Provenance analyses of early Mesozoic sediments in the Ningwu basin: Implications for the tectonic–palaeogeographic evolution of the northcentral North China Craton

This paper reports results from detrital zircon U–Pb geochronology, Hf isotopic geochemistry, sandstone modal analysis, and palaeocurrent analysis of the early Mesozoic strata within the Ningwu basin, China, with the aims of constraining the depositional ages and sedimentary provenances and shedding new light on the Mesozoic tectonic evolution of the northcentral North China Craton (NCC). The zircons from early Mesozoic sandstones are characterized by three major populations: Phanerozoic (late Palaeozoic and early Mesozoic), late Palaeoproterozoic (with a peak at approximately 1.8 Ga), and Neoarchaean (with a peak at approximately 2.5 Ga). Notably, three Phanerozoic zircons in the Early Triassic Liujiagou Formation were found to have positive ε_Hf(t) values and characteristics typical of zircons from the Central Asian Orogenic Belt (CAOB). Therefore, the CAOB began to represent the provenance of sediment in the sedimentary basins in the northern NCC no later than the Early Triassic (261 Ma), implying that the final amalgamation of the NCC and CAOB occurred before the Early Triassic. The U–Pb geochronologic and Hf isotopic results show that the Lower Middle Triassic sediments were mainly sourced from the Yinshan–Yanshan Orogenic Belt (YYOB), and that a sudden change in provenances occurred, shifting from a mixed YYOB and CAOB source in the Middle Jurassic to a primarily YYOB source in the Late Jurassic. The results of the sandstone modal analysis suggest that the majority of the samples from the Lower Middle Jurassic rocks were derived from either Continental Block or Recycled Orogen sources, whereas all the samples from the Upper Jurassic rocks were derived from Mixed sources. The change in source might be ascribed to the southward subduction and closure of the Okhotsk Ocean and the resulting intense uplift of the YYOB during the Late Jurassic. This uplift likely represents the start of the Yanshan Orogeny.     

Proterozoic VanDieland in Central Victoria: ages,compositions and source depths for late devonian silicic magmas

The Proterozoic to Cambrian VanDieland microcontinent was accreted to mainland Australia at ca 400?Ma, and its northern tip, the Selwyn Block, forms the basement in central Victoria. Here, mainly Late Devonian, silicic magmas were derived from the Selwyn Block and intruded into the shallow crust. We use the phase petrology of Late Devonian, S-type rhyolitic ignimbrites and a xenolith of pelitic migmatite, together with Nd-model ages for the silicic magmatic rocks to constrain the lithological characteristics of the metasedimentary component of the Selwyn Block, to infer minimum depths and temperature conditions here in the Late Devonian, and the likely ages of the source rocks for the S-type magmas. The most abundant source rocks are inferred to be volcaniclastic metagreywackes, with minor metadacites, meta-andesites and metapelites. The metapelitic xenolith cannot have been the source for any of the silicic magmas but constrains the upper amphibolite-facies part of the Selwyn Block to depths around 17?km, where temperatures reached ～775?°C. The older ignimbrite magma was formed by partial melting at perhaps 770?°C and a depth of at least 33?km, while the younger ignimbrite magma formed at ～23?km and 900?°C. These depths suggest source rocks in the Paleoproterozoic to Mesoproterozoic lower parts of the Selwyn Block. Nd-model ages of the silicic magmatic rocks confirm a dominance of Mesoproterozoic to Paleoproterozoic sources. If the inferred rock types in the Mesoproterozoic formations were as current correlations suggest, the sources for the Late Devonian silicic magmas would have to lie in the undocumented Paleoproterozoic basement of the Selwyn Block. Rock types here must include andesitic to dacitic volcanic components as well as volcaniclastic greywackes and minor pelites, which suggests a continental arc setting. The Late Devonian magmatism in the region may record the progression from amphibolite- to granulite-facies conditions during post-orogenic extension, with heat advected to the crust by mantle-derived mafic magmas. These processes would have resulted in mafitisation of the deep Selwyn Block.     

