Journal of Earth Science最新文献

In this study, 90 surface water samples were collected from Shandong Province (SDP) in the dry and wet seasons and analyzed using statistical analysis, hydrochemical methods and water quality index (WQI). The content of main ions showed seasonal variations, with a higher average value in the dry season than in the wet season. Sampling points exhibiting high contents of the main chemical components were mainly distributed in areas southwest of SDP, north of Weifang, and around Jinan. The saturation index of carbonate minerals was greater than zero, while that of evaporite minerals was less than zero. The hydrochemical characteristics of surface water are mainly dominated by rock weathering as well as cation exchange. In addition, surface water in SDP has significantly been affected by anthropogenic factors. Most of the surface water could be classified as weakly alkaline soft-fresh water, with the hydrochemical types of SO₄·Cl-Ca·Mg and SO₄·Cl-Na. In terms of WQI, 47.88% and 37.88% of the water samples in SDP were classified as poor water in the dry and wet seasons, respectively. On the whole, the water quality is higher in the wet season than in the dry season, and surface water in SDP is generally suitable for agricultural irrigation.

‘Single shot’ laser-ablation split-stream (SS-LASS) technique analyzing unpolished zircon grains makes their thin rims tenable for determination, which thus offers great potential in deciphering the timing of multiple and short-lived episodes of anatexis and metamorphism in deeply-subducted continental crusts. Dominated granitic gneisses in the deeply subducted continental crust undergoing considerable fluid-melt activities persist multistage growth of zircon. Therefore, a comparative study of SS-LASS and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon dating was conducted on the granitic gneisses from the Sulu belt in this study. Zircons mostly show a core-mantle-rim structure with CL-bright rims thinner than 5 µm. For LA-ICP-MS dating, relict magmatic zircon cores yield protolith ages of ca. 756–747 Ma; whereas the dark mantles record synexhumation anatexis at ca. 214 Ma. By contrast, according to the U-Pb dates, trace element features, zircon crystallization temperatures and geological context, SS-LASS zircon petrochronology deciphers three episodes of anatectic events, as follows: (i) the first episode of anatexis at ca. 218–217 Ma dominated by phengite-breakdown melting, likely facilitating the exhumation of the UHP slice from mantle depth; (ii) the second episode of anatexis at ca. 193–191 Ma indicating part of northern Dabie-Sulu belt was still “hot” because of buried in the thickened orogenic crust at that time; (iii) the third episode of anatexis (ca. 162–161 Ma) consistent with the intrusion ages (ca. 161–141 Ma) of the Jurassic to Cretaceous granitoids in this orogen, suggesting the initial collapse of the orogenic root of the Sulu belt occurred at Late Jurassic due to the Izanagi plate initially subducting beneath the margin of Eastern Asia. This study sheds new light upon the utilization of SS-LASS petrochronology deciphering multiple anatectic events in the deeply-subducted continental crust and supports us in better understanding the tectonic evolution of Dabie-Sulu Orogen.

The Gengma-Lancang-Menghai seismic belt, the southernmost part of the North-South seismic belt, is controlled by four active faults: the Nantinghe fault (NTHF), the Sanjianshan fault (SJSF), the Hanmuba-Lancang fault (HMB-LCF), and the Heihe fault (HHF), from northwest to southeast. However, the tectonic activity of the faults in the Gengma-Lancang-Menghai seismic belt has not been fully studied yet. In the present work, we conducted tectonic geomorphic indices to analyze the relative tectonic activity along the faults in the seismic belt based on the digital elevation model. We interpreted asymmetric factor, index of drainage basin shape, hypsometric integral, normalized stream-length gradient, valley floor-to-width to height ratio, and longitudinal profiles to show that the relative tectonic activity is higher in the north and lower in the south, and is strong in the region from Shanjia to Huimin in the center of the seismic belt.

