Weichselian ice movement in South Norway and adjacent areas

Three main phases of ice-movement pattern in South Norway during the Weichselian are reconstructed. During Phase II (possibly of Middle Weichselian age) the ice divide was located far to the west. Phase III (assumed Middle/Late Weichselian age) had an easterly situated ice divide. During Phase IV (Preboreal age) the ice divide had moved back to the west and had partly fragmented into separate domes. The migration of the ice divide from west to east may be due to glacier surges, whilst the ice-divide migration from Phase III to IV was probably a result of a general reduction in size of the ice sheet.     

Age determination of intermoraine areas, Austerdalen, southern Norway

This paper is concerned with the size variation of thalli of the lichen Rhizocarpon geographicum agg. on intermoraine surfaces in the proglacial valley of Austerdalen, southern Norway, and with the use of thallus dimensions for both relative and absolute dating of intermoraine deposits. Measurements of the five largest lichens in 200 m² search areas at 255 sites show significant cross-valley and down-valley variations, with the smallest thalli located towards the centre of the valley and at up-valley sites. This variation has been examined in greater detail by dividing the intermoraine areas into twelve morphological zones, for which geomorphological and stratigraphical relations enable the construction of a relative time sequence of formation. This relative time sequence was then found to he confirmed by mean values of measurements of the largest lichen thalli in 100 m square quadrats within each morphological zone. This approach has allowed not only the relative age of morainic and intermorainic deposits to he established from geomorphological evidence but also, using tentative dates for the moraines, the construction of a chronology of moraine and intermoraine depositional events.     

The geotectonic history of the Makran and adjacent areas of southern Iran

The Makran mountain range in Southern Iran has been entirely covered by regional mapping on a scale of 1:250,000, but, in contrast to the mapping of Oman on the other side of the Gulf, the recent mapping is little known. The Cenozoic accretionary prism in the south fronts onto a Mesozoic melange zone representing earlier subduction and to the north of this is an eastwards tapering microcontinental sliver, which is followed by a zone of largely intact Mesozoic ophiolite complexes. To the north of this lies the Jaz Murian depression, a desert expanse with no bedrock outcrop. The Sanandaj-Sirjan/Bajgan–Dur-Kan microcontinental sliver, which extends from Turkey through the Zagros to the Makran, is one of a number of microcontinents which detached from Gondwana no later than the early Triassic (NW Iran, Yazd, Tabas, Lut, Birk, Helmand, Farah). During the Mesozoic, these were enclosed by tracts of ocean now represented by ophiolites and the sectors closed at different times, ranging from early Cretaceous to end-Palaeogene. An analogy is drawn with the present-day Mediterranean. The “Sistan Ocean”, in the east, was infilled with an immense thickness of abyssal turbidites during the Eocene before it closed. The field evidence indicates that there was a second Cenozoic accretionary prism here, but sedimentation ceased after the Eocene, on its collision with the back of the main Makran prism. This eastern Sistan trough, now completely occluded, is compared with the still open tract separating the Makran from Oman at the present time and its northern extension which has been similarly occluded by collision beneath the Zagros. Some residual, very shallow inland seas persisted inland from the Makran through the Neogene. The occurrence of blueschists in the inner ophiolite belt of the Makran is discussed. Abyssal turbidite sedimentation continued in the main southern zone of the Makran into the early Miocene, to be succeeded by thick shallow water sequences including reefal limestones. Intense tectonic dislocation at the end of the Miocene was accompanied by a shift of the subduction front to its present position out in the Indian Ocean and uplift, leading to the deposition of spectacular Pliocene–Pleistocene fanglomerates.     

Geophysical lineaments of Western Ghats and adjoining coastal areas of central Kerala,southern India and their temporal development

A family of geophysical lineaments have been identified in ~15,000 km~2 in central Kerala between9 30'N to 10 45'N and 76 00'E to 77°30′E,integrating geophysical data with geological and geomorphological features. The characteristics of these lineaments in the magnetic and gravity fields and their derivatives have been analysed. The evolution of the lineaments has been traced to the temporal phases of global evolution of the region. A group of these faults have formed by reactivation of the deep-seated distensional fractures associated with and accompanying dyke emplacements during the episodic breakup of Gondwana at ~90 and 65 Ma under distinctive mantle thermal regimes. It is possible that reactivation of these distensional faults may have started during the cooling interval of time between the two distensions in the 90 and 65 Ma and post 65 Ma periods and later in the Cenozoic, when the lineaments were enlarged to their present dimension, possibly under the influence of forces that led to the uplift of the western Ghats. These may extend down to the crust-mantle interface. A cluster of youngergeophysical lineaments has been generated by reactivation along the weak planes of transformation of the charnockitic rocks of the Precambrian. They seem to have a strike-slip character. They are devoid of any dyke association and were formed on a cold crust. They may be confined to the upper-middle crust.They were generated in the high intensity intra-plate palaeo-stress fields of the triple forces arising from(1) the back-thrust from the Himalayan Collision;(2) the impact of epeirogenic forces and related isostatic uplift of the Western Ghats and(3) the flexural isostatic uplifts due to surface loads of late Mesozoic basaltic lavas and Cenozoic sedimentation in the coastal rifted basins in late Cenozoic, probably in the time span of 20 Ma to the present, when the palaeostress fields were most intense.     

