A late ultramafic suite in the Kap Edvard Holm layered gabbro complex, East Greenland

1993 ◽  
Vol 130 (4) ◽  
pp. 431-442 ◽  
Author(s):  
Christian Tegner ◽  
J. Richard Wilson
Keyword(s):  
Chrome Spinel ◽  
Olivine Gabbro ◽  
Contact Zones ◽  
The North ◽  
Early Tertiary ◽  
Host Olivine ◽  
Layered Gabbro ◽  
Western Side ◽  
Ocean Ridge ◽  
Marginal Zones

AbstractThe Kap Edvard Holm Complex is an early Tertiary layered gabbro situated on the western side of the Kangerdlugssuaq fjord. Layered olivine gabbros in the Taco Point area are cut by several wehrlitic sill-like bodies which comprise a late ultramafic suite. An intrusive wehrlitic facies in the inner part of the bodies consists of olivine (+minor chrome-spinel) orthocumulate with clinopyroxene oikocrysts and interstitial plagioclase, kaersutite and phlogopite. A replacive facies which occurs in the marginal zones is texturally similar to the intrusive facies but contains no chromespinel and is more feldspathic, varying from a melanocratic olivine gabbro to a feldspathic wehrlite. It occurs where the sills wedge out laterally, in the lower contact zones where finger structures are widely developed, and in the upper contact zones where wehrlitic pipes feed melanocratic sheets, called parasol structures, which preferentially follow mafic layers in the host olivine gabbro. The wehrlites formed by the intrusion of hot, hydrous, ultrabasic magma into consolidated layered olivine gabbro. The replacive facies was formed by the volume for volume metasomatic replacement of olivine gabbro; dissolution of plagioclase was accompanied by crystallization of olivine. Some clinopyroxene was initially resorbed and later reprecipitated during this process. The relatively dense pore magma migrating upwards was restricted to pipes and spread out laterally when it encountered readily replaced mafic layers, while below the sills gabbro was replaced en masse and finger structures were formed. Similar late ultramafic suites occur in ophiolites, and their presence in the Kap Edvard Holm Complex supports suggestions that it acted as an ocean ridge type magma chamber during the initiation of early Tertiary sea floor spreading in the North Atlantic.

Whole-rock and mineral chemistry of cumulates from the Kızıldağ (Hatay) ophiolite (Turkey): clues for multiple magma generation during crustal accretion in the southern Neotethyan ocean

2005 ◽  
Vol 69 (1) ◽  
pp. 53-76 ◽  
Author(s):  
U. Bağci ◽  
O. Parlak ◽  
V. Höck
Keyword(s):  
Tectonic Setting ◽  
Mineral Chemistry ◽  
Chromian Spinel ◽  
Olivine Gabbro ◽  
Crustal Accretion ◽  
Magma Generation ◽  
The North ◽  
Rock Types ◽  
Suprasubduction Zone ◽  
Ocean Ridge

AbstractThe late Cretaceous Kızıldağ ophiolite forms one of the best exposures of oceanic lithospheric remnants of southern Neotethys to the north of the Arabian promontory in Turkey. The ultramafic to mafic cumulate rocks, displaying variable thickness (ranging from 165 to 700 m), are ductiley deformed, possibly in response to syn-magmatic extension during sea-floor spreading and characterized by wehrlite, olivine gabbro, olivine gabbronorite and gabbro. The gabbroic cumulates have an intrusive contact with the wehrlitic cumulates in some places. The crystallization order of the cumulus and intercumulus phases is olivine (Fo86–77)± chromian spinel, clinopyroxene (Mg#92–76), plagio-clase(An95–83), orthopyroxene(Mg#87–79). The olivine, clinopyroxene, orthopyroxene and plagioclase in ultramafic and mafic cumulate rocks seem to have similar compositional range. This suggests that these rocks cannot represent a simple crystal line of descent. Instead the overlapping ranges in mineral compositions in different rock types suggest multiple magma generation during crustal accretion for the Kızıldağ ophiolite. The presence of high Mg# of olivine, clinopyroxene, orthopyroxene, and the absence of Ca-rich plagioclase as an early fractionating phase co-precipitating with forsteritic olivine, suggest that the Kızıldağ plutonic suite is not likely to have originated in a mid-ocean ridge environment. Instead the whole-rock and mineral chemistry of the cumulates indicates their derivation from an island arc tholeiitic (IAT) magma. All the evidence indicates that the Kızıldağ ophiolite formed along a slow-spreading centre in a fore-arc region of a suprasubduction zone tectonic setting.

