Chen Z.,Chinese Academy of Sciences |
Zhou C.,Chinese Academy of Sciences |
Meyer M.,Virginia Polytechnic Institute and State University |
Xiang K.,Hunan Institute of Geological Survey |
And 3 more authors.
Precambrian Research | Year: 2013
Distinguishing Ediacaran trace fossils from tubular body fossils can be a challenge, and several Ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils. Nonetheless, true Ediacaran trace fossils are present, but they are relatively few and morphologically simple, dominated by horizontal trails and shallow burrows. Such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the Cambrian explosion. Here we report three types of trace fossils-horizontal tunnels, surface tracks/trails, and vertical traces-from the latest Ediacaran Dengying Formation (551-541Ma) in the Yangtze Gorges area of South China. Cross-cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils; instead, these three types of traces likely represent animal activities related to under-mat feeding, epibenthic locomotion, and temporary dwelling, respectively. We show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and O2 resources. These animals heralded a new age in ecosystem engineering, animal-sediment interaction, and biogeochemical cycling. © 2012 Elsevier B.V.
Luo Z.,China University of Geosciences |
Chen B.,China University of Geosciences |
Chen B.,Hunan Institute of Geological Survey |
Jiang X.,China University of Geosciences |
And 2 more authors.
Acta Petrologica Sinica | Year: 2012
This article is contributed to propose a new methodology for targeting prospecting districts of the endogenic ore deposits, using the Wide composition-Spectrum Dike Swarm(WSDS). A Permian dike swarm, which consists of the lamprophyric, the basaltic, the andesitic, the dacitic, and the rhyolitic dikes, is extensively exposed in the South Alatao Mountains, and can be felled to the WSDS. The WSDS intrudes the Permian granitic plutons and their country rocks, and is the products of the latest epoch of magmatism in this region. The WSDS generation is accompanied by violent activity of the ore-bearing fluids because(1) many dike's rocks have the fumarolic structure, and contain numerous water-bearing mafic minerals: (2) a part of the dike's rocks have poly-phenocryst porphyritic texture with a cryptocrystalline or glassy matrix: (3) a part of the dike's rocks contain disseminated sulphides: (4) all dikes have the similar pattern of the incompatible and the ore-forming elements: (5) all the strata and plutons have the similar pattern of the oreforming elements. Accordingly, we can conclude that the WSDS and their country rocks are infiltrated and chemically modified by the ore-bearing fluids, and can be considered as the deterministic targeting element. The spatial patterning of the dike swarm is controlled by both the regional and the local fracture system. This can be explained by emplacement of the dike magmas into both the pre-existing and the self-propagating fractures. Therefore, the WSDS is resulted from the melt-fluid flows through rapid ascending and emplacement, and has a stronger potentiality to produce ore deposits. The spatial patterning of the dike swarm may suggest transport of the ore-bearing fluids, and thus can be used to predict the localities where the ore-forming metals have extensively cumulated. Along the transport paths of ore-bearing fluids, the ore-forming metals are largely discharged at the places where the fluid flow encounters: (1) carbonate rocks: (2) massive igneous blocks, in which fractures are poorly developed: (3) moderately broken regions cross-cut by faults: (4) strata with a high permeability: (5) minor magma bodies in the fields where the dikes are clustered. Accordingly, six prospecting regions can be targeted from the South Alatao Mountains. They are: A. the Xiaeraola, B. the Mierqike intrusion, C. the Legenwusu-Keketashugenwusu, D. the Aerxiati, E. the southwest Butuhamaer intrusion, and F. the Noerte. The divided prospecting regions cover 8 of the 20 mineralized points discovered in previous regional investigations. When the prospecting regions are slightly enlarged, they can cover 15 of them. It is clear that the new methodology is effective.
Qiu J.-T.,China University of Geosciences |
Yu X.-Q.,China University of Geosciences |
Santosh M.,China University of Geosciences |
Santosh M.,Kochi University |
And 3 more authors.