黔中隆起及周缘地区下组合含油气流体包裹体研究

应用均一法测温及激光拉曼探针等技术对黔中隆起地区下组合含油气流体包裹体进行了研究,结果表明该区烃类包裹体个体较小,无色,形态不规则,其烃类成分以CH4为主,具明显干气特征,部分包裹体内含CO2,分析认为是碳酸盐(碳酸氢钙)因温度、压力的变化分解所致.均一温度测试结果显示下组合油气包裹体形成时的温度分别位于85～125℃、125～165℃两个温度段,结合该地区埋藏史及古地温史研究,确定本区成藏期分别为早中寒武世-早三叠世及早三叠世-中晚侏罗世.     

Esker formation and glacier dynamics in eastern Skane and adjacent areas, southern Sweden

Eskers were investigated in an area with overall terrestrial deglaciation - the eastern part of the province of Skåne and adjacent areas in southern Sweden. On the basis of the proposed model of esker formation, the dynamics of the receding Weichselian Ice Sheet are discussed. The deglaciation was characterized by the gradual retreat of an active ice sheet, bordered by a zone of thin, stagnant ice. For the most part, the ice sheet was probably at the pressure melting point in a marginal zone, where it was penetrated by surface meltwater which constituted most of the subglacially flowing meltwater. The esker sediments, consisting of glaciofluvially reworked basal debris and basal till, accumulated progressively in an up-glacier direction. Deposition took place close to the live ice boundary in the zone with stagnant ice that fringed the receding ice sheet. The time-transgressive formation of the eskers is reflected by repeated sediment sequences (morphosequences), i.e. sedimentary units composed of ridges that merge into extended hummocky deposits in a down-glacier direction. They represent the momentary deposition of stratified drift in the proximal portion of the zone with stagnant ice.     

A seismic hazard map of India and adjacent areas

We have produced a probabilistic seismic hazard map showing peak ground accelerations in rock for India and neighboring areas having a 10% probability of being exceeded in 50 years. Seismogenic zones were identified on the basis of historical seismicity, seismotectonics and geology of the region. Procedures for reducing the incompleteness of earthquake catalogs were followed before estimating recurrence parameters. An eastern United States acceleration attenuation relationship was employed after it was found that intensity attenuation for the Indian region and the eastern United States was similar. The largest probabilistic accelerations are obtained in the seismotectonic belts of Kirthar, Hindukush, Himalaya, Arakan-Yoma, and the Shillong massif where values of over 70% g have been calculated.     

Reactivation of intrabasement structures during rifting: A case study from offshore southern Norway

Pre-existing structures within crystalline basement may exert a significant influence over the evolution of rifts. However, the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood. Using borehole-constrained 2D and 3D seismic reflection data from offshore southern Norway we identify and constrain the three-dimensional geometry of a series of enigmatic intrabasement reflections. Through 1D waveform modelling and 3D mapping of these reflection packages, we correlate them to the onshore Caledonian thrust belt and Devonian shear zones. Based on the seismic-stratigraphic architecture of the post-basement succession, we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events. Reactivation preferentially occurs along relatively thick (c. 1 km), relatively steeply dipping (c. 30°) structures, with three main styles of interactions observed between them and overlying faults: i) faults exploiting intrabasement weaknesses represented by intra-shear zone mylonites; ii) faults that initiate within the hangingwall of the shear zones, inheriting their orientation and merging with said structure at depth; or iii) faults that initiate independently from and cross-cut intrabasement structures. We demonstrate that large-scale discrete shear zones act as a long-lived structural template for fault initiation during multiple phases of rifting.     

南蒙古典型金属矿床地质特征及对中国相邻地区的找矿启示

伴随南蒙古洋的开合，南蒙古地区从早古生代到晚中生代经历不同类型地体的增生、碰撞拼贴以及碰撞后伸展活动，发育不同规模和类型的岩浆岩。与之对应，南蒙古地区发育Au、Cu、Mo、Ag、W、Sn、Nb、Ta、Be、REE等金属成矿作用，主要产出斑岩型Cu-Au和Cu-Mo矿床、石英脉/角砾岩型Au-Ag矿床、云英岩/石英脉型W-Sn-Mo矿床和碱性岩型Nb-Ta-Be-REE矿床。对比南蒙古地区和相邻的中国二连—东乌旗地区的地质条件，确定二连—东乌旗地区的找矿方向和部分找矿标志。     

