Lu Hf Isotopic Studies Research Articles

Petrogenesis and Geodynamic Mechanisms of Porphyry Copper Deposits in a Collisional Setting: A Case from an Oligocene Porphyry Cu (Au) Deposit in Western Yangtze Craton, SW China

The Xifanping deposit is a distinct Cenozoic porphyry Cu (Au) deposit located in the Sanjing porphyry metallogenic belt 100–150 km east of the JinshajFiang fault in the western Yangtze craton. We present new zircon U–Pb–Lu–Hf isotopic studies and geochemical data of the ore-bearing quartz monzonite porphyry from the Xifanping deposit to determine their petrogenesis and geodynamic mechanisms. LA–ICP–MS zircon U–Pb dating yielded precise emplacement ages of 31.87 ± 0.41 Ma (MSWD = 0.86) and 32.24 ± 0.61 Ma (MSWD = 1.8) for quartz monzonite porphyry intrusions, and 254.9 ± 5.1 Ma (MSWD = 1.7) for inherited zircons of the monzonite porphyry. The ore-bearing monzonite porphyry is characterized by high-K calc–alkaline to shoshonite and peraluminous series, relatively enriched in light over heavy REEs, with no distinct Eu anomalies, as well as enrichment in LILEs and depletion of HFSEs, with adakitic affinities. The zircon Lu–Hf isotope data ranged from εHf(t) values of −2.94 to +3.68 (average −0.47) with crustal model (TDM2) ages ranging from 0.88 to 1.30 Ga, whereas the inherited zircons displayed positive εHf(t) values ranging from +1.83 to +7.98 (average +5.82), with crustal model (TDM2) ages ranging from 0.77 to 1.17 Ga. Results suggest that the Xifanping porphyry Cu (Au) deposit is related to two periods of magmatic activities. Early magmas were generated from the Paleo-Tethys oceanic subduction during the Late Permian. The subsequent porphyry magma was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by the continental collision between the Indian and Asian plates in the Cenozoic. The deep magmas and late hydrothermal fluids took advantage of the early magma transport channels along tectonically weak zones during the transition from an extrusive to an extensional–tensional tectonic environment. Early dikes from remelted and assimilated crust contributed to the two age ranges observed in the porphyry intrusions from the Xifanping deposit. The juvenile lower crust materials of the early magmatic arc were potential sources of the Cenozoic porphyry magmas, which has significant implications for mineral exploration and the geological understanding of porphyry Cu deposits in this region.

Petrogenesis and Tectonic Implications of the Qulihai Pluton in the Northern Margin of the Yili Block, NW China

Abstract Despite extensive research work that has been done, whether the northern margin of the Yili Block (YB) is still an active continental margin during the early Carboniferous period is still in debate. Herein, we conducted zircon U–Pb geochronology, geochemistry, and zircon Lu–Hf isotope studies on the Qulihai pluton in the northern margin of the YB to constrain the petrogenesis and dynamic process. The Qulihai pluton is a granitoid complex that is composed of quartz diorite, quartz monzonite, and syenogranite. The zircon U–Pb dating results revealed that the pluton was formed and emplaced between 346 and 342 Ma. The three different Qulihai pluton rock types had comparable εHf(t) values, ranging from +3 to +8. The corresponding two-stage model ages of 817–1182 Ma indicated their potential derivation from the Meso-Neoproterozoic juvenile crust. The Qulihai pluton typically features medium-to-high SiO2, K2O, and Al2O3 contents and low MgO and Fe2O3T contents. The quartz diorite and quartz monzonite samples had Mg# values of 43–47, indicating the input of mantle-derived melts in the source area. In contrast, the source region of syenogranite was purely crustal material. The Qulihai pluton is mainly characterized as strong metaluminous moderate-to-high-K cal-alkaline rocks of the I-type granite series, which are enriched in large-ion lithophile elements and depleted in high field strength elements while exhibiting active continental margin island arc magmatism. Our findings, combined with the comprehensive analysis of previous studies, suggest that the Qulihai pluton formation resulted from the subduction of the North Tianshan oceanic crust beneath the YB during the early Carboniferous period, contemporary with the tectonic regime transition from subduction advance to subduction retreat.

Magmatic evolution of the Schiel Alkaline Complex, Bushveld large igneous province, South Africa

The Paleoproterozoic Schiel Alkaline Complex (SAC) in the Limpopo Belt is a composite pluton that coevally formed with the layered intrusion of the Bushveld large igneous province. The SAC is mainly composed of alkaline felsic rocks, pyroxenite, gabbro, syenodiorite/−gabbro, and minor carbonatite and gabbroic dikes. Here we present a new geochemical, geochronological, and isotopic study of the felsic and (ultra)mafic rock suites of the western SAC. The whole rock SmNd isotope study of the felsic rocks revealed εNd2059 Ma values between −6.5 and − 3.8, while those of the syenodiorite/−gabbros and gabbros vary from −7.9 to −8.8, and − 4.3 to +1.1, respectively. The pyroxenites have εNd2059 Ma values of +7.4 to +2.7. The LuHf isotope study displays εHf2059 Ma values of −15.9 to −9.0 for the syenites, alkali granites and syenodiorite/−gabbros, and significantly higher εHf2059 Ma of −3.1 to +3.4 for the gabbros. LA-SF-ICPMS UPb zircon dating yields 2079 ± 10 Ma and 2088 ± 30 Ma for the syenodiorite/−gabbros, and 2086 ± 51 Ma and 2107 ± 30 Ma for the gabbros. In conjunction with published data from the eastern SAC, we propose a close petrogenetic link between the mafic and felsic rocks of the SAC. The positive εNd and εHf values of the pyroxenite and gabbro favor a depleted mantle source, while variable εNd and εHf values, and trace element ratios of the gabbros are ascribed to crustal contamination during magma ascent. The felsic rocks, however, mainly formed by fractional crystallization from the gabbros as revealed by major and trace element correlation trends, isotopic data and thermodynamic modelling.

