Hong-Fei Ling

Early Cambrian ocean anoxia in South China

Arising from: M. Wille, T. F. Nägler, B. Lehmann, S. Schröder & J. D. Kramers 453, 767–769 (2008)10.1038/nature07072; Wille et al. replyThe cause of the most marked changes in the evolution of life, which define the first-order stratigraphic boundary between the Precambrian and the Phanerozoic eon, remains enigmatic and a highly topical subject of debate. A global ocean anoxic event, triggered by large-scale hydrogen sulphide (H2S) release to surface waters, has been suggested by Wille et al., on the basis of two data sets from South China and Oman, to explain the fundamental biological changes across the Precambrian/Cambrian (PC/C) boundary. Here we report a new precise SHRIMP U–Pb zircon age of 532.3 ± 0.7 million years (Myr) ago (Fig. 1) for a volcanic ash bed in the critical unit that reflects the ocean anoxic event, the lowermost black shale sequence of the Niutitang Formation in the Guizhou Province, South China. This age is significantly younger than the precise PC/C boundary age of 542.0 ± 0.3 Myr ago, approximately 10 Myr younger than the extinction of the Ediacaran fauna, and thus challenging the view of a major ocean anoxic event having been responsible for the major changes in the direction of evolution at the PC/C boundary.

Contrasting origins of late Mesozoic adakitic granitoids from the northwestern Jiaodong Peninsula, east China: implications for crustal thickening to delamination

Two suites of granitoids, the Late Jurassic (158 ± 3 Ma) Linglong suite and the Early Cretaceous (130–126 Ma) Guojialing suite, crop out in the northwestern Jiaodong Peninsula, eastern China. The Linglong suite is a monzogranite, comprising alkali feldspar, plagioclase, quartz and Fe-rich biotite. The Guojialing suite includes at least five plutonic bodies of both granodiorite and monzo-granite. The rocks are composed of plagioclase, alkali feldspar, quartz, Mg-rich amphibole and Mg-rich biotite. Both the Linglong and Guojialing suites have adakitic affinity. They are enriched in LREE with high La/Yb ratios and show positive Eu anomalies. The rocks are also enriched in LILE and depleted in HFSE with high Sr/Y ratios. The Linglong granite shows very uniform Sr–Nd isotopic compositions with initial 87 Sr/ 86 Sr ratios of 0.7119–0.7126 and e Nd (T) values of −21.3 to −21.6, which are similar to those of the local Neoarchaean basement. The Guojialing suite has variable initial 87 Sr/ 86 Sr ratios (0.7108–0.7120) and e Nd (T) values (−10.8 to −17.2), which are distinct both from those of the Neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area. Detailed petrological and geochemical data indicate that the Linglong suite was derived by partial melting of Neoarchaean metamorphic lower-crustal rocks at depth of > 50 km with a eclogite residue, whereas the Guojialing suite was formed by the reaction of delaminated eclogitic crust-derived melt with the upwelling asthenospheric mantle. The petrogenesis of these two contrasting adakitic granitoids suggests intensive lower-crustal delamination during Early Cretaceous times, following a crustal thickening process from the late stage of the Early Jurassic to early stage of the Late Jurassic with crustal thickness of 50 km, respectively.

Petrology and geochemistry of shoshonitic plutons from the western Kunlun orogenic belt, Xinjiang, northwestern China: implications for granitoid geneses

