1 and D2) and metamorphism (M1 and M2) for the garnet - muscovite - biotiteschists interleaved with meta dolomite, Banded Iron Formation (BIF) amphibolite, and foliated granite. The D2 deformation corresponds to the northeast-trending Jahazpur shear zone on a regional scale. Garnet porphyroblasts, syntectonic with the D2 deformation, are chemically zoned with spessartine-rich cores. Geothermobarometry and pseudosection analyses yield peak P-T conditions of ~7.5 kbar, 580°C, followed by decompression and cooling along a clockwise P-T path. The Sm-Nd isotope analysis of the whole rock yields a date of ~3.0 Ga from an amphibolite. This data is interpreted as the age of formation of the litho-units of the Hindoli Group. Sm-Nd analyses of garnet grains yield an age of ~957 Ma. This date corresponds with the age of nucleation of the Jahazpur shear zone. A good correlation is established between the Neoproterozoic crustal segments of the Jiangnan Fold Belt of the South China Craton and that of the ADFB during the formation of the Rodinia Supercontinent.

Genesis of the Yidonglinchang gold deposit, Lesser Xing’an Range, China: Insights from fluid inclusions, H-O-S-Pb isotopes, and Sm-Nd and U-Pb geochronology

The origin and evolution of the newly discovered Yidonglinchang gold deposit in the Lesser Xing’an Range, Northeast China, remain poorly understood. This article focuses on the investigations of the geological characteristics, fluid inclusions, H-O-S-Pb stable isotopes and geochronology of the deposit. The Yidonglinchang gold deposit is mainly controlled by NEE-trending faults, and the ore bodies are present in volcanic rocks of the Early Cretaceous Ningyuancun Formation (K1n). Silicification, pyritisation, and argillization zones develop sequentially from near the ore center outwards. The ore minerals mainly include electrum and argentite. The gangue minerals are mainly quartz, calcite, and a small amount of sericite, plagioclase and adularia. The main gold-bearing minerals are quartz and calcite. The primary fluid inclusion types in quartz are pure-liquid-phase, gas-rich-phase, and liquid-rich-phase inclusions. Most of the inclusions are classified as a H2O-NaCl system which were formed under low-temperature, low-salinity conditions, indicating that Yidonglinchang is an epithermal gold deposit. The occurrence of boiling fluid inclusion assemblage indicates that the fluids underwent decompression boiling. Sm-Nd dating of calcite from the main ore-forming stage yields an age of 97.5 ± 2.3 Ma, which is interpreted as the timing of mineralisation. Zircon U-Pb dating of dioritic porphyrite yields ages of 98.8 ± 1.1 and 98.0 ± 1.3 Ma, which are consistent with the mineralisation age, suggesting a potential genetic link between the intrusive rocks and the ore formation. H-O-S-Pb isotopic compositions indicate that the ore-forming fluids were magmatic water during the early mineralisation stage, with the addition of meteoric water during the late stage. These isotopic compositions are also indicative of an origin of the ore-forming materials from the mixed crustal and mantle components. The mineralisation of the Yidonglinchang gold deposit was related to the slab rollback of the subducted Palaeo-Pacific Plate in the early Late Cretaceous.

Crustal growth in the northeast portion of the Rhyacian Bacajá domain, SE Amazonian craton, based on U-Pb, Lu-Hf, and Sm-Nd data

The Bacajá domain, southeastern Amazonian craton, comprises Mesoarchaean and Siderian terrains reworked during the Transamazonian cycle. Combined analyses of zircon LA-ICP-MS U-Pb and Lu-Hf with whole-rock Sm-Nd from the northeast portion of this domain made it possible to propose an evolutionary sequence between ca. 2.60 and 2.06 Ga. Gneisses with an igneous protolith age of 2630±15 Ma show negative signatures (ɛHft = -0.3 to -1.7 and ɛNdt = -3.08 to -2.98) and a Mesoarchaean formation (Hf-TDMC and Nd-TDM model ages range from 3.0 to 3.2 Ga). Rhyacian granite genesis lasted about 40 million years (2.10–2.06 Ga) and was divided into two magmatic periods. The first is represented by deformed granitoids with zircons yielding crystallization ages between 2.10 and 2.09 Ga and model ages (Hf-Nd) at about 2.5 Ga. The second event is represented by granitoids with preserved magmatic texture, crystallization ages of 2.06 Ga, and Siderian model ages (Hf-Nd) of around 2.3 Ga. The overall Hf isotopic analyses of this Rhyacian granite genesis exhibit a spread of ɛHft values between 1.8 and -2.9, which show a probably underestimated mantle-derived contribution in this period.

