U–Pb and Re–Os geochronology and geochemistry of the Donggebi Mo deposit,Eastern Tianshan,NW China: Insights into mineralization and tectonic setting

The Donggebi Mo deposit located in NW China is a newly discovered, large, stockwork-type Mo deposit with ore reserves of 441 Mt @ 0.115% Mo. Ore bodies occur along faults and fractures at the external contact zone of a concealed porphyritic granite and volcaniclastic rocks of Gandun Formation, spatially associated with a fine-grained granite. Mo-bearing veins are mainly assemblages of volatile-rich K-feldspar-quartz-oxide, K-feldspar-quartz, polymetallic sulfides and calcite-quartz. Zircon LA-ICP-MS U–Pb dating yielded concordant ages of 234.6 ± 2.7 Ma and 231.8 ± 2.4 Ma for the porphyritic granite and the fine-grained granite, respectively; molybdenite Re–Os dating gave an isochron age of 234.0 ± 2.0 Ma. These ages further confirm an important and extensive magmatic-metallogenic event in Eastern Tianshan during the Triassic Indosinian orogeny. Whole-rock major and trace element analyses indicate that the granitic rocks associated with Mo mineralization are high in Si, K, Rb, Th, Nb, Ta, Ga and LREE, but low in P, Ti, Sr and Ba, belonging to high-K calc-alkaline granites with A-type features. Magma was likely derived from the re-melting of thickened lower crust in a post-collision compression environment in the Late Permian, experienced strong crystal fractionation and formed the large Donggebi Mo deposit under an intra-plate extension setting in the Early to Middle Triassic.     

In–situ LA–ICP–MS trace elemental analyzes of magnetite: The Tieshan skarn Fe–Cu deposit,Eastern China

The Tieshan Fe–Cu deposit is located in the Edong district, which represents the westernmost and largest region within the Middle–Lower Yangtze River Metallogenic Belt (YRMB), Eastern China. Skarn Fe–Cu mineralization is spatially associated with the Tieshan pluton, which intruded carbonates of the Lower Triassic Daye Formation. Ore bodies are predominantly located along the contact between the diorite or quartz diorite and marbles/dolomitic marbles. This study investigates the mineral chemistry of magnetite in different skarn ore bodies. The contrasting composition of magnetite obtained are used to suggest different mechanisms of formation for magnetite in the western and eastern part of the Tieshan Fe–Cu deposit. A total of 178 grains of magnetite from four magnetite ore samples are analyzed by LA–ICP–MS, indicating a wide range of trace element contents, such as V (13.61–542.36 ppm), Cr (0.003–383.96 ppm), Co (11.12–187.55 ppm) and Ni (0.19–147.41 ppm), etc. The Ti/V ratio of magnetite from the Xiangbishan (western part of the Tieshan deposit) and Jianshan ore body (eastern part of the Tieshan deposit) ranges from 1.32 to 5.24, and 1.31 to 10.34, respectively, indicating a relatively reduced depositional environment in the Xiangbishan ore body. Incorporation of Ti and Al in magnetite are temperature dependent, which hence propose that the temperature of hydrothermal fluid from the Jianshan ore body (Al = 3747–9648 ppm, with 6381 ppm as an average; Ti = 381.7–952.0 ppm, with 628.2 ppm as an average) was higher than the Xiangbishan ore body (Al = 2011–11122 ppm, with 5997 ppm as an average, Ti = 302.5–734.8, with 530.8 ppm as an average), indicating a down–temperature precipitation trend from the Jianshan ore body to the Xiangbishan ore body. In addition, in the Ca + Al + Mn versus Ti + V diagram, magnetite is plotted in the skarn field, consideration with the ternary diagram of TiO₂–Al₂O₃–MgO, proposing that the magnetite ores are formed by replacement, instead of directly crystallized from iron oxide melts, which provide a better understanding regarding the composition of ore fluids and processes responsible for Fe mineralization in the Tieshan Fe–Cu deposit.     

Remote Sensing Geological Exploration Model for Copper and Gold Deposits in the East Tianshan, Xinjiang

Based on the identification and enhancive processing of information about strata, structure, magmatite, and alteration in ore-concentrated area in the eastern Tianshan, an exploration mode of remote sensing geology is established. The mode covers basic images composed of TM (7, 4, 1), Munsell space transformation for recognizing rock type, directional matched filtering for enhancing structures, multi-layer separating and extracting weak alteration information. It will provide a rapid and effective method for geological mapping and metallogenic prediction in this region.     

