Uplift-denudation history of the Qinling orogen: Constrained from the detrital-zircon U–Pb geochronology

This paper presents a great number of detrital zircon U–Pb ages from the Middle Triassic to the Middle Jurassic sediments in the Jiyuan basin, southern North China. The results represent age spectra from 2.9 Ga to 216 Ma, with five peaks at 2.5 Ga, 1.9 Ga, 840 Ma, 440 Ma, and 270 Ma and two grains of ∼220 Ma. The ages of 2.5 Ga and 1.9 Ga are mainly derived from the Precambrian basement of the North China Block, whereas the others are typical characteristics of the Qinling orogenic belt. An important observation is that the Qinling-sourced detrital zircons become older as the strata get younger. Samples from the Middle Triassic to early Late Triassic strata are characterized by the age peak at 270 Ma, whereas the Late Late Triassic to Early Middle Jurassic samples are dominated by age peaks at 840 Ma and 440 Ma and minor grains within 800–650 Ma. Two grains of ∼220 Ma are preserved in the Late Middle Jurassic sample, which may be contributed by the Carnian deep plutons. These signatures indicate that the unroofing pattern of the Qinling orogenic belt developed by the denudation of materials from young covers to old basements and the Carnian deep plutons. Integrated with the data reported from the Hefei Basin, it is well-established that the intensity of unroofing increased from the Qinling to the Dabie orogen in the Early Jurassic, and the denudation timing of the ultra-high pressure (UHP) and high pressure (HP) rocks or Carnian plutons changed successively from the Early Jurassic in the Dabie to the Late Middle Jurassic in the Qinling orogen.     

Contribution of SHRIMP U–Pb zircon geochronology to unravelling the evolution of Brazilian Neoproterozoic fold belts

The South-American continent is constituted of three major geologic–geotectonic entities: the homonym platform (consolidated at the end of the Cambrian), the Andean chain (essentially Meso-Cenozoic) and the Patagonian terrains, affected by tectonism and magmatism through almost all of the Phanerozoic. The platform is constituted by a series of cratonic nuclei (pre-Tonian, fragments of the Rodinia fission) surrounded by a complex fabric of Neoproterozoic structural provinces.     

Reconnaissance-style EPMA chemical U–Th–Pb dating of uraninite

EPMA chemical U-Th-Pb uraninite analysis has been used to constrain the age of the granite-related, Rössing South uranium prospect in Namibia and the Kintyre unconformity-related uranium deposit in Western Australia. Uraninite from the Rössing South prospect has an age of 496.1 ± 4.1 Ma, which is similar to the age of other uranium deposits in the region at Rössing and Goanikontes. Uraninite grains analysed from the Kintyre deposit have an age of 837 +35/-31 Ma suggesting that the uranium mineralisation occurred during or after the latest period of sedimentation in the Yeneena Basin during the ca 850 to ca 800 Ma Miles Orogeny.     

Migrating magmatism in the northern US Cordillera: in situ U–Pb geochronology of the Idaho batholith

New in situ laser ablation-inductively coupled plasma-mass spectrometry and sensitive high-resolution ion microprobe U–Pb geochronology of zircons from the Idaho batholith and spatially overlapping Challis intrusions reveals a series of discrete magmatic belts of different ages and compositions. Following the accretion of the Blue Mountains province to North America along the Salmon River suture zone, two compositionally diverse belts of metaluminous plutons formed both adjacent to the suture and well inboard of it. These were constructed from ~100 to 85 Ma and were followed by a voluminous pulse of peraluminous magmatism, forming the bulk of the Atlanta lobe and largest fraction of the batholith between ~80 and 67 Ma. Around 70 Ma, a later and more spatially restricted suite of metaluminous plutons formed around the Bitterroot lobe of the batholith. This was followed by another pulse of voluminous peraluminous magmatism in the Bitterroot lobe, lasting from ~66 to 54 Ma. The changes from low volume metaluminous to high volume peraluminous magmatism may reflect a combination of changes in the angle and segmentation of the subducting Farallon plate and over thickening of the continental lithosphere. All of these features were then cut by plutons and dikes associated with the Challis volcanic field, lasting from ~51 to 43 Ma. Inherited components are pervasive in zircons from most phases of the batholith. While Precambrian components are very common, zircons also often contain cores or mantles that are 5–20 million years older than their rims. This suggests that the early phases of the batholith were repeatedly cannibalized by subsequent magmas. This also implies that the older suites may have been originally more aerially extensive than their currently exposed forms.     

