Zircon Hf Isotopic Data Research Articles

Petrogenesis and tectonic implications of the Eocene-Oligocene potassic felsic suites in western Yunnan, eastern Tibetan Plateau: Evidence from petrology, zircon chronology, elemental and Sr-Nd-Pb-Hf isotopic geochemistry

In western Yunnan, potassic felsic suites with important Cu mineralization have been interpreted as being genetically associated with the Ailao Shan-Red River (ASRR) shear zone. In this paper, we show that the magmatism is unrelated to the shear zone, but shares many characteristics in common with potassic suites along the Jinsha suture to the north and northwest on the northern Tibetan Plateau, representing a magmatic response to the continued India-Asia convergence since the collision in the early Eocene. These felsic suites include syenite, monzogranite porphyries and granite porphyries. We dated 15 representative samples using zircon U-Pb method that gives a tight emplacement age of ~37–35 Ma. On 45 representative samples, we have done bulk-rock major element, trace element and Sr-Nd-Pb isotope analysis. We use these data, together with zircon Hf isotope data and the literature data on potassic mafic suites in the region to discuss the petrogenesis of these rocks. We conclude that the petrogenesis of the felsic potassic suites is most consistent with a scenario of deep (≥ 40 km) melting of thickened crust. The crustal melting is caused by intrusion and underplating of potassic mafic melts derived from melting of metasomatized mantle lithosphere. The mafic potassic suites in the region result from such mantle melts. Mixing of the mafic melts with the felsic melts explains the syenite and monzogranite porphyries and their extended fractional crystallization gives rise to the granite porphyries. The potassic suites along the Jinsha suture, including those from northern Tibet, western Yunnan and Vietnam, share the same tectonic setting during the Eocene-Oligocene. In response to the continued India-Asia convergence, removal of the lower continental lithospheric mantle triggered by Rayleigh-Taylor convective instability induces asthenosphere upwelling, partial melting of the metasomatized mantle lithosphere. We hypothesize that the eastward migration of the potassic magmatism along the Jinsha suture in the period of Eocene-Oligocene results from eastward thickening and removing of the continental lithospheric mantle along the suture, which, in time and space, correlates with the dischronal subduction of the torn Indian continental slab at ca. 52 Ma along the India-Asia collision zone.

Petrogenesis of the southern Qiangtang mafic dykes, Tibet: Link to a late Paleozoic mantle plume on the northern margin of Gondwana?

AbstractThis study presents 13 new U-Pb zircon ages obtained by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) together with whole-rock geochemical, Sr-Nd isotopic and zircon Hf isotopic data for a mafic dike swarm in the southern Qiangtang area of Tibet. These data provide the basis for a new model of the late Paleozoic evolution of the Tethys. Combined with the results of previous zircon U-Pb dating, the magmatic zircon grains extracted from mafic dikes yield latest Carboniferous to Early Permian ages (317–279 Ma). The geochemistry of the southern Qiangtang mafic rocks indicates the presence of low-Ti (QLT) and high-Ti (QHT) suites. The magmas that formed the QLT suite underwent higher degrees of partial melting (>5%) and display evidence of crustal contamination, whereas the QHT suite was derived from magmas generated by low-degree (1%–5%) partial melting of a garnet-bearing mantle source, with a greater extent of fractional crystallization than the QLT suite, and no evidence of crustal contamination. We propose that the QHT and QLT suites may have been derived from magmas from different parts of a single mantle plume. The formation of the southern Qiangtang mafic dikes (latest Carboniferous to Early Permian; 317–279 Ma) may have been related to the northward drift of the Cimmerian continent from the northern Gondwana margin, which resulted in the opening of the Meso-Tethys Ocean.