Petrogenesis and Geodynamic Significance of the Early Triassic Nanpo Adakitic Pluton of the Luang Prabang-Loei Tectonic Belt (Northwestern Laos) in the East Tethys Domain: Constraints from Zircon U-Pb-Hf Isotope Analyses and Whole-Rock Geochemistry

Adakites are magmatic rocks with specific geochemical characteristics and specific dynamics that provide important clues to understanding the magmatic-tectonic evolution of orogenic belts. We studied the Early Triassic Nanpo adakitic pluton of the Luang Prabang-Loei tectonic belt in the Eastern Tethys domain (Laos Sarakan) using detailed petrological, zircon U-Pb chronological, whole-rock geochemical, and zircon Lu-Hf isotope studies to constrain their petrogenesis. The rocks are predominantly diorites and granodiorites with Early Triassic zircon U-Pb emplacement ages ranging from 247.9 ± 1.0 to 249.0 ± 2.4 Ma. Moderate SiO2 (56.26–65.95 wt%) and Na2O (3.24–5.00 wt%) contents, with Na2O/K2O values between 1.76 and 2.51 and A/CNK values between 0.81 and 0.94, indicate that the rocks belong to the metaluminous calc-alkaline rock series. The high Sr content (590–918 ppm), low Y (6.30–11.89 ppm) and Yb (1.99–3.44 ppm) contents, intermediate Mg# (42–50) values, and high Sr/Y and (La/Yb) N ratios (Sr/Y = 24–41, (La/Yb) N = 6.84–13.8) are typical for adakites. Zircon Hf isotope analysis shows a significant variation in the εHf(t) values (6.7–12.0), with a mean value of 9.4 and a TDM2 of 512–845 Ma. Geochemical evidence indicates that the Nanpo adakitic rock was formed by the partial melting of the thickened lower crust in the plate-breaking environment and has an important contribution to the underplated mantle-derived magma. We propose that the Early Triassic adakites in the Luang Prabang-Loei tectonic belt formed during the transition from subduction to a continental collision, and the mixing of crust- and mantle-derived magmas is the main mechanism for the growth of continental crust in the Paleo-Tethys orogenic belt of southeastern Asia.

Identification of the early cretaceous granitic pluton and tectonic implications in the middle gangdese belt, southern tibet

The Gangdese magmatic belt of southern Tibet is an ideal place to study Neo-Tethyan subduction, continental crustal growth and reworking. However, there are still controversies with regard to the evolution of the Neo-Tethys Ocean, the magma source and the detailed diagenetic processes of igneous rocks in the Gangdese belt. The Early Cretaceous magmatic exposures are sporadic in the Gangdese magmatic belt. Thus the finding of the new exposure is key to understanding the scenarios of the Neo-Tethys Ocean and geological background of southern Tibet during the Early Cretaceous. In this contribution, we undertook systematic geochronology, whole-rock geochemistry and zircon Lu-Hf isotopic studies on a newly identified granitic pluton in the middle Gangdese belt (Quesang area), southern Tibet. The results show that zircon U-Pb dating of three representative samples yielded a weighted age of 120 ± 1.4 Ma, 117.3 ± 2.5 Ma and 114.0 ± 1.3 Ma, respectively, which indicate the emplacement and crystallization age belonging to the Aptian stage of the Early Cretaceous in response to the northward subduction of the Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane. In situ zircon Lu-Hf isotopic analyses indicate that ƐHf(t) values of the studied granitic pluton are predominantly positive ranging from 7.2 to 11.4, and one zircon shows negative ƐHf(t) value (−6.26), implying that a small amount of ancient continental crustal materials might have participated in the magma evolution. Geochemically, the granite samples are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in heavy rare earth elements (HREE), indicating arc-type geochemical characteristics or subduction-related tectonic setting. In addition, combined with mineral assemblages, zircon Lu-Hf isotopic features and low molar Al2O3/(CaO+Na2O+K2O) (A/CNK) ratios of 0.91–1.10, the studied samples show a close affinity with I-type granites. Moreover, zircon oxygen fugacity results show that Ce4+/Ce3+ values range from 185 to 12, with a mean value of 78, indicating a low oxygen fugacity setting similar to the Chile ore-barren granitic plutons. In combination with published data, we argue that the Gangdese magmatic belt may have developed continuous magmatism (145–105 Ma), and the notion of magmatic lull might deserve more consideration during the Early Cretaceous. In this study, the Early Cretaceous granitic pluton might be the result of the northward subduction of Neo-Tethys oceanic lithosphere beneath the Lhasa terrane at a normal angle.

