Whole-rock geochemistry and Sr-Nd-Pb isotope systematics of the Late Carboniferous volcanic rocks of the Awulale metallogenic belt in the western Tianshan Mountains (NW China): Petrogenesis and geodynamical implications
Ge S.,CAS Institute of Geology and Geophysics |
Ge S.,University of Chinese Academy of Sciences |
Zhai M.,CAS Institute of Geology and Geophysics |
Safonova I.,Novosibirsk State University |
And 5 more authors.
Lithos | Year: 2015
The Awulale metallogenic belt (AMB) of the western Tianshan (NW China) includes Late Carboniferous (ca. 320Ma) ore-bearing volcanic rocks of the Dahalajunshan Formation. The petrogenesis and tectonic setting of these volcanic rocks are important for the understanding of the tectonic evolution and metallogeny of the western Tianshan. This paper presents new major and trace elements and Sr-Nd-Pb isotope data from the Dahalajunshan volcanic rocks, which are mainly calc-alkaline basaltic trachy-andesite and trachy-andesite with subordinate basalt, trachy-basalt and rhyolite. The variations of major and trace elements in the mafic and intermediate volcanic rocks indicate the fractionation of pyroxene and magnetite or hornblende, magnetite, apatite and plagioclase, respectively, during their petrogenesis. The Dahalajunshan volcanic rocks have similar primitive mantle-normalized diagrams and chondrite-normalized rare-earth element (REE) patterns suggesting their similar mantle source(s). They are characterized by enrichment in large ion lithophile elements (LILEs) and light REEs (LREEs), depletion in heavy REEs (LaN/YbN≈2.80 to 9.59) and high field strength elements (HFSEs) and εNd(t) ranging from +1.2 to +6.0 at 86Sr/87Sr(t)=0.7047-0.7063 and 206Pb/204Pbi=17.49-18.19. Both the geochemical and isotopic data indicate that the volcanic rocks were probably derived by low-degree melting of sub-arc lithospheric mantle modified by fluids in a continental arc setting. Our obtained results, in conjunction with previous published data, allow us to suggest that the southward subduction of Junggar oceanic crust continued until the Late Carboniferous and was followed by a tectonic shift from continental arc to post-collisional extension environment. © 2015 Elsevier B.V.
Yan Z.,Peking University |
Liu J.,Peking University |
Ezaki Y.,Osaka City University |
Adachi N.,Naruto University of Education |
Du S.,Shandong Geological science Institute
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016
The Cambrian Series 3 thrombolites from the Changhia Formation, at the Jiulongshan section in Shandong Province, northern China, provide an excellent example for studying the development of calcimicrobial structures. Thrombolites constructed by calcimicrobes have particular stacking patterns, which are controlled by their environments and are reflected in the relationships between micro-, meso- and macroscopic structures, requiring an approach we term "multiscopic". Under high-energy conditions, . Epiphyton A (with dense micritic bifurcating thalli) grew sporadically and adapted to the environment by taking a bushy-lateral form, because the bushy-upward form is more likely to be broken by waves or currents. . Epiphyton A was fused with each other to form spotted frameworks at the mesoscopic level. The weak baffling of spotted frameworks led to the formation of low-relief tabular/lentoid macrostructures via preferential lateral accretion. In low-energy, deep-subtidal settings, . Epiphyton A and . Epiphyton B (with microsparry segments in the bifurcating thalli) coexisted with . Hedstroemia A (with a wide terminal) and B (with a narrow terminal). These calcimicrobes grew abundantly in both the vertical and lateral directions, fusing together to form meshed frameworks, or dendritic frameworks if vertical fusion of bushy-upward calcimicrobes was predominant. The preferential vertical stacking of meshed and dendritic mesostructures highlights the ability of these frameworks to actively baffle lime mud, and ultimately to form large-domed macrostructures. Stacking patterns in these multiscopic structures help to inform environmental interpretations of thrombolites. The thrombolitic growth model we present here provides important insights into the environmental interpretations of thrombolites in other cases, especially the calcimicrobe-dominated early and middle Palaeozoic thrombolites. © 2016 Elsevier B.V.
Li D.-P.,Shandong Geological science Institute |
Li D.-P.,Key Laboratory Of Gold Mineralization Processes And Resources Utilization Of Min Of Land And Resources |
Du Y.-S.,China University of Geosciences |
Yu X.-F.,Shandong Geological science Institute |
And 5 more authors.
