吉林永吉县头道沟地区镁铁—超镁铁质岩U-Pb年代学研究及地质意义

吉林省永吉县头道沟地区出露许多与头道沟岩组相伴产出的镁铁—超镁铁质岩,鉴于其处于长春-延吉构造带附近而受到业内关注,但由于缺少高精度年代学资料,制约了对区域大地构造的深入研究。本文采用锆石U-Pb(LA-ICP-MS)方法,对镁铁—超镁铁质岩进行了年代学研究。变质辉绿岩年龄为270±5 Ma,变质橄榄岩中捕获锆石最小年龄为297 Ma,考虑岩石组合及二者紧密相伴产出,认为二者均形成于中二叠世。镁铁—超镁铁质岩中捕获的锆石记录了华北克拉通及其北缘多次重要的构造热事件。其中,变辉绿岩中获得446±6 Ma的年龄与变质橄榄岩中获得的不一致线下交点434±240 Ma年龄共同对应了华北克拉通北缘早古生代的重要构造岩浆热事件;大量的1.8~2.4Ga年龄对应古元古代辽吉造山带热事件;1377 Ma、1542 Ma与蓟县系建造时代对应;869~997 Ma与青白口系建造时代对应;在变质辉绿岩中还存在众多3.0~3.2Ga锆石年龄。分析上述年龄结构及龙岗陆块北缘古生代地质体分布特征,推测研究区深部可能存在古老的变质基底,同时也表明研究区出露的镁铁—超镁铁质岩形成于陆内构造环境,而非蛇绿岩的组成成分,这对深化区域大地构造研究具有重要意义。     

云南会泽铅锌矿区地下水化学和同位素分析

本文通过调查和采样测试,分析云南会泽铅锌矿区地下水的水化学特征,划分其水化学类型;根据不同水文年、不同埋深δ2 H和δ18 O的变化,分析了地表水体与地下水的相互关系,认为矿区中部含水层受到地表水的入渗,地表水与深部岩溶水的混合作用加大,中部岩溶含水层水力活动范围不断扩大,相对长江流域同位素分布规律,矿区降雨中重同位素偏富,深部岩溶水有显著的埋深效应,季节效应不明显。提供了一个矿区地下水水化学和同位素研究实例,对同类研究有借鉴价值。     

The Hissar–Alay and the Pamirs: Deep-Seated Structure,Geodynamic Model,and Experimental Evidence

The structural and geodynamic features of the Pamirs and the Hissar–Alay have been revealed based on geological and geophysical evidence supplemented by experimental data. It has been shown that both the Pamirs and the Hissar–Alay are geodynamic systems, the formation of which is related to interference of two geodynamic regimes: (i) global orogeny covering extensive territories of Eurasia and determining their similarity and (ii) regional regimes differing for the Pamirs and the Alay, which act independently within Central Asian and Apline–Himalayan mobile belts, respectively. The Pamirs do not act as an indentor during the formation of structure of the Hissar–Alay and areas to the north. It is stated that the Pamir–Alay segment of Asia is a reflection of the geodynamic countermotion setting (3D flow of mountain masses) of several distinct segments of the continental lithosphere, while the Pamirs are an intracontinental subduction domain at the surface, which represents a special tectonic–geodynamic type of structures.     

Deformations and Manifestations of Degassing in the Sedimentary Cover of the Equatorial Segment of the West Atlantic: Implications for Lithospheric Geodynamics

Manifestations of fluids and deformations in the sedimentary cover, which are both factors of brightening (blanking anomalies) in seismoacoustic records, in the equatorial segment of the Atlantic coincide with the sublatitudinal zones of the activated passive parts of transform faults and with zones of lower gravity anomalies and higher values of remnant magnetization, which form as a result of serpentinization. The cause-and-effect sequence of intraplate phenomena includes: the contrasting geodynamic state → horizontal movements that form macrofractures → water supply to the upper mantle → serpentinization of rocks in the upper mantle → deformations associated with vertical uplift of basement and sedimentary cover blocks, coupled with fluid generation → and fluid accumulation in the sedimentary cover, accompanied by the formation of anomalies in seismoacoustic records. Based on the seismic data, we have identified imbricate-thrust deformations, diapir structures, stamp folds, and positive and negative flower structures, indicating the presence of strike-slip faults in the passive parts of transform faults. The general spatial distribution of deformation structures shows their concentration in cold mantle zones. Correlative comparison of the structural characteristics of deformations shows the direct relationship between the heights of structures and the development of serpentinization processes. As per the age of the basement, deformations range from 27–38 to 43–53 Ma; a quite thick sedimentary cover makes it possible to reveal them based on the characteristic types of seismoacoustic records. The formation of the Antilles arc ca. 10 Ma ago affected the equatorial segment of the Atlantic; it formed kink bands where lithospheric blocks underwent displacements with counterclockwise rotations, deformations related to compression and vertical uplift of crustal fragments, and local extension that favored degassing of endogenous fluids. Sublatitudinally oriented imbricate-thrust deformations with different vergences indicate irregularity and alternating strike-slip directions as blocks between fractures were laterally influenced.     