Late Mesozoic magmatism in the East Qinling Orogen, China and its tectonic implications

The Qinling Orogen in Central China records the history of a complex geological evolution and tectonic transition from compression to extension during the Late Mesozoic, with concomitant voluminous granitoids formation. In this study, we present results from petrological, geochemical, zircon U-Pb-Lu-Hf isotopic studies on the Lengshui felsic dykes from Luanchuan region in the East Qinling Orogen. We also compile published geochronological, geochemical, and Hf isotopic data from Luanchuan region and present zircon Hf isotopic contour maps. The newly obtained age data yield two group of ages at ∼145 Ma and 140 Ma for two granite porphyries from the Lengshui felsic dykes, with the ∼145 Ma interpreted as response to the peak of magmatism in the region, and the ∼140 Ma as the timing of formation of the felsic dykes. The corresponding Hf isotopic data of the granite porphyries display negative εHf(t) values of –16.67 to –4.61, and Hf crustal model ages (TDMC) of 2255–1490 Ma, indicating magma sourced from the melting of Paleo- to Mesoproterozoic crustal materials. The compiled age data display two major magmatic pulses at 160–130 Ma and 111–108 Ma with magmatic quiescence in between, and the zircon Hf isotopic data display εHf(t) values ranging from –41.9 to 2.1 and TDMC values of 3387–1033 Ma, suggesting mixed crustal and mantle-derived components in the magma source, and correspond to multiple tectonic events during the Late Mesozoic. The Luanchuan granitoids are identified as I-type granites and most of these are highly fractionated granites, involving magma mixing and mingling and crystal fractionation. The tectonic setting in the region transformed from the Late Jurassic syn-collision setting to Early Cretaceous within-plate setting, with E–W extension in the Early Cretaceous. This extension is correlated with the N–S trending post-collisional extension between the North China Craton and Yangtze Craton as well as the E–W trending back-arc extension triggered by the westward Paleo-Pacific Plate subduction, eventually leading to lithospheric thinning, asthenospheric upwelling, mafic magma underplating, and crustal melting in the East Qinling Orogen.

Late Triassic ridge subduction of Paleotethys: Insights from high-Mg granitoids in the Songpan-Ganzi area of northern Tibet

The time of final closure of the Paleotethys Ocean is still hotly debated in particular regarding the Jinsha Ocean in northern Tibet. This study reports new geochronologic, geochemical and zircon Hf isotopic data of six granodiorites-diorites, which intrude the Mid-Late Triassic Songpan-Ganzi complex (SGC). LA-ICP-MS zircon U-Pb analyses of three quartz diorites (214.9 ± 2.2, 211.0 ± 1.3, 205.8 ± 1.4 Ma) and three granodiorites (210.8 ± 2.7, 206.7 ± 3.3, 205.9 ± 3.5 Ma) gave a Late Triassic age range (214.9–205.8 Ma). These granodiorite-diorite rocks have relatively high MgO (up to 9.1%) and Mg# (up to 70.2), Al2O3, Cr, Ni, but low TiO2, and high magnesium andesite/diorite (HMA) chemical signatures with low Sr and Y content, and slight-moderate negative Eu anomaly. Also, the dioritic enclaves and Late Triassic detrital zircons (as young as 208 Ma) were captured by studied rocks. Hf isotope data show overall slight to moderate negative zircon εHf(t) values (−1.97 to −5.76, −4.12 to −6.72) and heterogeneous TDMC ages (1.38−1.61Ga, 1.51−1.68Ga) for quartz diorites and granodiorites respectively, together with other published Hf isotopic data in SGC, are in highly concert with those around ~240 and ~440Ma magmas (as potential sources for SGC turbidites) in east Kunlun orogenic belt. Taken together, the HMA magmas were probably derived from a reaction between subducted marine sedimentary siliceous melts and peridotites from a mantle wedge.The linear distribution of Late Triassic HMAs and their eastward-younging trend (from northern Qiangtang to southern SGC), in combination with the contrasting distribution of volcanic rocks in the northern Qiangtang terrane, lead us to suggest that a slab window opened in the downgoing oceanic crust with two diverse slab angles during oblique subduction. Accordingly, the final closure of the Paleotethys Ocean was later than 205 Ma, and most likely in the end of the Late Triassic to Early Jurassic.

Ages and nature of the protolith of the Tulovchikha metamorphic complex in the Bureya Massif, Central Asian Orogenic Belt, Russia: Evidence from U–Th–Pb, Lu–Hf, Sm–Nd, and 40Ar/39Ar data