Results of integrated dating of eclogites of the belomorian mobile belt

Generalized overview of all points of view on the timing of eclogite metamorphism of Belomorian Mobile Belt (BMB) with critical analysis of underlying arguments was made. The author’s interpretation of the age of eclogite metamorphism within the BMB is based on a combination of independent isotope-geochemical dating methods: local U-Pb dating of heterogeneous zircons with magmatic cores and eclogite rims, Lu-Hf and Sm-Nd dating of rock-forming minerals of eclogite paragenesis (garnet and omphacite). All three methods independently determine the age of eclogitic metamorphism as Svecofennian, with the same value of about 1900 Ma.

Jingwenite-(Y) from the Yushui Cu deposit, South China: The first occurrence of a V-HREE-bearing silicate mineral

Abstract Jingwenite-(Y), Y2Al2V24+(SiO4)O4(OH)4, the first V-HREE-bearing silicate mineral discovered in nature, is an abundant component of a sediment-hosted stratiform Cu (SSC) deposit, Yushui, South China. The mineral occurs in bedded/massive sulfide-bearing ore and is associated with bornite, chalcopyrite, galena, xenotime-(Y), nolanite, thortveitite, roscoelite, barite, and quartz. Optically, jingwenite-(Y) is biaxial (+), with α = 1.92(4), β = 1.95(2), γ = 1.99(3) (white light), and 2V (calculated) = 83°. The dispersion is medium with r < v, and the pleochroism is with X = light brown, Y = brown, Z = dark brown. The color, streak, luster, and hardness (Mohs) are light brown, yellowish gray, vitreous, and 4½–5, respectively. Jingwenite-(Y) is monoclinic, with space group I2/a, Z = 4, and unit-cell parameters a = 9.4821(2) Å, b = 5.8781(1) Å, c = 19.3987(4) Å, β = 90.165(2)°, and V = 1081.21(4) Å3. The structure of jingwenite-(Y) has chains of edge-sharing Al(V,Fe)-O octahedra and V(Ti)-O octahedra extending along the b-axis and linked by insular Si-O tetrahedra, leaving open channels occupied by HREEs. Jingwenite-(Y) is a new nesosilicate structural type. Sm-Nd dating and Nd isotope signatures of jingwenite-(Y) reveal an epigenetic origin and suggest that HREEs and V were added to the SSC system via leaching of abundant heavy minerals in the footwall red sandstone by oxidized basinal brines. The abundance of jingwenite-(Y) at Yushui indicates that it could potentially be a valuable resource for HREE and V. Moreover, HREE and V mineralization can also occur in the same sediment-hosted Cu mineral system.

Paleoproterozoic Pt-Pd Fedorovo-Pansky and Cu-Ni-Cr Monchegorsk Ore Complexes: Age, Metamorphism, and Crustal Contamination According to Sm-Nd Data

This paper continues the Sm-Nd isotope geochronological research carried out at the two largest Paleoproterozoic ore complexes of the northeastern Baltic Shield, i.e., the Cu-Ni-Cr Monchegorsk and the Pt-Pd Fedorovo-Pansky intrusions. These economically significant deposits are examples of layered complexes in the northeastern part of the Fennoscandian Shield. Understanding the stages of their formation and transformation helps in the reconstruction of the long-term evolution of ore-forming systems. This knowledge is necessary for subsequent critical metallogenic and geodynamic conclusions. We applied the Sm-Nd method of comprehensive age determination to define the main age ranges of intrusion. Syngenetic ore genesis occurred 2.53–2.85 Ga; hydrothermal metasomatic ore formation took place 2.70 Ga; and the injection of additional magma batches occurred 2.44–2.50 Ga. The rock transformation and redeposited ore formation at 2.0–1.9 Ga corresponded to the beginning of the Svecofennian events, widely presented on the Fennoscandian Shield. According to geochronological and Nd-Sr isotope data, rocks of the Monchegorsk and the Fedorovo-Pansky complexes seemed to have an anomalous mantle source in common with Paleoproterozoic layered intrusions of the Fennoscandian Shield (enriched with lithophile elements, εNd values vary from −3.0 to +2.5 and ISr 0.702–0.705). The data obtained comply with the known isotope-geochemical and geochronological characteristics of ore-bearing layered intrusions in the northeastern Baltic Shield. An interaction model of parental melts of the Fennoscandian layered intrusions and crustal matter shows a small level of contamination within the usual range of 5–10%. However, the margins of the Monchetundra massif indicate a much higher level of crustal contamination caused by active interaction of parental magmas and host rock.

