Characteristics of Lower Crustal Granulite Xenoliths from the East Qinling Orogenic Belt and Their Tectonic Significance

The Tongbai granulites are present mainly as xenoliths in granodioritic gneisses. The xenoliths with a zircon age of 470Ma are older than the host rocks of granodioritic gneisses which yield a zircon age of 435Ma. It is suggested that the granulites were transported from the lower crust to the upper level along with granodioritic magma. Geothermometrical and geobarometrical studies based on the coexisting minerals (Opx-Cpx and Opx-Gar) show that the granulites were crystallized at 818 –840 °C and 9.5−9.8 × 10⁸ Pa corresponding to the lower crust. Tectonically, the Shangdan suture zone constitutes the boundary between the North China and Yangtze plates. The zone is char acterized by the occurrence of ophiolites in the western part and by that of granulites in the eastern part. So the western part marks the upper crustal level of the Qinling belt, while the eastern part represents the exposure of a deeper level. The results of isotopic dating and the geochemical characteristics of the xenoliths are consistent with those of metatholeiites of the ophiolites in the western part. Therefore, it is assumed that both ophiolites found in the west and granulites found in the east all represent the remnants of the ancient Qinling ocean plate. The difference is that the ophiolites are pieces of obducted fragments from the ocean floor during the subduction in the Early Palaeozoic. However, in the Tongbai area, when the ocean floor was subducting towards the lower crust, it underwent a granulite fades metamorphism. Subsequently, granodioritic magma formed by partial melting trapped some fragments of granulite upwards. This project was jointly granted by the National Natural Science Foundation of China and Stiftung Volkswagenwerk of Germany     

High-Temperature Metasomatism of the Layered Mafic–Ultramafic Massif in Kiy Island,Belomorian Mobile Belt

The paper presents results of a detailed petrologic study of metasomatites and their host metagabbroids in the northwestern part of Kiy Island, Onega Bay, White Sea. The first evidence is acquired that coronitization and amphibolization of the host rocks took place at the peak of Svecofennian metamorphism at Т = 700–640°C, Р = 9–10 kbar, and \({a_{{H_2}O}}\) = 0.2–0.3. Accompanying metasomatism has formed a number of long (up to several meters long) melanocratic hornblendite and garnet–amphibole veins 0.3–2 m thick. In this area, metasomatites of another type make up single relatively thin amphibole–zoisite lenses that sometimes host ruby-like corundum. The fluid phase that induced metasomatism was poor in salts (Na,K)Cl, and hence, the rocks do not contain sodic plagioclase, and their amphibole is tschermakite but not pargasite. The compositions of the metasomatites of the two types are proved to be complementary, and this indicates that they were most likely produced by high-temperature metasomatism but not via the removal of components by fluid from migmatization zones.     

Crystallization temperature of anatectic melt: An example of biotite–muscovite granite in the Rikolatvi structure,Belomorian Mobile Belt

Zircon hosted in granite, which crystallized from local pools of anatectic melt among migmatites, in the Rikolatvi structure, Belomorian Mobile Belt, contains minute inclusions of various minerals, biotite and garnet among others. The compositions of the biotite and garnet in the microinclusions differ from those of the same minerals in the granite containing the zircon. The crystallization temperature of the anatectic melt was estimated by the biotite–garnet geothermometer and the composition of the biotite and garnet inclusions at ~800°C.     

The Lu–Hf Isotope Composition of Zircon from Syenites of the Saharjok Alkaline Massif,Kola Peninsula

Geology of Ore Deposits - Zircon crystals from the alkaline and nepheline syenites of the Saharjok massif, which were formed during the magmatic (2645 ± 7 Ma), hydrothermal (1832 ± 7 Ma),...     