点云数据的多几何面片特征自动识别

针对人工构筑物丰富的面片特征,提出一种基于局部采样优化的多种几何面片（平面、柱面、球面）点云数据分割方法。该方法首先利用三维格网建立点云数据的空间划分,然后根据随机采样点确定局部格网单元,在格网单元内部拟合多种几何模型,通过局部打分确定局部候选模型（集）,利用统计推断估算候选模型集的全局打分区间,最终获得当前最优模型及其一致集,从而实现点云数据分割。试验结果表明：该方法能够对富含规则几何特征的人工构筑物进行有效分割。     

Tectonic regime switchover of Triassic Western Qinling Orogen: Constraints from LA-ICP-MS zircon U–Pb geochronology and Lu–Hf isotope of Dangchuan intrusive complex in Gansu,China

The Qinling Orogenic Belt, linking the Kunlun and Qilian Mountains to the west and continuing farther east to the Dabie Mountain, was assembled by the convergence and collision between the Greater South China and the North China blocks. The precise timing of the subduction and collision processes between these continental blocks and tectonic regime switchover is very equivocal. Zircon in-situ LA-ICP-MS U–Pb dating in this contribution indicates that the biotite monzogranite and monzogranite phases of the Dangchuan complex were crystallized at ca. 239.8 ± 2.3 Ma and 227.8 ± 1.2 Ma, respectively. The ca. 240 Ma biotite monzogranite displays ε_Hf(t) values ranging from −2.4 to +2.9, and corresponding T_DM2 of 1.72–1.94 Ga and T_DM1 of 0.77–0.88 Ga. The ca. 228 Ma monzogranite exhibits ε_Hf(t) values ranging from −4.3 to +1.9, and corresponding T_DM2 of 1.73–2.08 Ga and T_DM1 of 0.81–0.88 Ga. Lutetium–Hf isotopic composition indicates that the biotite monzogranite and monzogranite probably have the same parental magmas which were originated from hybrid sources of both reworking of Paleoproterozoic ancient crust and partial melting of the Neoproterozoic juvenile crust. The more negative ε_Hf(t) values of the monzogranite suggest more contribution of the ancient crust during the source contamination, or more possible crustal assimilation during their crystallization at ca. 228 Ma than precursor biotite monzogranite. Integrated with previous research and our detailed petrography, we propose that the Dangchuan complex underwent an episodic growth documenting the tectonic regime switchover from early Paleozoic to Triassic. The ca. 439 Ma inherited zircon recorded the persistent subduction of the oceanic crust, the ca. 240 Ma biotite monzogranite emplaced during the northward subduction of the Mianlue oceanic crust beneath the South Qinling block, and the ca. 228 Ma monzogranite emplaced during the syn-collisional process in a compressional setting.     

Age,nature, and origin of early cretaceous plutons in the Dabie Mo Mineralization belt: the Xinxian example

The Mesozoic granitoids in the Dabie Orogen are of particular geological interest as indicators for Mesozoic lithospheric evolution and because of their close association with porphyry Mo mineralization. Here, we present a study using zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating, petrogeochemistry, and Hf isotopic data to constrain the timing of the magmatism and petrogenesis of the Xinxian granites in the Dabie Mo mineralization belt (DMB), Henan Province, China. Field investigations combined with previously published data show that the Xinxian pluton mainly consists of four phases. Zircon LA-ICP-MS U–Pb dating yielded ages from 153.4 ± 1.1 Ma for Phase 1 to 146.4 ± 1.6 Ma for Phase 2, 131.6 ± 1.8 Ma for Phase 3, and 125.5 ± 1.5 Ma for Phase 4. The Xinxian granites have high SiO₂ contents of 74.94–78.70 wt.% (average: 76.63 wt.%), Al₂O₃ contents of 11.59–13.68 wt.% (average: 13.01 wt.%), and K₂O contents of 3.85–4.86 wt.% (average: 4.36 wt.%) with Na₂O/K₂O ratios of 0.78–1.03 (average: 0.92) and low MgO (0.04–0.15 wt.%), TiO₂ (0.03–0.13 wt.%), and P₂O₅ (0.006–0.07 wt.%) contents. They are enriched in Rb, U, K, and Hf, but depleted in Ba, Nb, Ta, Sr, P, and Ti. The zircon ε_Hf(t) values for Phases 1, 2, 3, and 4 vary as follows: from – 22.8 to – 20.3 with T_DM2 values from 2682 to 2869 Ma, from – 24.2 to – 21.2 with T_DM2 values from 2738 to 2925 Ma, from ?24.5 to ?21.5 with T_DM2 values from 2722 to 2915 Ma, and from ?22.9 to ?19.4 with T_DM2 values from 2421 to 2643 Ma, respectively. By integrating previous geological, geochronological, and geochemical data for the DMB, we propose that the Xinxian pluton was dominantly sourced from the crust. The granites were most likely derived from the partial melting of the Northern Dabie Complex (NDC) with some Yangtze lower crust and Southern Dabie Complex (SDC). The Xinxian pluton may have formed in a post-collision extensional setting.     