南岭东段燕山期镁铁质岩石Nd-Sr同位素研究及意义

南岭东段燕山期镁铁质岩浆活动可划分为4个阶段(中侏罗世、晚侏罗世、早白垩世和晚白垩世),分别对应4次重要的伸展拉张作用时期。镁铁质岩石具有基本类似的Nd—Sr同位素特征,ISr较高(一般介于0．705～0．710之间),εNd值变化范围较大(介于-7．90～5．16之间),表明其岩浆源为壳-幔混合源性质。镁铁质岩石具有板内拉斑玄武岩特征,系形成于板内拉张环境,表明该区在燕山早期的中侏罗世即已进入后造山演化阶段。岩石的成因模式为地幔镁铁质岩浆在上升至地壳底部过程中,受到地壳组分的混染,在岩石圈伸展的深部背景和浅部拉张状态下形成。     

The origin of variable-δ18O zircons in Jurassic and Cretaceous Mo-bearing granitoids in the eastern Xing–Meng Orogenic Belt,Northeast China

This study reports new zircon U–Pb ages, Lu–Hf isotope data, and oxygen isotope data for Mesozoic Mo-bearing granitoids in the eastern Xing–Meng Orogenic Belt (XMOB) of Northeast China, within the eastern Central Asian Orogenic Belt. Combining these new laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U–Pb ages with the results of previous research indicates that two stages of Mo-bearing granitoid magmatism occurred in the eastern XMOB, during the Early–Middle Jurassic (200–165 Ma) and the Early Cretaceous (ca. 111 Ma). The eastern XMOB also contains Mo-bearing granitoids with variable δ¹⁸O compositions that record variations in source oxygen isotopic compositions. Combining δ¹⁸O data with zircon U–Pb and Hf isotopic data provides evidence of the origin of these granitoids. Three types of zircon have been identified within these granitoids. Type 1 zircons formed during the Mesozoic and having high δ¹⁸O values (5.71–7.05‰) that are consistent with the compositions of magmatic zircons from the Luming, Jiapigou, and Kanchuangou areas. These zircons suggest that the Mo-bearing granitoids were derived from a source containing supracrustal materials. The type 2 zircons have extremely low and heterogeneous δ¹⁸O values (4.64–4.89‰) that are consistent with the compositions of magmatic zircons from the Jidetun and Fuanpu areas. These magmas were generated by the remelting of juvenile crustal material that was previously significantly modified by interaction with fluids. Type 3 zircons generally have mantle-like δ¹⁸O values (5.42–5.57‰), with several zircons yielding higher δ¹⁸O values, suggesting that these intrusions formed from mantle-derived magmas that assimilated and were metasomatized by crustal material. Combining these geochemical data with the geology of this region indicates that the Mo-bearing granitoids were generated as a result of subduction of the Palaeo-Pacific Plate beneath the Eurasian continent.     

A hidden suture within the northern Paleotethyan margin: Paleogeographic/paleo-tectonic constraints on the late Paleozoic 'Veles Series' (Vardar Zone,North Macedonia)

There is little consensus in characterizing the effects of the migrated late Pan-African/Lower Paleozoic configuration (western Paleotethys and precursory Paleozoic oceans) and its Variscan, late Variscan, and Eo-Cimmerian involvement. Constrained by a limited choice of the geological, biostratigraphical, and paleogeographical constraints, the focus of this regional geological synthesis is the little-known Devonian – Lower Carboniferous polymetamorphic 'Veles Series' (southern Vardar-Axios Zone, Northeast Mediterranean). Kinematic reconstructions indicate that the drifted carbonate platform assemblage of the 'Veles Series' including its Lower Carboniferous collision occurred along an active margin of southwestern Moesia, Laurussian foreland. Despite the fact that the dominant, low-grade metamorphic imprint across the 'Veles Series' is compatible with the ‘soft’ Eo-Cimmerian docking (i.e. Triassic), the documented Lower Carboniferous age suggests a Variscan involvement.A distinctive Late Paleozoic age is consistent with the north Gondwana and Variscan developments, reflected by the peculiar protoliths pallet portraying the presence of the oceanic crust to deep-marine equivalents. Accommodated to the west (paleo-south) of the late Cadomian Serbo-Macedonian Unit (a segment of the former peri-Gondwanan terrane assembly) and to the north of the Cimmerian Minoan system (East Mediterranean), the 'Veles Series' reflects a migrated rift to carbonate platform system. Despite the significant Alpine overprinting, based on this regional geological synthesis we propose that the 'Veles Series' is a 60 km-long suture segment documenting a so far rather poorly explored Variscan segment of the Paleotethyan lithosphere exposed within Balkans/Northeast Mediterranean.     

东准噶尔乌尊塔格辉长岩LA-ICP-MS锆石U-Pb年龄、地质地球化学特征及构造意义

乌尊塔格辉长岩位于东准噶尔地区卡拉麦里造山带东段,卡拉麦里蛇绿混杂岩带北侧。岩性为辉长岩、石英闪长岩。岩石化学成分显示,辉长岩具高Al2O3(18.87%~14.11%)、CaO(8.64%~12.35%),低碱K2O(0.34%~0.86%)、Na2O(1.68%~3.08%)、P2O5(0.06%~0.20%)和TiO2(0.96%~1.76%)特征。岩石具弱富集大离子亲石元素Rb,K,Sr,Ba,显著亏损Nb,Ta,反映源区为受俯冲流体交代改造的岩石圈地幔。锆石LA-ICP-MS测年结果表明,辉长岩形成年龄为(337±17) Ma(MSWD=2.3, n=6)。结合地质背景认为,乌尊塔格辉长岩形成于俯冲结束之后挤压环境向拉张环境过渡的构造环境。     