Mineralium Deposita | Year: 2013
The Tongcun Mo porphyry deposit in northwest Zhejiang is hosted in three porphyry units: Huangbaikeng, Songjiazhuang, and Tongcun, from southwest to northeast. U-Pb zircon ages of 162 ± 3.0 Ma for the Huangbaikeng porphyry, 159.9 ± 3.0 Ma for the Songjiazhuang porphyry, and 167.6-155.6 Ma for the Tongcun porphyry indicate that these intrusions formed during the Jurassic and are most likely associated with the northwestward subduction of the Izanagi Plate. Trace element compositions of zircons from the Tongcun deposit constrain the oxygen fugacity (fO2) of the magma using zircon Ce anomalies and Ti-in-zircon temperatures. The average magmatic fO2 for the porphyries in the Tongcun deposit is fayalite-magnetite-quartz (FMQ) + 2.7, which is similar to the Shapinggou (FMQ + 3.2) and Dabaoshan (FMQ + 3.5) Mo porphyry deposits, but much higher than that of the reduced Cretaceous ore-barren Shangjieshou porphyry (FMQ-1.1) around 8 km away from the Tongcun deposit. The distinct difference in magmatic oxygen fugacity between the Jurassic and Cretaceous porphyries may help to explain the absence of Mo porphyry mineralization in northwest Zhejiang during the Cretaceous. © 2013 Springer-Verlag Berlin Heidelberg.
Jiang X.M.,China University of Geosciences |
Luo Z.H.,China University of Geosciences |
Chen B.H.,China University of Geosciences |
Chen B.H.,Hunan Institute of Geological Survey |
And 2 more authors.
Acta Petrologica Sinica | Year: 2014
The identification of causing intrusions is an important part of the metallogenia study and resources exploration, which is also a difficulty for many other types of deposits. The case study, the Aerxiati iron-copper skarn deposit, Xinjiang province, puts forward the understanding that the Tuimuerte batholith is the shielding layer of ore-bearing fluids, through the identification methods that establishing five kinds of contacts and the geology, petrology, mineralogy, geochemistry and metallogeny signs. The close spatial contact between the Tuimuerte batholith and skarn would easily be mistaken-making the batholith as a causing intrusion. However, the diagenetic stage of the batholith is earlier than the mineralization, its enplacement causes the thermal contact metamorphism of the country rocks, resulting the forming of marble and hornfels, which cannot be the resource of the ore-bearing fluids. In contrast, the small intrusive body in the region (the diorite intrusion) and the kinds of dykes not only have close spatial contacts with the ore body and the skarn, but also themselves and the country rocks suffers the intense hydrothermal alteration, which make the role that the channel of the ore-bearing fluids and the real causing intrusions.
Liu Y.,Chinese Academy of Geological Sciences |
Li T.-D.,Chinese Academy of Geological Sciences |
Xiao Q.-H.,Chinese Academy of Geological Sciences |
Geng S.-F.,Chinese Academy of Geological Sciences |
And 2 more authors.
Geological Bulletin of China | Year: 2010
The zircons from Ningyuan alkali basalt show euhedral-subhedral shapes and striped absorption on their cathodoluminescence (CL) images. Most zircons ring with a clear plate, which is the typical structure of basic igneous rocks zircon. The Th/U ratios of Baoanxu Zhongxinpu zircons range from 0.37 to 0.95, and Baoanxu Lizhaixiang zircons range from 0.43 to 2.53, indicating that they were formed by normal crystallization of magma. U-Pb dating of 20 zircons from Baoanxu Zhongxinpu, and Baoanxu Lizhaixiang was made on LA-ICP-MS. The results show that the data of Zhongxinpu 34 zircons cluster around the concordia of 204~221 Ma, yielding a weighted mean Pb206/U238 age of 212.3 Ma± 1.7 Ma, and that the data of Lizhaixiang 23 zircons yield a weighted mean Pb206/U238 age of 205.5 Ma±3.0 Ma, which implied that the crystallization of the Ningyuan alkali basalt occurred in Late Triassic.