Tracking deep ancient crustal components by xenocrystic/inherited zircons of Palaeozoic felsic igneous rocks from the Altai–East Junggar terrane and adjacent regions,western Central Asian Orogenic Belt and its tectonic significance

The deep crustal continental components and architecture of the western Central Asian Orogenic Belt (CAOB) have long been a matter of debate. This article presents an integrated study of published geochronological and Hf-in-zircon isotopic data for inherited zircons from the Palaeozoic granitoid rocks and associated felsic volcanic rocks of the Chinese Altai, East Junggar, and nearby regions. The aim is to trace the age spatial distribution of deep old crustal components. Our data set comprises 463 published age data obtained by SHRIMP and LA-ICP-MS from felsic igneous rocks in these areas. Among these samples, zircon xenocrysts were observed in 69 granitic rocks and 15 felsic volcanic rocks from the Chinese Altai and 30 granitoid rocks and five felsic volcanic rocks in the East Junggar, respectively.

Three major zircon xenocrysts provinces are defined based on the distribution of these inherited zircon ages, combined with Hf-in-zircon isotopes. Province I, mainly situated in the eastern part of the central Chinese Altai, is characterized by the abundant inherited zircons with Meso-Proterozoic and Palaeo-Proterozoic ages (1000–1600 and 1600–2500 Ma, respectively), and variable ε_Hf(_t) values ranging from ?15 to +7 with ancient Hf crustal model ages (T_DMC) ranging from 1.5 to 2.9 Ga. A few scattered parts of province I are scattered situated in the East Junggar (individual areas, e.g. Taheir and Shuangchagou). Province II, situated mostly in the central Chinese Altai, is characterized by abundant xenocrystic zircons with Neo-Proterozoic ages (542–1000 Ma), ε_Hf(t) values ranging from ?6.8 to +8.1, and corresponding Hf crustal model ages of ~1.0–1.3 Ga. Province III contains abundant Phanerozoic (<541 Ma) xenocrystic zircons that show highly positive ε_Hf(t) values ranging from +5 to +16 and the youngest Hf crustal model ages (0.4–0.95 Ga). The main part of Province III occupies most areas of the East Junggar and the southernmost and northern parts of the Chinese Altai. Identification of the ancient (pre-Neoproterozoic) Hf crustal model ages in the eastern part of the central Chinese Altai (Province I) supports the suggestions that ancient concealed crustal components exist in the Chinese Altai. In contrast, Province III in the East Junggar predominantly displays young model ages, which indicates that it is mainly composed of juvenile components and likely a typical accretionary belt. Besides, a few small areas with ancient model ages are recognized in the East Junggar, providing evidence for the local existence of Precambrian crust or micro-blocks within the accretionary belt. The zircon xenocrysts provinces are consisted with the Nd isotopic province and provide further evidence for the ancient and juvenile compositions in deep. In addition, the tectonic division of the region is discussed based on the distribution of deep crustal components. The Erqis fault zone can be regarded as the boundary between the Chinese Altai and East Junggar regions and its western extension is constrained to be closer to the Altai–Qinghe Fault than previously considered. The central Chinese Altai can be subdivided into two distinct tectonic units.     