Abstract

The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth’s evolution. To provide important insights into the issues, we carried out a detailed investigation of whole-rock geochemistry and Sm-Nd isotopes, and zircon U-Pb-Hf isotopes for the Late Neoarchean metamorphosed basalts in eastern Hebei, North China Craton. U-Pb isotopic dating using the LA-ICP-MS on zircons reveals that the basalts in eastern Hebei erupted at ca. 2.48–2.51 Ga and subsequently experienced multiple regional metamorphic events at 2 477 and 1 798 Ma, respectively. The metamorphosed basalts are featured by low SiO₂, MgO, K₂O + Na₂O, and high FeO contents, endowed with the subalkaline and high-Fe tholeiitic affinities. The radiogenic initial Nd and Hf isotope values and correlations among V, Ni and Cr contents strongly imply that the basalts experienced significant clinopyroxene and olivine fractionation and minor crustal contamination during magma evolution. They are also characterized by the relatively low total REE contents and exhibit significant depletions to moderate enrichments in the LREE contents, indicating the derivation from a deep mantle source in an Archean proto-mantle plume setting.

Abstract

The Daqing Shan (DQS) located in the Yinshan-Yanshan Orogenic Belt plays an important role in the Mesozoic to Cenozoic evolution of the North China Craton. However, the cooling and exhumation history since the Cretaceous is still controversial. Integrating the apatite fission track (AFT) data in both this study and previous works, a three-stage exhumation history from Cretaceous to Neogene of the DQS is proposed. (1) The first stage is composed of the early exhumation during Early Cretaceous driven by the collision between the North China and Siberia cratons (ca. 148–132 Ma) and the far-field effect of the subduction of the Pacific Plate (ca. 132–114 Ma). (2) Due to the subsidence of the Hetao Basin and the subsequent compensation between the DQS and the Hetao Basin, the DQS experienced the second rapid exhumation from Early Eocene to Early Oligocene (ca. 54–29 Ma). (3) Since the Late Miocene (ca. 13.5 Ma), the third rapid cooling and exhumation of the DQS occurred due to the far-field effect of the uplift of the Tibetan Plateau and the subduction of the Pacific Plate.

Abstract

The Permian-Triassic transition saw extreme climatic changes that severely impacted the terrestrial ecosystem. Fossil plants, particularly fossil woods, are sensitive to climatic changes, and they, therefore, are unique materials revealing extreme environmental and climatic changes on land at that time. Abundant conifer woods were discovered in the Lopingian (Late Permian) strata of the Sunjiagou Formation in Shanxi Province, North China. The newly finding permineralized woods record the unique landscape of Lopingian North China. They represent a new conifer genus and species: Shanxiopitys zhangziensis gen. et sp. nov. Analyses of growth pattern and anatomical characteristics of the fossil woods indicate these trees grew under optimal growing conditions, and without seasonal growth cessation. However, climate signals from leaf fossils, vertebrate fossils and sedimentary evidences indicate a strongly seasonal climate in North China during the Lopingian. Thus, it is speculated that these trees likely lived in the gallery forests, which were distributed along the paleo-rivers within a seasonal landscape in the central North China block during the Lopingian.

The method of LA-MC-ICP-MS has become one choice for the analysis of many isotopic systems due to its relatively low cost, high analysis speed, high spatial resolution, and low matrix effect. However, there are still many challenges in the accuracy, precision, and spatial resolution of in situ isotopic composition determination by LA-MC-ICP-MS, which mainly include: (1) how to improve instrument sensitivity, further improve the spatial resolution, and achieve simultaneous determination of isotopes, multiple isotopes, or isotopes with trace elements in low-content samples? (2) how to deduct and correct interference to improve the accuracy of isotopic determination? (3) how to correct isotope fractionation? (4) how to reduce the matrix effect of isotopes? how to develop matrix-matched reference materials? and (5) how to achieve non-matrix-matched correction of isotopes? The high-sensitivity cone combinations, gas mixture, shield torch, and reasonable detector array can be applied to improve the elemental sensitivity. The interferences include the background interference and the interferences from the matrix elements (the isobaric interference, the polyatomic interference, and doubly charged ions interference). To reduce or even eliminate the interference, commonly used methods including interference elimination, background correction, and interference correction by evaluating with an interference-free isotope. Isotopic fractionation correction mainly involves external standard calibration and internal and pseudo-internal standard normalization. For non-matrix matched calibration, many methods can be applied, such as the femtosecond laser, line scan, low laser energy, wet plasma condition, optical setup below the sample surface, and matching the intensity of the sample and standard. In this review, we systematically summarized the above challenges and solutions to promote the study and application of LA-MC-ICP-MS in isotopic determination.