Unravelling source and tectonic environment of an Ediacaran magmatic province from southeast Brazil: Insights from geochemistry and isotopic investigation

This work focuses on the 575–540 Ma meta-igneous units that crop out near Rio de Janeiro city, southeast Brazil. Tectonically, they are located in the southern part of the Oriental Terrane known as Costeiro Domain, near to the suture with the Cabo Frio Tectonic Domain. We present new zircon U-Pb and oxygen isotope SHRIMP along with geochemical data to investigate the possible source(s) and tectonic setting of this magmatic event related to the final stages of Western Gondwana consolidation. Five units comprise this Late Ediacaran magmatic province: Facoidal orthogneiss, Cassorotiba garnet-biotite orthogneiss, Maricá porphyritic orthogneiss, Tinguí hornblende-biotite orthogneiss, and Itacoatiara porphyritic meta-granite. These acid to intermediate plutons show similar whole-rock geochemistry, Sm-Nd data, and petrographic characteristics. The original magmas are calc-alkaline that evolved to a high-K calc-alkaline, and a shoshonitic term. Geochronological data indicate three intervals of magmatic activity: 575–565 Ma medium to high-K calc-alkaline intrusions; 555–545 Ma high-K and shoshonitic magmas; and the 545–540 Ma calc-alkaline medium-K Itacoatiara meta-granite, with Nd isotopic ratios presenting the highest εNd (3.7–5.1), and TDM ages (1.3–1.8 Ga). The TDM Nd model ages of all units range from 1.3 Ga to 1.8 Ga and the εNd(t) values vary mostly from −3.7 to −5.7 corroborating with the crustal affinity of these rocks. The oxygen isotope (δ18O) values average is 8‰ with slight differences among the units. These high δ18O ratios suggest crustal values, typical for continental crust in a collisional environment. Based on the geochemical data allied with melting experiments from literature, we envisage that the Late Ediacaran magmatic province could be formed by partial melt from a lower crust amphibole-biotite rich source. All the presented data point to magmatic activity in a transitional environment from subduction to continental collision in the Cambrian.

Mantle-like Hf[sbnd]Nd isotope signatures in ~3.5 Ga greenstones: No evidence for Hadean crust beneath the East Pilbara Craton

The geological setting of extensive ~3.5 Ga greenstone sequences in the Pilbara Craton (Australia) has been controversial for many years. Models range from a purely oceanic origin to emplacement over a pre-existing, possibly Hadean, sialic basement. Here we present new isotopic (NdHf) and trace element data for a geographically extensive suite of komatiitic-tholeiitic metavolcanic rocks which comprise much of the Pilbara Supergroup. Most of the samples have flat to mildly enriched normalised trace element patterns, often associated with a slight NbTa depletion. A small subset of samples, represented throughout the stratigraphy, show strong LREE enrichment and pronounced HFSE anomalies (low Nb/Th, high La/Nb and Zr/Y) either requiring a different magma source or the addition of an enriched component (possibly pre-existing continental crust). Despite this compositional diversity, the SmNd and LuHf data for all samples define ~3.5 Ga isochrons and yield homogeneous initial ratios (εNd = 1.15 ± 0.19; εHf = 2.29 ± 0.65) suggesting a magma source — or sources — slightly more depleted than the putative primitive (chondritic) mantle but consistent with recent observations of other primordial, deep mantle reservoirs. Published SmNd data for the Dresser Formation obtained during the Pilbara Drilling Project appear to be affected by alteration processes and are considered unreliable for the estimation of an accurate initial isotopic composition.The data for the enriched samples are inconsistent with assimilation of known examples of locally exposed continental crust as a mechanism responsible for their trace element characteristics. If an alternate crustal contaminant is invoked it cannot be much older than the basaltic magmatism itself. As a consequence, we see no evidence for an extensive Hadean (>4.0 Ga) sialic basement in the region.