Abstract A series of granitoids from Proterozoic to Cenozoic age occurred in the western Kunlun orogenic belt, Xinjiang, northwestern China. Several intrusions such as the West Datong (Middle Caledonian age), North Kuda (Late Caledonian age) and Kuzigan, Karibasheng, Zankan (Himalayan age) plutons have shoshonitic affinity. Their rock assemblages include (quartz) monzodiorite–(quartz) monzonite–quartz syenite (Middle Caledonian) or monzonitic granite–granite (Late Caledonian) or biotite (monzonitic) granite–diopside granite–diopside syenite (Himalayan). Generally, biotite is iron–phlogopite, with some eastonite and high Mg/(Mg+Fe T ) and Fe 3+ /Fe 2+ ratio. Amphibole is mainly edenitic hornblende and magnesian hastingsitic hornblende, with some edenite and higher Mg/(Mg+Fe T ) and Fe 3+ /Fe 2+ ratio. The rocks show SiO 2 contents of 52.77–71.85% and high K 2 O+Na 2 O (mostly >8%, average 9.14%), K 2 O/Na 2 O (mostly >1, average 1.50) and Fe 2 O 3 /FeO (0.85–1.51, average 1.01) and low TiO 2 contents (0.15–1.12%, average 0.57%). Al 2 O 3 contents (13.01–19.20%) are high but variable. The granitoids are prominently enriched in LILE, LREE and volatiles such as F. However, the studied shoshonitic granitoids among the three intrusive periods also show differences in isotopic compositions and trace element concentrations, suggesting their different geneses: the origin of the West Datong pluton is probably related to the involvement of subducted oceanic crust sediments into the mantle source; the North Kuda and Himalayan plutons could have been generated by partial melting of subducted oceanic crust sediments or metasediments of thickened continental lower crust in the process of late-orogenic slab break-off or lithospheric thinning.

Petrogenesis of Late Jurassic Qianlishan granites and mafic dykes, Southeast China: implications for a back-arc extension setting

A late Mesozoic belt of volcanic-intrusive complexes occurs in Southeast China. The Qianlishan granites are distributed in the northwest of the belt. The pluton is composed of porphyritic biotite granite (153 Ma) and equigranular biotite granite (151 Ma) and was intruded by granite-porphyry dykes (144 Ma) and mafic dykes such as lamprophyre and diabase (142 Ma). The granitic rocks, consisting mainly of K-feldspar, plagioclase, quartz and Fe-rich biotite, have SiO 2 contents of 72.9–76.9%, and are enriched in alkalis, rare earth elements (REE), high field strength elements (HFSE) and Ga with high Ga/Al ratios, but depleted in Ba, Sr and transition metals. Trace-element geochemistry and Sr–Nd isotope systematics further imply that the Qianlishan granitic magmas were most probably derived by partial melting of Palaeo- to Mesoproterozoic metamorphic lower-crustal rocks that had been granulitized during an earlier thermal event. These features suggest an A-type affinity. The Qianlishan lamprophyre and neighbouring coeval mafic dykes (SiO 2 = 47.9–53.8 wt%) have high MgO and compatible element contents. These rocks also have high K 2 O contents and are enriched in alkalis, light REE, large ion lithophile elements, and depleted in HFSE. They have low initial e Nd values and relatively high initial 87 Sr/ 86 Sr ratios. We suggest a subduction-modified refractory lithospheric mantle (phlogopite-bearing harzburgite or lherzolite) for these high-Mg potassic magmas. The Qianlishan diabases (SiO 2 = 48.4–48.7 wt%) are alkaline and have high TiO 2 and total Fe 2 O 3 contents, together with the positive initial e Nd value, suggesting derivation from fertile asthenopheric mantle (phlogopite-bearing lherzolite). A back-arc extensional setting, related to subduction of the Palaeo-Pacific plate, is favoured to explain the petrogenesis of the Qianlishan granites and associated mafic dykes. Between 180 and 160 Ma, Southeast China was a continental arc, forming the 180–160 Ma plutons of the late Mesozoic volcanic-intrusive complex belt, and the lower-crust was granulitized. Since 160 Ma the northwestern belt has been in a back-arc extensional setting as a consequence of slab roll-back, resulting in the lithosphere thinning and an influx of asthenophere. The upwelling asthenosphere, on the one hand, induced the local lithospheric mantle to melt partially, forming high-Mg potassic magmas, and on the other hand it underwent decompression melting itself to form alkaline diabase magma. Pulsatory injection of such high-temperature magmas into the granulitized crustal source region induced them to partially melt and generate the A-type magmas of the Qianlishan granitic rocks.