The Bureya Massif is located in the eastern segment of the Central Asian Orogenic Belt (CAOB) and its tectonic affinity and Precambrian evolution is highly controversial. Here we present mineralogical, whole-rock geochemical (major and trace elements and Sm–Nd isotopes) and zircon Hf isotopic data, together with zircon geochronological and mica 40Ar/39Ar dating of the biotite and amphibole gneisses from the Tulovchikha metamorphic complex (previously considered as Archean or Paleoproterozoic basement) in the Bureya Massif, in order to investigate their protolith, metamorphic and deformation ages, petrogenesis, and tectonic implications. LA-ICP-MS U–Pb dating of magmatic zircons from the biotite gneiss, the amphibole–biotite gneiss, and the amphibolite yields single zircon age populations cluster at ~950 Ma, ~920 Ma and ~940 Ma, respectively. The narrow zircon age ranges, together with the morphological features of the zircon crystals and the geochemical data, indicate that the studied metamorphic rocks have a magmatic origin and their protoliths were formed in the early Neoproterozoic (i.e., 950–920 Ma). The consistent formation ages further suggest that the Neoproterozoic gabbro–granitic rocks within the Nyatygran Complex in the Bureya Massif probably represent the protolith of the studied metamorphic rocks. The biotite and amphibole-biotite gneisses of the Tulovchikha metamorphic complex yield whole-rock Nd model ages (tNd(DM)) of 2.4–1.5 Ga and Hf zircon crustal model ages (tHf(C)) of 1.7–1.2 Ga, indicating that the precursors of the Tulovchikha Complex gneisses formed from the reworking of Meso–Paleoproterozoic rocks or mixed Neoproterozoic juvenile and Meso–Paleoproterozoic crustal sources. Considering that the Bureya and Jiamusi massifs experienced similar Neoproterozoic magmatic events, we suggest that these massifs form a contiguous crustal unit and share a common geological history. The rocks of Tulovchikha metamorphic complex in the studied area experienced epidote-amphibolite to amphibolite facies metamorphism probably in the early Paleozoic, as evidenced by the 471 ± 19 Ma age of a metamorphic zircon with a low Th/U ratio (<0.1). According to 40Ar/39Ar biotite dating of the biotite gneiss, the Tulovchikha Complex experienced a youngest thermal event at 227 ± 3 Ma. This event may be related to the final closure of the Paleo-Asian Ocean, or may have been caused by the deformation of the blocks of East Asia in connection with the initial stages of the closure of the Mongol–Okhotsk Ocean.

Permian subduction of the Paleo-Pacific (Panthalassic) oceanic lithosphere beneath the Jiamusi Block: Geochronological and geochemical evidence from the Luobei mafic intrusions in Northeast China

The late Paleozoic tectonic evolution of eastern northeast China and, in particular, the Jiamusi Block and its relationship with the Paleo-Pacific (Panthalassic) Ocean are controversial. Here we present petrological, zircon U-Pb age, whole-rock major and trace elements, and zircon Hf isotopic data for Permian (273–260 Ma) subduction-related mafic intrusions from the Luobei region along the western margin of the Jiamusi Block. These intrusions have mineral assemblages of pyroxene, Ca-rich plagioclase, and hornblende, indicating their crystallization from a water-saturated parental magma. The Luobei mafic rocks are calc-alkaline, enriched in large-ion lithophile and light rare earth elements, depleted in high-field-strength elements, and have variable zircon εHf(t) values (−7.7 to +5.0). These geochemical features suggest that their parental magma was probably derived by <10% melting of a spinel-facies mantle wedge metasomatized by variable amounts of sediment-derived melts and fluids from the subducted Paleo-Pacific (Panthalassic) oceanic slab. Crystal fractionation, mineral accumulation, and heterogeneous mantle sources were responsible for the geochemical and zircon Hf isotopic variations of the Luobei mafic intrusive rocks. Based on our results and regional geological data, a broadly N–S-trending magmatic arc that is 302–245 Ma in age and displays a westward younging trend is present in the Jiamusi Block. This suggests that persistent westward subduction of the Paleo-Pacific (Panthalassic) oceanic lithosphere occurred beneath the Jiamusi Block during the latest Carboniferous to earliest Triassic.