Two-stage Cu[sbnd]Pb[sbnd]Zn mineralization of the Baoshan deposit in southern Hunan, South China: Constraints from zircon and pyrite geochronology and geochemistry

The Baoshan CuPbZn deposit is one of the representative polymetallic deposits in the middle of the Nanling Range, the western part of the Qin–Hang ore belt. In order to better understand the magmatic activity (granodiorite porphyry and porphyritic granodiorite) and mineralization in the Baoshan deposit, in situ UPb and LuHf isotope studies of zircons and trace element compositions of two generations of pyrite (ore stage: Py I and post-ore stage: Py II) have been carried out. This constrains the geochronology, magma source, fluid composition, and the origin of the ore-forming materials. The zircon UPb dating results from two types of intrusions show two geochronological populations: (i) ~180 Ma for the Cu (PbZn) mineralization that is related to the porphyritic granodiorite, and (ii) ~160 Ma for the CuPbZn mineralization which is associated with the granodiorite porphyry. The similar REE patterns, Hf/U, Nb/Ta, and Y/Ho ratios along with Hf isotopic characteristics of both granite types indicate that these rocks were sourced from the partial melting of lithospheric mantle and lower crust. Zircons from the granodiorite porphyry have higher Nb, Ta, Lu, and Hf contents, but lower Ti contents and Th/U ratios than those from the porphyritic granodiorite, suggesting that the magma-forming granodiorite porphyry had lower temperature, higher oxygen fugacity, and probably experienced strong crystal fractionation. Py I and Py II are associated with the porphyritic granodiorite and are related to the mineralization that occurred at ~180 Ma. The composition of pyrite in the two stages indicates the contribution of granite and limestone to mineralization. The higher contents of metals (Cu, Pb, Zn, Bi, Ag, except Co and Ni) in Py I than in Py II indicate the cooling and mixing process of ore-forming fluid with meteoric water. The geochemical characteristics of the pyrite generations and UPb dating of zircons suggest that the small-scale mineralization occurred at ~180 Ma under a relatively high-temperature and lower oxidized magmatic environment, whereas the major metallogenic event occurred at ~160 Ma under a low-temperature, medium oxidized, and strongly fractionated magmatic environment. This study reveals that the multi-stage magmatic and mineralization processes mainly occurred during the Early to Late Jurassic in South China.

Geochemical, geochronological and isotopic studies of the Taishanmiao batholith and the Zhuyuangou Mo deposit it hosted, Qinling, China

The Qinling Orogen is well known for its huge Mo resource. The porphyry Mo deposits are associated with small granite porphyries, albeit great batholiths accommodate limited Mo mineralization. In this study, detailed geochemical, isotopic, and geochronological studies were carried out to constrain the petrogenesis of the Taishanmiao batholith and time framework of magmatism and associated Mo mineralization at Zhuyuangou. Zircon geochronology reveals gradually decreasing emplacement ages, from 124.8 ± 1.0 Ma for the medium- to coarse-grained syenogranite, through 122.8 ± 1.4 Ma for fine- to medium-grained syenogranite, to 115.1 ± 0.95 Ma for porphyritic syenogranite. The last two phases hosted the Zhuyuangou Mo mineralization with a molybdenite Re-Os isochron age of 117.7 ± 1.0 Ma. Major and trace element features support highly fractionated I-type affinity for Taishanmiao. Zircon Lu-Hf isotopic studies yield εHf(t) values of −19.6 − -8, and two-stage Hf model ages (TDM2) of 1679–2408 Ma. It thus supports ancient continental crust, especially Taihua Supergroup and Xiong'er Group, as the primary source. Compared to the source rock, the low Mo concentrations of the batholith are attributed to the massive fluid flux that contributes to the formation of the Zhuyuangou and Donggou deposits. Small porphyries can effectively concentrate exsolved fluids and metal compared with great batholith. Their shallow emplacement depths result in greater temperature/pressure/composition gradient with the wall rocks, higher cooling rate, more fractures or even breccia, and fluid boiling and mixing, facilitating intensive hydrothermal alteration and mineralization.

НОВЫЙ ВЗГЛЯД НА СТРАТИГРАФИЮ СЕЛЕМДЖИНСКОГО И ТОКУРСКОГО ТЕРРЕЙНОВ МОНГОЛО-ОХОТСКОГО ПОЯСА: РЕЗУЛЬТАТЫ U-Pb, Lu-Hf, Sm-Nd ИЗОТОПНЫХ ИССЛЕДОВАНИЙ

Results of U-Pb and Lu-Hf isotopic studies on detrital zircons from metasedimentary rocks in the eastern part of the Selemdzha and Tokur terranes of the Mongol-Okhotsk belt and Sm-Nd isotopic data for whole-rocks are in complete contradiction with existing ideas about the stratigraphy of the region under consideration and indicate the need to revise the traditional principles of mapping within the belt. Two types of deposits have been established, differing in Sm-Nd isotopic characteristics of whole-rocks and Lu-Hf isotopic composition of detrital zircons. Deposits of different types are involved in the formation of the two opposing accretion systems: in front of the Siberian Craton margin (type I) and the Amur superterrane (type II). Among type I deposits, discrete groups are distinguished that differ in the lower age limit: 553–498 Ma, Late Ediacaran-Cambrian; ~373 Ma, Upper Devonian; 333–327 Ma, Upper Mississippian; ~304 Ma, Pennsylvanian. The deposits of tectonic-stratigraphic units show a general pattern of younging from north to south. Thus, we observe a structure typical of accretionary wedge-shaped terranes with a rear part in the north and a frontal part in the south. Tectonic-stratigraphic units formed by type I deposits and previously considered part of the Selemdzha and Tokur terranes, apparently, are components of the Galam terrane of the accretionary wedge.