The role of mafic microgranular enclaves in the generation of Early Cretaceous granitic rocks of SE China: evidence from zircon U–Pb geochronology,geochemistry, and Hf isotopic data for the Liangnong pluton,eastern Zhejiang Province

In order to constrain the timing and petrogenesis of both the hosting rocks and the inner mafic microgranular enclaves (MMEs) of the Liangnong pluton, SE China, we have performed a series of bulk-rock geochemistry, zircon U–Pb, and Hf isotopic analysis, respectively. Zircon laser ablation–inductively coupled plasma–mass spectrometry U–Pb isotopic analysis yielded ages of 106.3 ± 1.1 Ma for the granodiorite and 103.9 ± 1.6 to 105 ± 1.8 Ma for monzogranite phases within the hosting pluton, as well as an age of 104.7 ± 0.8 Ma for the associated MMEs. The host rocks are metaluminous, have A/CNK values of 0.91–1.09, contain relatively high concentrations of SiO₂ and K₂O, are enriched in Rb, Th, Ba, Zr, and Hf, are depleted of Sr, P, Ti, Nd, and Ta, contain high concentrations of the rare earth elements (REE) and the light REE, and have moderately negative Eu anomalies (Eu*/Eu = 0.6–0.8). In comparison, the MMEs contain high concentrations of Al₂O₃, FeO, MgO, and TiO₂, are relatively enriched in Ba, U, and Sr, and are depleted in Th, Nd, and Zr. They have lower total REE concentrations and higher Eu*/Eu values than the hosting granites. The zircons within the hosting granites have Hf crustal model ages (T_DM^C) that show a peak at 1.29–1.85 Ga. Zircons within the MMEs have different εHf(t) values (–3.7 to +4.9) than the zircons within the hosting granites (–10.8 to –1.9). The results indicate that the MMEs and the hosting granites crystallized from magmas with different sources, thereby showing that the Early Cretaceous magmatism in the coastal areas of SE China was generated by the widespread injection of mantle-derived magmas caused by rollback of the subducting palaeo-Pacific Plate.     

Metallogenesis and hydrothermal evolution of Middle Jurassic porphyry Mo deposits in the southern Zhangguangcai Range,NE China: evidence from fluid inclusions,H–O–S isotopes,and Re–Os geochronology

A major metallogenic belt with substantial resources of gold, lead, zinc, copper, and molybdenum is present in the southern Zhangguangcai Range, NE China. Several large porphyry Mo deposits are located in this belt, as for example at Jidetun, Fu’anpu, and Daheishan. Five molybdenite samples from the Jidetun deposit yielded an Re–Os isochron age of 168.6 ± 2.1 Ma (mean standard weighted deviation = 0.20), and this is consistent with the Re–Os isochron ages of the other Mo deposits in the southern Zhangguangcai Range, giving a Middle Jurassic age for metallogenesis. The Jidetun, Fu’anpu, and Daheishan deposits all tend to have weakly enriched ³⁴S values of 0.80‰–3.20‰ and relatively low Re contents ranging from 3.073 to 43.567 ppm, which indicates the ore-forming materials were derived mainly from granitic magmas that had an origin in the mixture of crust and mantle. Three stages of mineralization can be identified in the deposits at Jidetun, Fu’anpu, and Daheishan. The original ore-forming fluids in stage I were characterized by high-temperature magmatic hydrothermal fluids that were most likely derived by exsolution from the Middle Jurassic ore-bearing magmas. However, two different fluid systems, NaCl–H₂O–CO₂ fluids and NaCl–H₂O fluids, were widespread in stage I of porphyry Mo deposits in the southern Zhangguangcai Range. Taking into account the regional geological characteristics and tectonic setting, we suggest that two different emplacement modes of the ore-bearing magmas explain the different fluid systems in stage I: the first magmas were emplaced along the contact zones between the strata and earlier granitoids, whereas the second magmas were emplaced entirely within the earlier granitoid intrusions. The stage II and III fluids were characterized by relatively lower temperatures and low H–O isotopic values, indicating a gradual evolution from magmatic to meteoric sources.     

