Journal of Earth Science最新文献

Voluminous Early Cretaceous granitoids and associated large-scale ore deposits are distributed within the southern Great Xing’ an Range (SGXR), NE China. Based on previously published geochronology and zircon Hf-isotope data, Hf isotope mapping is undertaken to improve our understanding of crustal architecture and its controls on ore deposits. The ore-related Early Cretaceous granitoids were sourced predominantly from juvenile crust, with the involvement of variable proportions of ancient crustal materials. The crustal architecture, as inferred from Hf isotopic contour maps, indicates two distinct Hf isotopic domains in SGXR, including (1) a higher-ε_Hf (+7 to +11) juvenile crust containing minor ancient crustal material, and (2) a lower-ε_Hf (+2 to +6) juvenile crust containing a greater proportion of ancient crustal materials. The Hf isotopic maps identify links between crustal architecture and regional metallogeny. Copper deposits and other deposits with significant Cu production are restricted mainly to the higher-ε_Hf juvenile crustal regions in the northern and eastern SGXR. Deposits dominated by other metals (e.g., Mo, Sn, W, Pb, Zn, and Ag) occur mainly in the lower- ε_Hf juvenile crustal regions in the southern and western SGXR. Interaction between juvenile crust-derived melts and ancient crustal components played an important role on the distribution of various ore metals.

The dynamic effect is a very important issue widely debated by scholars when studying the genetic and disaster-causing mechanisms of earthquake-triggered landslides. First, the dynamic effect mechanism and phenomena of earthquake-triggered landslides were summarized in this paper. Then, the primary types of dynamic effects were further used to interpret the Mogangling landslide in Moxi Town of Luding County, China. A field investigation, remote sensing, numerical calculation and theoretical analysis were carried out to illustrate the failure mechanism of slope rock masses affected by earthquakes. The interaction between seismic waves and slope rock masses and the induced dynamic effect of slope rock masses were primarily accounted for in the analysis. The slope topography, rock mass weathering and unloading characteristics, river erosion, regional seismogenic structure, and rock mass structure characteristics were also discussed. The results showed that the formation of the Mogangling landslide was mainly related to the high amplification effect of seismic acceleration and back slope effects, interface dynamic stress effects, and double-sided slope effects of seismic waves caused by the catastrophic Ms 7.75 Moxi Earthquake in 1786. The principles for the site and route selection of large-scale infrastructure in the planning stage and the scientific prevention of seismic geological disasters were proposed on the basis of the dynamic effect of earthquake-induced landslides.

While acid mine drainage (AMD) issues have become a topic of global concern, few studies have focused on acid drainage problems of non-mining activities. We conducted field research and a series of laboratory experiments to investigate the characteristics, release processes and formation of acid drainage contamination. Spoil rock samples and adjacent surface water, groundwater, soil and sediment samples were collected at a railway tunnel construction site in central China, and various parameters, such as the pH, mineral ion concentrations, and heavy metal concentrations, were measured. Based on the measured concentrations, surface water and sediments were seriously contaminated by acids, sulfate salts and heavy metals. Contamination in surface water showed a decreasing tendency as the distance from the spoils increased, while that in sediments showed a greater influence of coprecipitation and adsorption processes of heavy metal ions. The eluviation experiments of three rock samples indicated that R2 (silty fine sandstone) was the most likely major acid drainage contributor. Thiobacillus ferrooxidans was cultured and isolated from contaminated water to study the oxidation conditions during the release processes. The significant release of acid drainage when air and bacteria were both in the culture container suggested that oxygen and bacteria were necessary to produce acid drainage from spoils.

Arroyo Verde epithermal deposit, in the North Patagonia region of Argentina, is located within the Lower Chon Aike volcanism and is developed between 192.6 ± 2.5 Ma (mineralization host rock) and 189.5 ± 2.6 Ma (overlying lava). Marifil volcanic complex is the host rock for these veins, veinlets and breccias. This particular small deposit has developed low to intermediate sulphidation characteristics, with gangue mineral textures associated with several ore minerals. Electron probe microanalysis determines electrum, silver minerals such as acanthite, and tetrahedrite, related Ag-Cu minerals like jalpaite, mckinstryite, stromeyerite, and base metals like chalcopyrite, sphalerite, galena and pyrite. Fluid inclusions in quartz of two out of five events indicate that these Low Jurassic veins were formed due to subtle boiling and dilution mechanisms and by low-salinity (3.4 wt.% to 6.7 wt.% NaCl Eq) magmatic-hydrothermal fluid at 225 to 310 °C. The fluid inclusion measurements that indicate boiling (Event 3) were plotted, and based on this data, we interpret that the Arroyo Verde deposit has been eroded between 550 and 700 m. This particular character has not been previously recorded for other sectors of the eastern north Patagonian region.

The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon. This iron district contains numerous iron mineralization hosted by the Mewongo, Bibole, Kouambo, and Zambi banded iron formations (BIFs). These BIFs contain magnetite as the main iron ore mineral associated with pyrite, and gangue minerals are quartz with minor chlorite and amphibole. The origin of iron ore from these BIFs was investigated using a combination of in-situ magnetite and whole-rock chemistry. The studied BIF ore samples have a narrow range of TFe between 30.90 wt.% and 43.20 wt.%, indicating a low-grade ore. The geochemical signatures of magnetite such as low contents of base metals (e.g., Cu, Co, V, and Zn) and low Co/Zn ratios < 0.85 indicate a hydrothermal origin. Combined with the geochemical features of these BIFs, e. g., high Fe/Ti and Fe/Al ratios (mean > 600 and > 75, respectively), we suggest that magnetite was derived from a mixture of seawater and ∼0.1% low-temperature hydrothermal fluids in an oxidizing environment. Collectively, low-temperature hydrothermal and later metamorphic fluids were necessary for the transformation of the protolith Nyong Complex BIFs to iron ore.

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.