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Prydz Bay is an important part of the Pan-African high-grade tectonic mobile belt. The focus of this investigation, by applying zircon LA-ICP-MS U-Pb geochronology, zircon Lu-Hf isotope systematics, and whole-rock geochemistry, is on Pan-African pegmatites in the Larsemann Hills of Prydz Bay, East Antarctica, their association with country rocks, and the formation conditions. Based on the obtained results, it is concluded that the pegmatites exhibit elevated levels of silica and alkali and possess peraluminous features. These pegmatites originated during the late Neoproterozoic–Early Cambrian (Pan-African) event, specifically in the D2–D4 stages. The D2 stage occurred between 546 and 562 Ma, followed by D3-stage pegmatites around 534 Ma. The pegmatites from the D2–D3 stages are considered to originate from Paleoproterozoic crustal materials, while there are at least two phases of pegmatites in the D4 stage (~517 Ma and ~521 Ma). The D4-1 pegmatite (~521 Ma) suggested both Paleo–Mesoproterozoic crustal origin, perhaps connected to extension. The D4-2 pegmatite (~517 Ma) originated from the crust layers. In the Larsemann Hills, Pan-African pegmatites formed in a recurring regime of tension. Therefore, the obtained data elucidate that a Pan-African stretching process might have occurred in Prydz Bay. [ABSTRACT FROM AUTHOR]

The Early Cretaceous Weideshan granites are associated with large-scale Au and polymetallic Cu-Mo-Pb-Zn mineralization. To investigate the petrogenesis of the Weideshan granite and constrain its tectonic setting during the Early Cretaceous, we conducted a zircon U-Pb-Hf isotope and whole-rock geochemical and Sr-Nd isotopic study of the granite. In situ zircon U-Pb dating of three granite samples yielded Early Cretaceous ages of 112.83 ± 0.80, 112.64 ± 0.91, and 111.82 ± 0.78 Ma. The samples had high-K calc-alkaline compositions and were enriched in the light rare earth and large-ion lithophile elements (e.g., K, Rb, Ba, Th, and U) and depleted in high-field-strength elements (e.g., Nb, Ti, and P). The samples had small negative Eu anomalies and initial 87Sr/86Sr and εNd(t) values of 0.70853–0.71029 and –18 to –14, respectively. The zircon εHf(t) values varied between −16 and −12, with corresponding two-stage model ages (tDM2) of 2180–2000 Ma. These characteristics indicated that the Weideshan pluton was formed in a back-arc extensional environment caused by subduction of the Paleo-Pacific Plate toward the Asian continent during the early Cretaceous. The magma was generated by crust–mantle interaction during lithospheric thinning. The diagenetic age of the Weideshan granites was the same as the formation age of gold and polymetallic ores in the Jiaodong area. The extensive fluid circulation induced by the magma emplacement may be the main source of ore-forming materials for the gold and polymetallic Cu-Mo-Pb-Zn deposits. [ABSTRACT FROM AUTHOR]

The Xinghongpu Formation is very important for understanding the Devonian tectonic evolution of the South Qinling orogenic belt. Geochemical, detrital zircon U-Pb-Hf isotopic studies were carried out on the Late Devonian metasedimentary rocks of the Xinghongpu Formation to constrain the depositional age, the provenance, and the tectonic setting. The detrital zircon U-Pb dating results revealed that the depositional age of the Xinghongpu Formation of the Late Devonian was not earlier than 363.2 Ma. The whole-rock geochemistry suggested that (1) this suite of metasedimentary rocks was mainly derived from quartzose sediments of mature continental provenance, with a small contribution from mafic and intermediate igneous provenance, and (2) the metasedimentary sandstone of the Xinghongpu Formation from the Late Devonian was deposited in an active continental margin to continental arc setting. The detailed detrital zircon U-Pb dating showed that the age spectra of detrital zircon could be divided into four groups: (1) 416–480 Ma, accounting for about 23%; (2) 740–850 Ma, accounting for about 19%; (3) 889–1017 Ma, accounting for about 19%; and (4) 1072–1146 Ma, accounting for about 12%. It also contained a group of Early Proterozoic zircons. The age and Hf isotope of the detrital zircons suggested that the clastic sediment deposited in the Xinghongpu Formation mainly came from the South Qinling Orogenic Belt and the North Qinling Orogenic Belt. The detrital zircon Lu-Hf isotopes indicated that most zircons were the products of the ancient crustal remelting, and the mantle-derived magmatic sources contributed to the provenance. The Xinghongpu Fm. formed in an oceanic basin in a continental margin environment with arc systems. [ABSTRACT FROM AUTHOR]

