Ancient Crustal Materials Research Articles

Ore-hosting igneous rocks in the Xiahe–Hezuo district, West Qinling orogen, China, and their relationships with gold mineralization

• The Gulangdi Formation in West Qinling orogen (WQO) was formed prior to Triassic. • Gold-bearing igneous rocks in WQO were crystallized prior to gold mineralization . • Gold-bearing igneous rocks were generated by subduction of the Mian–Lue Ocean. • The Mian–Lue Ocean started the subduction process since ca. 251 Ma. • The gold metallogeny in WQO postdates regional magmatism by 40 to 20 m.y. The Xiahe–Hezuo district in the West Qinling orogen hosts a large number of gold deposits, most of which are spatially associated with igneous rocks. However, the nature and origin of these igneous rocks and their possible relation with gold mineralization remain poorly understood. In this study, the ore-hosting igneous rocks from the Zaozigou, Yidi’nan, and Gangcha gold deposits are selected to perform geochronological and geochemical analyses, aiming to clarify their petrogenesis and their role in gold mineralization. The quartz diorite porphyry from the Zaozigou gold deposit, the quartz diorite from the Yidi’nan gold deposit, and the andesite from the Gangcha gold deposit yield LA-ICP-MS zircon U-Pb ages of 250 ± 2, 251 ± 1, and 247 ± 1 Ma, respectively, representing the earliest Triassic magmatic rocks in the West Qinling orogen. The quartz diorite porphyry and quartz diorite display relatively high ( 87 Sr/ 86 Sr) i ratios (0.707188–0.710693), negative ε Nd (t) (−11.7 to −6.2) and zircon ε Hf (t) values (−13.0 to −1.6), and ancient two-stage Nd and Hf model ages (2073–1357 Ma), indicating they were generated by partial melting of ancient crustal materials. The andesite exhibits slightly positive ε Nd (t) values (0.8–1.8) and negative ε Hf (t) values (−20.6 to −2.2), indicating it was derived by partial melting of a metasomatized lithospheric mantle with significant crustal contamination. All of these igneous rocks show enrichments in large ion lithophile and light rare earth elements, depletions in high field strength elements, and high Mg # values (>50), indicating their generation in a subduction-related magmatic arc. These imply that the northward subduction of the Mian–Lue Ocean beneath the West Qinling orogen may had already started since the earliest Triassic. The geological and geochronological evidences suggest these igneous rocks were not genetically associated with the ore-forming process, and they merely provided the space for gold deposition.

The role of island-arc oceanic, collisional and intraplate magmatism in the formation of continental crust in the Mongolia-Trasnbaikalia region: geostructural, geochronological and Sm-Nd isotope data

The formation of continental crust in the Mongolia-Transbaikalia region is researched to identify the mechanisms of interactions between the crust and the mantle in the development of the Neoarchean, Proterozoic and Paleozoic magmatic and sedimentary complexes in the study area. Using the results of his own studies conducted for many years and other published data on this vast region of Central Asia, the author have analysed compositions, ages and conditions for the formation of Karelian, Baikalian, Caledonian and Hercynian structure-formational complexes in a variety of geodynamic settings. Based on the geostructural, petrological, geochemical, geochronological and Sm-Nd isotope data, he determines the crustal and mantle sources of magmatism, conducts the identification and mapping of isotopic provinces, and reveals the role of island-arc oceanic, accretion-collision and intraplate magmatism in the formation of continental crust. Considering the formation of the bulk continental crust, three main stages are distinguished: (1) Neoarchean and Paleoproterozoic (Karelian) (almost 30% of the crust volume), (2) Meso-Neoproterozoic (Baikalian) (50%), and (3) Paleozoic (Caledonian and Hercynian) (over 20%). This sequence of the evolution stages shows the predominance of the ancient crustal material in igneous rocks sources at the early stage. During the subsequent stages, tectonic structures created earlier were repeatedly reworked, and mixed crustal-mantle and juvenile sources were widely involved in the formation of the bulk continental crust in the study area.

Early crustal evolution of the Yangtze Block: Constraints from zircon U-Pb-Hf isotope systematics of 3.1–1.9 Ga granitoids in the Cuoke Complex, SW China

The newly identified Cuoke Complex preserves voluminous early Precambrian granitoids, bearing key information for the early evolution of the Yangtze Block, South China. Here, we report new field observations, petrology, zircon U-Pb-Hf isotopes and trace elements for eight granitoids from this complex. The analyzed zircon domains are of magmatic origin, as evidenced by their oscillatory zoning, high Th/U ratios and magmatic rare earth element patterns. Three trondhjemitic gneisses yield crystallization ages of 3.11–3.06 Ga, documenting the oldest known rocks in the southern Yangtze Block. Their εHf(t) values vary from −3.2 to + 2.6 with depleted mantle two-stage (TDM2) model ages of 3.6–3.3 Ga, indicating reworking of Paleoarchean crustal materials. Three gneissic granitoids crystallized at 2.86–2.85 Ga and reveal a significant episode of granitoid magmatism in the late Mesoarchean. They possess positive εHf(t) values (+0.2 to +5.0) and slightly older TDM2 model ages (3.3–3.0 Ga), suggesting that these granitoids were most likely derived from remelting of juvenile continental crust. Two monzogranites with crystallization ages of 1.94 and 1.89 Ga display negative εHf(t) values (−13.0 to −8.1) and older TDM2 model ages (3.3–3.1 Ga), indicating substantial involvement of ancient crustal materials. Available zircon U-Pb-Hf isotopic data from the Cuoke Complex have revealed that the earliest crustal growth probably occurred in the early Paleoarchean, with significant crustal growth and reworking during the early Mesoarchean, followed by multistage crustal reworking during the late Mesoarchean to Paleoproterozoic. Integrating the results of this study with records from other Archean basement complexes in the Yangtze Block (i.e., Kongling, Zhongxiang, Douling, Yudongzi and Phan Si Pan), we propose that these complexes have diverse formation histories and generally experienced tectonothermal events at ca. 2.0–1.9 Ga, probably responding to the global-scale assembly of the Nuna supercontinent.