New carbon isotope stratigraphy of the Ediacaran–Cambrian boundary interval from SW China: implications for global correlation

The Yangtze Platform preserves relatively thick carbonate successions and excellent fossil records across the Ediacaran–Cambrian boundary interval. The intensely studied Meishucun section in East Yunnan was one of the Global Stratotype Section candidates for the Precambrian–Cambrian boundary. However, depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified. The Laolin section located in NE Yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the Precambrian–Cambrian boundary. However, the stratigraphic framework and correlations were controversial. We studied and systematically sampled the Laolin section and present here new carbon isotope data for this section. The Laolin section consists of, in ascending order, the Baiyanshao dolostone of the Dengying Formation, the Daibu siliceous dolostone, Zhongyicun dolomitic phosphorite, lower Dahai dolostone and upper Dahai limestone of the Zhujiaqing Formation, and the black siltstone of the Shiyantou Formation. Our data reveal a large negative δ 13 C excursion (−7.2‰, L1′) in the Daibu Member, which matches the previously published data for the Laolin section, and a large positive excursion (+3.5‰, L4) in the Dahai Member, which was not shown in the published data. The excursion L1′ correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in Siberia and Mongolia. Similar magnitude excursions are also known from Morocco and Oman, for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 Ma, thus confirming a global biogeochemical event near the Ediacaran–Cambrian boundary. Our data also indicate that deposition was more continuous at the Laolin section compared with the Meishucun section, where there are no records of a comparable negative excursion near the Ediacaran–Cambrian boundary, nor any comparable positive excursion in the Dahai Member. Therefore, the Laolin section has proven potential to be a supplementary Global Stratotype Section for the Ediacaran–Cambrian boundary on the Yangtze Platform.

Re-Os isotopes and PGE geochemistry of black shales and intercalated Ni-Mo polymetallic sulfide bed from the Lower Cambrian Niutitang Formation, South China

The Lower Cambrian Niutitang Formation consists of a thick black shale sequence with a regionally distributed conformable Ni Mo polymetallic sulfide horizon and a chert bed at its basal strata on theYangtze Platform, South China. In this paper, we discuss all available data on Re Os isotopes and Platinum Group Element (PGE) distribution pattern of the Ni Mo polymetallic sulfide ore and its host rocks (black shales, cherts, and phosphorites) from Guizhou and Hunan provinces. Our results show that the black shales and the Ni Mo sulfide ore have a high initial 187 Os/ 188 Os ratio of 0.78～0.86, indicating that the Early Cambrian ocean across the Yangtze Platform had a highly radiogenic Os value. This ratio is slightly lower than but still similar to present day seawater, possibly as a result of high continental weathering at that time. The Ni Mo sulfide ore yields a Re Os isochron of 537±10 Ma (MSWD=11.9), possibly representing the depositional age of the Niutitang Formation. The chondrite normalized PGE pattern, Pt anomaly (Pt/Pt *), Pt/Pd, Ir/Pd, Au/Ir and Re/Mo ratios of the Ni Mo sulfide ore and its host rocks from South China indicate a varying source contribution of the PGE and other metals for different rocks. It is suggested that the cherts and Ni Mo sulfide ore may have a significant proportion of PGE and probably other metals deriving from submarine hydrothermal fluids with a mantle signature.

Paleoceangraphic significance of redox-sensitive metals of black shales in the basal Lower Cambrian Niutitang Formation in Guizhou Province, South China

Abstract Black shales of the Lower Cambrian Niutitang Formation occurwidely on the Yangtze Platform. In this study, we analyzed black shales from two sections (Zhongnan and Zhijin) in Guizhou Province. The redox-sensitive metal concentration and distribution of black shales from the two sections provide good evidence for the anoxic conditions of the basal Cambrian ocean on the Yangtze Platform. Our geochemical data suggest that the black shales from the Zhongnan section may have deposited in a more strongly anoxic environment than the black shales in the Zhijin section.