Implication of dating of Early Tertiary volcanic rocks from the north-Chilean Precordillera

1992 ◽  
Vol 202 (1) ◽  
pp. 55-81 ◽  
Author(s):  
K. Hammerschmidt ◽  
R. Döbel ◽  
H. Friedrichsen
Keyword(s):  
Volcanic Rocks ◽  
The North ◽  
Early Tertiary

New data on the fauna and the biogeographic structure of the Hydrozoa, Scyphozoa, Staurozoa and Alcyonacea (Anthozoa) of the Kara Sea

2021 ◽  
Vol 325 (2) ◽  
pp. 143-155
Author(s):  
N.E. Zhuravleva
Keyword(s):  
Cold Water ◽  
Kara Sea ◽  
Novaya Zemlya ◽  
The North ◽  
Anna Trough ◽  
New Material ◽  
Western Side ◽  
Academy Of Sciences ◽  
North Western ◽  
Arctic Fauna

The paper considers the species composition of the fauna of several cnidarian groups of the Kara Sea. The author presents a list of species of the studied groups and indicates the types of habitat for each species. The analysis was based on the literature data, the collections of the Zoological Institute of the Russian Academy of Sciences and material collected in the Kara Sea during the expedition to the R/V Professor Multanovsky in 2019. In total, 87 species of Hydrozoa, 3 species of Scyphozoa, 4 species of Staurozoa, and 5 species of the order Alcyonacea from the class Anthozoa were recorded for the fauna of the Kara Sea, based on the new material obtained by the author and published literature data. The report presents the biogeographic structure of the discussed cnidarian groups. According to the types of biogeographic ranges, the fauna of the above-mentioned cnidarian groups in the Kara Sea mostly consists of representatives of the Boreal-Arctic type of habitat (63%), the Boreal and Amphiboreal biogeographic groups each containing 12% of the total number of described species, and the Panoceanic and Arctic groups together accounting for only 9% and 4% of the fauna of the Kara Sea. Two species new for the Kara Sea, Neoturris pileata (Forsskål, 1775) and Neoturris pileata (Forsskål, 1775), are described. Neoturris pileata is an element of the warm-water Atlantic fauna that penetrated into the Kara Sea with waters of Atlantic genesis. Nausithoe werneri is an element of the cold-water Arctic fauna that penetrated into the Novaya Zemlya Trough of the Kara Sea from the north-western side from the St. Anna Trough, which was open to the Polar Basin.

scholarly journals The concurrence of Atmospheric Rivers and explosive cyclogenesis in the North Atlantic and North Pacific basins

2017 ◽  
Author(s):  
Jorge Eiras-Barca ◽  
Alexandre M. Ramos ◽  
Joaquim G. Pinto ◽  
Ricardo M. Trigo ◽  
Margarida L. R. Liberato ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Reanalysis Data ◽  
Water Vapour Flux ◽  
Atmospheric Rivers ◽  
The North ◽  
Explosive Cyclones ◽  
The North Atlantic ◽  
Characteristic Features ◽  
Western Side

Abstract. The explosive cyclogenesis of extra-tropical cyclones and the occurrence of atmospheric rivers are characteristic features of baroclinic atmospheres, and are both closely related to extreme hydrometeorological events in the mid-latitudes, particularly on coastal areas on the western side of the continents. The potential role of atmospheric rivers in the explosive cyclone deepening has been previously analysed for selected case studies, but a general assessment from the climatological perspective is still missing. Using ERA-Interim reanalysis data for 1979–2011, we analyse the concurrence of atmospheric rivers and explosive cyclogenesis over the North Atlantic and North Pacific Basins for the extended winter months (ONDJFM). Atmospheric rivers are identified for almost 80 % of explosive deepening cyclones. For non-explosive cyclones, atmospheric rivers are found only in roughly 40 % of the cases. The analysis of the time evolution of the high values of water vapour flux associated with the atmospheric river during the cyclone development phase leads us to hypothesize that the identified relationship is the fingerprint of a mechanism that raises the odds of an explosive cyclogenesis occurrence and not merely a statistical relationship. This insight can be helpful for the predictability of high impact weather associated with explosive cyclones and atmospheric rivers.

scholarly journals Monument Boundary Definition and Exploration Pits at the Krasnyy Vostok Site in the River Kuma Basin

2020 ◽  
Author(s):  
А.В. Субботин
Keyword(s):  
Western Slope ◽  
Left Bank ◽  
North Caucasus ◽  
Mountainous Regions ◽  
The North ◽  
Boundary Definition ◽  
Northern Side ◽  
Western Side ◽  
Object Of Study ◽  
Stone Walls