Cambrian and Cryogenian tectonothermal events in the Amdo microcontinent, Central Tibet: Implications for paleogeographic reconstruction and tectonic evolution of northern Gondwana

The Early Paleozoic paleogeographic locations of the Tibetan terranes in Gondwana remain poorly constrained. This study reports petrology, zircon LA-ICP-MS U-Pb ages, whole-rock major and trace element compositions, and Sr-Nd-Hf isotopic data for the gneissic granites in the Amdo microcontinent, central Tibetan Plateau. LA-ICP-MS zircon U-Pb dating yielded Cambrian ages of ca. 500 Ma for the granites. A Cryogenian age of ca. 800 Ma was recognized from inherited zircons. Geochemical data indicate that these granites belong to high-K calc–alkaline I-type granitoids. They mostly exhibit negative values of zircon εHf(t) (−7.1 to +0.1) and whole-rock εNd(t) (−5.9), as well as old zircon Hf model ages (TCDM = 1718–1472 Ma) and whole-rock Nd model ages (TCDM = 1771 and 1777 Ma). These granites can be interpreted as resulting from partial melting of ancient crustal materials that have been modified by mantle-derived magmas. Integrating previous magmatic studies with the data presented in this contribution, we suggest that the Amdo microcontinent was linked to the Indian Gondwanan margin and recorded the arc-related magmatism along the proto-Tethyan margin.

Chemolithotrophy on the Noachian Martian breccia NWA 7034 via experimental microbial biotransformation

Multiple lines of evidence indicate an active hydrogeological history of Mars and chemolithoautotrophy-suited environments within its Noachian terrains. As a result, one of the primary aims of upcoming missions to Mars is to search for signs of ancient life. Here we report on laboratory-scaled microbially assisted chemolithoautotrophic biotransformation of the Noachian Martian breccia Northwest Africa (NWA) 7034 composed of ancient (~4.5 Gyr old) crustal materials from Mars. Nanoanalytical hyperspectral analysis provides clues for the trafficking and distribution of meteorite inorganic constituents in the microbial cell. We decipher biomineralization patterns associated with the biotransformation and reveal microbial nanometer-sized lithologies located inside the cell and on its outer surface layer. These investigations provide an opportunity to trace the putative bioalteration processes of the Martian crust and to assess the potential biogenicity of Martian materials.

Zircon U–Pb ages, geochemistry, and Sr–Nd–Pb–Hf isotopes of the Mugagangri monzogranite in the southern Qiangtang of Tibet, western China: Implications for the evolution of the Bangong Co‐Nujiang Meso‐Tethyan Ocean

We present in‐situ zircon laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U–Pb ages, whole‐rock geochemistry, and Sr–Nd–Pb–Hf isotopes of the Mugagangri monzogranite in the southern margin of the Qiangtang Block, Tibet, western China. The zircons yield a U–Pb age of ca. 123 Ma. The hornblende‐bearing monzogranite shows metaluminous to weak peraluminous and high‐K calc‐alkaline characteristics exemplified by high silica (SiO2 = 67.57–70.57 wt%), high aluminium (Al2O3 = 14.68–15.78 wt%), high potassium (K2O = 4.00–5.14 wt%), high alkali (K2O + Na2O = 7.88–8.62 wt%), and low calcium contents (CaO = 1.72–2.17 wt%), with the aluminium saturation index (A/CNK) ranging from 0.98 to 1.09, suggesting that the Mugagangri monzogranite is a metaluminous to weak peraluminous I‐type high‐K calc‐alkaline granite. Geochemically, similar to the arc magmas, the monzogranite is enriched in large‐ion lithophile elements, and relatively depleted in high‐field‐strength elements. The monzogranite displays relatively high (87Sr/86Sr)i values (0.70972–0.71240), uniform εNd(t) values (−2.24 to −3.40), variable zircon εHf(t) values (−14.1 to +8.0), and high radiogenic Pb isotopic values (206Pb/204Pb = 18.588–18.790, 207Pb/204Pb = 15.616–15.642, and 208Pb/204Pb = 38.838–39.053). These geochemical characteristics indicate that the monzogranite was derived from a mixed source comprising ancient crustal and mantle materials, and experienced fractional crystallization during emplacement. We propose that the parental magma of the Mugagangri monzogranite was most likely generated during northward subduction of the Bangong Co‐Nujiang Meso‐Tethys Ocean.