ИСТОЧНИКИ КЛАСТИЧЕСКОГО МАТЕРИАЛА И УСЛОВИЯ НАКОПЛЕНИЯ ОСАДОЧНЫХ ПОРОД ДАУРСКОЙ СЕРИИ АРГУНСКОГО КОНТИНЕНТАЛЬНОГО МАССИВА

The paper presents the results of geochemical and isotopic-geochemical (Sm-Nd) studies of the Upper Riphean (?) (in the Stratigraphic Scale of Russia) sedimentary rocks of the Urulungui and Dyrbylkey formations of the Daur Series in the Argun continental Massif, as well as U-Th-Pb and Lu–Hf isotopic studies of detrital zircons from these formations. Rocks of the Urulungui and Dyrbylkey formations differ significantly in mineral composition and content of the main elements, which is probably due to the degree of chemical weathering of the source rocks. Analysis of concentrations of trace elements in sedimentary rocks of the Urulungui and Dyrbylkey formations enabled to establish that they were formed in a subduction-related setting. The presence of conglomerate-breccias, conglomerates, gravelstones, fragments of igneous and volcanic rocks, a weak degree of roundness of clastic material, as well as abundant Neoproterozoic detrital zircons in the formations is evidence of tectonic and igneous activities in the region during sedimentation. Sedimentary rocks of the Urulungui Formation are characterized by two-stage model ages TNd(DM2) = 2.0–2.1 Ga, and the Dyrbylkei Formation – TNd(DM2) = 1.6–1.8 Ga according to the results of Sm-Nd isotopic-geochemical studies. The abundant Neoproterozoic zircons in sandstones of the Urulungui and Dyrbylkey formations suggest that Neoproterozoic igneous rocks widely developed within the western Argun continental Massif were the main source of clastic materials. At the same time, the presence of Early Precambrian detrital zircons is evidence that Early Precambrian rocks were also present in the source area. However, Early Precambrian igneous and metamorphic associations whose age would be reliably determined from geochronological data have not yet been found so far within the Argun continental Massif, and thus it is not out of the question that rocks of the Daur Series form a «detached block» intruded in the Argun Massif.

Recognition of Late Carboniferous arc‐related volcanic rocks from Ongniud Banner, southeastern Inner Mongolia: Evidence of southward subduction and implication of closure time for Palaeo‐Asian Ocean

Newly recognized Late Carboniferous volcanic rocks occur in Ongniud Banner on the northern margin of the Sino‐Korean palaeoplate, including rhyolite, dacite, and related volcaniclastic. The volcanic rocks have for a long time been considered to form in the Early Permian. Our new LA‐ICP‐MS U–Pb zircon dating of two rhyolite samples and one dacite sample yielded ages of 305.6 ± 1.6 Ma, 312.2 ± 2.3 Ma, and 305.3 ± 1.7 Ma, respectively, corresponding to the Late Carboniferous. The volcanic rocks are enriched in light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high‐field‐strength elements (HFSEs, e.g., Nb, Ta). The positive zircon εHf(t) values (+6.64 to +9.49) of the volcanic rocks and the high Mg# values (47.05–51.47) of some samples indicate the contribution of mantle materials to the sources. Integrated with geological, geochemical, and Lu–Hf isotopic studies, it is considered the volcanic rocks formed in a subduction‐related continental margin arc setting. Combined with the studies in the southeastern part of the Central Asian Orogenic Belt on the ophiolitic mélanges, magamatic belts and sedimentary environment of the Late Palaeozoic, collision‐related granites, and so on; it is suggested that the southward subduction for the eastern segment of the Palaeo‐Asian Ocean beneath the northern margin of Sino‐Korean palaeoplate was still occurring in the Late Carboniferous.

Ubiquitous post‐peak zircon in an eclogite from the Kumdy‐Kol, Kokchetav UHP‐HP Massif (Kazakhstan): Significance of exhumation‐related zircon growth and modification in continental‐subduction settings

AbstractU–Pb geochronological, trace‐element and Lu–Hf isotopic studies have been made on zircons from ultrahigh‐pressure (UHP) mafic eclogite from the Kumdy‐Kol area, one of the diamond‐facies domains of the Kokchetav Massif (northern Kazakhstan). The peak eclogitic assemblage equilibrated at > 900 °C, whereas the bulk sample composition displays light rare‐earth element (LREE) and Th depletion evident of partial melting. Zircons from the eclogite are represented by exclusively newly formed metamorphic grains and have U–Pb age spread over 533–459 Ma, thus ranging from the time of peak subduction burial to that of the late post‐orogenic collapse. The major zircon group with concordant age estimates have a concordia age of 508.1 ±4.4 Ma, which corresponds to exhumation of the eclogite‐bearing UHP crustal slice to granulite‐ or amphibolite‐facies depths. This may indicate potentially incoherent exhumation of different crustal blocks within a single Kumdy‐Kol UHP domain. Model Hf isotopic characteristics of zircons (εHf(t) +1.5 to +7.8, Neoproterozoic model Hf ages of 1.02–0.79 Ga) closely resemble the whole‐rock values of the Kumdy‐Kol eclogites and likely reflect in situ derivation of HFSE source for newly formed grains. The ages coupled with geochemical systematics of zircons confirm that predominantly late zircon growth occurred in Th–LREE‐depleted eclogitic assemblage, that experienced incipient melting and monazite dissolution in melt at granulite‐facies depths, followed by amphibolite‐facies rehydration during late‐stage exhumation‐related retrogression.