SHRIMP U-Pb zircon dating for lamprophyre from Liaodong Peninsula： Constraints on the initial time of Mesozoic lithosphere thinning beneath eastern China

It is undebated fact that the lithospheric mantle beneath eastern China was considerably thinned during the Mesozoic time. However, it has no adequate evidence for the exact timing when the lithosphere thinning started. The Liaodong Peninsula is located in the eastern segment of the North China Craton and is one of the important domains to explore the event of lithosphere thinning. SHRIMP U-Pb zircon dating and geochemical study were carried out for the lamprophyre dike swarm that intruded into the magnesite ore-beds in the Dashiqiao Formation of Paleoproterozoic Liaohe Group at the Huaziyu magnesite ore district, Liaodong Peninsula. The results indicate that these lamprophyre dikes were intruded in late Jurassic (155±4 Ma) and show some geochemical characteristics of potassic magmas. It is now accepted that the lithosphere thinning took place in the late Mesozoic, and the peak thinning stage occurred in early Cretaceous (130–120 Ma). Considering the potassic mafic magmatism marking the onset of the lithospheric thinning, we therefore suggest that the studied late Jurassic potassic lamprophyre dike swarm could imply that the late Jurassic is the time that lithosphere thinning started.

Geochemical characteristics and genesis of Neoproterozoic granitoids in the northwestern margin of the Yangtze Block

Abstract Geochemistry of nine Neoproterozoic granitoid bodies in the northwestern margin of the Yangtze Block (YB) has been studied in this paper. Their ages range from 876 Ma to 786 Ma based on U-Pb zircon dating. These granitoids can be divided into three groups in terms of major and trace elements. Rocks of Group I are alkaline series granites characterized by evident negative Eu anomaly (Eu/Eu* = 0.31 to 0.41) with total REE concentrations between 274 to 122 ppm. Group III includes migmatized granites characterized by low REE concentrations (14 to 45 ppm) and positive Eu anomaly (Eu/Eu* = 1.1 to 2.5). Group II comprises tonalite and diorite with REE between the above two groups (ΣREE = 105 to 212 ppm, Eu/Eu* = 0.73 to 0.79). Granitoids of Group II and III belong to calc-alkaline series and I-type, which were formed during the Jinning Orogeny before 820 Ma related to subduction or collision between the Yangtze Block and oceanic Qinghai-Yunnan-Tibet Plate. The Group I granites were formed after 805 Ma in the late stage of or post the Jinning Orogeny. The Neoproterozoic granitoids have e Nd (T) values ranging from −4.3 to +4.5 and initial 87 Sr/ 86 Sr ratios ⩽ 0.705, similar to those of the Neoproterozoic granitoids in the other margins of the YB, but different from those of coeval granitoids within the YB which have e Nd (T) of −8.1 to −14.2 and initial 87 Sr/ 86 Sr of 0.705 to 0.708. The difference in geochemistry of the three groups was due to difference in their sources. The Neoproterozoic granitoids of this study were formed by magmas probably derived from sources with different proportions of juvenile crust and Meso- to Paleo-Proterozoic crust. The granites of Group III were derived probably from the lower crust. The crust sources for Group I granitoids probably contain less amounts of juvenile crust component and have higher maturity when compared with those for Group II.

Zircon effect alone insufficient to generate seawater Nd‐Hf isotope relationships

[1] Many studies have suggested that continental weathering inputs have controlled the dissolved oceanic budget of hafnium (Hf). However, whether the offset of seawater Nd‐Hf isotope compositions from the terrestrial array can be fully generated by incongruent weathering of continental rocks (the zircon effect) is still not well constrained. In recent years, an increasing amount of combined U‐Pb ages and Hf‐isotopic compositions of riverine detrital zircons have been published. Here a new model of the Nd‐Hf isotopic compositions of the weathered zircon‐free part of the upper continental crust is presented, which is based on published Hf isotope compositions and formation ages of modern riverine detrital zircons combined with Nd isotopic compositions of rocks from the upper continental crust. Our model results indicate that the Nd‐Hf isotopic composition of the weathered zircon‐free part of the upper continental crust is not consistent with the seawater isotopic compositions. This suggests that the elevated seawater Hf isotope compositions for given Nd isotope compositions cannot be fully explained by incongruent zircon weathering of the continents, which is also supported by a recent study demonstrating incongruent weathering of other minerals than zircon.