Petrogenesis and tectonic setting of the early-middle triassic subduction-related granite in the eastern segment of East Kunlun: evidences from petrology, geochemistry, and zircon U-Pb-Hf isotopes

ABSTRACT The subduction process of the Paleo-Tethyan Ocean is still under controversy. We report zircon U-Pb ages and geochemistry (major and trace elements, and Hf isotopic compositions) for the Xiangjiananshan granitic plutons in the eastern segment of the East Kunlun Orogenic Belt, northern Tibetan Plateau, to constrain the subduction-related granitoids in its petrogenesis and to reconstruct the subduction prosess of the Buqingshan-A’nyemaqing Ocean. Zircon U-Pb dating yields coeval ages of 246.6 ± 4.1 Ma for granodiorite and 246.4 ± 3.9 Ma for biotite monzogranite of the Xiangjiananshan granitoid pluton. The granitoids include granodiorites, biotite monzogranites, and pseudo-porphyritic monzogranites. The granitoids have high contents of SiO2 (66.60–73.19 wt.%) and Al2O3 (13.28–16.38 wt.%), consistent with the high-K calc-alkaline series. The A/CNK ratios range from 0.98 to 1.02, indicating that the granodiorite is metaluminous and weakly peraluminous. The mafic microgranular enclaves (MMEs) in granodiorite and biotite monzogranite have a restricted SiO2 range (57.24–60.03 wt.%), and have higher Fe2O3 T, and MgO contents than the host granitoids, as well as higher total rare earth element (REE) concentrations. All samples are depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti and P) and heavy rare earth elements (HREEs), and are enriched in large ion lithophile elements (LILEs; e.g., Rb, Nd and La) and light rare earth elements (LREEs). Zircons from the pseudoporphyritic monzogranite yield two-stage model ages of 1137.32 to 1588.12 Ma, together with εHf(t) values from −5.01 to +2.11. These results indicate that the parental magma of pseudoporphyritic monzogranite was generated by partial melting of Paleoproterozoic to Mesoproterozoic rocks of the lower crust with contamination of ancient crustal material. Field and petrological observations, together with elemental and Hf isotopic data, indicate that the Xiangjiananshan granitic plutons was formed by magma mixing of mafic and felsic magmas. The felsic magma was derived from partial melting of the lower crust, while the mafic magma was derived from partial melting of an enriched lithospheric mantle metasomatized by slab-derived fluid due to the subduction of the Buqingshan-A’nyemaqing Ocean. Therefore, we propose that the northward subduction of the Buqingshan-A’nyemaqing ocean north to the Bayan Hara block under East Kunlun initiated in the Middle Permian (ca. 270 Ma), yielding calcium metaluminous arc magmatic rocks with I-type granite characteristics at East Kunlun, including the XG pluton in this study. Subsequently, the Buqingshan-A’nyemaqing ocean closed and resulted in collision of the Bayan Hara and East Kunlun blocks from 240 to 230 Ma.

Geochronology and petrogenesis of the Late Triassic A-type granitoids in the Yeongnam Massif and its implication for Late Triassic geodynamics of northeast Asia

The Late Triassic A-type granitoids along the continental margins of East Asia are important for deciphering the crust-mantle interactions, transformation of tectonic regime, and termination of the Indosinian Orogeny (known as the Songrim Orogeny in South Korea). The newly identified Wangdong plutons are distributed in the southwestern part of Yeongnam Massif, South Korea. U–Pb dating of zircons from the Wangdong plutons has established its date of emplacement at ca. 226–221 Ma, similar to the emplacement ages of the Daegang and Ian alkali granites. Geochemical data have shown that the Wangdong granitoid samples are magnesian to ferroan in composition and can be further classified in the range from alkalic to calc-alkalic. They have a high zircon saturation temperature (~ 850 °C), K2O/Na2O and, Ga/Al ratios, and are enriched with high field strength elements (e.g., Zr and Y), indicating an A-type granite affinity. Their classification into A2-type granites based on the A-type subdivision diagrams suggest that they formed in an extension-related tectonic setting. Moreover, the Wangdong A-type granitoids have high (La/Nb)N and (Th/Nb)N ratios with peraluminous characteristics (value of aluminum saturation index >1.0). In addition, magmatic zircons from the Wangdong granitoids have negative ɛHf(t) values (−6.6 to −15.5) with a Paleoproterozoic to Mesoproterozoic two-stage Hf model ages (from 1.99 to 1.49 Ga). This suggests that the Wangdong granitoids were derived from ancient crustal materials with compositions similar to metagraywackes. Based on geochemical, isotopic, and geochronological studies, we concluded that the lithospheric mantle delamination induced by slab roll-back of the subducted Paleo-Pacific plate is the main trigger in the production of Late Triassic magmatism in Yeongnam Massif, South Korea.

Geochronology, geochemistry, and Sr–Nd–Pb–Hf isotopes of ore-related diorites in the Erdaohe Pb-Zn-Ag deposit, Great Hinggan Range, NE China: Constraints on timing, petrogenesis and tectonic setting

The Erdaohe deposit is a newly discovered large-sized skarn Pb-Zn-Ag deposit located in the middle segment of the Great Hinggan Range, NE China. Geochronologic and geochemical data for the ore-related diorites in the deposit are presented here to explore the age, petrogenesis and geodynamic setting of these rocks. Zircon U–Pb LA-ICP-MS dating results show that the ore-related diorites were emplaced at 145–142 Ma. Geochemically, the ore-related diorites are generally characterized by high Y (22.5–32.7 ppm) and Yb (2.23–3.28 ppm) contents, low Sr/Y (14–40) ratios, light rare earth element (LREEs) and large ion lithophile element (LILE) (e.g., Rb and K) enrichments, and high field strength element (HFSE) (e.g., Nb, Ta, and Ti) depletions. These geochemical features are similar to those of arc magmas. Furthermore, the diorites have low (87Sr/86Sr)i compositions, fairly variable εNd(t) values and positive εHf(t) values, corresponding to 0.70604 to 0.70720, −7.8 to +2.6 and +4.5 to +8.0, respectively. These diorites have relatively young Sm–Nd and Hf model ages of 1564 to 721 Ma and 955 to 619 Ma, respectively. The whole-rock Pb isotopes show a narrow range. These isotopic data suggest that the parental magma was sourced mainly from juvenile crustal components, followed by assimilation and fractional crystallization in the crust with limited concomitant input of ancient crustal materials during magma ascent. In the Late Jurassic, the Great Hinggan Range was under compression due to the closure of the Mongol–Okhotsk Ocean, while in the Early Cretaceous, it was under extension related to the influence of the Paleo-Pacific plate. Based on the geochemical evidence and regional geodynamic evolution, we conclude that the formation of the Erdaohe deposit was associated with Paleo-Pacific plate subduction.