Geochemistry of meta-sedimentary rocks associated with the Neoarchean Dagushan BIF in the Anshan-Benxi area, North China Craton: Implications for their provenance and tectonic setting

The Anshan-Benxi area is situated in the northeastern part of the North China Craton (NCC) and consists predominantly of Neoarchean supracrustal rocks and plutons with minor Eoarchean to Mesoarchean rocks. These supracrustal rocks were originally considered to be formed synchronously (∼2.5 Ga) at different localities on an active continental margin. Recently, more detailed petrographic, geochemical, and geochronological analyses showed that the supracrustal strata in the Benxi area (2.56–2.53 Ga) were slightly older than those in the Anshan area (2.53–2.51 Ga), which further indicates that they were formed during opening and closure of the back-arc basin, respectively. However, the Dagushan banded iron formation (BIF) and associated supracrustal rocks in the Anshan area were interpreted to be deposited in Mesoarchean (∼3.10 Ga), which constructs a clear contrast with other supracrustal rocks in the Anshan-Benxi area and renders previous tectonic models controversial.On the basis of detailed field investigations in the Dagushan area, we present in situ zircon U-Pb-Hf isotopic, whole-rock geochemical and Sm-Nd isotopic data of a suite of meta-sedimentary rocks (i.e., meta-arenites, meta-shales, and high-Fe meta-shales), in order to provide constraints on their depositional age, provenance, and tectonic setting. The weighted mean U-Pb ages of the youngest group of detrital zircons for the meta-arenite in the Dagushan area, coupled with the maximum metamorphic age of ∼2.51 Ga in the Anshan-Benxi area, suggest that the Dagushan BIF was deposited between 2.53 and 2.51 Ga. Geochemical features such as the Al2O3/TiO2 and Th/Zr values, and REE patterns suggest that the meta-arenites and meta-shales were mainly derived from felsic igneous sources, whereas the high-Fe meta-shales were predominantly sourced from mafic rocks. The U-Pb age spectrum diagram of detrital zircons within meta-arenites further indicates that the dominant source rocks may be the coeval volcanic rocks in the Benxi area. Our zircon Hf isotopes, coupled with other previously published zircon Hf isotopic data from Neoarchean supracrustal rocks in the Anshan-Benxi area, suggest that major juvenile crustal growth and reworking events occurred at 2.9–2.7 Ga and ∼2.5 Ga, respectively. In all, the Dagushan meta-sedimentary rocks were probably deposited in a back-arc basin on the ancient continental margin.

Cambrian intra–oceanic arc trondhjemite and tonalite in the Tam Ky–Phuoc Son Suture Zone, central Vietnam: Implications for the early Paleozoic assembly of the Indochina Block

The Truong Son and Kon Tum terranes in northeastern Indochina are thought to, respectively, form part of the Indian and Australian margins of Gondwana and separated one another by the Tam Ky–Phuoc Son Ocean during the early Paleozoic. In this paper, we present results of a comprehensive geochronological and geochemical study on a trondhjemite–tonalite suite identified in the Tam Ky–Phuoc Son Suture Zone. LA–ICP–MS zircon U–Pb dating yielded weighted mean 206Pb/238U ages of 518.5 ± 7.1 Ma and 502.1 ± 6.0 Ma for the trondhjemite and tonalite, respectively. These are the oldest magmatic zircons recorded in this area so far. Both rocks consist primarily of plagioclase (oligoclase), quartz, with minor, variable amounts of hornblende and biotite. They have high SiO2, Na2O and Y, but low Al2O3, K2O, Sr and Rb contents, and are characterized by depletion in LREEs with flat HREE patterns. These features are similar to those of typical oceanic plagiogranites. Our new evidences from field geology, geochemistry, and zircon Hf isotopic data, along with previously published data from the Tam Ky–Phuoc Son Suture Zone, suggest that the plagiogranites were originated from extensive fractionation of hydrous basaltic magmas. Furthermore, they were generated in an intra-oceanic arc system above a northward subduction zone within the Tam Ky–Phuoc Son Ocean. The final closure of this ocean took place before the late Silurian, marked by collision of the Truong Son Terrane with the Kon Tum Terrane along the Tam Ky–Phuoc Son Suture Zone to form the Indochina Block. After elimination of the southeastward offset along the Red River shear zone and the clockwise rotation of Indochina relative to South China since the Tertiary, the eastern part of the Tam Ky–Phuoc Son Suture aligns well with the Kuungan Suture on Hainan Island, together they have likely recorded the final assembly of Gondwana in this region.