Zircon U–Pb–Hf isotopes and geochemistry analyses of the Huyu igneous rocks in northwestern Beijing,China: possible new evidence for the initial destruction of the North China Craton

The timing and extent of cratonic destruction are crucial to understanding the crustal evolution of the North China Craton (NCC). Zircon U–Pb–Hf isotope data and the whole-rock major and trace element characteristics of the Huyu igneous rocks in northwestern Beijing, China, provide possible new evidence for the initial destruction of the NCC. The igneous rocks occur as several sills and dikes, including lamprophyre, monzonite porphyry, and aplite. The lamprophyres have high Mg^# and K₂O contents. The monzonite porphyries have high Mg^#, high K₂O contents, and negative ε_Hf(t) values with zircon U–Pb ages of 225.5–227.7 Ma. These two types of rocks are both enriched in large ion lithosphere elements (LILEs) and light rare earth elements (LREEs) but are depleted in high field strength elements (HFSEs) and high rare earth elements (HREEs) and have almost no Eu anomalies and relatively high total rare earth element (ΣREE) contents. In contrast, the aplites exhibit high silica and K₂O contents, low MgO contents, and more negative ε_Hf(t) values with a zircon U–Pb age of 206.2 Ma. The aplites are also enriched in LILEs and LREEs but are depleted in HFSEs and HREEs, with strongly negative Eu, Ti, P, La, Ce, and Sr anomalies and relatively low ΣREE contents. These results indicate that the lamprophyres and monzonite porphyries represent a continuous cogenetic magma evolution series after melt derived from an enriched metasomatized lithospheric mantle experienced crust assimilation and fractional crystallization. The aplites were produced by the fractional crystallization of low-Mg parental magma derived from melting of the ancient Archaean crust. The occurrence of the Huyu intrusive rocks with many other plutons of similar ages on the northern margin of the NCC suggests that the northern NCC entered an intraplate extensional tectonic environment in the Late Triassic.     

The Structure and Formation Conditions of the Callovian–Oxfordian Deposits of Sudak Bay (Crimea)

The composition and origin of the Callovian–Oxfordian deposits of the Sudak Bay were characterized on the basis of the generalization and analysis of our own results, as well as published and unpublished data. The botanical future was first implemented for the geological mapping of the Oxfordian deposits.     

Patterns of Spatial Methane Distribution in the Upper Layers of the Permafrost in Central Yakutia

This article presents the results of long-term field studies on methane in the upper part of the permafrost for different geomorphological levels of Central Yakutia. Patterns of the spatial distribution of the methane content across different landscapes were found. The difference in the methane content in sediments of the Late Pleistocene ice complex on the left and right banks of the Lena River was found for the inter-alas areas. This was caused by different conditions of formation: the formation of a thin cover of deposits occurred under sub-aqua conditions favorable for methanogenesis on the left bank and in more dry aerobic conditions on the right bank. The highest concentrations of methane were found in alas deposits, where the major role belongs to the duration of freezing after draining the thermokarst lake in subaerial conditions. The methane content is highly variable both laterally and with depth in the studied deposits, but there is no redistribution after freezing; this allows one to use methane as a paleo indicator of the conditions of accumulation and freezing of sediments.     

The Effect of Aggregation of Impurity Nitrogen on Diamond X-Ray Luminescence

Two samplings of 65 diamond crystals divided by the intensity of a slow X-ray luminescence component are studied from the Arkhangel’skaya and Karpinskogo-1 pipes. IR and EPR spectroscopies revealed a relationship between the nitrogen A and P2 centers of the diamonds and the presence of a slow X-ray luminescence component. Its absence in most diamonds with high content of P1 (C) centers is explained by the low number of A and P2 centers.     

Integrated Geophysical Works on the Kozlovka Anomaly (Kaluga Region)

This work presents integrated geophysical studies that were carried out to identify the nature of the intense magnetic anomaly detected by the results of land surveying on the right bank of the Slushka River in the territory of the Yukhnovskii district of Kaluga Region. The comprehensive interpretation of the geophysical data and the laboratory measurements of the core made it possible to determine the nature and parameters of the anomaly-forming object that is located in the upper part of the section; it consists of loams that contain such magnetic minerals as greigite, pyrrhotite, and magnetite.