Episodic crustal growth and reworking at the southeastern margin of the North China Craton: evidence from zircon U–Pb and Lu–Hf isotopes of Archean tonalite–trondhjemite–granodiorite gneisses in the Bengbu-Wuhe area

The cratonization history of the North China Craton (NCC) and the nature of tectonothermal events are still highly controversial. Tonalite-trondhjemite-granodiorite (TTG) gneisses, as the dominant lithological assemblages in Archean metamorphic terranes, can provide significant clues to the magmatic and metamorphic evolution of Precambrian crust. This study presents zircon laser-ablation inductively-coupled-plasma mass spectrometry U–Pb ages, trace-element, and in-situ LA-MC-ICP-MS zircon Hf isotope data for the TTG gneisses from the Bengbu-Wuhe area on the southeastern margin of the NCC. Cathodoluminescence images and trace elements indicated that magmatic zircons display the characteristics of euhedral-subhedral crystals with oscillatory growth zoning structures, high ΣREE contents, marked Ce positive anomalies, and Pr–Eu negative anomalies. The metamorphic zircons display the spherical-oval crystals with distinct core-rim structures, high and homogeneous luminescent intensity, lower ΣREE, Nb, Ta, Hf contents, relative flat REE patterns, weak Ce positive anomalies, and Pr-Eu negative anomalies. The Ti–in–zircon geothermometer data indicate that the crystallization temperature of the TTG gneiss ranged from 754 to 868 °C. Zircon U–Pb ages indicate that the TTG gneisses formed at 2.79–2.77 Ga and 2.50 Ga and underwent metamorphism at 2.57–2.52 Ga. The Hf isotopic data indicate that the magmatic zircons exhibit high, positive eHf(t) values close to those of the coeval depleted mantle, whereas the metamorphic zircons exhibit negative or nil eHf(t) values. This implies that the TTG gneisses were derived from the partial melting of the ~ 2.9–2.6 Ga juvenile crustal sources mixed with ~ 3.0–2.8 Ga ancient crustal materials. Combined with the regional tectonic evolution, we propose that the metamorphic basement at the southeastern margin of the NCC underwent episodic crustal growth at ~ 2.7 and ~ 2.5 Ga and subsequently underwent crustal reworking or re-melting of the ancient crust during the Neoarchean. The Neoarchean TTG gneisses might have been derived from the partial melting of lower crustal materials related to plate subduction.

Early Cretaceous magmatism of the Langxian complex in the eastern Gangdese batholith, southern Tibet: Neo-Tethys ocean subduction re-initiation