Contrasting deep crustal compositions between the Altai and East Junggar orogens, SW Central Asian Orogenic Belt: Evidence from zircon Hf isotopic mapping

There are long–standing uncertainties over the deep crustal composition and basement nature of the Chinese Altai and Junggar orogens of the southwestern Central Asian Orogenic Belt (CAOB). Zircon LuHf isotopic tracer techniques applied to granitoids are helpful in distinguishing old from young deep crustal compositions. This study aims to characterize the basement nature (ancient & juvenile) of the Chinese Altai and East Junggar orogens using Hf isotopic mapping of granitoids (510–200 Ma). Zircon Hf isotopic data (18 new and 79 published samples) indicate that the study area can be divided into six Hf isotopic provinces on the basis of TDMC ages: Province I, >1.4 Ga; II, 1.4–1.2 Ga; III, 1.2–1.0 Ga; IV, 1.0–0.8 Ga; V, 0.8–0.6 Ga; and VI, 0.6–0.4 Ga. Provinces I, II, and III occur mainly in the central (units 2 and 3) and southern (unit 4) Altai orogen, and have slightly positive zircon εHf(t) values of +0.5 to +9.1 with slightly old TDMC ages of 1.53–0.81 Ga. Provinces IV and V are mainly distributed in the northern (unit 1) and southernmost (unit 5) Altai orogen, with zircon εHf(t) values of +7.5 to +11.1 and young TDMC ages of 0.84–0.60 Ga. In contrast, Province VI (East Junggar orogen) has zircon εHf(t) values of +11.6 to +14.9, with much younger TDMC ages of 0.59–0.35 Ga, except for the small Taheir area with a negative εHf(t) value of −2.5 and an older TDMC age of 2.5 Ga. There is a sharp contrast between the deep crustal compositions of the Altai and Junggar orogens, which are ancient in central Altai and relatively juvenile in East Junggar. This confirms that significant Neoproterozoic–Phanerozoic continental crustal growth occurred in the southern Altai and Junggar orogens, with juvenile crust occupying ~78% of the study area, and that the CAOB is a site of significant Phanerozoic continental growth. The distribution of juvenile and ancient crust in the Altai and East Junggar orogens provides new evidence for the tectonic division of the two orogens by the Erqis fault zone, and explains the heterogeneity of crustal growth in the southwestern CAOB.

A Palaeoproterozoic basement beneath the Rangnim Massif revealed by the in situ U–Pb ages and Hf isotopes of xenocrystic zircons from Triassic kimberlites of North Korea

AbstractIn situ U–Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U–Pb age spectrum of the zircons has a prominent population at 1.9–1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ϵHf(t) values (−9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2σ), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9–1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao–Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton.

Petrogenesis and tectonic implications of Late Mesoproterozoic A1- and A2-type felsic lavas from the Huili Group, southwestern Yangtze Block

AbstractThis paper presents new LA-ICP-MS zircon U–Pb chronology, whole-rock geochemical and zircon Hf isotopic data for the felsic lavas of the Huili Group from the southwestern Yangtze Block. LA-ICP-MS zircon U–Pb dating shows that these rocks were emplaced in Late Mesoproterozoic time (∼1028 to 1019 Ma). Relative to typical I-type and S-type granitoids, all the samples are characterized by low Sr and Eu, and high high-field-strength element contents, highTFeO/MgO, enriched rare earth element compositions and negative Eu anomalies, indicating that they share the geochemical signatures of A-type granitoid. They can be further divided into two groups: Group I and Group II. Group I are A1-type felsic rocks and were produced by fractional crystallization of alkaline basaltic magmas. The Group II felsic lavas belong to the A2-type and were derived by partial melting of a crustal source with mixing of mantle-derived magmas. Both Group I and Group II felsic lavas may erupt in a continental back-arc setting. The coexistence of A1- and A2-type rocks in the southwestern Yangtze Block suggests that they can occur in the same tectonic setting.

Early Precambrian tectono-thermal events in Southern Jilin Province, China: implications for the evolution of Neoarchean to Paleoproterozoic crust in the northeastern North China Craton