Genesis of the Angeer Yinwula Pb–Zn deposit,Inner Mongolia,China: constraints from fluid inclusions,C–H–O–S–Pb isotope systematics,and zircon U–Pb geochronology

Arabian Journal of Geosciences - Soil toxic metal pollution is one of the most prominent environmental problems in the rapid industrialization of societies because of the considerable harm caused...     

Precise U–Pb zircon–baddeleyite age of the Jinchuan sulfide ore-bearing ultramafic intrusion, western China

The Jinchuan ultramafic intrusion in western China hosts the third-largest magmatic Ni–Cu deposit in the world. The crystallization age of the intrusion has long been debated. Here, we present a U–Pb ID-TIMS zircon age of 831.8 ± 0.6 Ma obtained on thermally annealed and chemically etched zircons from a lherzolite sample. The coexisting baddeleyite in the sample is indistinguishable from the age of zircon. Our new results confirm that the emplacement of the Jinchuan ultramafic intrusion was temporally related to the breakup of the Rodinia supercontinent.     

Alpha-recoil in U–Pb geochronology: effective sample size matters

Displacement of the daughter isotope by a-recoil results in an open system on the nanoscale. For a heterogeneous distribution of U and Th, this redistribution of intermediate and stable daughter isotopes results in subvolumes with a deficit of Pb and others with an excess of Pb. Whether such heterogeneities affect the analyzed U–Pb system depends on: (1) the volume of the analyzed sample, (2) the degree and scale of heterogeneity in the U and Th distribution, and (3) the analytical procedure. Spatial separation of parent and daughter through a-recoil affects the U–Pb systematics of leached samples, where leaching gives access to domains less than 1 µm wide. Anomalous data patterns originating from recoil induced parent-to-daughter fractionation are more important if there are strong heterogeneities in the U and Th distribution, whereby Pb excess appears more pronounced than Pb deficit. Fractionation of parent and daughter elements through selective dissolution of U-REE-rich growth zones in zircon and U-inclusions in columbite, as well as the presence of U–Th-rich micro-inclusions in silicates dated using a step-leaching scheme, may result in anomalous ²⁰⁷Pb _rad/ ²⁰⁶Pb _rad, scattered ²⁰⁶Pb _rad/ ²³⁸U and ²⁰⁷Pb _rad/ ²³⁵U, and reverse discordance. The accumulated structural damage controls the leaching and dissolution behavior, but may also influence the non-stoichiometric element mobilization during sputtering or ablation in the analysis of U-rich samples by SHRIMP and LA-MC-ICP-MS.     

SHRIMP zircon U–Pb geochronology,geochemistry and H–O–Si–S–Pb isotope systematics of the Kanggur gold deposit in Eastern Tianshan,NW China: Implication for ore genesis

The Kanggur gold deposit is located in the southern margin of the Central Asia Orogenic Belt and in the western segment of the Kanggur–Huangshan ductile shear belt in Eastern Tianshan, northwestern China. The orebodies of this deposit are hosted in the Lower Carboniferous volcanic rocks of the Aqishan Formation and mainly consist of andesite, dacite and pyroclastic rocks. The SHRIMP zircon U–Pb age data of the andesite indicate that the volcanism in the Kanggur area might have occurred at ca. 339 Ma in the Early Carboniferous, and that the mineralization age of the Kanggur gold deposit was later than the age of volcanic rocks in the area. Geochemically, the andesite rocks of the Aqishan Formation belong to low-tholeiite and calc-alkaline series and display relative depletions in high field strength elements (HFSEs; i.e. Nb, Ta and Ti). The δ¹⁸O_w and δD_w values vary from − 9.1‰ to + 3.8‰ and − 66.0‰ to − 33.9‰, respectively, indicating that the ore-forming fluids were mixtures of metamorphic and meteoric waters. The δ³⁰Si values of 13 quartz samples range from − 0.3‰ to + 0.1‰ with an average of − 0.15‰, and the δ³⁴S values of 18 sulphide samples range from − 0.9‰ to + 2.2‰ with an average of + 0.54‰. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb values of 10 sulphide samples range from 18.166 to 18.880, 15.553 to 15.635 and 38.050 to 38.813, respectively, showing similarities to orogenic Pb; these values are consistent with those of the andesite from the Kanggur area, suggesting a common lead source. All of the silicon, sulphur and lead isotopic systems indicate that the ore-forming fluids and materials were mainly derived from the Aqishan Formation, and that the host volcanic rocks of the Aqishan Formation probably played a significant role in the Kanggur gold mineralization. Integrating the data obtained from studies on geology, geochronology, petro-geochemistry and H–O–Si–S–Pb isotope systematics, we suggest that the Kanggur gold deposit is an orogenic-type deposit formed in Eastern Tianshan orogenic belt during the Permian post-collisional tectonism.     