新特提斯洋长期俯冲消减作用在早白垩世可能经历二次俯冲启动或板片俯冲几何形态的重大转换。确定西藏南部冈底斯岩基早白垩世岩浆作用的岩石地球化学特征和作用方式是甄别上述过程的关键，对理解新特提斯洋的俯冲演化过程至关重要。本文就冈底斯岩基东段朗县杂岩中保存的各类早白垩世岩浆岩，开展了锆石U-Pb地质年代学和Hf同位素、全岩元素和同位素（Sr-Nd）组成分析。数据结果表明：1）基性岩侵位时代为早白垩世晚期（103.6~100.8Ma），为高钾钙碱性偏铝质岩石，锆石ε_Hf（t）=+0.3~+5.7，全岩ε_Nd（t）=-0.8和-0.3，暗示其岩浆源区具有大量俯冲沉积物或流体的混入，为沉积物熔体和流体交代的地幔楔物质部分熔融的产物，经历了一定程度的角闪石分离结晶作用；2）中性岩形成于99.8~97.6Ma，略晚于基性岩，其主量元素与基性岩具有较好的线性关系，全岩ε_Nd（t）=+1.1，具有较多的地幔物质参与，为基性岩浆进一步演化形成；3）酸性岩（脉体）记录了多阶段岩浆作用（124.1~95.3Ma），根据同位素组成不同进一步划分为两类，第一类具有较低的全岩ε_Nd（t）值（-8.3~-6.0），其岩浆源区显示富集特征，t_DM2=1385~1586Ma，由古老地壳物质的再熔融形成；第二类的锆石ε_Hf（t）值（-2.8~+3.2）变化较大，岩脉的锆石ε_Hf（t）=+0.4~+8.1，t_DM=428~906Ma，全岩ε_Nd（t）=+0.1和+0.8，表明岩浆源区具有不均一性，为古老地壳物质被富流体地幔岩浆改造形成；和4）镁铁质包体的主量元素与寄主花岗岩具有较好的线性关系，锆石的Hf同位素组成变化较大（ε_Hf（t）=-9.3~+4.1），变化范围可达13个ε单位，为岩浆混合成因。寄主花岗岩和角闪辉长岩分别作为酸性和基性端元，是基性岩浆与其诱发古老地壳熔融形成的花岗质岩浆经混合形成。结合冈底斯岩基早白垩世岩浆岩的研究结果，朗县杂岩在早白垩世（124~97Ma）的岩浆作用具有明显的岩浆混合现象，锆石Hf和全岩Sr-Nd同位素组成变化较大，可达13个ε单位，其岩浆源区复杂且富含流体，代表了新特提斯洋在早期（240~144Ma）经历漫长的俯冲之后，在早白垩世时期（~120Ma）俯冲带发生跃迁或俯冲角度达到临界点，导致大量俯冲沉积物和流体沿俯冲带俯冲下去，与发生部分熔融的地幔楔物质混合，底侵导致上覆古老地壳物质的再熔融，形成早白垩世复杂的岩浆岩组合，很可能是新特提斯洋二次俯冲开始的标志。;The subduction of the Neo-Tethyan oceanic lithosphere might experienced a major shift in the subdcution geometry in the Early Cretaceous time during its long-lasting subducion. Knowing the geochemical nature and the mode of the Early Cretaceous magmatism in the Gangdese batholith is critical to deccriminate the subdcution processes in this time. Data from zircon U-Pb geochronology and geochemical (whole-rock element and isotope, zircon Hf) analyses on various rock types preserved in the Langxian complex show that: 1) the mafic rocks formed at 103.6~100.8Ma are of high-K calc-alkaline aluminous in composition. They are characterized by relatively low zircon ε_Hf(t) (+0.3~+5.7) and bulk ε_Nd(t) (-0.8 and -0.3), indicating that they were drived from partial melting of depeled mantle wedge metasomatized by fluids from subducted sediment; 2) the intermediate rocks formed at 99.8~97.6Ma and have slightly higher Nd isotope compositions with ε_Nd(t)=+1.1. They display a good linear relationship in major oxides with those in the mafic ones, suggesting that they are derivative products from the mafic suite; 3) the felsic rock (pluton and dike) crystallized at 124.1~95.3Ma. They could be subdivided into two types based on their isotopic compositions. The first type has a lower ε_Nd(t) (-8.3~6.0) but higher t_DM2 (1385~1586Ma). They formed by remelting of ancient crustal materials. In contrast, ε_Hf(t) and ε_Nd(t) in the second type granitic rocks vary widely with ε_Hf(t) ranging from -2.8 to +3.2 for the plutonic granite and from +0.4 to +8.1 for the dike, respectively. Together with relatively low Nd isotope (ε_Nd(t)=+0.1 and +0.8) and t_DM(428~906Ma), these characteristics suggest a relative young source region due to modification of ancient crustal materials by melts derived from fluid-enriched mantle; 4)enclaves hosted by the granitic rocks show good linear relationship in major oxides with the host rocks. They display a rather large shift of ~13 epsilon units in zircon Hf isotope compositions (ε_Hf(t)=-9.3~+4.1) and might represent the melts formed by various degrees of mixing an acidic end member of the hosted granite wih a mafic end member of hornblende gabbro. Combined with literature data of the Gangdese batholith, magmatic rocks from the Langxian complex preserved a key record of a major magmatic process during the Early Cretaceous (122~97Ma). Melting and mixing of various source components (ancient crustal material, fluid-enriched mantle, and depleted mantle) is one of the important features of the Early Cretaceous magmatism due to subduction of the Neo-Tethyan ocean and resulted in large shifts (up to ~13 epsilon units) in zircon Hf as well as in bulk Sr-Nd isotope compositions. To introduce various components into and achieve a large isotopic heterogeneity in the source region, it requires a major change in the subduction geometry in the long subduction of the Neo-Tethyan subdction system. Since the initation of the subduction at ~240Ma, subdcition of the Neo-Tethyan Ocean might experinecd a critical reorganization enabling the introduction of an increased amount of sediments and fluids into the subduting system and the modification of the mantle wedge in the Early Cretaceous (~120Ma). The mafic magmas caused remelting of the overlying ancient crustal material and finally formed the complex magmatic activity in the Early Cretaceous, which is likely to be a sign of the beginning of the second subduction of the Neo-Tethyan Ocean.

Geochemical Characteristics and Genesis of Biotite Monzogranite in Southeastern Guangxi Province, South China

The South China Block experienced intense tectonic–magmatic evolution during the Indosinian period, which was recorded by Indosinian granite and has attracted numerous researchers. This paper presents data on the geochronology and geochemistry of Darongshan biotite monzogranite. LA–ICP–MS U–Pb zircon analyses yielded a weighted average age of 250.1±1.6 Ma, which represents the magma crystallization age of the Early Triassic. According to petrographic observation, the main diagenetic minerals of Darongshan biotite monzogranite are quartz, K-feldspar, plagioclase, biotite, and small amounts of cordierite, tourmaline, and garnet. Darongshan biotite monzogranite is aluminum-rich and high in silica. It shows weak negative Eu anomalies (δEu=0.13–0.57) and depleted HREEs. Darongshan biotite monzogranite exhibits significant negative anomalies of high field strength elements (HFSE, e.g., Nb, Ta, Ti, and P) and positive anomalies of large-ion lithophile elements (LILE, e.g., Rb, Th, U, and Pb). Geochemical analyses suggested that Darongshan biotite monzogranite has undergone highly differentiated evolution. According to this study, Darongshan biotite monzogranite is an S-type granite, and its source material developed from the remelting of ancient crustal material. The Darongshan biotite monzogranite granite formed in the island arc environment of oceanic subduction and orogenic stage, further confirming the geological records of the remaining oceanic basin in Qinfang.