Isotopic and geochemical constraints for a Paleoproterozoic accretionary orogen in the Borborema Province, NE Brazil: Implications for reconstructing Nuna/Columbia

The Alto Moxotó Terrane of the Borborema Province presents a wide exposure of Paleoproterozoic crust, but unlike other continental blocks of South America, its orogenic history is strongly obliterated by late Neoproterozoic deformation. New isotopic and geochemical studies were conducted in mafic-ultramafic (Fazenda Carmo Suite) and granitic-gneissic rocks (Riacho do Navio Suite) within the terrane. The former present zircon U-Pb crystallization ages at ca. 2.13 Ga, whereas Sm-Nd data suggests a juvenile origin via melting of early Paleoproterozoic to Archean peridotitic sources. Geochemical data for these rocks are compatible with tholeiitic magmas with some degree of crustal contamination and trace element distribution points to a continental-arc related setting interpreted as remnants of the early stages of subduction. In contrast, the Riacho do Navio Suite was emplaced at ca. 2.08 Ga and has highly negative εNd(t) values indicating crustal reworking. The suite displays calc-alkali to alkali-calcic and ferroan geochemical signatures compatible with Cordilleran magmas. In addition, trace-element distribution as well as discriminant diagrams suggest that the precursor magmas were generated during the later stages of a continental arc or in a syn-collisional setting. Based on our results, we suggest that the studied units might represent missing pieces of a Paleoproterozoic accretionary orogen that formed the crustal framework of the Alto Moxotó Terrane, and that this represents a block associated with assembly of the Nuna/Columbia supercontinent, which is now largely hidden within the Neoproterozoic orogenic belts of West Gondwana.

O and H isotopic evidence for a mantle source of water in appinite magma: An example from the late Neoproterozoic Greendale Complex, Nova Scotia

Appinite suite rocks occur as small plutonic bodies, ranging from ultramafic to felsic in composition, that are characterized by abundant idiomorphic amphibole suggesting they are the products of water-rich mafic magmas. Appinites are also understood to record tectono-magmatic processes during the waning stages of subduction in convergent to collisional tectonic settings. Measuring D/H and 18O/16O ratios of hornblende in appinitic rocks offers opportunities to constrain the sources of water (mantle, crustal, sea water and or meteoric) in the magma during its crystallization, and to shed light on the role of water as arc magmatism shuts down. The ca. 607 Ma Greendale Complex in the Avalon terrane of Nova Scotia, Canada, is characterized by spectacular exposures of appinite suite rocks ranging from ultramafic to felsic in composition. Two populations of amphiboles are identified: one is characterized by δ18O values between 4.7 and 6.8‰ and anomalously low δD values (ca. < −90‰). These isotopic signatures are interpreted to represent incorporation of mantle-derived fluids into the crystal structure, possibly associated with mixing between a region of mantle upwelling and a subducting slab. This mixing process allows for hydration of the magma during its ascent into the overlying lithospheric mantle wedge. Some amphiboles retain mantle-like δ18O and δD values, but others may have partially re-equilibrated during low T assimilation of supracrustal units (e.g. organic-rich sediments) and or fluids derived from such bodies. A second generation of hornblende yields δ18O varying from 0.9 to 4.6‰ and δD from ca. −106 to −64‰, which supports equilibration with fluids from crustal sources. Assimilation of volatiles sourced from previously hydrothermally altered intruded sheets and or country rock is interpreted to produce these second-generation isotopic signatures. Regional syntheses indicate that arc magmatism in the Avalon terrane ended with the generation of a transform system, implying the potential generation of a slab window behind that system. In that context, the Appinites in the Avalon terrane have previously been interpreted to have been emplaced after the cessation of subduction in a slab window or slab failure setting behind the transform system, in which asthenospheric upwelling generated juvenile magmas and/or facilitated melting of the overlying continental lithospheric mantle. Our δD and δ18O data support this model and together with available Sm-Nd data, suggest asthenospheric upwelling triggered melting of the continental lithospheric mantle that was previously hydrated by subduction and this mantle-derived water contributed to the origin of appinites.