Effects of fracture lineaments and in-situ rock stresses on groundwater flow in hard rocks: a case study from Sunnfjord, western Norway

Systematic field mapping of fracture lineaments observed on aerial photographs shows that almost all of these structures are positively correlated with zones of high macroscopic and mesoscopic fracture frequencies compared with the surroundings. The lineaments are subdivided into zones with different characteristics: (1) a central zone with fault rocks, high fracture frequency and connectivity but commonly with mineral sealed fractures, and (2) a damage zone divided into a proximal zone with a high fracture frequency of lineament parallel, non-mineralized and interconnected fractures, grading into a distal zone with lower fracture frequencies and which is transitional to the surrounding areas with general background fracturing. To examine the possible relations between lineament architecture and in-situ rock stress on groundwater flow, the geological fieldwork was followed up by in-situ stress measurements and test boreholes at selected sites. Geophysical well logging added valuable information about fracture distribution and fracture flow at depths. Based on the studies of in-situ stresses as well as the lineaments and associated fracture systems presented above, two working hypotheses for groundwater flow were formulated: (i) In areas with a general background fracturing and in the distal zone of lineaments, groundwater flow will mainly occur along fractures parallel with the largest in-situ rock stress, unless fractures are critically loaded or reactivated as shear fractures at angles around 30° to σ_H; (ii) In the influence area of lineaments, the largest potential for groundwater abstraction is in the proximal zone, where there is a high fracture frequency and connectivity with negligible fracture fillings. The testing of the two hypotheses does not give a clear and unequivocal answer in support of the two assumptions about groundwater flow in the study area. But most of the observed data are in agreement with the predictions from the models, and can be explained by the action of the present stress field on pre-existing fractures.     

Topographic and geomorphological features and tectogenesis of the southern section of the Kyushu-Palau Ridge (KPR) and its adjacent areas

The Philippine Sea is the largest marginal sea in the Western Pacific Ocean and is divided into two parts by the Kyushu-Palau Ridge (KPR). The western part is the West Philippine Basin, and the eastern part consists of the Shikoku and Parece Vela basins. Based on surveyed data of massive high-resolution multibeam bathymetric data and sub-bottom profiles data collected from the southern section of the KPR from 2018 to 2021, this paper analyzes the topographic and geomorphological features, shallow sedimentary features, and tectonic genesis of the southern section of the KPR, obtaining the following conclusions. The southern section of the KPR has complex and rugged topography, with positive and negative topography alternatingly distributed and a maximum height difference of 4086 m. The slope of seamounts in this section generally exceeds 10° and is up to a maximum of 59°. All these contribute noticeably discontinuous topography. There are primarily nine geomorphological types in the southern section of the KPR, including seamounts, ridges, and intermontane valleys, etc. Among them, seven independent seamount groups are divided by five large troughs, forming an overall geomorphological pattern of seven abyssal seamount groups and five troughs. This reflects the geomorphological features of a deep oceanic ridge. Intramontane basins and intermontane valleys in the southern section of the KPR are covered by evenly thick sediments. In contrast, sediments in ridges and seamounts in this section are thin or even missing, with slumps developing locally. Therefore, the sediments are discontinuous and unevenly developed. The KPR formed under the control of tectonism such as volcanic activities and plate movements. In addition, exogenic forces such as underflow scouring and sedimentation also play a certain role in shaping seafloor landforms in the KPR.©2021 China Geology Editorial Office.     

A uranium and thorium enriched province of the Fennoscandian shield in southern Norway

The Precambrian Flå, Iddefjord, and Bohus granites lie along a line striking roughly northwest which crosses the Permian Oslo Province to the southwest of Oslo. Radioelement investigations in the three bodies show they all contain abnormally high thorium and uranium concentrations relative to the published literature on average radioelement contents of granitic rocks. Trend surface analysis of the radioelement distribution in the Iddefjord granite suggests there was relative movement of uranium to the east with respect to thorium, possibly as the result of Permian activity in the adjacent rocks. Geological considerations, radiometric evidence and published gravimetric data suggest that the 3 granites represent a continuous belt enriched in thorium and uranium during the Sveconorwegian orogeny. A portion of the belt was later involved in the Permian igneous activity which produced the igneous Oslo Province. There is some evidence that the Permian Drammen and Finnemarka granites represent that part of the belt which was modified in Permian time.     