В статье излагаются результаты инструментальной съемки и шурфовки на раннесредневековом городище, выявленном в начале 1970-х гг. Х. Х. Биджиевым. Городище и связанное с ним селище занимают высокое мысовое плато над каньоном левого берега р. Кумы в Карачаево-Черкесии. Площадь укрепленного городища – 4 га, селища – немногим меньше. С трех сторон городище абсолютно неприступно, с четвертой, западной, надежно защищено высоким валом и глубоким рвом. На городище и селище зафиксирован ряд западин, которые, скорее всего, являются заросшими остатками построек. Содержимое шести шурфов – каменные развалы фундаментов (?) строений и фрагменты сосудов. Керамика может быть датирована VII–X вв. н. э. Памятник являлся одним из звеньев в цепи достаточно известных (несколько десятков) укрепленных крепостей данного времени в предгорьях и горах Северного Кавказа. Строительство сети сложных оборонительных сооружений свидетельствует о высокой строительной культуре и социальной дифференциации общества в это время. The article presents the results of instrumental surveys and pitting at an early medieval site, identified in the early 1970s by Kh.Kh. Bidzhiev. The investigated site and the settlement associated with it occupy a high cape plateau above the canyon of the left bank of the river Kuma in the Karachay-Cherkess Republic. The object of study is located in 2.4 km south-west of the southern outskirts of the village Krasnovostochny. The area of the fortified site is 4 hectares, the area of the settlement is slightly less. On three sides, this site is absolutely impregnable. On the forth western side,on its western slope, it is reliably protected by a rampart of up to 6 to 7 m high and a moat of1 to 2 m deep. On the outside of the southern part of the rampart, a small outcrop of masonry constructed of the large blocks of limestone formed in the dry stone wall was discovered. The gates to the site were most likely located on the northern side of the rampart, in the place where a slight decrease was discovered, not at the southern end of the rampart (according to Bidzhiev) because no sign of an entrance was found there. The site revealed several shallow depressions of a sub-square, sub-rectangular or oval shape with a noticeable roller along the contour. There are at least 7 such depressions in the sectional area from 8 to 15 m. Probably, these depressions are the overgrown remains of the foundations of some buildings in the central part of the site. The content of 6 pits made on the territory of the site and the settlement are stone remains of the foundations (?) of ancient buildings and fragments of vessels. The collection of ceramics consists of medium-sized fragments of the walls of pottery (?) vessels, or vessels that are corrected on a wheel. The ceramics are diverse in the color of clay, density of the paste, firing, and impurities. According to the character, paste and collar shapes, ceramics can be dated to the last third of the 1st millennium AD, which does not contradict the opinion of the site’s discoverer on this issue (7th to 10th cent. AD). The examined site was one of the links in the main chain of fairly widely known (several dozen) fortified stone fortresses of this time in the foothills and mountains of the North Caucasus. Specialists know more than 130 similar stone sites, sometimes located in groups in the foothills and mountainous regions: settlements with defensive stone walls. Such small fortresses were built every 2 to 3 km along the tip of the cape above the river. The construction of a network of complex defensive structures indicates a high building culture and a social differentiation of society at the time.

Inferred seismic fault associated with the 1998 M = 6.2 Zhangbei-Shanyi earthquake, Hebei Province, China

1999 ◽  
Vol 89 (2) ◽  
pp. 550-554 ◽  
Author(s):  
Aiming Lin ◽  
Guochun Zhao ◽  
Guozhe Zhao ◽  
Xiwei Xu
Keyword(s):  
Seismic Data ◽  
Active Fault ◽  
Lateral Displacement ◽  
Displacement Component ◽  
The North ◽  
Seismic Fault ◽  
Direction Change ◽  
Western Side ◽  
Northwest Region ◽  
Beijing China

Abstract The shallow, Ms = 6.2, 1998 Zhangbei-Shanyi earthquake that affected the northwest region of Beijing, China, occurred at the intersection of two active fault zones, located on the north and east edges of the Ordos tableland. A detailed map of the intensity distribution of damaged building shows that the most damaged area was centered 8 to 10 km away from the epicenter, including an ellipsoidal region with a strike of NNE, where more than 70 to 90% of buildings were destroyed. Many chimneys and gate pillars were broken and fell toward the SSE-SSW direction in the western side of the most damaged area and to the NNE-NNW direction in the eastern side. Aftershocks were also concentrated in the most damaged area. It is inferred that the boundary of the downfallen direction change is the surface trace of the seismic fault. Based on the seismic data, the distribution of damaged buildings, and the downfallen directions of 70 chimneys and gate pillars, it is identified that the seismic fault is a thrust fault striking NNE and dipping 40° to 50° northwest with a large right-lateral displacement component.