Mesozoic crustal melting and metamorphism in the U.S. Cordilleran hinterland: Insights from the Sawtooth metamorphic complex, central Idaho

In this study, we present whole-rock geochemistry and Sm-Nd data; zircon trace element, U-Pb, and Lu-Hf data; titanite U-Pb dating; and structural analysis of igneous and metasedimentary rocks of the Sawtooth metamorphic complex that provide insight into regional metamorphism, partial melting, and crustal thickening in the Idaho batholith segment of the Cordilleran orogen. Four magmatic events are revealed: (1) pre-tectonic felsic magmatism at ca. 156 Ma, (2) syn-tectonic mafic and felsic magmatism between ca. 100 Ma and ca. 92 Ma, (3) felsic magmatism concurrent with late-stage deformation at ca. 89−84 Ma, and (4) post-tectonic felsic magmatism at ca. 77 Ma. The multiple generations of felsic magmatism include a variety of sedimentary- and igneous-derived granitoids distinguished by zircon trace element compositions (e.g., U/Ce versus Th and Ce/Sm versus Yb/Gd) and were sourced from progressively more evolved crustal components as shown by Lu-Hf and Sm-Nd isotopic data. U-Pb data of metamorphic zircons and titanites from high-grade metasedimentary rocks suggest that regional metamorphism occurred from ca. 100−93 Ma, which was characterized by granulite-facies partial melting and concurrent growth of metamorphic zircons and garnets. The episodic magmatism in the Sawtooth metamorphic complex records pervasive melt migration in a hot, mid-crustal setting at ca. 100‒92 Ma and additional magma ascent in a cool, upper-crustal setting at ca. 77 Ma. The uplift of the Sawtooth metamorphic complex from mid- to upper-crust was likely caused by underthrusting at lower crustal levels coupled with erosion and thinning of the upper crust. This work suggests that the crust of the Cordilleran hinterland in the Idaho batholith region underwent significant thickening from ca. 100‒84 Ma, and a crust of Andean-like thickness was probably achieved by ca. 84 Ma. By ca. 77 Ma, the central Idaho crust started to thin likely due to mid-crustal flow and surface erosion. The new data from the Sawtooth metamorphic complex are consistent with the two major magmatic flare-ups in the Late Jurassic and Late Cretaceous in the U.S. Cordilleran orogen.

Integrated garnet and zircon petrochronology reveals the timing and duration of orogenic events in the North China Craton

Radiometric data from accessory zircon in long-lived polymetamorphic granulite facies rocks frequently show a large spread, with no clear relationship to zircon textures. For example, the granulites and associated rocks of the North China Craton which have an apparently continuous spread of metamorphic zircon dates through the Palaeoproterozoic from c. 1.95–1.80 Ga. The data are commonly interpreted to reflect long-lived metamorphism or discrete metamorphic events, with intermediate data reflecting variable Pb loss or a mixture of multiple growth domains. Herein, we present an approach that integrates direct dating of the P–T indexed mineral garnet with accessory zircon petrochronology which allows diagnostic time constraints for polymetamorphic processes in high-temperature rocks. We present high-precision LuHf and SmNd dates for two garnet-bearing mafic granulites and the adjoining granite and quartzite from the Gushan area between the Khondalite Belt and the Trans-North China Orogen, North China Craton. Statistically robust LuHf dates of 1815 ± 4 Ma and 1808 ± 3 Ma and corresponding SmNd isochron dates of 1790 ± 6 Ma and 1800 ± 9 Ma were obtained from the two mafic granulites, overlapping the zircon UPb date range of c. 1959–1785 Ma. Samarium–Nd dates from the accompanying garnet-bearing granite and quartzite are indistinguishable at 1794 ± 6 Ma and 1780 ± 6 Ma. The corresponding bulk garnet LuHf isochrons are poorly constrained—two-point garnet–matrix dates range from 1945 ± 10 Ma to 1849 ± 10 Ma for the granite and from 1936 ± 10 Ma to 1840 ± 9 Ma for the quartzite. Upper intercept UPb dates of 1950 ± 24 Ma (granite) and 1936 ± 17 Ma (quartzite) are obtained from the metamorphic zircons in equilibrium with garnet. The close agreement of SmNd isochron-dates (c. 1.80 Ga), the overlapping clusters of zircon UPb dates (c. 1.96 Ga), the identical LuHf and UPb dates of c. 1.80 Ga within uncertainty in the two granulites, and the older LuHf dates and comparable zircon UPb dates (c. 1.96 Ga) obtained in the garnet-bearing granite and quartzite than in those of the mafic granulites, strongly indicate that these rocks experienced coeval metamorphism from c. 1.95–1.80 Ga. These data require a prolonged episodic tectonometamorphic event in the North China Craton, which is probably related to the amalgamation of the Columbia supercontinent.