Age and Provenance of the Daur Series Sedimentary Rocks (Riphean), Argun Continental Massif: Results of U–Th–Pb and Lu–Hf Isotope Studies of Detrital Zircons

The first results of U–Th–Pb and Lu–Hf isotope studies of detrital zircons from sedimentary rocks of the Daur Series (Argun continental massif of the Central Asian Fold Belt) are presented. It is established that the youngest detrital zircons from sandstones of the Urulungui and Dyrbylkei formations of the Daur Series have the ages of 899 and 771 Ma, respectively. These data determine the maximum depositional age of the Daur Series and agree with the current ideas about the Late Riphean age of this series. The majority of Late Riphean detrital zircons from sedimentary rocks of the Daur Series are characterized by Early Precambrian Lu–Hf model ages. In addition, the Archean and Early Proterozoic detrital zircons are present in the studied rocks. This suggests either the presence of ancient (Early Precambrian) recycled material in the sedimentary rocks of the Daur Series or the fact that the studied part of the Argun massif is an “exotic block,” whose origin requires additional research.

Timing and origin of multi-stage magmatism and related W–Mo–Pb–Zn–Fe–Cu mineralization in the Huangshaping deposit, South China: An integrated zircon study

The Huangshaping deposit (South China) is closely related to hypabyssal granites (e.g., quartz porphyry, granophyre, and granite porphyry), developing massive skarn-type W–Mo–Fe polymetallic mineralization, skarn-type Pb–Zn–Cu mineralization, and vein-type PbZn (Cu) mineralization. To better constrain the geochronology, fluid composition, magma source, metallogenic affinity, and source of ore-forming materials in the Huangshaping deposit, morphological, textural, in situ geochronological, compositional, and LuHf isotopic studies on zircons hosted in granitoids, skarns (ores), and wall rocks have been carried out. Overall, five types of zircons are identified: low-U magmatic (abbreviated as LUMZ), high-U magmatic (HUMZ), hydrothermally-altered metamict (HAZ), inherited, and detrital types. Round-shaped inherited and detrital zircons with low trace element compositions are rarely captured in the granite porphyry and largely hosted in sulfide skarn ores and wall rocks. The HUMZ are mainly observed in the granophyre and are easily distinguished from LUMZ by their much higher U, Th, and Y contents, black CL images, and stronger Eu anomalies. In addition, the crystallization time of HUMZ was later than that of LUMZ. The HAZ uniquely exists in granite porphyry and genetic-related skarns with cracked and porous textures and strong enrichment of many trace elements. These zircons were originally HUMZ that have undergone rapid partial metamictization and subsequent fluid-zircon interaction. This study demonstrates that the granophyre is a two-stage intrusion with ages of 179 ± 0.3 Ma and 163 ± 0.7 Ma, whereas the granite porphyry yields younger ages of 157 ± 0.5 Ma. The discovery of Triassic inherited zircons in the latter leads us to propose the presence of a concealed Triassic pluton (~220 Ma). The zircon populations of W−Mo−Fe mineralized garnet skarns are mainly composed of ~160 and 180 Ma magmatic zircons, whereas magnetite skarn ores contain both magmatic zircons (~50%) and inherited zircons (~50%). In contrast, inherited zircons are the dominant zircon population of the skarn Pb−Zn ores. This may indicate that the granite porphyry (the foremost one) and granophyre mostly contributed to the skarn-type W−Mo−Fe mineralization, whereas the Carboniferous and Devonian carbonate strata significantly contributed to the skarn-type Pb−Zn (Cu) mineralization. Fluids separated from the granite porphyry that modified the zircons are likely the principal ore-forming fluids, which are enriched in F, U, Th, Y, REE, Nb, Ta, Hf, Ca, P, Ti, Pb W, Mo, and Fe. Zircon Hf isotopes suggest that these magmas, at least the granophyre and granite porphyry, were generated by reworking of Mesoproterozoic crustal rocks without significant input of mantle materials. This study highlights the use of different types and generations of zircons from variable rock types to reveal fluid compositions and mineralization potentials in complex metallogenic systems.