东秦岭造山带的地壳演化

东秦岭造山带地壳演化过程,大致可划分为五个阶段:前震旦纪洋壳向陆壳演化期;震旦—早寒武世古地台发育期;中寒武世—志留纪末期陆壳裂陷地槽发育期;泥盆纪—三叠纪大陆裂谷闭合造山期;中、新生代推覆构造与断块掀斜构造发育期。     

Iron Speciation in Precipitation in the North-Eastern Mediterranean and Its Relationship with Sahara Dust

Precipitation samples collected at Erdemli, Turkey, during February 1996–June 1997 were analysed to determine iron content and speciation. The purpose of the measurements was to examine the atmospheric abundance of iron and to quantify its solubility in the region. Spectrophotometric analyses of Fe(II) and reducible Fe(III) in precipitation samples, along with measurements of pH, conductivity, filterable iron (Fe_filt), particulate aluminium (Al_par) and particulateiron (Fe_par) were performed to determine iron solubility, which principally affects its bioavailability. Backward trajectories corresponding to the sampling dates were analysed to determine the sources of atmospheric constituents arriving at the site. Among these, the mineral dust transported from the Great Sahara to the region is considered to be a rich source of iron. The concentration of Fe(II) varied from below detection limit (0.02 M) up to 0.42 M,while the maximum concentration of total reactive Fe (referred as Fe(II) + reducible Fe(III) = Fe_reac) was found to be 1.0 M in precipitation. A strong correlation was found between particulate Fe and Al fractions, both of crustal origin. No correlation was observed between the soluble and insoluble fractions of iron. The soluble iron fraction, Fe(II) concentration varied independently from the concentrations of reducible Fe(III), Fe_filt, Fe_par, and from the pH of the precipitation. The Fe_filt fraction (size < 0.45 m), measuredby Atomic Absorption Spectrophotometer, and frequently interpreted to be the soluble iron fraction in the literature, was found to be significantly higher than the corresponding Fe_reac fraction inprecipitation samples, most likely due to the colloidal iron content of the Fe_filt fraction passing through the 0.45 m pore size filter. The volume weighted mean Fe_filt concentration of the precipitation samples collected during the episodic `red rain' events was found to be relatively higher. The geometric mean ratios of soluble Fe(II) and of Fe_reac to Total Fe (Fe_filt + Fe_par), werefound to be 1.6% and 2.1%, respectively, while the mean ratioof Fe_filt to Total Fe was 9.6%. The flux of bioavailable iron (Fe_reac)fraction in most atmospheric wet deposition events was found to be sufficient for supporting the maximum primary production rates that are typical for the Eastern Mediterranean Sea.     

Contribution of tsunami data analysis to constrain the seismic source: the case of the 1693 eastern Sicily earthquake

The January 11, 1693 eastern Sicilyearthquake is comparable only with the December 28,1908 Messina Straits event in the Italian seismichistory as regards magnitude (M _L 7), level ofdestruction and number of victims. The shock generateda strong tsunami, which hit the entire eastern coastof Sicily and particularly the town of Augusta. Theproblem of which fault was responsible for theearthquake is still open. Several hypotheses have beenformulated in the literature on the basis of differentkinds of geological, macroseismic and tectonic data,but a general agreement has not been reached yet. Animportant contribution to the discussion may come fromthe analysis of the tsunami data. In two previouspapers (Piatanesi et al., 1996; Piatanesi and Tinti,1998), the hydro-dynamical study of the tsunami basedon finite-element (FE) numerical simulations wascarried out taking into consideration mostlytheoretical faults, i.e. faults selected for theirsignificance in tsunami generation irrespective of thecorresponding geological evidence. This paper has tobe considered the continuation of the mentioned works.We have studied new sources proposed in theliterature, consistent with macroseismic data and/orgeological observations, and simulated thecorresponding tsunamis. We also built a new FE gridintroducing significant improvements in the coastlinerepresentation, and developed and applied a newalgorithm in order to account for the effect of thesea-bottom topography on the tsunami initialcondition. Some of the examined faults are located inthe Scordia-Lentini (SL) graben region and interceptthe coastline, others are placed in correspondencewith the Hyblaean-Malta (HM) escarpment and runparallel or sub-parallel to the coast. The conclusionof our work is that none of these faults respectsfully the available observations on tsunami, and thatthe faults exhibiting the best fit are those placed inthe SL region. It is worth stressing that our resultsare important for the assessment of seismic andtsunami hazard/risk in eastern Sicily, keeping also inmind that the 1693 earthquake has been selected as thereference event for an earthquake-scenario study inCatania and in south-eastern Sicily, called `CataniaProject', funded by CNR/GNDT (Consiglio Nazionaledelle Ricerche/Gruppo Nazionale Difesa dai Terremoti).