Nd isotope re-equilibration during high temperature metamorphism across an orogenic belt: Evidence from monazite and garnet

Monazite is a powerful U-Th-Pb geochronometer commonly used to determine the tempo of orogenic processes. As a light rare earth element (LREE)-enriched mineral, monazite also records key information for understanding the behavior of Sm-Nd isotope systematics during tectonothermal events. However, Sm-Nd isotope studies of monazite have received far less attention than its use as a U-Pb geochronometer. Here we investigate coupled U-Pb ages and Sm-Nd isotopic compositions of monazite from partially melted metasedimentary rocks in the Jiao-Liao-Ji orogenic belt (JLJB), North China craton, to provide insight into Sm-Nd isotope behavior during high-temperature metamorphism and crustal melting. We utilize several complementary dating systems in the same sample, including garnet Lu-Hf and Sm-Nd, zircon U-Pb, and monazite U-Pb geochronology, to gain precise time constraints on the P-T evolution of the JLJB. Garnet Lu-Hf isochron dates of 1.97–1.94 Ga are interpreted to represent prograde garnet growth, consistent with the prograde metamorphic zircon dates of 1.96–1.90 Ga; garnet Sm-Nd dates agree with retrograde metamorphic zircon dates, and all monazite U-Pb dates define a relatively narrow age range of 1.86–1.83 Ga, interpreted to represent retrograde cooling. The lack of older monazite grains matching zircon or garnet dates suggests the dissolution of pre-existing monazites into partial melt. Monazite in all samples, irrespective of occurring as garnet inclusions or in the matrix, yields homogenous Nd isotope compositions (εNd ~ −5) at ~1.85 Ga, which are consistent with the garnet and bulk-rock values. Thus, Nd isotope re-equilibration between bulk-rock and minerals occurs synchronously across the orogenic belt during high-T metamorphism (~750 °C) where melting was involved, with no evidence of a pre-metamorphic isotope signature. This suggests mobility in the Sm-Nd isotope system during high-grade metamorphism and melting, where the Nd isotope signature of monazite likely represents the most recent tectonothermal event.

Geochronological constraints on the Baguamiao gold deposit, West Qinling orogen, central China: Implications for ore genesis and geodynamic setting

The Baguamiao gold deposit, located in the Fengxian-Taibai ore district, is one of the largest gold deposits in the West Qinling orogen, central China. The poor age constraints on the gold mineralization event at the Baguamiao has caused strong debate on ore genesis and associated geodynamic controls. We carried out Sm-Nd and 40Ar-39Ar geochronological studies to determine more precise age constraints on the god deposition. The gold mineralization at Baguamiao deposit was developed during four hydrothermal stages that formed sequentially: (I) NW-trending ankerite-quartz veins, (II) deformed and folded NW-trending sulfide-ankerite-quartz veins, (III) joint-hosted NE-trending sulfide-ankerite-quartz veinlets, and (IV) NW- and NE-trending quartz fissure veins. Stages II and III define the main gold mineralization. The Sm-Nd dating of dolomite, ankerite, and calcite yielded isochron ages of 209.3 ± 4.2 Ma (MSWD = 1.80) and 208.1 ± 3.1 Ma (MSWD = 0.50) for gold mineralization of stages Ⅱ and III, respectively. The 40Ar-39Ar dating of muscovite intergrown with sulfides of stage Ⅱ yielded a plateau age of 209.5 ± 1.4 Ma (MSWD = 0.30). The age data obtained from the two geochronological methods are consistent with each other within uncertainties, indicating clearly the Baguamiao gold deposit formed at ca. 209 Ma. Integrating deposit geology from this and previous studies, geochronological data, and regional tectonics, we classify Baguamiao as an orogenic gold deposit, which was resulted from a number of fluid pulses but during a single ore-forming episode in late Norian-Rhaetian time of the Late Triassic. The ore-forming fluids and metals are suggested to have been derived from both metamorphic and magmatic processes in a post-collisional regime of the West Qinling orogen.

The timing of lunar solidification and mantle overturn recorded in ferroan anorthosite 62237