The Shiquanhe–Laguoco–Yongzhu–Jiali ophiolite mélange belt in Tibet includes the Laguoco Tso ophiolite as part of its western segment. Researchers studying the evolution of the Tibetan Plateau and the Tethys have taken a keen interest in the debated relationship between this ophiolite belt and the Bangong–Nujiang ophiolite belt. However, there is little research in this field. This study reports the rock geochemistry, SIMS (the secondary ion mass spectrometry) zircon U-Pb ages, and O isotope compositions of gabbro from the Laguoco ophiolite. Gabbro has substantial depletion in HFSEs (the high field strength elements) such as Th, Nb, Zr, and Hf, as well as exhibits comparatively high Mg# (80.6 on average), and low K, N, P, and Ti contents. Therefore, it was possibly formed in an intra oceanic subduction island arc environment originating from ~30% partial melting of the depleted spinel lherzolite. The SIMS zircon U-Pb ages of the gabbro samples are 187 ± 1.2 Ma and 189 ± 2.1 Ma, and the weighted averages of δ18O are 5.24‰ ± 0.12‰ and 5.34‰ ± 0.13‰, which are close to mantle-derived zircon δ18O (5.3‰ ± 0.3‰). These results suggest that during the Early Jurassic, the Laguoco ophiolite recorded the intra oceanic subduction of the northern branch of the Neo-Tethys. [ABSTRACT FROM AUTHOR]

Paleoproterozoic tectonic evolution of the northern North China Craton has been a hot research topic. We firstly identified a 1.85 Ga hornblendite from the Gaositai mafic–ultramafic complex, in northern Hebei. Systematic studies of petrology, zircon U-Pb geochronology, and in situ mineral major and trace elements of hornblendite are the key to revealing the petrogenesis of the Paleoproterozoic ultramafic rock and the tectonic evolution of northern North China Craton. LA-ICP-MS zircon U-Pb dating suggests the Gaositai hornblendite formed at 1851 ± 44 Ma. The late Paleoproterozoic ultramafic rocks, together with coeval post-collisional granites, formed a bimodal igneous assemblage. Both hornblende and its equilibrium melt compositions show strongly fractionated HREE patterns, relative enrichments in LREEs and LILEs, and depletions in HREEs and HFSEs. The phlogopite-bearing hornblendite magma could have originated from a hydrous garnet-facies mantle source metasomatized by slab-derived silicate melt. Furthermore, the variations of major and trace elements in hornblende from core to rim also reveal the mineral fractional crystallization and magma recharge. Zircon trace elements, melt composition equilibrium with hornblendes, and the bimodal igneous assemblage suggest that the generation of the Gaositai Paleoproterozoic hornblendite was likely the product of post-collisional extension related to the collision between eastern and western North China blocks. [ABSTRACT FROM AUTHOR]

The Jiao-Liao-Ji belt (JLJB), in the Eastern Block of the North China Craton, is a major Paleoproterozoic orogen and underwent a complicated tectonic evolution during 2.2–1.8 Ga. The Liaohe Group, an important stratigraphic unit in the JLJB, is key to understanding the complex evolution of this belt. In this paper, we present new detrital zircon U–Pb ages and Hf isotope data for meta-sedimentary rocks from the Gaixian Formation in different areas of the JLJB, in addition to compiled data for other formations of the Liaohe Group, to establish the depositional age and source of detrital materials of the group. U–Pb age results show that the age ranges of zircons from the different samples are broadly similar. The youngest zircon group is ca. 2.06 Ga, and the youngest single-grain age is ca. 2.0 Ga, constraining the depositional age of the Gaixian Formation to between 2.0 Ga and the metamorphic age of ca. 1.9 Ga. The zircon age data indicate that the provenance was primarily Archaean basement of the Nangrim Block and Paleoproterozoic volcanic rocks of the Li'eryu Formation. On the basis of the new geochronological data and results from previous studies, it is inferred that the JLJB underwent a successive process of rifting–subduction–collision, with the different formations of the Liaohe Group being deposited in different stages from rift to passive continental margin and then to active continental margin. Zircon Hf isotope data from the JLJB and adjoining Longgang and Nangrim blocks indicate that a major crustal growth event occurred at 2.9–2.5 Ga, followed by crustal growth and intense recycling of ancient crust at ca. 2.2 Ga. [ABSTRACT FROM AUTHOR]