The early Precambrian basement of the North China Craton, China, records a complex history during the Neoarchean and Paleoproterozoic. Southern Jilin Province is one of the best regions to evaluate the early Precambrian crustal growth of the Eastern Block of the North China Craton. We herein present new zircon cathodoluminescence images, U–Pb dates, trace element and Lu–Hf isotope data for three late Neoarchean tonalitic–trondhjemitic–granodioritic (TTG) gneisses and one Paleoproterozoic mafic dyke from Tonghua region, southern Jilin Province. These results lent convincing support to the occurrence of multiple tectono-thermal events in southern Jilin Province during the Archean and Paleoproterozoic, and shed light on the formation and evolution of continental crust in the northeastern Eastern Block. Zircon LA–ICP–MS U–Pb isotopic analyses indicated three episodes of magmatism. Inherited (or captured) zircons with ages of ca. 2.6 Ga provided strong evidence for a pre-2.5 Ga magmatic event in this region. The second magmatic episode occurred at 2556–2522 Ma, as evidenced by extensive exposures of TTG gneisses. The third episode occurred at ca. 2200 Ma and is recorded by several mafic dykes that intruded the Archean TTG gneisses. Metamorphic zircons yielded consistent ages of 2493–2465 Ma, indicating a regional metamorphic event immediately after the late Neoarchean magmatism in southern Jilin Province. Zircon Hf isotope data of the TTG gneisses indicated that the main phase of crustal growth occurred in the late Neoarchean, with a minor input of Mesoarchean continental crustal materials. The combined geochronological, geochemical, and geological data suggested that the three episodes of crustal growth in the northeastern Eastern Block occurred at 2.8–2.7, 2.6–2.5, and 2.2 Ga.

Origin of the Mo-bearing Xiaoshuijing Syenogranite in the Tengchong Terrane, SW China

The Xiaoshuijing Syenogranite is the host of Mo mineralisation recently discovered in the Tengchong Terrane of southwestern China. Here, we present new zircon U-Pb ages and molybdenite Re-Os ages, whole-rock geochemical data, and zircon Hf isotopic data for the Xiaoshuijing Syenogranite hosting disseminated Mo mineralisation. The syenogranite’s mineralogical and geochemical characteristics indicate it is a high-K, alkaline, and peraluminous granite. LA-ICP-MS analysis of zircon yields an age of 65 ± 1 Ma (n = 14, MSWD = 2.1), and yields negative zircon εHf(t) values ranging from −18.23 to −12.92, interpreted to have a crustal source. The Re-Os Mo age of 64 ± 2 Ma (n = 4, MSWD = 2.2) for the mineralisation is the same as the syenogranite’s age, within error. The geochemistry also indicates that the syenogranite is related to a thickened crust resulting from the eastward subduction of the Neo-Tethyan oceanic lithosphere shortly before the collision of the Indian and Eurasian continental crusts.

The Diaoquan Ag-Cu polymetallic skarn mineralization in central North China Craton: Timing, source and genetic model

The North China Craton (NCC) has been the focus of investigations on metallogeny in relation to craton destruction. The Diaoquan Ag-Cu polymetallic skarn mineralization is one of the large Ag deposits in central NCC. Here we present new mineralogical, geochronological and geochemical data from this deposit with the objective to gain an insight into the magmatic hydrothermal processes in relation to decratonization. The timing of polymetallic mineralization in this deposit is constrained as ca. 130 Ma by phlogopite Ar-Ar and molybdenite Re-Os dating. The physico-chemical conditions of the magmatic evolution estimated from amphibole, biotite, magnetite-ilmenite mineral thermobarometer indicate that the monzonite and porphyritic granite magma developed in a magma chamber at a palaeoburial depth of 2–3.3 km, and was subsequently emplaced at 1–2 km palaeodepth. The oxygen fugacity conditions were relatively high (>ΔNNO + 1.6 buffer) in the early stage and rapidly dropped (<ΔFMQ buffer). The major and trace element features suggest magma mixing as a possible mechanism that generated the different intrusions. Sr-Nd-Pb and zircon Hf isotope data indicate that lower crust is the major source of the magma and that part of metallogenic elements might have been sourced from mantle-derived components. We constructed the magmatic hydrothermal system as follows: (1) mafic magma formed by the partial melting of thinned mantle lithosphere; (2) the mafic magma underplating resulted in the partial melting of the lower crust, and generated granitic magma; (3) mixing of the mafic and felsic magmas generated the intermediate magma; (4) ore-forming fluids from the magma chamber migrated into the contact zone through fractures, resulting in Ag-Cu mineralization by skarnization; and (5) Mo-bearing fluid separated from the granite magma deposited the molybdenite in the inner contact zone.

