Fold-Thrust-Belt Structure of the Proterozoic Eastern Ghats Mobile Belt: A Proposed Correlation Between India and Antarctica in Gondwana

The Proterozoic Eastern Ghats Mobile Belt along the east coast of India shares a thrusted lower contact with the surrounding cratons. The thrust, known as the Terrane Boundary shear zone, is associated with two large lateral ramps resulting in a curved outline on the northwestern corner of the mobile belt. The Eastern Ghats Mobile Belt is divided into two lithotectonic units, the Lathore Group and the Turekela Group, based on their lithological assemblages and deformational history. On the basis of published data from a Deep Seismic Sounding (DSS) profile of the Eastern Ghats crust, the Terrane Boundary Shear Zone is considered to be listric in nature and acts as the sole thrust between craton and mobile belt. The Lathore and Turekela Groups are nappes. With this structural configuration the NW part is described as a fold thrust belt. However, the thrusting postdates folding and granulite metamorphism that occurred in the Eastern Ghats, as in the Caledonide type of fold thrust belt of NW Scotland. The Terrane Boundary Shear Zone is interpreted to be contiguous with the Rayner-Napier boundary of the Enderby Land in a Gondwana assembly.     

北京延庆北部地区后城组火山岩岩石化学特征与成因探讨

根据TAS图解 ,北京延庆北部地区后城组火山属于玄武粗安岩 流纹岩 (和粗面岩 )的双峰式组合。该套火山岩不属于典型的钾玄岩系列 ,在基性岩和中性岩中总体上以碱性系列和向碱性系列过渡的高钾钙碱性系列、钾玄岩系列为主 ,流纹岩类属于富钾质的拉斑系列。该套火山岩轻稀土元素明显富集。玄武粗安岩类岩石没有负铕异常或负铕异常不明显 ,而流纹岩存在明显的负铕异常。延庆北部地区后城组火山岩形成于燕山运动早期或中期阶段的造山变形事件趋于结束时的后碰撞构造环境中。     

Deformation History of the Kunavaram Complex, Eastern Ghats Belt, India: Implications for Alkaline Magmatism Along the Indo-Antarctica Suture

The Kunavaram alkaline complex is a NE-SW trending elongate body located along a major lineament, the Sileru Shear Zone (SSZ) that is regarded as a Proterozoic suture related to Indo-Antarctica collision. The complex is hosted within migmatitic quartzofeldspathic gneisses, mafic granulites retrogressed to amphibolites, and quartzites. The structural evolution of the country rocks and the alkaline complex are similar. The first phase of deformation, D₁, produces a pervasive segregation banding (S₁) in all rock units within and outside the complex. A second deformation phase D₂ isoclinally folded S₁ along subvertical axial planes with shallow plunging axes. F₂ isoclinal folds are ubiquitous in the country rocks and the eastern extremity of the complex. In the interior of the alkaline body, D₂ strain decreases and S₁ is commonly subhorizontal. While amphibolite to granulite facies conditions prevailed during deformation, post-D₂ annealing textures testify to persisting high grade conditions. In the west, a NNE-SSW trending dextral shear zone with strike-slip sense (D₃) truncates the complex. Within this shear zone, quartzofeldspathic country rocks are plastically deformed, while hornblende-K-feldspar assemblages of the complex are retrogressed to biotite and plagioclase. Warping related to D₃ shears also resulted in fold interference patterns on the subhorizontal S₁ foliation in low D₂ strain domains. Based on its steep dip, north-easterly trend, and non-coaxial nature with dextral strike-slip sense, the D₃ shear zone can be correlated with the SSZ. Since this shear zone, i.e., the SSZ, is not associated with primary igneous fabrics and resulted in solid state deformation of the complex, it cannot be considered as a conduit for alkaline magmatism, but is probably responsible for the post-tectonic disposition of the pluton.     