Late Paleozoic Age and Nature of Protolith of Metamorphic Rocks of the Djagdagle Formation, Bureya Terrane, Central Asian Fold Belt

The results of geological, geochemical, Sm–Nd isotopic geochemical studies of metamorphic rocks of the Djagdagle Formation and U–Pb geochronological studies of its zircons are presented. In correlation schemes of geological complexes of the Bureya Terrane, this formation is the oldest (conditionally, Late Archean) amid other formations of the terrane; thus, it is considered its basement. The biotite and two-mica garnet-bearing gneisses of the formation formed owing to transformation of primary sedimentary rocks. The maxima on the relative probability curve of zircon age correspond to 487, 541, 690, 778, and 896 Ma. Thus, the Djagdagle Formation is Paleozoic rather than Early Precambrian, as was considered before. The lower age boundary of the accumulation of the protolith is identified by the age of the youngest zircon population of ~487 Ma. Similar ages of some cores and rims of zircons indicate that the rocks of the protolith underwent structural metamorphic transformations under PT conditions of amphibolite facies. The results of Sm–Nd and Lu–Hf isotopic studies indicate that the geological complexes which originated by means of reworking of the Mesoproterozoic crust could have been the source of primary sedimentary rocks. Taking into account the lack of Mesoproterozoic (and older) rocks in the structure of the Bureya Terrane, it can be suggested that the sources included some amount of ancient recycled material. Similar geological evolution of the Bureya and Jiamusi terranes is suggested on the basis of similar age ranges of metasedimentary rocks of the Djagdagle Formation and Turan Group of the Bureya Terrane and the Kimkan Formation of the Jiamusi Terrane. This is also evident from their synchronous Neoproterozoic magmatism.

Ages and Sources of Sedimentary Rocks of the Lan Terrane in the Mongol-Okhotsk Fold Belt: Results of Zircon U-Pb and Lu-Hf Isotope Studies

The paper presents the results of U-Pb and Lu-Hf isotope studies of detrital zircons from the terrigenous the Lan 410 Ma (Lower Devonian), Terrane in the eastern part of the Mongol-Okhotsk fold belt. The lower age rocks limits are for the Nivakh formation ~ for the Verkholan series ~332 Ma (Mississippian), for the Ugokhan series ~239 Ma (Middle Triassic). The evidences were obtained for the Lower Triassic (or Middle-Late Triassic) age of the sediments assigned to the Ugokhan series previously classified as Upper Paleozoic. These data indicate that the Lower Mesozoic sedimentary complexes in the structure of this belt are developed much wider than is currently believed. The main sources of clastic material for the Devonian, Carboniferous, and Triassic sedimentary rocks of the Lan terrane were mainly igneous and metamorphic complexes of the North Asian craton framing, along with island arcs. The Lan Terrane can be considered as a fragment of the accretionary complex formed in front of the southeastern margin of the North Asian craton.

Tectonic Nature of the Ul’ban Terrane (Mongol–Okhotsk Fold Belt): Results of U–Pb and Lu–Hf Isotope Studies of Detrital Zircons

The U–Pb and Lu–Hf isotope studies of detrital zircons from Mesozoic metasedimentary rocks of the Sorukan and Naldinda formations of the Ul’ban terrane are performed for the first time. It is shown that Early Precambrian zircons are almost completely absent in these rocks, while Early Mesozoic zircons with Paleozoic, Neoproterozoic, and Mesoproterozoic Hf model ages dominate. Based on the data obtained, it is assumed that the Ul’ban terrane is a part of the accretionary complex of the northern framing of the Amur superterrane and is neither a depression superimposed on the Paleozoic formations of the Mongol–Okhotsk belt nor an accretionary complex in the southern framing of the North Asian Craton, as was believed earlier.

Geochemistry, geochronology and Sr–Nd–Hf isotopes of two types of Early Cretaceous granite porphyry dykes in the Sulu orogenic belt, eastern China

Late Mesozoic granitic rocks are widely distributed in the Sulu orogenic belt, but the source, tectonic affinity, and associated geodynamic setting that produced the respective magmas remain controversial. To provide insights into these issues, we present field-based petrological, whole-rock major and trace element and Sr–Nd isotope geochemical, zircon U–Pb dating, and Lu–Hf isotope studies on two types of granite porphyry dykes that are newly recognized from the central Sulu belt. U–Pb dating of magmatic zircons from both types yields consistent ages that vary between 124 ± 2 and 118 ± 2 Ma, constraining the timing of intrusion as Early Cretaceous. The granitic rocks have high-K calc-alkaline peraluminous compositions with low Mg# values and are characterized by fractionated rare earth element patterns with strong depletion in high field strength elements. Compared with type I of the granite porphyry dykes, type II exhibits higher SiO2 but slightly lower Na2O and K2O abundances, contains higher Rb/Sr and 87Sr/86Sr ratios, and shows more pronounced negative Eu, Sr, and Ba anomalies. Both types I and II have high initial 87Sr/86Sr ratios of 0.709–0.711 and negative εNd(t) values of −19.8 to −18.4. The magmatic zircons possess negative εHf(t) values of −29.1 to −20.8, with mostly Neoarchean Hf model ages of 3001–2478 Ma. These features, together with the presence of Neoproterozoic inherited zircons, indicate that the two types of granite porphyries successively crystallized from a joint granite magma that derived from partial melting of the continental crust of the Yangtze Craton. Therefore, an interrelationship between the granite porphyry dykes and massive magmatic granitoids from adjacent regions in the Sulu belt may be documented, recording evidence of a joint ancient crustal reworking and recycling in a fossilized continental subduction zone during the Early Cretaceous.