Geochemistry and Zircon U–Pb–Hf Isotopic Systematics of the Sanchahe Quartz Monzonite Intrusion in the North Qinling Tectonic Zone, Central China: Implications for its Petrogenesis and Tectonic Setting

The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#(55.0–59.0), and enrichments in Na2 O+K2 O(7.28–8.94 %), Ni(21-2312 ppm), Cr(56-4167 ppm), Sr(553-923 ppm), Ba(912-1355 ppm) and LREE((La/Yb)N =9.47–15.3), from negative to slightly positive Eu anomalies(δEu=+0.61 to +1.10), but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O+K2 O(7.20– 8.30%), Sr(455–1081 ppm) and(La/Yb)N(27.6–47.8), with positive Eu anomalies(δEu=1.03–1.57) and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry(LA-ICPMS) zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf(t) values ranging from +0.3 to +15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf(t) values ranging from 21.6 to +10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.     

Geochemistry and Zircon U–Pb–Hf Isotopic Systematics of the Sanchahe Quartz Monzonite Intrusion in the North Qinling Tectonic Zone,Central China： Implications for its Petrogenesis and Tectonic Setting

The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#（55.0–59.0）, and enrichments in Na2 O＋K2 O（7.28–8.94 %）, Ni（21-2312 ppm）, Cr（56-4167 ppm）, Sr（553-923 ppm）, Ba（912-1355 ppm） and LREE（（La/Yb）N =9.47–15.3）, from negative to slightly positive Eu anomalies（δEu=＋0.61 to ＋1.10）, but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O＋K2 O（7.20– 8.30%）, Sr（455–1081 ppm） and（La/Yb）N（27.6–47.8）, with positive Eu anomalies（δEu=1.03–1.57） and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry（LA-ICPMS） zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf（t） values ranging from ＋0.3 to ＋15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf（t） values ranging from 21.6 to ＋10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.     

Uranium-Lead and Lu–Hf Isotope Systematics of Zircon and Sm–Nd Isotopes in Rocks of the Dyumtaley Ore-Bearing Intrusion (Taimyr,Russia): New Evidence for the Role of the Depleted Mantle in Its Genesis

Doklady Earth Sciences - This study utilized SHRIMP, LA MC–ICP–MS and ID-TIMS analytical techniques and presents for the first time U–Pb age, Lu-Hf-isotope features of zircon and...     

U–Pb Age and Hf–Nd–Sr Isotopic Systematics of Vein Rocks of the Volkovsky Massif,Middle Urals,Russia

This paper reports chemical, geochronological, and Hf–Nd–Sr isotopic-geochemical data on granite, leucogabbro, and microgabbro porphyrite vein bodies in the gabbro of the Volkovsky massif. It was proved that the vein granite and leucogabbro are genetically related to the leucogabbro–anorthosite–plagiogranite (anorthosite–granite) series of the Urals Platinum Belt. The granite was dated by U-Pb laser ablation inductively coupled plasma mass spectrometric method at 409.0 ± 2.3 Ma. The rock has ⁸⁷Sr/⁸⁶Sr_{(409 Ма)} = 0.70358, high ε_{Nd(409 Ма)} = 6.4–6.5, and ε_{Hf(409 Ма)} ≥ 10.8. Similar values of ⁸⁷Sr/⁸⁶Sr_{(409 Ма)} = 0.70370 and ε_{Nd(409 Ма)} = 5.9 were obtained for the vein leucogabbro. The isotopic-geochemical data are consistent with existing concept of the formation of the leucogabbro–anorthosite–plagiogranite (anorthosite–granite) series through partial melting of the olivine gabbro. The measured ¹⁴³Nd/¹⁴⁴Nd = 0.512939 value obtained for the microgabbro porphyrite reflects their more radiogenic composition and likely a mantle source. The granite, associated leucogabbro, and microgabbro porphyrite were emplaced at the final magmatic stage in the massif evolution. This event marks the upper age boundary of the Au–Pd mineralization related to the gabbroic rocks. The vein rocks lack any signs of the mineralization. However, it is highly probable that they were sources of energy and fluid for reworking of the earlier olivine gabbro and redeposition of ore components in this rock.     