Historical measurements of the Earth's magnetic field compared with remanence directions from lava flows in Italy over the last four centuries

Direct measurements of the Earth's magnetic field in Italy since 1640 a.d. have been used to check the remanence directions derived from historically dated volcanic rocks of Etna and Vesuvius. Direct measurements consist of the records of L’Aquila and Pola geomagnetic observatories, the repeat stations of the Italian Magnetic Network and the data base of the Historical Italian Geomagnetic Data Catalogue. All have been relocated to the same reference site (Viterbo — lat. 42.45°N, long. 12.03°E) in order to draw a reference secular variation (SV) curve. The direction of the Earth's field at Viterbo has also been calculated from the historical records (2000-1600) of ref. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Phil. Trans. R. Soc. London, Ser. A 358, 957-990] database. The remanence directions from Etna show a general agreement with the trend of the SV curve, although their inclination is usually lower than that from the direct measurement. The directions from Vesuvius are more scattered. Large discrepancies occur at both volcanoes and in some cases have been ascribed in the literature to poor geographic information, making it difficult to identify the flows actually emplaced during the eruptions reported in the chronicles. Closer examination shows that the great majority of the best-defined remanence directions (semi-angle of confidence α₉₅ < 2.5°) deviate significantly from the geomagnetic direction measured at the time of the emplacement, the angle between the two directions being larger than the α₉₅ value. The value of 2.5-3.0° can thus be regarded as a conservative evaluation of the error when dealing with dating Etna and Vesuvius lava flows older than 17th century, even when the accuracy attained in remanence measurements is higher. In default of a SV curve for Italy derived from archaeological artefacts, a further error in dating is introduced when reference is made to SV curves of other countries, even if well-established, as these are from regions too far from Italy (>600 km) to confidently relocate magnetic directions.     

Ground deformation of Nisyros Volcano (Greece) for the period 1995–2002: Results from DInSAR and DGPS observations

Differential GPS (DGPS) and Differential Interferometric Synthetic Aperture Radar (DInSAR) analyses were applied to the Kos-Yali-Nisyros Volcanic Field (SE Hellenic Volcanic Arc) to quantify the ground deformation of Nisyros Volcano. After intense seismic activity in 1996, a GPS network was installed in June 1997 and re-occupied annually up to 2002. A general uplift ranging from 14 to 140 mm was determined at all stations of the network. The corresponding horizontal displacements ranged from 13 to 53 mm. The displacement vectors indicate that the island is undergoing extension towards the East, West and South. A two-source “Mogi” model combined with assumed motion along the Mandraki Fault was constructed to fit the observed deformation. The best-fit model assumes sources at a depth of 5500 m NW of the centre of the island and at 6500 m offshore ESE of Yali Island. DInSAR analysis using four pairs of images taken between May 1995 and September 2000 suggests that deformation was occurring during 1995 before the start of the seismic crisis. An amplitude of at least 56 mm along the slant range appeared for the period 1996 through 1999. This deformation is consistent with the two-source model invoked in DGPS modelling. Surface evidence of ground deformation is expressed in the contemporaneous reactivation of the Mandraki Fault. In addition, a 600 m long N-S trending irregular rupture in the caldera floor was formed between 2001 and 2002. This rupture is interpreted as the release of surface stress in the consolidated epiclastic and hydrothermal sediments of the caldera floor.     

Active Fault and Volcanic Activity in the Longhai-Zhangpu Coastal Area, Fujian Province

INTRODUCTION TheLonghai ZhangpucoastalareaofFujianProvinceliesonthesouthernsideoftheoutletofthe JiulongjiangRiver.Tectonically,itislocatedonthesouthernsegmentoftheChangle Zhao’anfault zone.Previously,alotofseismogeologicresearchworkhasbeencarriedoutinthi…     