Timing and origin of the Shesuo skarn Cu-polymetallic deposit in the northern Lhasa subterrane, central Tibet: Implications for Early Cretaceous Cu(Mo) metallogenesis in the Bangong-Nujiang metallogenic belt

The Bangong-Nujiang metallogenic belt is a newly discovered copper-polymetallic belt in the Tethyan domain. To date, the Shesuo skarn Cu-polymetallic deposit is the only productive Early Cretaceous Cu deposit in the middle segment of this belt. We conducted zircon U-Pb and molybdenite Re-Os dating of this deposit, and the results show that the Shesuo skarn Cu-polymetallic deposit formed at 117–112 Ma. Within the mining area, granodiorites and monzogranites are the main metallogenic granitic bodies. The petrogeochemical features imply that the granodiorites and monzogranites were derived from the partial melting of juvenile lower crust resulting from mantle-derived magmatic underplating, with the additional involvement of ancient crust in the magma chamber, whereas the monzogranites experienced significant fractional crystallization. The δ34S values of sulfide ores suggest that they were mainly sourced from the magma and slightly contaminated by surrounding strata. The Pb isotope compositions of sulfides and Re contents of molybdenite indicate that the metals were derived from the juvenile lower crust, with a small fraction from ancient crustal materials. Our study suggests that the generation of the Shesuo deposit was most likely triggered by slab breakoff during the southward subduction of the Bangong-Nujiang Ocean lithosphere. The Shesuo and Xiongmei deposits have low zircon Ce4+/Ce3+ and EuN/Eu* ratios and low whole-rock average V/Sc, Sr/Y and (EuN/Eu*)/YbN ratios. We propose that these values are due to the input of reduced components, leading to the generation of metallogenic magmas with relatively low magmatic oxidation states and water contents and rendering the magmas infertile for later porphyry-skarn Cu formation in the Xiongmei area.

Paleozoic crustal evolution and tectonic switching in the Northeastern Tianshan: insights from zircon Hf isotopes of granitoids

Decoding the crustal and tectonic evolution of ancient accretionary orogens is not always straightforward. Here, four episodes of Paleozoic granitoids have been identified with distinct zircon–Hf isotopic characteristics from the Northeastern Tianshan. The first stage granitoids in the Dananhu–Harlik arc system are characterized by highly positive zircon ε Hf ( t ) values and short crustal incubation times with a rising event signature, suggesting a northward trench advance for the Kangguer Ocean. During the second stage, granitoids in the Dananhu and Kangguer belts have high zircon ε Hf ( t ) values and short crustal incubation times, but with a decreasing event signature for the Dananhu granitoids, implying a reworking of the juvenile arc crust. However, the near-zero ε Hf ( t ) values and the longest crustal incubation times of the Yamansu granitoids in this stage elucidate an origin from a Precambrian basement. These variations suggest that the northern trench of the Kangguer Ocean retreated southward while the southern trench advanced southward. During the third stage, the enlarged ranges of zircon ε Hf ( t ) values and crustal residence ages as well as crustal incubation times for the Dananhu and Kangguer granitoids show an interaction of juvenile material and the pre-existing crust, whereas the highly positive zircon ε Hf ( t ) values with a sharp rising event signature of the Yamansu granitoids suggest an significant crustal growth, indicating that a northward trench advance and a southern trench retreat for the Kangguer Ocean. However, the last stage granitoids in the Northeastern Tianshan entirely exhibit decreasing zircon ε Hf ( t ) values and long crustal incubation times, demonstrating a reworking of the pre-existing juvenile crust with minor input of ancient crustal materials in a post-collisional setting. Supplementary material : Table S1 and S2 and analytical methods are available at https://doi.org/10.6084/m9.figshare.c.5197889

Tracking decratonization process along a cratonic edge through late Permian to late Triassic magmatic flare-up in northwestern Liaoning, North China Craton

Resolving magmatic tempos of multiple scales along convergent plate margins presents a pivotal task in any regional tectonic and supercontinental reconstructions, as is of paramount importance for the northern North China Craton (NCC) that converged with the Central Asian Orogenic belt (CAOB) during the Paleozoic to early Mesozoic. This study applies the integrated zircon U–Pb dating and geochemical tracing to late Permian to late Triassic intrusive flare-up in northwestern Liaoning, with three episodes of granitic suites deciphered. Their contrasting elemental and isotopic features called for three distinct crustal end-members involved in their formation: ancient amphibolitic protolith, Paleozoic-accreted mafic meta-igneous ingredients and relaminated juvenile intermediate arc plutons. Sequential crustal anatexis of these multiply juxtaposed protoliths in a felsic hot zone tends to yield successive parental magmas for forming three granite suites. While the late Permian (260–250 Ma) granites, with their felsic adakitic affinity and variably evolved isotopic compositions (87Sr/86Sri = 0.70637 to 0.70659, εNd(t) = −16.7 to −10.2, zircon εHf(t) = −18.1 to +1.1), are consistent with partial melts of major ancient crustal materials and minor newly-underplated mafic ingredients, the middle Triassic (242–240 Ma) granites show a more juvenile isotope signature (εNd(t) = −11.8 to −4.7, zircon εHf(t) = −14.7 to +4.1) and attest to distinctively higher input from newly-underplated mafic lower crust in their formation. By contrast, the late Triassic (227–223 Ma) granites exhibit an A-type magmatic affinity. Their radiogenic whole-rock Nd (εNd(t) = −3.7 to +1.1) and zircon Hf (εHf(t) = +0.7 to +12.0) isotopic values suggest magma derivation from high-temperature fusion of dominantly relaminated juvenile charnockitic protolith. What follows is one phase of shoshonitic mafic dykes that fingerprint a slab-melt metasomatized asthenosphere source with depleted isotopic compositions (87Sr/86Sri = 0.70374 to 0.70388, εNd(t) = +3.5 to +4.1). Synthesizing these events with the previously recognized ones leads to a first-order duration of ca. 260–218 Ma for the flare-up and its further differentiation into three secondary pulses including ca. 260–250 Ma appinite and granite, ca. 242–238 Ma ferroan granites and ca. 227–218 Ma A-type granites and mafic dykes. While such primary duration is typical of post- collisional/orogenic magmatic tempos of convergent continental margins, three secondary pulses encapsulate successive geodynamic processes from crustal thickening through orogenic collapse to lithospheric dripping in the aftermath of the Paleo-Asian oceanic closure. Featuring a coupled scenario of lithospheric thinning and crustal growth, the northwestern Liaoning case of cratonic-edge destruction serves as a prelude but also a contrast to the late Mesozoic large-scale decratonization across the eastern NCC possibly due to oceanic subduction of the paleo-Pacific plate.