Acta Geoscientica Sinica | Year: 2014
It is generally accepted that mantle input under crust-mantle interaction plays an important role in sustainable magma fractionation and eventually leads to release of magmatic fluids and formation of world class W, Sn and other types of ore deposits. Many models dealing with the evolution of mantle-derived magmas are derived from numerical simulations based on isotopic geochemistry, temperature and pressure or physical geography data. Few models use detailed chemical analysis of mantle-derived rock enclaves. The authors found direct evidence for crust-mantle interaction in Tongling area, East China, in the form of mafic clots (MFC), which are interpreted to represent fragments of altered alkaline basaltic magma in magma chambers at the base of the continental crust (BCC). These MFC are unevenly distributed within the microgranular dioritic enclaves (MME) which, in turn, are included in the host quartz monzodiorite. The authors have combined all available data with new element distribution maps of the MFC in order to present a general framework model for the evolution of mafic to siliceous magmas. Observations and researches indicate that the MFC were formed from the fractional crystallization and evolution alkaline basaltic magma in magma chambers at the BCC. The basaltic magma resulting from previous partial melting of the upper mantle was eventually brought to the magma chambers at the BCC by magmatic underplating and crust-mantle interaction at 140 Ma. And the MME were formed from the fractional crystallization and evolution dioritic magma by the assimilation of the derived magma from the base of the continental crust with the metamorphic rocks in a crust magma chamber at the depth of 12~16 km. The discovery of the MFC and MME effectively prove that the dioritic magma in the middle crust originated from the mixing basaltic magma of mantle-crust at the BCC.
Zhang Y.,Key Laboratory of Gold Mineralization Processes and Resource Utilization |
Zhang Y.,Shandong Key Laboratory of Mineralization Geological Processes and Resource Utilization in Metallic Minerals |
Zhang Y.,Shandong Geological science Institute |
Zhang S.,Key Laboratory of Gold Mineralization Processes and Resource Utilization |
And 16 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016
High resolution magnetic survey and borehole triple-component magnetometry are the effective magetic prospecting methods, especially much more significative for the exploration of banded iron formation (BIF) type iron deposits around coverage region. The Shanzhuang iron deposit, located in the covered regions of north of the Yellow River in Shandong Province, is a medium- to large-scale magnetite-quartzite type iron deposit. The deposit includes more than 20 iron bodies, which occur in the Shancaoyu Formation of the Neoproterozoic Taishan Group. The iron bodies dip to the southwest at 56°-70°. Average grade is about 28% for the total iron, and 22% for the magnetic iron. Taking the prospecting of the Shanzhuang iron deposit as an example, it aims to introduce an integrated prospecting method for BIF iron deposits in covered regions. Based on regional geological and geophysical characteristics, such as aeromagnetic anomaly, a high-resolution magnetic survey and profile measurement in favorable prospecting places were carried out, and the best drilling spot is chosen. It is found in the study that the borehole triple-component magnetometry during drilling and right before ending of drilling should be paid special attention, which could not only help find blind ore bodies, but also indicate abnormity around the borehole. © 2016, Editorial Department of Earth Science. All right reserved.
Xiang Z.,Henan Polytechnic University |
Gu X.,China University of Geosciences |
Zhang Y.,China University of Geosciences |
Yang W.,China University of Geosciences |
And 4 more authors.
Earth Science Frontiers | Year: 2014
As 3D geological information technology is improving, the 3D prediction becomes an important method and developing trend for large scale deep metallogenic prediction,. By taking 313# vein of the Liubagou gold field, Inner Mongolia as a case study, the paper discusses the technical procedure and method of large scale 3D deep prospecting prediction from comprehensive information based on 3D geological modeling and visualization. Through building geological entity model such as strata, faults, rock dyke, ore body and alteration zone, and visibly analyzing the ore-forming geological conditions, the authors constructed the prospecting model of synthetic information on the K-feldsparization and silication type of gold ore combined with 3D anomaly analysis on primary halos, delineated and estimated three prospect areas with the method of element overlay through establishing block mode and quantifying 3D metallogenic prognosis factors. The results show that the Mid-Eastern deep area has a good potential for prospecting minerals and that the large scale prediction method based on 3D geological modeling and visualization technology is very effective.