Ferroan anorthosite suite (FAS) rocks are widely interpreted to represent primordial lunar crust. Despite their importance in pinpointing the timing of lunar crust formation, robust chronological investigations for this rock type are scarce. Here, we report the Ar-Ar, Rb-Sr, and Sm-Nd isotopic systematics for the FAS troctolitic anorthosite 62237. The Ar-Ar isotopic system has been reset by a thermal event at 3710 ± 48 Ma, and the Rb-Sr isotopic systematics has been disturbed such that a Rb-Sr isochron age cannot be determined. However, an internal isochron for the Sm-Nd isotopic system has yielded an age of 4350 ± 73 Ma (MSWD = 2.0) with an initial ϵ143NdCHUR of −0.53 ± 0.26. The mineral and whole-rock fractions of 62237 plot on the same internal isochron as FAS sample 60025. The combined datasets define an age of 4372 ± 35 Ma (MSWD = 4.0) with an initial ϵ143NdCHUR of −0.17 ± 0.22. Literature Sm-Nd data for FAS and Mg-suite whole-rocks also plot on the 60025-62237 isochron. The coherence of data from both FAS and Mg-suite rocks examined thus far suggests that both rock suites formed contemporaneously from identical, or nearly identical, sources. In addition, the concordance of FAS and Mg-suite ages suggests that primordial crust solidification either involved both magmatic suites, or that Mg-suite magmatism was contemporaneous with FAS magmatism within resolution of the Sm-Nd chronometer. The ages for FAS and Mg-suite also coincide with the formation ages of the mare basalt source regions and urKREEP. Ferroan anorthosite suite rocks and urKREEP are thought to represent primordial LMO solidification products, whereas Mg-suite and the mare basalt source regions are argued to represent mixtures of various LMO crystallization products that were formed during density-driven overturn of the LMO. The concordance of ages implies that the 4372 ± 35 Ma Sm-Nd isochron records the age of mantle overturn, and that overturn occurred during, or shortly after, solidification of the LMO.

Magmatic and tectonic evolution of the Chaval Granite at the end of the Neoproterozoic, northwestern border of the Borborema Province

Abstract The northwestern region of Borborema Province is represented by the Ceara Central and Northwest Ceara crustal blocks connected by an extensive transcurrent shear zone that represents the northern portion of the Transbrasiliano Lineament in a complex geological context, which brings together geological units of nature, origin, and ages of the Archean to the Paleozoic. In this scenario, there is a large amount of granitic bodies, with different natures, age and tectonic environment, but predominantly representing a more intense granitogenesis in the Paleozoic Neoproterozoic and early Paleozoic, with plutons emplaced in different stages of the Brazilian Orogeny. In this context, the Chaval Granite corresponds to an isolated body in the extreme northwest of Borborema Province, located near the Atlantic coast, in the northern states of Ceara and Piaui. It is an intrusive batholith housed in Siderian orthogneisses (Granja Complex) and in Neoproterozoic supracrustal rocks (Martinopole Group), but is partly covered by sedimentary rocks from the Parnaiba Paleozoic Basin (Serra Grande Group), and coastal Cenozoic deposits. Field data and petrographic studies highlight the porphyritic texture with microcline megacrystals involved in coarce matrix as a remarkable feature. The predominant petrographic types are granodiorites, with variations for monzogranites and tonalites. The predominant primary mineral constituents are pertitic microcline, oligoclase, and quartz; biotite and rarely hornblende as qualified minerals and additionally titanite, apatite, zircon, alanite, and opaque minerals. Another peculiar characteristic is the deformational features related to the installation of the Santa Rosa Transcurrent Shear Zone along its eastern flank. The effects of the transcurrent shear deformation led to the modification of the original magmatic fabrics in much of the eastern half of the batolith, generating various types of mylonites. Thus, the typically igneous textures preserved in the western half of the pluton were gradually replaced by tectonic fabrics, which initially evolved into proto-mylonites in the central portion of the body, grading to mylonites eastward, highlighting strongly stretching, comminution associated with dynamic recrystallization, highlighting the formation of microcline and plagioclase porphyroclasts in a mylonitic matrix, which are involved by mylonitic foliation. Geochemical studies reveal compositional similarities, compatible with petrographic classifications, in which they mostly present granodioritic composition, followed by monzogranites and tonalites, classified as I-type granites, peraluminous with compatible with the calcium-alkaline series. The geochemical signatures of the Chaval Granite indicate the character of the tectonic magmatic arc environment. U-Pb zircon analysis by Mass Spectrometry (LA-ICP-MS) indicates crystallization age of 633 Ma, placing it in the Neoproterozoic, late Cryogenic-Early Ediacaran period, being one of the oldest granitoids in northwestern Borborema Province, correlated to the granites of the Santa Quiteria Magmatic Arc in the Ceara Central Domain. Hf-TDM model ages (2.65 to 2.13 Ga) and eHf(t = 633 Ma) values from -9.6 to -18.1 suggest incorporation of neoarchean and paleoproterozoic crustal sources in their formation with a long crustal residence time. Similar Sm-Nd data in whole-rock indicate Nd-TDM model ages of 1.27, 1.72 and 2.04 Ga and negative eNd(t = 633 Ma) values of -2.64 to -9.13, indicating paleoproterozoic and mesoproterozoic sources, with considerable crustal residence time implying a more evolved nature.