Mafic Intrusions of ca. 2400 Ма Large Igneous Province in the Belomorian Mobile Belt: First Baddeleyite U–Pb ID-TIMS Data

Doklady Earth Sciences - U–Pb ID-TIMS dating of igneous baddeleyite from metamorphosed coronitic gabbronorites in the сentral part of the Belomorian mobile belt, Fennoscandian shield...     

Variations of Oxygen Isotopic Composition in Magmas of Okhotsk–Chukotka Volcanic Belt

Doklady Earth Sciences - First data on oxygen isotopic composition in phenocrysts in volcanic rocks from Okhotsk–Chukotka volcanic belt (106–78 Ma, North-Eastern Russia) together with...     

Zircon U-Pb Geochronology and Hf Isotopic Geochemistry of the Liwan Cu–Mo Deposit, Guichi Ore Cluster Field

Please refer to the attachment(s) for more details.     

Zircon U–Pb Ages and Lu–Hf Isotope of the Dongchuan Group in Central Yunnan,China, and their Geological Significance

On the southwestern margin of the Yangtze Block, the Dongchuan Group consists of slightly metamorphosed sedimentary rocks, including silty slate, argillaceous slate, clayey slate, arkose, dolomite, and minor volcanic rocks. To date, it is still a controversy over the depositional age and stratigraphic sequence of the Dongchuan Group. In this study, we analyzed five samples of meta-sedimentary rocks and one sample of meta-tuff from the Yinmin, Luoxue and Etouchang Formations of the Dongchuan Grou...     

Age and Sources of Metasedimentary Rocks of the Tokur Terrane of the Mongol–Okhotsk Fold Belt: Results of U–Pb and Lu–Hf Isotope Studies

Doklady Earth Sciences - This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the...     

Zircon ages and Nd–Hf isotopes in UHT granulites of the Ider Complex: A cratonic terrane within the Central Asian Orogenic Belt in NW Mongolia

The Ider Complex of the Tarbagatai Block in northwestern Mongolia is part of a Precambrian microcontinental terrane in the Central Asian Orogen Belt and has experienced a polymetamorphic tectono-metamorphic evolution. We have investigated an enderbitic gneiss, derived from a quartz diorite and a charnockite, derived from a leucogranite, and zircon SHRIMP data reveal late Archaean protolith ages of 2520–2546 Ma for these rocks. Metamorphic overgrowth on these zircons as well as newly-formed metamorphic zircons document a high-temperature metamorphic event (T = 930–950 °C) at about 1855–1860 Ma. Nd whole-rock isotopic systematics show these and other gneisses of the Ider Complex straddling the CHUR-line in a Nd isotope evolution diagram, suggesting both crustal reworking and input of some juvenile material, with Nd model ages ranging between ca. 2.5 and 3.1 Ga. Hf-in-zircon isotopic data provide a similar pattern and also yielded Archaean Hf crustal model ages. The metamorphic zircons seem to have inherited their Hf isotopic composition from the igneous grains, suggesting a complex process of dissolution, transportation, and re-precipitation involving a fluid phase during high-grade metamorphism. The zircon age patterns do not make it possible to unambiguously assign the Tarbagatai Block to any of the cratons bordering the Central Asian Orogenic Belt, since age peaks at ca. 2520–2550 and ca. 1860 Ma are common in the Siberian, North China and Tarim cratons.     