6: Classification of VMS deposits: Lessons from the South Uralides

VMS deposits of the South Urals developed within the evolving Urals palaeo-ocean between Silurian and Late Devonian times. Arc-continent collision between Baltica and the Magnitogorsk Zone (arc) in the south-western Urals effectively terminated submarine volcanism in the Magnitogorsk Zone with which the bulk of the VMS deposits are associated. The majority of the Urals VMS deposits formed within volcanic-dominated sequences in deep seawater settings. Preservation of macro and micro vent fauna in the sulphide bodies is both testament to the seafloor setting for much of the sulphides but also the exceptional degree of preservation and lack of metamorphic overprint of the deposits and host rocks. The deposits in the Urals have previously been classified in terms of tectonic setting, host rock associations and metal ratios in line with recent tectono-stratigraphic classifications. In addition to these broad classes, it is clear that in a number of the Urals settings, an evolution of the host volcanic stratigraphy is accompanied by an associated change in the metal ratios of the VMS deposits, a situation previously discussed, for example, in the Noranda district of Canada.Two key structural settings are implicated in the South Urals. The first is seen in a preserved marginal allochthon west of the Main Urals Fault where early arc tholeiites host Cu–Zn mineralization in deposits including Yaman Kasy, which is host to the oldest macro vent fauna assembly known to science. The second tectonic setting for the South Urals VMS is the Magnitogorsk arc where study has highlighted the presence of a preserved early forearc assemblage, arc tholeiite to calc-alkaline sequences and rifted arc bimodal tholeiite sequences. The boninitc rocks of the forearc host Cu–(Zn) and Cu–Co VMS deposits, the latter hosted in fragments within the Main Urals Fault Zone (MUFZ) which marks the line of arc-continent collision in Late Devonian times. The arc tholeiites host Cu–Zn deposits with an evolution to more calc-alkaline felsic volcanic sequences matched with a change to Zn–Pb–Cu polymetallic deposits, often gold-rich. Large rifts in the arc sequence are filled by thick bimodal tholeiite sequences, themselves often showing an evolution to a more calc-alkaline nature. These thick bimodal sequences are host to the largest of the Cu–Zn VMS deposits.The exceptional degree of preservation in the Urals has permitted the identification of early seafloor clastic and hydrolytic modification (here termed halmyrolysis sensu lato) to the sulphide assemblages prior to diagenesis and this results in large-scale modification to the primary VMS body, resulting in distinctive morphological and mineralogical sub-types of sulphide body superimposed upon the tectonic association classification.It is proposed that a better classification of seafloor VMS systems is thus achievable using a three stage classification based on (a) tectonic (hence bulk volcanic chemistry) association, (b) local volcanic chemical evolution within a single edifice and (c) seafloor reworking and halmyrolysis.     

How a wet tropical rainforest copes with repeated volcanic destruction

The Holocene Period for the province of West New Britain, Papua New Guinea, is characterised by periodic catastrophic volcanism. The region is mantled in dense wet tropical rainforest, and has been occupied by people since the Pleistocene. Analyses of peat from two nearby sites within a lowland rainforest environment provide us with a macro-level landscape account of the periodic destruction and recovery of the coastal forests during seven periods of volcanic activity in the latter part (2900 yr ago to present) of the Holocene. Radiocarbon dating shows the very close correlation of the peat and tephra layers at both sites, yet the pollen analysis reveals different vegetation communities. These initial results allow us to begin identifying the processes of recovery, and to recognise different ecological pressures placed on vegetation at these neighbouring sites. Evidence of hydrological changes are observed beginning with a marine incursion recorded at Garu Site 3 1360 ¹⁴C yr B.P. The distinct differences in the vegetation re-establishment and community regeneration rates suggest the greater level of disturbance at Garu Site 1 could be related to the depth of the ashfall, although the proximity of a known human settlement may also be a contributing factor. Of note, palynologically, we found that the fern spore flora is particularly rich and believe it will be useful for ecological interpretation.     

Analytical prediction of aggregates' effects on the ITZ volume fraction and Young's modulus of concrete

In order to evaluate analytically the ITZ volume fraction (f_ITZ) in concrete, a three phase model is proposed for the random concrete microstructure using the Voronoï tessellation. Within this model, the ITZ local thickness is a statistical variable depending on the local paste thickness available between each couple of neighbouring aggregates. The f_ITZ is found to not exceed 7% for typical concretes. Then, the concrete Young's modulus is predicted analytically using a four‐phase generalized self consistent model but in which the proposed f_ITZ is considered. It is found that the concrete Young's modulus increases when increasing aggregates volume fraction, aggregates maximum size and the proportion of coarse aggregates and when decreasing the ITZ thickness and Young's modulus. Finally, the validity of the proposed model is discussed based on a comparison between its predictions and three sets of experimental results related to normal and high strength concretes taken from literature. Copyright © 2016 John Wiley & Sons, Ltd.     

三塘湖盆地石炭系卡拉岗组火山岩岩相研究

三塘湖盆地石炭系卡拉岗组火山岩岩性揭示该区火山岩岩相主要包括火山爆发相、溢流相,火山沉积相不发育。为了明确不同岩相分布规律,本文系统利用测井、地质、地震等多种资料,建立测井岩性识别模板,以单井相作为约束,开展地震反演,明确火山岩岩相的平面分布规律。研究结果表明:该区火山喷发方式以裂隙式为主,火山口呈串珠状沿主断裂排列;溢流相平面呈层状分布,溢流相安山岩最为发育。研究结果可有效指导该区火山岩油藏的勘探评价工作,同时为火山岩岩相研究提供可借鉴的研究思路。