U–Pb geochronology and Pb isotope characteristics of the Chahgaz volcanogenic massive sulphide deposit,southern Iran

The Chahgaz Zn–Pb–Cu volcanogenic massive sulphide (VMS) deposit occurs within a metamorphosed bimodal volcano–sedimentary sequence in the south Sanandaj–Sirjan Zone (SSZ) of southern Iran. This deposit is hosted by rhyodacitic volcaniclastics and is underlain and overlain by rhyodacitic flows, volcaniclastics, and pelites. Peperitic textures between rhyodacite flows and contact pelites indicate that emplacement of the rhyodacite occurred prior to the lithification of the pelites. The rhyodacitic flows are calc-alkaline, and show rare earth and trace elements features characteristic of arc magmatism. Zircons extracted from stratigraphic footwall and hanging-wall rhyodacitic flows of the Chahgaz deposit yield concordant U–Pb ages of 175.7 ± 1.7 and 172.9 ± 1.4 Ma, respectively, and a mean age of 174 ± 1.2 Ma. This time period is interpreted to represent the age of mineralization of the Chahgaz deposit. This Middle Jurassic age is suggested as a major time of VMS mineralization within pull-apart basins formed during Neo-Tethyan oblique subduction-related arc volcano-plutonism in the SSZ. Galena mineral separates from the layered massive sulphide have uniform lead isotope ratios of ²⁰⁶Pb/²⁰⁴Pb?=?18.604–18.617, ²⁰⁷Pb/²⁰⁴Pb?=?15.654–15.667, and ²⁰⁸Pb/²⁰⁴Pb?=?38.736–38.769; they show a model age of 200 Ma, consistent with the derivation of Pb from a Late Triassic, homogeneous upper crustal source.     

Cenomanian-? early Turonian minimum age of the Chubut Group,Argentina: SHRIMP U–Pb geochronology

Four new SHRIMP U–Pb zircon ages older than 93 Ma from samples of the two uppermost formations accumulated in two different depocenters (Golfo de San Jorge and Cañadón Asfalto basins) of the Chubut Group in central Argentinean Patagonia, establish a pre-late Cenomanian-? early Turonian age for the group. It also confirms a coeval and comparable evolution of the two depocenters, where distal pyroclastic material was deposited together with fluvial and lacustrine facies.     

Metallogeny of precious and base metal mineralization in the Murchison Greenstone Belt, South Africa: indications from U–Pb and Pb–Pb geochronology

The 3.09 to 2.97 Ga Murchison Greenstone Belt is an important metallotect in the northern Kaapvaal Craton (South Africa), hosting several precious and base metal deposits. Central to the metallotect is the Antimony Line, striking ENE for over 35?km, which hosts a series of structurally controlled Sb–Au deposits. To the north of the Antimony Line, hosted within felsic volcanic rocks, is the Copper–Zinc Line where a series of small, ca. 2.97 Ga Cu–Zn volcanogenic massive sulfide (VMS)-type deposits occur. New data are provided for the Malati Pump gold mine, located at the eastern end of the Antimony Line. Crystallizations of a granodiorite in the Malati Pump Mine and of the Baderoukwe granodiorite are dated at 2,964?±?7 and 2,970?±?7?Ma, respectively (zircon U–Pb), while pyrite associated with gold mineralization yielded a Pb–Pb age of 2,967?±?48?Ma. Therefore, granodiorite emplacement, sulfide mineral deposition and gold mineralization all happened at ca. 2.97?Ga. It is, thus, suggested that the major styles of orogenic Au–Sb and the Cu–Zn VMS mineralization in the Murchison Greenstone Belt are contemporaneous and that the formation of meso- to epithermal Au–Sb mineralization at fairly shallow levels was accompanied by submarine extrusion of felsic volcanic rocks to form associated Cu–Zn VMS mineralization.     