金堆城钼矿集区及邻区重磁场特征

通过对东秦岭金堆城钼矿集区及邻区已有重、磁测量资料系统整理和研究,并结合地质、钻井等前人研究成果,对研究区的重、磁资料进行了处理,推断了研究区的断裂构造,分析了重、磁局部异常与已知钼矿点的分布特征,进而探讨了研究区的成矿有利区。研究结果表明,研究区主要断裂可以分为近东西向、北东向和北西向3组,近东西向和北东向两组断裂构造的交切点控制了岩浆岩体的空间侵位,并且控制了研究区钼矿点(床)的产出位置;钼矿(床)点分布在重力低异常区、重力局部低异常向高异常过渡的舌状伸出部位和化极后局部正负磁异常的边界上,并且与负磁异常相关;根据地质构造和已知钼矿点在局部重、磁异常中的反映,结合化探异常和断裂控矿特点,圈定了4个找矿有利区。     

祁连山地区东段马衔山群及其邻区岩石学研究

祁连造山带是中国主要造山带之一,大致分为北祁连、中祁连、南祁连和拉鸡山4个变质区.本文研究的中祁连地块前震旦纪马衔山群及其邻近的震旦纪地层与奥陶纪地层位于距兰州市东北150 km处,由东向西北依次为寺儿沟、铁成沟、天祝三峡森林公园、北山国家公园(那新沟)和岗口子北等剖面.对上述剖面进行的矿物组合、微构造和矿物化学成分研究结果表明,马衔山群变质作用过程为:峰期角闪岩相变质,矿物组合为黑云母+角闪石,温压分别为618℃和0.65 GPa;绿帘角闪岩相变质,矿物组合为绿帘石+钠长石+钙质角闪石;绿片岩相变质,矿物组合为阳起石±脆绿泥石+方解石.马衔山群的石榴石具生长环带,从核心到边缘,Mn含量减少,Fe含量渐增,在压力不变的情况下此种成分变化指示温度的上升,核心和边缘的温度分别为418℃和545℃.钙质角闪石不具化学环带.Ar-Ar法定年结果显示,角闪岩中角闪石与花岗岩中黑云母的坪年龄分别为340.0±0.50 Ma和323.4±0.65 Ma,反映了前震旦纪马衔山群在石炭纪受区域变质活动发生再活化作用的下限年龄.震旦纪地层的岩石类型主要为绿片岩,矿物组合为绿泥石+钠长石+赤铁矿+方解石+石英,局部受韧性剪切带影响而产生糜棱岩化作用.奥陶纪地层主要岩石类型为大理岩,碳酸盐类矿物主要为方解石和白云石,其中除有磷灰石夹层外,还有高镁的金云母.     

Structure of terrestrial crust in southern Sakhalin and adjacent aquatoria

Recent deep seismic sounding and other data suggest presence of a deep rift which cuts across southern Sakhalin, Aniva Bay, La Perouse Strait, and Hokkaido Island, a suboceanic type of crust in the Sea of Okhotsk, and a continental one in Sakhalin. The density-velocities relationship determined here may account for the observed gravity anomalies as due primarily to variations in thickness of the crust (fig. 6), without resorting to other hypotheses.     

Gravity field and isostatic state of Ethiopia and adjacent areas

Over 35,000 onshore and offshore gravity stations have been compiled in order to test isostatic models against geologic structures over a part of the Afro–Arabian shield. The area of Ethiopia covers an important part of this system because it contains the major section of the ≈5000 km Afro–Arabian rift and includes the transition between the Arabo-Nubian-Shield (ANS) and the Mozambique Belt (MB).Isostatic residual anomalies have been calculated using both Airy and Vening-Meinesz (flexural rigidity D = 10²² Nm) models. The isostatic residual anomalies outline the major Precambrian belts, the Cenozoic rifts and associated major structures. Positive residual anomalies associated with the main Ethiopian Rift (MER) and Kenyan rift systems could be the expressions of an axial intrusive body and swarms of local faults and fractures. The residual anomalies indicate relative stability in the MER and increased tectonic activity in the areas of the Red Sea, Gulf of Aden and Afar. Near-zero isostatic residuals flank the MER and Kenya rifts and are found within the Danakil Alps and some plateau regions.The small mean isostatic residual anomaly (about 8 mGal) and the isostatic analysis show a slight positive bias indicating under compensation. The undercompensation may imply that there are upper crustal features that are not compensated regionally (probably supported by the rigidity of the lithosphere) and isostatic disequilibrium in the region. Therefore, the high topography of Ethiopia and East African plateau is partly compensated by thicker crust (broad negative isostatic regional anomaly) and partly by dynamic forces.The results of the qualitative interpretation form the basis of continuing three-dimensional gravity modelling and quantitative analysis that also integrates data from eastern Sudan.     

祁连及邻区成矿区带的划分

文章借鉴中国成矿区带划分方案,在分析了祁连山及邻区成矿地质背景基础上,将祁连及邻区划分为5个Ⅱ级成矿省、11个Ⅲ级成矿带和19个Ⅳ级成矿亚带,并对划分出的Ⅳ级成矿亚带进行了成矿条件、优势矿种及矿床成因类型等主要地质特征的分析。