Carbonate alteration of ophiolitic rocks in the Arabian–Nubian Shield of Egypt: sources and compositions of the carbonating fluid and implications for the formation of Au deposits

Ultramafic portions of ophiolitic fragments in the Arabian–Nubian Shield (ANS) show pervasive carbonate alteration forming various degrees of carbonated serpentinites and listvenitic rocks. Notwithstanding the extent of the alteration, little is known about the processes that caused it, the source of the CO₂ or the conditions of alteration. This study investigates the mineralogy, stable (O, C) and radiogenic (Sr) isotope composition, and geochemistry of suites of variably carbonate altered ultramafics from the Meatiq area of the Central Eastern Desert (CED) of Egypt. The samples investigated include least-altered lizardite (Lz) serpentinites, antigorite (Atg) serpentinites and listvenitic rocks with associated carbonate and quartz veins. The C, O and Sr isotopes of the vein samples cluster between ?8.1‰ and ?6.8‰ for δ¹³C, +6.4‰ and +10.5‰ for δ¹⁸O, and ⁸⁷Sr/⁸⁶Sr of 0.7028–0.70344, and plot within the depleted mantle compositional field. The serpentinites isotopic compositions plot on a mixing trend between the depleted-mantle and sedimentary carbonate fields. The carbonate veins contain abundant carbonic (CO₂±CH₄±N₂) and aqueous-carbonic (H₂O-NaCl-CO₂±CH₄±N₂) low salinity fluid, with trapping conditions of 270–300°C and 0.7–1.1 kbar. The serpentinites are enriched in Au, As, S and other fluid-mobile elements relative to primitive and depleted mantle. The extensively carbonated Atg-serpentinites contain significantly lower concentrations of these elements than the Lz-serpentinites suggesting that they were depleted during carbonate alteration. Fluid inclusion and stable isotope compositions of Au deposits in the CED are similar to those from the carbonate veins investigated in the study and we suggest that carbonation of ANS ophiolitic rocks due to influx of mantle-derived CO₂-bearing fluids caused break down of Au-bearing minerals such as pentlandite, releasing Au and S to the hydrothermal fluids that later formed the Au-deposits. This is the first time that gold has been observed to be remobilized from rocks during the lizardite–antigorite transition.     

Structure and geochronology of the Tongbai complex and their implications for the evolution of the Tongbai orogenic belt,central China

The Tongbai orogenic belt has an overall antiformal geometry and the hinge of the antiform is sub-horizontal and trends NW–SE. The Tongbai complex (TBC) in the core of the antiform is bounded by the S-dipping Yindian–Malong shear zone in the south, the sub-horizontal Taibaiding shear zone at the top and the N-dipping Hongyihe–Tongbai shear zone in the north. The three shear zones have dextral, top-to-NW and sinistral movement, respectively. They are parts of a single shear zone, termed the Tongbai shear zone, that has a uniform top-to-NW sense of shear. Three samples of deformed granitoid (mylonite or protomylonite) from the shear zone have U–Pb zircon ages of 145 ± 6 Ma, 142 ± 2 Ma and 131 ± 6 Ma, respectively. An L-tectonite in the TBC yielded a metamorphic age of 137 ± 8 Ma and a migmatite an age of 137 ± 1 Ma. The Tongbai shear zone is intruded by undeformed Early Cretaceous granite and dykes and deformation in the shear zone is constrained to ca. 140–135 Ma, synchronous with metamorphism and migmatization in the TBC. Early Cretaceous magma emplacement and the associated uplift modified the TBC into a gentle antiform and the uplift may have continued to ca. 102–85 Ma. Similar geometry and kinematics have been documented in the Dabie orogenic belt to the east, which suggests that the Central Orogenic Belt in China probably experienced a uniform orogen-parallel extension and top-to-NW shearing in the ductile lithosphere in the Early Cretaceous.