Petrogenesis and tectonic implications of Indosinian granitoids from Western Qinling Orogen, China: Products of magma-mixing and fractionation

The Western Qinling Orogen (WQO) is characterized by voluminous distribution of Indosinian granitoids, the formation of which provides an important window to unravel the geochemical and geodynamic evolution and associated metallogeny. Here we investigate a group of intrusions termed “Five Golden Flowers” based on petrological, geochemical, zircon U–Pb geochronological and Lu–Hf isotopic studies on the granitoids and their mafic microgranular enclaves (MMEs). Our results show that these intrusions are genetically divided into two types, namely, magma-mixing and highly fractionated. The Jiaochangba, Lujing, Zhongchuan, and Luchuba granitoids are biotite monzogranites (220 ​± ​0.8 ​Ma to 217 ​± ​2.6 ​Ma) with abundant coeval MMEs (220 ​± ​1.1 ​Ma to 217 ​± ​2.7 ​Ma). The rocks contain moderate to high SiO2, high MgO, Rb, Sr, Ba, and Th contents, but low TiO2, P2O5, and Sc values, A/CNK of <1.1, and a range of εHf(t) values of −11.7 to +2.23 with corresponding TDM2 values of 1967–1228 ​Ma. The MMEs possess K-feldspar megacrysts, abundant acicular apatites, and show lopsided textures. They have lower SiO2, Al2O3, and Th contents, but higher MgO, TiO2, and Sc, with εHf(t) values of −18.0 to +3.18 and TDM1 of 849–720 ​Ma. The data indicate that the MMEs were derived from a magma sourced from the enriched lithospheric mantle. We suggest that these host granitoids were produced by partial melting of late-Paleoproterozoic to early-Mesoproterozoic lower crust with the involvement of Neoproterozoic SCLM-derived mafic magmas. The Baijiazhuang pluton is dominantly composed of leucogranite (muscovite granite and two-mica monzogranite, 216 ​± ​1.5 ​Ma) without MMEs. The rocks are peraluminous with high A/CNK (1.06–1.27). Compared with the other four granitoids, the Baijiazhuang leucogranite shows higher SiO2 content, markedly lower concentrations of TiO2, MgO, Al2O3, CaO, and Fe2O3T, and lower LREE/HREE and (La/Yb)N values. These leucogranites are also rich in Rb, Th, and U, and display marked depletions in Ba, Sr, Ti, and Eu, indicating that they experienced significant fractionation. Zircon εHf(t) values (−10.2 to −3.27) and TDM2 (1868–1424 ​Ma), as well as the Nb/Ta and K2O/Na2O values are similar to the other four granitoids, indicating that they are likely to have been derived from a similar source; with sediments playing only a minor role in the magma generation. The low contents of Yb and Y suggest that their partial melting was controlled by garnets and micrographic texture of K-feldspar reflects high-temperature melting through undercooling. Based on the above features, we infer that the Baijiazhuang leucogranite likely represents the product of high degree fractionation of the I-type biotite monzogranite magma which generated the other four granitoids at relatively high temperatures, within magma chambers at mid-crust depths. We propose that the granitoid suite was formed in the transitional setting from syn- to post-collision during the collisional orogeny between the SCB and NCB, following break-off of the subducted South China Block lithosphere during 220–216 ​Ma.

Geochronological and Lu-Hf isotopic study on detrital zircons of the Jianshan Formation, Bayan Obo Group in Shangdu area, Inner Mongolia: Constraints on Precambrian crustal evolution of the Western Block, North China Craton