First mid-ocean ridge-type ophiolite from the Meso-Tethys suture zone in the north-central Tibetan plateau

2020 ◽  
Vol 132 (9-10) ◽  
pp. 2202-2220 ◽  
Author(s):  
Yue Tang ◽  
Qing-Guo Zhai ◽  
Sun-Lin Chung ◽  
Pei-Yuan Hu ◽  
Jun Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Ocean Basin ◽  
Suture Zone ◽  
The Tibetan Plateau ◽  
Spreading Ridge ◽  
North Central ◽  
The North ◽  
Central Tibetan Plateau ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Abstract The Meso-Tethys was a late Paleozoic to Mesozoic ocean basin between the Cimmerian continent and Gondwana. Part of its relicts is exposed in the Bangong–Nujiang suture zone, in the north-central Tibetan Plateau, that played a key role in the evolution of the Tibetan plateau before the India-Asia collision. A Penrose-type ophiolitic sequence was newly discovered in the Ren Co area in the middle of the Bangong–Nujiang suture zone, which comprises serpentinized peridotites, layered and isotropic gabbros, sheeted dikes, pillow and massive basalts, and red cherts. Zircon U-Pb dating of gabbros and plagiogranites yielded 206Pb/238U ages of 169–147 Ma, constraining the timing of formation of the Ren Co ophiolite. The mafic rocks (i.e., basalt, diabase, and gabbro) in the ophiolite have uniform geochemical compositions, coupled with normal mid-ocean ridge basalt-type trace element patterns. Moreover, the samples have positive whole-rock εNd(t) [+9.2 to +8.3], zircon εHf(t) [+17 to +13], and mantle-like δ18O (5.8–4.3‰) values. These features suggest that the Ren Co ophiolite is typical of mid-ocean ridge-type ophiolite that is identified for the first time in the Bangong–Nujiang suture zone. We argue that the Ren Co ophiolite is the relic of a fast-spreading ridge that occurred in the main oceanic basin of the Bangong–Nujiang segment of Meso-Tethys. Here the Meso-Tethyan orogeny involves a continuous history of oceanic subduction, accretion, and continental assembly from the Early Jurassic to Early Cretaceous.

Grim's Bank, Padworth, Berkshire

Antiquity ◽  
1943 ◽  
Vol 17 (68) ◽  
pp. 188-195
Author(s):  
B. H. St. J. O'Neil
Keyword(s):  
The Other ◽  
Present Writer ◽  
Recent Past ◽  
The West ◽  
The Road ◽  
The North ◽  
Northern Side ◽  
Western Side

The immediate environs of Silchester consist of fields, which are either now under plough or else have been arable for many years in the recent past. Consequently there are few, if any, traces there of the Roman roads which led from the various gates to Dorchester, Speen and Cirencester, Sarum, Winchester, and London. A mile or more to the north and northwest of the Roman town, however, there is a belt of land, which is largely heathland except where trees have been planted. Here there are clear indications of the line of two Roman roads, one from the west gate, west-northwest to Speen and Cirencester, the other from the north gate to Dorchester (Oxon.)The road to Speen (FIG. I) was formerly thought to follow closely the modern road along the northern side of Silchester Common and thence to run along the straight county boundary between Berkshire and Hampshire. In recent years, however, Mr O. G. S. Crawford has shown that the road, instead of following this traditional line, ran west-northwestward to cross the river Kennet near Brimpton Mill. It is traceable as a raised camber or a deep hollow way from Catthaw Lands Copse, about half-a-mile from the west gate of Silchester, to the western side of Hungry Hill. Further west, in Decoy Plantation, and again beyond the road from Padworth Common, i.e. in Keyser's Plantation, it is clearly seen as a broad cambered way (o.s. 641-1. Berkshire XLIV, SE, Hampshire IV, SE). Beyond this point the present writer has not followed it, but Mr Crawford has noted its continuation.

A terrane interpretation of the Archaean Limpopo Belt

1993 ◽  
Vol 130 (6) ◽  
pp. 755-765 ◽  
Author(s):  
H. R. Rollinson
Keyword(s):  
Shear Zones ◽  
Kaapvaal Craton ◽  
Late Archaean ◽  
The North ◽  
Zimbabwe Craton ◽  
Marginal Zones ◽  
Limpopo Belt

AbstractThe Limpopo Belt is a zone of thickened Archaean crust whose origin is currently explained by a late Archaean continent-continent collision between the Kaapvaal and Zimbabwe cratons. This review shows that the two cratons have fundamentally different geological histories and that the Zimbabwe Craton was unlikely to have behaved as a stable ‘cratonic’ block at the time of the Limpopo Belt collision. The geological histories of the Zimbabwe Craton, the North Marginal, Central and South Marginal zones of the Limpopo Belt and the Kaapvaal Craton are shown to be sufficiently different from one another to warrant their consideration as discrete terranes. The boundaries between the five units outlined above are all major shear zones, further supporting a terrane model for the Limpopo Belt. The five units were all intruded by late- to syn-tectonic granites c.2.6 Ga, constraining the accretion event to c. 2.6 Ga.

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