The Sanjiang Indosinian orogen, located in the eastern part of the Paleo-Tethys tectonic domain, is a critical region to study the Paleo-Tethyan Ocean evolution. Middle Permian–Late Triassic magmatic rocks are widespread in the Deqin–Weixi–Madeng area of southwestern (SW) Sanjiang Indosinian orogen, yet their petrogenesis and tectonic setting remain disputed. In this study, LA-ICP-MS zircon U-Pb age and Hf isotopes, and whole-rock elemental and Sr-Nd isotope geochemistry of Madeng dacite were studied. The Madeng dacite was dated at ca. 241.7 and 243.4 Ma. The samples had high Al2O3 (12.91 to 14.39 wt.%) but low MgO (0.62 to 1.76 wt.%) contents, and were alkali-rich (Na2O + K2O = 6.97 to 8.66 wt.%) with A/CNK > 1.1, strongly resembling peraluminous S-type granites. The rocks were enriched in Rb, K, Th, U and LREE, but depleted in Ba, Sr, Nb, Ta, P and Ti, and showed obvious negative Eu anomalies, suggesting fractionation of Ti-bearing minerals (e.g., rutile and ilmenite) and plagioclase. The dacite had an initial 87Sr/86Sr value of 0.705698 to 0.710277, and negative εNd(t) (−11.28 to −10.64) and εHf(t) (−13.99 to −8.60), indicating a continental meta-sedimentary source. Their average Nb/Ta (12.24) and Th/U (4.65) were also consistent with continental crust. According to the lithological assemblage and geochemical features, we propose that the Deqin–Weixi–Madeng area intermediate-felsic magmatism was generated in a subduction-related tectonic setting. [ABSTRACT FROM AUTHOR]

The Tongkuangyu copper deposit in Zhongtiaoshan at the southern margin of the North China Craton is one of the oldest porphyry Cu deposits in the world and its metallogenesis and tectonic evolution have been debated. Here, porphyritic intrusion geochemical and geochronological data are reported to identify the diagenetic age, mineralization, tectonic setting, and evolution of the deposit. Geochemical data show that granodiorite porphyry is a peraluminous rock, with low concentrations of Fe (~3.99%) and Ti (~0.29%) and high concentrations of alkali (~6.13%) and high Al (~15.42%) and Mg numbers (~51). The rocks show comparative enrichment of Na, K, and Mg; higher La/Yb ratios, no significant Eu anomaly, and obvious Nb–Ta–Ti negative anomaly, showing similar geochemical characteristics to Archean TTG and sanukitoid. ΣREE vary greatly, ranging from 33.47 × 10−6 to 277.81 × 10−6 (average 137.09 × 10−6). The characteristics of REE show obvious fractionation of LREE and HREE, enrichment of LREE, and depletion of HREE. Some of the LREE (La and Ce) and LILE (K, Rb, and Ba) are enriched, but some of the LILE (Th and U) are depleted. In addition, some of the HFSE (Nb, Ta, P, and Ti) are depleted while some (Zr and Hf) are enriched. High precision LA–MC–ICP MS zircon U–Pb dating yield concordant ages of 2159 ± 19 Ma, which is broadly coeval with ore formation (~2.1 Ga) in the area. Zircon εHf(t) values range from −3.8 to 1.13, with a model age of 2778 to 2959 Ma, indicating that the formation of porphyry is related to the partial melting of Archean crust (~2.7 Ga) with a minor amount of mantle material added. Tongkuangyu granodiorite porphyry formed in the tectonic setting of the post-orogenic extension in the Paleoproterozoic, and Tongkuangyu Cu deposit may be related to the extension of the North China Craton in the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

In metamorphic rocks, mineral species react over a range of pressure–temperature conditions that do not necessarily overlap. Mineral equilibration can occur at varied points along the metamorphic pressure–temperature (PT) path, and thus at different times. The sole or dominant use of zircon isotopic compositions to constrain the evolution of metamorphic rocks might then inadvertently skew geological interpretations towards one aspect or one moment of a rock's history. Here, we present in-situ U–Pb/Sm–Nd isotope analyses of the apatite crystals extracted from two meta-igneous rocks exposed in the Saglek Block (North Atlantic craton, Canada), an Archean metamorphic terrane, with the aim of examining the various signatures and events that they record. The data are combined with published U–Pb/Hf/O isotope compositions of zircon extracted from the same hand-specimens. We found an offset of nearly ca. 1.5 Gyr between U-Pb ages derived from the oldest zircon cores and apatite U–Pb/Sm–Nd isotopic ages, and an offset of ca. 200 Ma between the youngest zircon metamorphic overgrowths and apatite. These differences in metamorphic ages recorded by zircon and apatite mean that the redistribution of Hf isotopes (largely hosted in zircon) and Nd isotopes (largely hosted in apatite within these rocks), were not synchronous at the hand-specimen scale (≤~0.001 m3). We propose that the diachronous redistribution of Hf and Nd isotopes and their parent isotopes was caused by the different PT conditions of growth equilibration between zircon and apatite during metamorphism. These findings document the latest metamorphic evolution of the Saglek Block, highlighting the role played by intra-crustal reworking during the late-Archean regional metamorphic event. [ABSTRACT FROM AUTHOR]