华北克拉通前寒武纪地壳生长过程是地质学的研究热点。本文对华北克拉通西部陆块北缘的白云鄂博群尖山组进行了碎屑锆石U-Pb定年和Hf同位素分析，并在此基础上对尖山组的沉积时限、物源及西部陆块北缘的前寒武纪地壳生长过程进行了探讨。样品TM33中碎屑锆石年龄主要集中在1872~2100Ma（n=64），并有~1960Ma的主年龄峰值和~2000Ma的次年龄峰值，Hf同位素分析结果显示锆石的ε_Hf（t）值在-2.6~7.9之间（除1个测点为-17.6），Hf同位素二阶段模式年龄（t_DM2）变化范围在2240~4386Ma之间。样品Z1724中碎屑锆石年龄分布于1784~2200Ma（n=44），并有~1965Ma的主年龄峰值和~2080Ma次年龄峰值。谐和线上最年轻一组锆石的加权平均年龄为1794±73Ma（n=2），ε_Hf（t）在-5.4~3.2之间，Hf同位素二阶段模式年龄（t_DM2）变化范围在2584~3203Ma之间。基于以上数据，结合侵入白云鄂博群底部1670Ma的辉长岩以及白云鄂博群底部全岩²⁰⁷Pb-²⁰⁶Pb等时线年龄为1649Ma的沉积碳酸盐岩，尖山组的沉积时间被限定在1800~1650Ma。尖山组的物源主要来自固阳、西乌兰不浪地区新太古代基底以及大青山和卓资地区古元古代晚期孔兹岩带。综合前人对研究区及邻区中新元古代沉积地层中碎屑锆石的Hf同位素研究结果，认为华北克拉通西部陆块北缘可能存在2600~2750Ma、~2500Ma和2000~2100Ma三期主要的地壳生长事件，且最后一次规模可能小于前两次。;The Precambrian crustal growth of North China Craton (NCC) has been a hot topic for geologists for a long time. This paper presents LA-ICP-MS U-Pb dating and in-suit Lu-Hf isotopic analysis results of detrital zircons from Jianshan Formation, Bayan Obo Group in the northern western block of North China Craton to illustrate its depositional time and provenance as well as the Precambrian crustal growth in this area. The ages of detrital zircons from Sample TM33 cluster at 1872~2100Ma (n=64), with a major age peak at ~1960Ma and a minor peak at ~2000Ma. The in-suit Lu-Hf isotopic analysis of the zircons indicate their ε_Hf(t) values vary from -2.6 to 7.9 (except one of -17.6), with two-stage Hf model ages (t_DM2) varying between 2240Ma and 4386Ma (averaged at 2749Ma). The ages of detrital zircons from Sample Z1724 are mainly between 1784~2200Ma (n=44), with a major age peak at ~1965Ma and a minor peak at ~2080Ma. The weighted average age of the youngest concordia ages is 1794±73Ma (n=2). In-suit zircon Lu-Hf isotopic analysis indicate their ε_Hf(t) values vary from -5.4 to 3.2, with two-stage Hf model ages (t_DM2) between 2584~3203Ma. Based on the above data and combined with the 1670Ma gabbro intruding into Bayan Obo Group and the carbonatite with whole rock ²⁰⁷Pb-²⁰⁶Pb age at 1649Ma, the depositional age for Jianshan Formation is between 1800Ma and 1650Ma. The main provenances for Jianshan Formation are the Neo-Archean basement in Guyang, Xiwulanbulang and Kondalite Belt in Daqingshan, Zhuozi. There might exist three crustal growth events in the northern western block of NCC at 2600~2750Ma、~2500Ma and 2000~2100Ma respectively, and the scale of the last one might be much smaller than the other two.

Geochemical evidence for reworking of the juvenile crust in the Neoarchean for felsic magmatism in the Yunzhongshan area, the North China Craton

The North China Craton experienced two phases of tectonothermal events at ca. 2.8–2.7 Ga and ca. 2.6–2.5 Ga, respectively. Although 2.6–2.5 Ga granitic gneisses and metavolcano-sedimentary sequences are widespread in the craton, the major stage of crustal growth has been determined to occur at 2.8–2.7 Ga in terms of whole-rock Sm-Nd and zircon Lu-Hf isotope studies. It has been intriguing how the vast 2.8–2.7 Ga juvenile mafic crust would have differentiated into the 2.6–2.5 Ga felsic crust. This issue is addressed in the present study by investigating zircon U-Pb ages and Lu-Hf isotopes as well as whole-rock major-trace elements and Sm-Nd isotopes in Neoarchean felsic igneous rocks from the Yunzhongshan area in the central part of the North China Craton. Zircon U-Pb dating of felsic volcanics, TTG gneisses and high-K granites yields three groups of crystallization ages at 2562–2508 Ma, 2537–2504 Ma and 2518–2508 Ma, respectively, consistent with ages for mafic volcanics in the target area. Zircon Lu-Hf and whole-rock Sm-Nd isotope data indicate that all these rocks were ultimately originated from the ca. 2.8–2.7 Ga juvenile mafic crust. The felsic volcanics are subdivided into low-Si and high-Si suites. The low-Si rocks have higher MgO and FeO contents and contain abundant 2.8–2.7 Ga relict zircons with an age peak of 2.72 Ga, and were produced by partial melting of ~2.72 Ga TTG at ~730 to 750 °C. The high-Si volcanics were derived from partial melting of mafic restites after extraction of the ~2.72 Ga TTG, with significant amounts of garnet and amphibole, but no or rare plagioclase as residual phases, corresponding to a melting pressure at ~15 kbar. The TTG gneisses were produced by partial melting of ~2.8 to 2.7 Ga garnet amphibolites at ~10 to 15 kbar with variable amounts of garnet, amphibole and plagioclase in the residue. The high-K granites were produced by partial melting of ~2.8 to 2.7 Ga medium-high K mafic rocks at pressures of <10 to 12 kbar with a considerable amount of plagioclase in the residue. The TTG rocks and high-Si volcanics require a subduction origin to account for their enrichment in LILE, so that they were mostly likely derived from partial melting of the older arc crust with moderate enrichment in LILE and LREE. By contrast, the ultimate sources of the high-K granites would be the ~2.8 to 2.7 Ga medium-high K basalts, which have lower Zr/Sm ratios than the TTG gneisses and felsic volcanics, and even lower than the bulk continental crust, but consistent with modern island arc basalts. It is possible that the 2.8–2.7 Ga magmatism was subduction-related, with a compositional change of the mafic arc crust from relatively sodic to more potassic at around 2.7 Ga. This may be caused by accretion of the ancient oceanic arc onto the ancient continental margin. It was followed by both growth of the juvenile crust and reworking of the older arc crust in the late Neoarchean. Such series of magmatic processes can account for the voluminous generation of the 2.56–2.50 Ga felsic and mafic igneous rocks in the central part of the North China Craton. Taken together, both growth and reworking of the juvenile crust were realized through accretionary and rifting orogeneses, marking the operation of plate tectonics in the Neoarchean.