U–Pb Zircon geochronology of the Cambro-Ordovician metagranites and metavolcanic rocks of central and NW Iberia

New U–Pb zircon data from metagranites and metavolcanic rocks of the Schist-Graywacke Complex Domain and the Schistose Domain of Galicia Tras-os-Montes Zone from central and NW Iberia contribute to constrain the timing of the Cambro-Ordovician magmatism from Central Iberian and Galicia Tras-os-Montes Zones which occurred between 498 and 462 Ma. The crystallization ages of the metagranites and metavolcanic rocks from the northern Schist-Graywacke Complex Domain are as follows: (a) in west Salamanca, 489 ± 5 Ma for Vitigudino, 486 ± 6 Ma for Fermoselle and 471 ± 7 Ma for Ledesma; (b) in northern Gredos, 498 ± 4 Ma for Castellanos, 492 ± 4 Ma for San Pelayo and 488 ± 3 Ma for Bercimuelle; (c) in Guadarrama, 490 ± 5 Ma for La Estación I, 489 ± 9 Ma for La Cañada, 484 ± 6 Ma for Vegas de Matute (leucocratic), 483 ± 6 Ma for El Cardoso, 482 ± 8 Ma for La Morcuera, 481 ± 9 Ma for Buitrago de Lozoya, 478 ± 7 Ma for La Hoya, 476 ± 5 Ma for Vegas de Matute (melanocratic), 475 ± 5 Ma for Riaza, 473 ± 8 Ma for La Estación II and 462 ± 11 Ma for La Berzosa; and (d) in Toledo, 489 ± 7 Ma for Mohares and 480 ± 8 Ma for Polán. The crystallization ages of the metagranites from the Schistose Domain of Galicia Tras-os-Montes Zone are 497 ± 6 Ma for Laxe, 486 ± 8 Ma for San Mamede, 482 ± 7 Ma for Bangueses, 481 ± 5 Ma for Noia, 480 ± 10 for Rial de Sabucedo, 476 ± 9 Ma for Vilanova, 475 ± 6 Ma for Pontevedra, 470 ± 6 Ma for Cherpa and 462 ± 8 Ma for Bande. This magmatism is characterized by an average isotopic composition of (⁸⁷Sr/⁸⁶Sr)_485Ma ≈ 0.712, (ε_Nd)_485Ma ≈ ?4.1 and (T_DM) ≈ 1.62 Ga, and a high zircon inheritance, composed of Ediacaran–Early Cambrian (65 %) and, to a lesser extent, Cryogenian, Tonian, Mesoproterozoic, Orosirian and Archean pre-magmatic cores. Combining our geochronological and isotopic data with others of similar rocks from the European Variscan Belt, it may be deduced that Cambro-Ordovician magmas from this belt were mainly generated by partial melting of Ediacaran–Early Cambrian igneous rocks.     

Phanerozoic reactivation of the Archean North China Craton through episodic magmatism: Evidence from zircon U–Pb geochronology and Hf isotopes from the Liaodong Peninsula

The Archean lithospheric root of the North China Craton (NCC) has been considerably eroded and modified by Phanerozoic magmatic processes. Here we investigate the decratonization of the NCC through U–Pb and Hf isotopic analyses of zircons from Cenozoic basalts in the Liaodong Peninsula using ion-probe and MC-ICPMS techniques. The U–Pb zircon geochronology identifies three zircon populations: Precambrian, Paleozoic and Mesozoic. The Precambrian zircons yield ²⁰⁷Pb/²⁰⁶Pb ages of 2275–2567 Ma with a peak at around 2.5 Ga. They define a U–Pb discordia with upper intercept ages of 2447 ± 50 Ma to 2556 ± 50 Ma and a wide range of Hf T_DM ages with a mode at 2.7–2.8 Ga. Our results clearly demonstrate the presence of an Archean lower crust in the Liaodong region. The Paleozoic zircons from the Liaodong region lack the clear internal zoning and are subhedral to rounded in shape, and yield a narrow ²⁰⁶Pb/²³⁸U concordant ages of 419–487 Ma with a weighted mean age of 462 ± 16 Ma. The Mesozoic zircons predominantly show crystallization in the early Cretaceous and yield a relatively large range in ²⁰⁶Pb/²³⁸U ages from 100 to 138 Ma (n = 53) with a peak around 120 Ma. Three samples give indistinguishable weighted mean ²⁰⁶Pb/²³⁸U ages of 120 ± 5 Ma, 120 ± 4 Ma and 121 ± 2 Ma. These early Cretaceous zircons have enriched Hf isotope compositions with ε_Hf(t) values from ?26 to ?16. Our results provide important constraints on episodic magmatism during the Phanerozoic in the Liaodong region, which led to substantial reactivation of the Archean basement of the North China Craton.     