The Mid-Cretaceous interval has been recognized as a crucial period in Earth’s history, and a number of studies on Neo-Tethyan successions illustrate intense evolutions in the nature of Mid-Cretaceous ocean chemistry, sea level, and marine faunal communities. However, much less investigations have been conducted in the Sistan Ocean, in the eastern Neo-Tethys. Here, the Nimbolook Section (Lut Block, central Iran) has provided an opportunity to address these shortcomings and provide a better understanding of the paleoenvironmental changes in this region. The biostratigraphic analysis and age interpretation of the Nimbolook Section have been performed in earlier investigations by means of planktonic foraminifera, ammonites and calcareous nannofossils. This provides a reliable age framework for the chemostratigraphic interpretations. In the Nimbolook Section, the δ¹³C stratigraphy was carried out on a total of 41 samples, which ranged between −3.26‰ and 2.86‰ with an average of 1.09‰ (standard deviation = 1.15‰), and expanded within the upper Aptian to lower Cenomanian stages. However, there is a prominent negative shift at the base of the section, accompanied by episodes of sea-level fluctuations. Notably, according to the age-diagnostic calcareous nannofossils records, this carbon isotope negative shift (0.88‰ to −3.26‰) straddle between late Aptian and early Albian ages. Furthermore, these new chemostratigraphic observations could be interpreted as being the coeval data from the reference well-studied successions in the other parts of the world, tentatively reflecting the oceanic anoxic event (OAE) 1b.

In this research, a new apparatus was developed to identify the tensile behavior of three loess samples from different regions. Influence of water contents on tensile strength characteristics was investigated. The variations of local longitudinal strains ε_xx field were analyzed using the DIC method. The design of narrow portion in the center of the soil sample provides an effective method for analyzing the tensile behaviors and for precisely measuring tensile strength of the tested soils. With the results of tensile behavior curves of loess in slurry state, the tensile process can be divided into three stages. The tensile behavior of loess is greatly influenced by water content, mineralogy and microstructure of soil samples. The tensile strength of soil is relatively smaller with a larger water content. However, it’s worth noting that the current research is limited to the analysis of the above factors. The future studies may explore additional parameters and their interactions to further enhance our understating of tensile behavior of loess. In addition, many tensile tests are conducted under controlled laboratory conditions, which may not accurately represent the in-situ case. The influence of environmental factors, such as temperature, humidity, and corrosion, on tensile behavior is not adequately considered in this research.

The Wuwei Basin is one of the most important oil- and gas-bearing basins in the Meso-Cenozoic basin groups in the Lower Yangtze River region. It has great shale gas resource prospects. The formation mechanism of this basin is poorly studied for lack of constraining data for deep structures. In this paper, a crustal electrical structure model of the Wuwei Basin and the adjacent areas is constructed based on the two-dimensional inversion of a magnetotelluric (MT) sounding profile achieved with the nonlinear conjugate gradient method. The results show that large-scale low-resistance bodies have developed in the underlying middle and lower crust of the Wuwei Basin, and are different from the uplifts on the two sides according to their high-resistance electrical characteristics. The electrical structure and regional geological and geophysical data suggest that the peak zone of the Chuzhou-Chaohu foreland fold-and-thrust belt is located on the east bank of the Yangtze River (Wuhu Section), which, together with the main thrust fault belt in the east, forms a typical thrust structure belt. An early Yanshanian sinistral strike-slip fault developed in the deep part of the Wuwei Basin, which may have controlled the formation and evolution of the basin, whereas the tectonic inversion of the early-developed thrust faults is relatively weak. These findings provide a geophysical basis for future studies of basin tectonic evolution and regional tectonic frameworks.