U-Pb geochronology of Paraná volcanics combined with trace element geochemistry of the zircon crystals and zircon Hf isotope data

The Paraná volcanic province is a window into mantle and crustal processes in the Cretaceous. The variability and complexity of this province can be determined through the study of minerals. An integrated study of zircon from Paraná lavas (one high-Ti basalt, one low-Ti andesite, one high-Ti rhyodacite and one high-Ti andesite sill) was achieved using backscattered electron imaging, sensitive high resolution ion microprobe (SHRIMP-IIe) for U-Pb geochronology, and laser ablation inductively coupled mass spectrometer (LA-ICPMS) to determine the Lu-Hf isotopes and the trace-element compositions. U-Pb-Hf and trace-element data indicate that zircon crystallized from the magma at approximately 134 Ma. This South American large igneous province originated from the mantle and was contaminated by crust either in the mantle or during ascent and crystallization of magma. Contaminant continental crust had Precambrian age. Trace elements point to a new compositional field for zircon, different from other types of provinces. Examination of volcanic zircon improves our understanding of age and contamination of the Paraná volcanics.

Structural setting and detrital zircon U–Pb geochronology of Triassic–Cenozoic strata in the eastern Central Pamir, Tajikistan

Abstract Integration of new geological mapping, detrital zircon geochronology, and sedimentary and metamorphic petrography south of the Muskol metamorphic dome in the Central Pamir terrane provides new constraints on the evolution of the Pamir orogen from Triassic to Late Oligocene time. Zircon U–Pb data show that the eastern Central Pamir includes Triassic strata and mélange that are of Karakul–Mazar/Songpan–Ganzi affinity and comprise the hanging wall of a thrust sheet that may root into the Tanymas Fault c. 35 km to the north. The Triassic rocks are unconformably overlain by Cretaceous strata that bear similarities to coeval units in the southern Qiangtang terrane and the Bangong Suture Zone of central Tibet. Finally, Oligocene or younger conglomerate and interbedded siltstone, the youngest documented strata in the Pamir Plateau proper, record an episode of juvenile magmatism at c. 32 Ma, which is absent in the extant rock record and other detrital compilations from the Pamir but overlaps in age with ultrapotassic volcanic rocks in central Tibet. Zircon Hf isotopic data from the Oligocene grains ( ε Hf (t) ≈ +9.6) suggest a primary mantle contribution, consistent with the hypothesis of Late Eocene lithospheric removal beneath the Pamir Plateau.

Genesis of Huoqiu banded iron formation (BIF), southeastern North China Craton, constraints from geochemical and Hf-O-S isotopic characteristics

The Huoqiu iron deposit is one of the few Superior-type BIF ore fields in China. To clarify the genesis of Huoqiu BIFs, we give out the geochemical and O-S isotopic data of the BIF samples and zircon Hf isotopic data of the wall-rock. The Huoqiu BIFs show dominant composition of SiO2 + Fe2O3T, and varying contents of Al2O3, MgO, CaO, Rb, Sr, Zr and Hf, suggesting their formation mainly through chemical precipitation and incorporation of terrigenous felsic clastics. Shale-normalized rare earth element patterns of the BIF samples show the features characteristic of other Archean and Paleoproterozoic BIFs, with HREE enrichment relative to LREE, positive La and Eu anomalies, and superchondritic Y/Ho ratios comparable to modern seawater. Positive Eu anomalies are attributed to an imprint of high-temperature hydrothermal fluids. None to negative Ce anomaly shown by the BIFs imply the Huoqiu BIFs was precipitated from the mildly oxidized seawater in a nearshore setting. The quartz separated form Huoqiu BIF has δ18OV-SMOW values of 11.8‰–14.8‰, within the extent of the siliceous rocks deposited from high-temperature hydrothermal. The δ34S values of pyrite grains vary from −2.84 to +4.38‰, which is similar as the sulfur derived from mixtures between mantle fluids and sediments; The Δ33S values varied from −0.08‰ to +1.03‰, imply that the Huoqiu BIFs deposited distally from the volcanic center. The Hf model ages of these detrital zircons from the wall rock give three prominent peak at 3.1–3.0 Ga, 2.9–2.7 Ga and 2.5 Ga, respectively, it suggest that there were three episodes of the crust growth in the Huoqiu area. Integrated these data with the pioneering studies on the Huoqiu BIFs and wall rocks, we confirmed that the Huoqiu BIFs were sourced from the high-temperature hydrothermal related with the volcanics and precipitated from the mildly oxidized seawater in a nearshore setting and distally from the volcanics at 2.5 Ga.