Age of the Marwar Supergroup,NW India:A note on the U–Pb geochronology of Jodhpur Group felsic volcanics

The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.     

In-situ U–Pb geochronology and Hf isotope analyses of the Rayner Complex,east Antarctica

In-situ zircon U–Pb and Hf isotopic analysis via laser ablation microprobe-inductively coupled plasma mass spectrometer (LAM-ICPMS) of samples from Kemp and MacRobertson Lands, east Antarctica suggests that the Kemp Land terrane evolved separately from the rest of the Rayner Complex prior to the ca. 940 Ma Rayner Structural Episode. Several Archaean metamorphic events in rocks from western Kemp Land can be correlated with events previously reported for the adjacent Napier Complex. Recently reported ca. 1,600 Ma isotopic disturbance in rocks from the Oygarden Group may be correlated with a charnockitic intrusion in the Stillwell Hills before ca. 1,550 Ma. Despite being separated by some 200 km, T^Hf_DM ages indicate felsic orthogneiss from Rippon Point, the Oygarden Group, Havstein Island and the Stillwell Hills share a ca. 3,660–3,560 Ma source that is indistinguishable from that previously reported for parts of the Napier Complex. More recent additions to this crust include Proterozoic charnockite in the Stillwell Hills and the vicinity of Mawson Station. These plutons have distinct ¹⁷⁶Hf/¹⁷⁷Hf ratios and formed via the melting of crust generated at ca. 2,150–2,550 Ma and ca. 1,790–1,870 Ma respectively.     

Geochemistry and zircon U–Pb geochronology of the Pulang complex,Yunnan province,China

The Pulang complex is located tectonically at the southern margin of the Yidun–Zhongdian island arc belt in Yunnan province, China, and is closely related to formation of the Pulang copper deposit, which is the largest copper deposit in Asia. The Pulang complex can be divided into three intrusion stages based on contact relationships and petrological characteristics: (1) a first stage of quartz dioritic porphyry; (2) a second stage of quartz monzonitic porphyry; and (3) a third stage of granodioritic porphyry. The crystallization ages of these intrusion stages were determined by single-zircon U–Pb dating, yielding ages of 221.0 ± 1.0, 211.8 ± 0.5, and 206.3 ± 0.7 Ma for the first, second, and third stages, respectively. These dates, integrated with previous geochronological data and field investigations, indicate that the second-stage quartz monzonitic porphyry has a close spatial and temporal relationship with the large Pulang porphyry copper deposit. These age data, geochemical and Sr–Nd isotopic results suggest that the Pulang complex formed in the Indo-Chinese epoch (257 ～ 205 Ma) by multiphase intrusion of a mixture of mantle- and crust-derived magmas.     

U–Pb geochronology and Hf isotope ratios of magmatic zircons from the Iberian Pyrite Belt

A geochronology and Hf isotope study, using laser ablation-ICP-MS analysis of zircon grains, has been conducted to date felsic volcanic rocks from the Portuguese sector of the Iberian Pyrite Belt and to establish possible sources for these rocks. The ages obtained range from the Famennian to the Tournaisian, with the oldest ages reported in the Belt so far being identified in its southwestern part (Cercal area). Results also indicate that within each area, volcanism may have extended for significant periods of time. This suggests that caution is needed in interpreting possible migration trends for the volcanism, as the exact stratigraphic position of the sampled rocks is not always clear. Despite of this, the new data, coupled with previously reported information, suggests that volcanism migrated within the basin from the southwest to the northeast (present day coordinates). Projection from initial zircon ?Hf values towards the depleted mantle evolution curve, via an intermediate reservoir, allows the calculation of Hf protolith model ages that are predominantly Meso-Proterozoic. This is compatible with acid magmas resulting from the fusion of Phyllite–Quartzite (PQ) Formation metasedimentary rocks, which are beneath the volcanic rocks. This is because zircon grains from one PQ Formation sample provided Late Neo-Proterozoic ages and Paleo-Proterozoic to Late Archean U–Pb ages, and the Hf isotope signatures of these zircons can be expected to mix during fusion and result in protolith model ages that would be intermediate between the two U–Pb age populations, as recorded. Further supporting this source for the magmas, the distribution of U–Pb ages of (pre-Variscan) inherited zircon grains in the volcanic rocks is very similar to that shown by the detrital zircon grains from a PQ sample.