The origin of the Quemocuo carbonate-hosted Pb-Zn deposit in the Sanjiang Tethyan Belt, SW China: Constrained by Sm-Nd isochronic age and Sr-S-Pb isotope compositions

The newly discovered Quemocuo Pb-Zn deposit (7.1 Mt of sulfide ores, grading 1.65–7.17 wt% Pb and 1.13–5.7 wt% Zn) is located in the Tuotuohe area of the Sanjiang Tethyan metallogenic belt, SW China. The stratiform and veined ore body is hosted in the limestone of the Upper Permian Labuchari Formation and occur along the NE-trending fault. Four main mineralization stages are distinguished as follows: (i) pyrite + calcite + quartz, (ii) sphalerite + galena + pyrite + calcite + barite + quartz, (iii) galena + sphalerite + pyrite + calcite + barite + quartz, and (iv) calcite + dolomite. Sm-Nd dating of five calcite samples in stage II yielded an isochronic age of 34.3 ± 2.2 Ma (MSWD = 7.1), possibly reflecting the formation age of the Quemocuo Pb-Zn deposit. In situ sulfur isotopic compositions of the sulfides in stages I, II and III range from −29.5‰ to −26.5‰, −4.7‰ to +6.0‰, and +1.7‰ to +6.9‰, respectively. Such sulfur isotope signatures indicate bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR) of seawater or sulfate minerals. In situ Pb isotopic ratios indicate a similar origin for the sulfides in stages I, II and III, which all are related to metamorphic basement rocks and ore-hosting sedimentary strata. Initial 87Sr/86Sr ratios of sphalerite are 0.7085–0.7117, indicating a mixed source as suggested by in situ Pb isotopes. The Quemocuo Pb-Zn deposit was proposed to be a strata-bound and normal fault-controlled epigenetic deposit, with a mixed source of basement and strata, and even volcanic rocks. Our study suggests that the formation of the Quemocuo Pb-Zn deposit is related to the Cenozoic collision event between the Indian and Eurasian plates.

Sm-Nd age of picrites of the Lysogorsk complex (Southern Urals): evidence of initial middle riphean magmatism

The article presents new data on the age of the picrites of the Lysogorsk complex, common in the Taratash metamorphic complex (Bashkir meganticlinorium, western slope of the Southern Urals). Based on Sm-Nd dating (1409 ± 89 Ma) and calculated data on the crystallization pressure and temperature of mineral parageneses, it is concluded that picrites belong to the initial type of magmatism, which characterizes the initial stages of the Mashak magmatic event.

“Ages and Hf isotopic compositions of detrital zircons in the Pinal schist, southern Arizona, USA: Provenance, tectonic setting, and evidence for pre-1.7 Ga crust in SW Laurentia”

The Pinal basin of southern Arizona is best known for the widely distributed Paleoproterozoic Pinal schist. Most detrital zircons from the Pinal schist yield ages in the 1.68–1.77 Ga range, suggesting provenance in the proximal Mazatzal and Yavapai Provinces. Hf isotopic compositions of these zircons yield εHf values that are positive, but less than estimated depleted mantle at this time, and yield single-stage depleted mantle model ages that indicate a minimum age of 1.85–2.0 Ga for an older crustal component in the source. New Sm-Nd data from Pinal schist whole rocks are compatible with the source(s) of the pelitic component of Pinal sediment being derived from a terrane with a component older than the 1.68–1.77 Ga granitoids in the Mazatzal and Yavapai Provinces, as suggested by the Lu-Hf data. If the Pinal sediments were derived from the Mazatzal and/or Yavapai arcs, these arcs should thus be considered continental arcs. The composition and age of the older crustal component(s) indicated by the Sm-Nd and Lu-Hf systematics is not uniquely defined by these data, but options on a Laurentian margin include the cryptic older crust of the Colorado Province, e.g., an extension of Trans-Hudson-Penokean age crust. If the arcs were built on non-Laurentian crust and accreted as exotic terranes several possibilities are viable in the SWEAT, AUSWUS, and other models for conjugates to southwestern Laurentia in the Nuna supercontinent.