Geochemical and Isotopic Characterization of Middle Eocene Hybrid Magmatism in the Gangdese Belt (Tibet) and Its Ancient Indian Crustal Fingerprint

AbstractWe present new geochemistry, geochronology, whole-rock Sr-Nd-Pb, and zircon Hf isotopic data from the Zhongba pluton in the western part of the Gangdese magmatic belt (GMB) and discuss its ...

Late Carboniferous–Early Permian high- and low-Sr/Y granitoids of the Xing'an Block, northeastern China: Implications for the late Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt

This study presents new zircon U-Pb geochronological, whole-rock geochemical, and zircon Hf isotopic data along with regional geological observations for five late Paleozoic granitic plutons within the Xing'an Block of northeastern China. These data provide insights into the petrogenesis of these granitoids and the late Paleozoic tectonic evolution of the region. The geochronological and geochemical data indicate that the intrusions were emplaced during two separate periods, with the resulting granites having distinct geochemical features. The early Late Carboniferous (321–310 Ma) granitic Lizishan (LZS), Xiaonangou (XNG), and Dabeigou (DBG) plutons have high Sr/Y values (33.15–126.73), with low concentrations of Y and heavy rare earth elements (HREE), indicating adakitic affinities. However, the XNG granodiorites contain higher concentrations of MgO, Cr, and Ni, and have higher Mg# values (57–59) than the other plutons. The latest Carboniferous–Early Permian (301–296 Ma) granitic Weilegesi (WLGS) and Wuyi (WY) plutons are high-K calc-alkaline, with low Sr/Y ratios (0.18–24.15), and show petrological and geochemical characteristics of I-type granites. In addition, the magmatic zircon crystals within these plutons yield positive εHf(t) values (+4.1 to +12.9) and juvenile two-stage model (TDM2) ages (1056–499 Ma). The timing of emplacement and geochemical and isotopic compositions of the LZS and DBG granitoids are indicative of derivation from magmas generated by the partial melting of thickened lower crustal material, whereas the XNG granitoids were most likely formed from magmas generated by the partial melting of delaminated lower crustal material that subsequently interacted with mantle material during ascent. The latest Carboniferous–Early Permian low-Sr/Y granitoids may have formed from magmas generated by the partial melting of a dominantly juvenile amphibolite-facies crustal source under relatively low-pressure conditions, with these magmas subsequently undergoing variable degrees of fractional crystallization. Combining these new data with the results of previous research indicates that the terminal collision between the Xing'an and Songliao blocks occurred between the late Early and early Late Carboniferous, and the voluminous Late Carboniferous to Early Permian granitoids in the Xing'an Block are most likely related to post-collisional delamination.

Geochemistry of Early Cretaceous volcanic rocks in the Northeastern Great Xing’an Range, northeast China and implication for geodynamic setting

ABSTRACTThe mechanism that triggered large-scale Late Mesozoic magmatism in the northeastern Great Xing’an Range (NE GXAR) is strongly controversial. In this paper, we present whole rock geochemistry and zircon trace element, U-Pb and Hf isotopic data on the volcanic rocks in the Longjiang and Guanghua formations in the northeastern Xing’an Block. Zircons with ages of 120–119 Ma indicate that these volcanic rocks were formed in the Early Cretaceous. Combined with previous data, it is clear that volcanic rocks in the NE GXAR erupted between 128 and 108 Ma. The andesite samples of the Longjiang Formation show high contents of Al2O3, CaO, and MgO, significant negative Nb, Ta, and Ti anomalies; εHf (t) values of zircons from the andesite sample vary from +4.13 to +7.67, indicating an enriched mantle source. The rhyolites of the Guanghua Formation show high SiO2 and K2O concentrations, low P2O5, MgO, Cr, and Ni contents and Mg# values. The positive εHf (t) values (+5.72 to +10.58) with two-stage Hf model ages ranging from 939 to 701 Ma indicate that the rhyolites are derived from the partial melting of basaltic lower crust. Combined with the regional geological evolution, we conclude that the generation of the Early Cretaceous volcanic rocks in the NE GXAR might be triggered by the dehydration, disintegration, and foundering of the Mongol-Okhotsk Oceanic flat-slab and the subsequent upwelling of the asthenosphere.