Ca. 1.7 Ga Magmatism on Southwestern Margin of the Yangtze Block: Response to the Breakup of Columbia

AbstractThis paper presents some data of the Jiaopingdu gabbro and Caiyuanzi granite at the southwestern margin of the Yangtze Block, on the geochemical compositions, zircon LA–ICP–MS U–Pb ages and Hf isotopic data. The Jiaopingdu gabbro gives the age of 1721 ± 5 Ma, the Caiyuanzi granite 1732 ± 6 Ma and 1735 ± 4 Ma, and the Wenjiacun porphyry granite 1713 ± 4 Ma, suggesting nearly contemporaneous formation time of the gabbro and granite. The bimodal feature is demonstrated by the gabbro SiO2content of 44.64–46.87 wt% and granite 73.81–77.03 wt%. In addition, the granite has high content of SiO2and Na2O + K2O, low content of Al2O3and CaO, enriched in REEs (except Eu) and Zr, Nb, Ga and Y, depleted in Sr, implying it belongs to A‐type granite geochemistry and origin of within‐plate environment. The zircon∊Hf(t) of the granite and gabbro is at the range of 2–6, which is near the 2.0 Ga evolution line of the crust, implying the parent magma of the gabbro being derived from the depleted mantle and a small amount of crustal material, and the parent magma of the granite from partial melting of the juvenile crust and some ancient crustal material at the same time. Compared with 1.8–1.7 Ga magmatism during breakup of other cratons in the world, we can deduce that the Columbia has initially broken sinceca. 1.8 Ga, and some continental marginal or intra‐continental rifts occurred atca. 1.73 Ga.

Neoproterozoic Crustal Reworking and Growth in the Zhangbaling Uplift, Tan–Lu Fault Zone: Evidence from the Feidong Complex and Zhangbaling Group

AbstractIntensive mid‐Neoproterozoic magmatism is the salient feature of the Yangtze Block, preserving abundant information about crustal reworking and growth. Zircon U–Pb–Lu–Hf isotope analysis was performed on material from the Feidong Complex (FDC) and Zhangbaling Group (ZBLG) of the Zhangbaling Uplift, in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks, to further provide important data for understanding the mid‐Neoproterozoic crustal evolution of the Northeast Yangtze Block. The amphibolite and gneissic granites in the Feidong Complex (FDC) gave similar protolith ages of 782–776 Ma. The synmagmatic zircons exhibited variable negative ∊Hf(t) values of –26.9 to –8.3. Early (ca. 2.4 Ga) to late Paleoproterozoic (ca. 2.0–1.9 Ga) inherited zircons were found in the gneissic monzogranite, with negative ∊Hf(t) values of –11.2 to –7.2, indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block. Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting‐related mafic magmas. The quartz–keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754–727 Ma with high ∊Hf(t) values of –2.0 to +5.6, indicating their derivation from the reworking of juvenile crustal materials. The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable 206Pb/238U ages (871–644 Ma) with a peak age at 741 ± 11 Ma and ∊Hf(t) values of –4.3 to +5.3, which is consistent with those of the Xileng Formation, but distinct from the FDC, indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation. The mid‐Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block, situated in different positions from the Susong Complex and the Haizhou Group. The transition from ancient to juvenile crustal sources for felsic magmatic rocks is attributed to gradually increased crustal extension during continental rifting.

The accretion history of the South China Block at its northwest margin in the Neoproterozoic: Records from the Changba complex in the Mianlue zone