Timing of high-pressure metamorphic events in the Bulgarian Rhodopes from Lu–Hf garnet geochronology

Within the Mediterranean realm, the Rhodopes represent a nappe stack of oceanic and continental fragments assembled along the Eurasian continental margin during the Alpine orogeny. The timing of the high-pressure (HP) metamorphism has long been ambiguous, lacking detailed geochronological and geochemical control on subduction-exhumation and nappe stacking processes. Here we apply the Lu–Hf and Sm–Nd chronometers to a suite of representative eclogite samples covering two different key units of the Rhodopean nappe stack: (1) the Kimi Complex (Upper Allochthon) and (2) the Middle Allochthon. In addition to geochronology, we also determined whole rock Hf and Nd isotope compositions as well as major and trace element concentrations in order to constrain the nature of the eclogite protoliths. Two HP metamorphic events were revealed by Lu–Hf geochronology: (1) a Lower Cretaceous event in the Upper Allochthon (126.0 ± 1.7 Ma) and (2) an Eocene event in the Middle Allochthon (44.6 ± 0.7 Ma; 43.5 ± 0.4 Ma; 42.8 ± 0.5 Ma), at conditions of ca. 700°C/20–25 kbar. Our new data provide direct evidence for multiple subduction events in the Rhodopes. Exhumation and subsequent thrusting of the Middle Allochthon on the Lower Allochthon can be narrowed down to the time span between 42 and 34 Ma. In a broader tectonic context, the Eocene ages for the HP metamorphism support the view that the Rhodopes represent a large-scale tectonic window, exposing the deepest nappe units of the Hellenides.     

Isotopic Ages of the Penglai Group in the Jiaobei Belt and Their Geotectonic Implications

The Penglai Group in the Jiaobei Belt is the only remaining cover of the Archaean to Early Proterozoic crystalline basement in eastern Shandong. The ages of deposition of the Penglai Group and of its deformation and metamorphism have long been a subject of speculation. Whole-rock Rb-Sr ages, illite-whole-rock pair Rb-Sr ages and illite K-Ar ages recently obtained from the Penglai Group slates are reported and interpreted in this paper. On the basis of structural and metamorphic studies coupled with analyses of illite crystallinity, XRD and SEM , a whole-rock age of 473±32 Ma (Ordovician) is interpreted as the time of termination of burial metamorphism experienced by the Penglai Group. Therefore, the age of the Penghai Group is older than Ordovician. The first-phase folding and syntectonic low greenschist facies metamorphism in the Penglai Group, i.e. the Penglai Movement, took place before 299±4 Ma B.P., i.e in the Late Carboniferous. The Penglai Movement that occurred in the Jiaobei Belt on the south     

Age and Sources of Metasedimentary Rocks of the Galam Terrane in the Mongol–Okhotsk Fold Belt: Results of U–Pb Age and Lu–Hf Isotope Data from Detrital Zircons

Geotectonics - The Mongol–Okhotsk fold belt is one of the major structural elements of East Asia. In this article, we present U–Pb age and Hf isotope data for detrital zircons from...     

Geochemistry, Zircon U–Pb Dating and Hf Isotopic Characteristics of Neoproterozoic Granitoids in the Yaganbuyang Area, Altyn Tagh, NW China

The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions:(1) Yaganbuyang granitoids mainly consist of two-mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high-K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ~954 Ma for granitoids, respectively.(2) The εHf(t) values of two–mica granite and granodiorite are in the range of-3.93 to +5.30 and-8.64 to +5.19, respectively. The Hf model ages(TDM2) of two-mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust.(3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.     

Evidence for the Lower Continental Crustal Origin of the Xihuashan Granite

The Xihuashan granite is typically representative of the tungsten-bearing granites widespread in theNanling area of South China. It was considered in the past to have been formed by partial melting of the upper continental crust, with its source rocks most probably of the Sinian or Cambrian. However, detailed REE analyses, studies of the Rb-Sr isotopic system and melting experiments of metasedimentary rocks all argue against this idea. Moreover, stable isotopic data also indicate a deep source origin for S, C, H and O. The authors thus propose a genetic concept of the lower continental crustal source of the Xihuashan granite, and point out further that tungsten deposits related to this kind of granite are linked in some way to deep-seated structure and concentrated along NNE-NE- and ENE-striking major deep fault belts above the transitional zone between mantle uplift and mantle depression.