To constrain the accretion history of the South China Block (SCB), a geochronological and geochemical study was carried out for the Changba Complex within the Mianlue zone in the northwestern margin of the SCB. Zircon U-Pb dating reveals that the metagabbros and metatonalites were formed at ca. 985–950 Ma, while the bt-amp gneisses have a younger protolith age of ca. 830 Ma. The metagabbro and metatonalite are low- to medium-K tholeiitic series and are significantly enriched in LILEs (Rb, Ba, Th, U, K) and slightly enriched in LREEs, but depleted in HFSEs such as Nb, Ta and Ti. In addition, they have highly positive zircon εHf(t) values (+11.3~ +16.9) and whole-rock εNd(t) values (+3.9~ +5.5) and εHf(t) values (+11.0 ~ +11.8). These geochemical features resemble to those of the magmatic rocks in juvenile oceanic arcs. Zircon δ18O value ranges from 3.0 to 6.2‰ for metagabbro and 4.6 to 5.34‰ for metatonalite, which are slightly lower than the mantle values. Hydrothermally altered gabbros in the lower oceanic crust often have lower δ18O values than mantle and can be primary components of arc lower crust. Therefore the Changba tonalite is interpreted to have been formed by partial melting of the hydrothermally altered gabbroic lower crust. The ca. 830 Ma gneisses are enriched in LREEs and incompatible elements and depleted in HFSEs, similar to the trace element pattern of the average bulk continental crust. They have enriched Sr-Nd-Hf isotopic compositions (0.7055 ~ 0.7060, −5.1 ~ −6.3, and −8.5 ~ −8.8, respectively), which is distinct from the juvenile arc crust. Besides, variable zircon εHf(t) values of −40.6 to 0 and slightly low to elevated zircon δ18O values of 4.2 to 6.6‰, suggesting derivation from reworking of a heterogeneous crustal source. In this regard, the Changba complex records the accretion of juvenile island arc and subsequent reworking of both juvenile and ancient crustal materials, which highlights the crustal growth and geodynamical evolution of the northern margin of the South China Block during the Neoproterozoic in response to the assembly of Rodinia.

Multi-stage Jurassic magmatism in the Liaodong Peninsula: Constraints on crustal evolution beneath the eastern North China Craton

Whole-rock geochemical and in situ zircon UPb and HfO isotope compositions have been measured for the Jurassic granitoids in the Liaodong Peninsula, in order to investigate their genesis and reveal the Jurassic crustal evolution of the eastern North China Craton. Our new data, combined with field and petrological observations, indicate multi-stage Jurassic magmatism, now represented by Early to Middle Jurassic biotite granites and monzogranites, and Late Jurassic two-mica monzogranites. The Early to Middle Jurassic granitoids have relatively low SiO2 contents (64.4–69.6 wt%) and K2O/Na2O ratios (0.4–1.0), adakitic characteristics with enriched LREE and depleted HREE contents, high Sr/Y ratios (52–189), positive Eu and Ba anomalies, and negative Nb and Ta anomalies. Together with their highly negative zircon ɛHf(t) (−26.6 to −16.1) and mantle-like δ18O (4.6‰ to 6.3‰) values, partial melting of a basaltic lower crust, which formed at ca. 2.5 Ga, can be proposed for the magma source of the Early to Middle Jurassic granitoids. These source rocks have not experienced significant water–rock alteration after formation. In contrary, the Late Jurassic two-mica granitoids exhibit relatively differentiated geochemical characteristics, with high SiO2 contents (>72 wt%) and K2O/Na2O ratios and variable Eu anomalies. Their parental magma was also enriched in LREEs and depleted in HREEs, with high Sr/Y (49.8–134) and (La/Yb)N (22.6–38.0) ratios. The magmatic zircons have extremely negative ɛHf(t) (−37.5 to −19.6) and relatively high δ18O (6.9‰ to 9.6‰) values, indicating the involvement of an ancient crustal component with high δ18O values, such as metasedimentary rocks. We propose, therefore, that the Late Jurassic two-mica monzogranites originated from partial melting of reworked ancient crustal materials at the depth of lower crust, and with the magma subsequently evolving as a result of plagioclase-dominated fractional crystallization. During Early to Middle Jurassic, westward subduction of the Paleo-Pacific plate, resulted in the partial melting of the mafic lower crust and the burial of ancient crustal materials in to deep crust, while crustal stretching in Late Jurassic might account for the decompression melting of the ancient crustal source. Thus, multi-stage Jurassic magmatism in the Liaodong Peninsula recorded a complex crustal evolution history, which closely related to the westward subduction of the Paleo-Pacific plate.

Middle Triassic arc magmatism in the southern Lhasa terrane: Geochronology, petrogenesis and tectonic setting

The voluminous Triassic magmatism within the Lhasa Terrane, Tibetan Plateau, has been studied for decades yet the petrogenesis of the magmas involved and the tectonic setting of this magmatism and associated events remain uncertain. This study presents new zircon U–Pb geochronological, Lu–Hf isotopic, and whole-rock geochemical data for the Middle Triassic volcanic rocks within the southern region of the Lhasa terrane. Zircon U–Pb dating of three samples from this area yield consistent ages of 233.9 ± 1.3, 232.5 ± 1.6, and 231.5 ± 1.6 Ma, representing the Middle Triassic magmatism in the southern Lhasa terrane. The whole-rock geochemistry of these volcanic rocks indicate they are enriched in the large ion lithophile elements (LILE) and the light rare earth elements (LREE). They have high εNd(t) (from +4.3 to +5.4) and zircon εHf(t) (from +16.6 to +21.8) values as well as low initial 87Sr/86Sr (0.7035–0.7037) values. These characteristics indicate that the Middle Triassic igneous rocks in this region formed from magmas generated by the partial melting of arc-type mantle wedge material. These magmas underwent fractional crystallization but did not assimilate significant amounts of ancient crustal material prior to emplacement and eruption. Combining our new data with the results of previous petrological, stratigraphic, paleomagnetic, and paleontological data from this region indicates that the Triassic magmatic rocks of the southern Lhasa terranes formed as a result of tectonism associated with the opening of the Neo-Tethyan Ocean. The driving force of the extension was most likely driven by correlated with the southward-subduction of the Banggonghu–Nujiang Oceanic plate.