The formation and genesis of the rhyolite series of the Upper Chegem Highlands (the North Caucasus)

2020 ◽  
pp. 3-12
Author(s):  
N. V. Koronovsky ◽  
M. S. Myshenkova
Keyword(s):  
Main Part ◽  
Volcanic Rocks ◽  
Lava Flows ◽  
New Materials ◽  
North Caucasus ◽  
Columnar Jointing ◽  
Limited Volume ◽  
Late Pliocene ◽  
The North ◽  
Supercritical Water Fluid

On the basis of new materials this article deals with the structure and origin of a huge (up to 2 km) thick massif of acidic volcanic rocks located in a volcanic-tectonic depression in the Upper Chegem River in the North Caucasus. Discussion on the lava’s, rather than pyroclastic, origin of the main part of the rock mass as a result of repeated outpourings of lava flows, which formed the series of acidic volcanic rocks without interruptions with perfectly pronounced columnar jointing in a limited volume of a deep volcanic-tectonic depression, which was forming simultaneously with eruptions in the Late Pliocene. Volcanic rocks formed as a result of boiling silicate meltas the exit from the vent, which could be due to the nature of the phase transition of the supercritical water fluid.

scholarly journals Late Miocene transcurrent tectonics in NW Turkey: evidence from palaeomagnetism and 40Ar–39Ar dating of alkaline volcanic rocks

2007 ◽  
Vol 144 (2) ◽  
pp. 379-392 ◽  
Author(s):  
N. KAYMAKCI ◽  
E. ALDANMAZ ◽  
C. LANGEREIS ◽  
T. L. SPELL ◽  
O. F. GURER ◽  
...  
Keyword(s):  
Fault Zone ◽  
Late Miocene ◽  
Active Faults ◽  
Volcanic Rocks ◽  
Volcanic Eruptions ◽  
North Anatolian Fault ◽  
Lava Flows ◽  
North Anatolian Fault Zone ◽  
The North ◽  
Nw Turkey

A number of intra-continental alkaline volcanic sequences in NW Turkey were emplaced along localized extensional gaps within dextral strike-slip fault zones prior to the initiation of the North Anatolian Fault Zone. This study presents new palaeomagnetic and 40Ar–39Ar geochronological results from the lava flows of NW Turkey as a contribution towards understanding the Neogene–Quaternary tectonic evolution of the region and possible roles of block rotations in the kinematic history of the region. 40Ar–39Ar analyses of basalt groundmass indicate that the major volume of alkaline lavas of NW Turkey spans about 4 million years of episodic volcanic activity. Palaeomagnetic results reveal clockwise rotations as high as 73° in Thrace and 33° anticlockwise rotations in the Biga Peninsula. Movement of some of the faults delimiting the areas of lava flows and the timing of volcanic eruptions are both older than the initiation age of the North Anatolian Fault Zone, implying that the region experienced transcurrent tectonics during Late Miocene to Pliocene times and that some of the presently active faults in the region are reactivated pre-existing structures.

An investigation of Superior Shoal, central Lake Superior, with a manned submersible

1991 ◽  
Vol 28 (1) ◽  
pp. 145-150 ◽  
Author(s):  
Matthew L. Manson ◽  
Henry C. Halls
Keyword(s):  
Lake Superior ◽  
Complex Structure ◽  
Volcanic Rocks ◽  
Lava Flows ◽  
Basaltic Lava ◽  
Isle Royale ◽  
Midcontinent Rift ◽  
Boundary Fault ◽  
The North ◽  
Manned Submersible

A Johnson-Sea-Link submersible was used to examine the geology of Superior Shoal in central Lake Superior. Here, glacially scoured, vertical cliffs, some more than 100 m high, are formed of 1.1 Ga middle Keweenawan basaltic lava flows displaying ophitic interiors and red amygdaloidal tops. Flat-lying sandstones, lithologically similar to the upper Keweenawan Bayfield–Jacobsville sequences, occur to the north of the volcanic rocks. These are inferred to have been downthrown along an eastward extension of the Isle Royale fault, a major boundary fault of the Midcontinent rift. The volcanic rocks are normally magnetized, supporting lithological evidence that they correlate with the middle Keweenawan sequence on Isle Royale. Paleomagnetic data suggest that the volcanics have a complex structure, possibly involving drag folding along the Isle Royale fault.

scholarly journals Mesozoic subalkaline rocks of Central part of the Northern Caucasus: geodynamical typification, geochemistry and minerageny

2019 ◽  
Author(s):  
В.М. Газеев ◽  
А.Г. Гурбанов ◽  
И.А. Кондрашов
Keyword(s):  
Volcanic Rocks ◽  
Fluid Phase ◽  
Northern Caucasus ◽  
Spinel Peridotite ◽  
Alkaline Basalt ◽  
North Caucasus ◽  
The North ◽  
Evolutionary Changes ◽  
Wide Range ◽  
Convective Cells

В Центральной части Северного Кавказа, в пределах КестантыХазнидонской неоаллохтонной зоны, выделенной в южной части Скифской платформы, встречаются лавовые потоки, силлы, мелкие штоки и дайки вулканитов хуламского комплекса с которыми ассоциирует золотосеребряное оруденение. В статье рассмотрена мезозойская геологическая история региона, существующие представления о геодинамической позиции и возрасте вулканитов. Проведено изучение наиболее распространенных пород, представленных щелочными и умереннощелочными базальтовыми порфиритами, диабазами, анальцимовыми долеритами, трахитами, трахириолитами. Кратко произведено петрографическое описание пород и приведены результаты их RFA, ICPMS анализа, рассмотрены петрохимические и геохимические характеристики. Показано, что изученные породы являются высоко и умеренноглиноземистыми, высоко и умереннотитанистыми, умеренно и низкомагнезиальными образованиями, среди которых отмечаются высококалиевые и высоконатриевые разновидности и в связи с этим наблюдается их изменчивая щелочность (Na2O/K2O0,0377,0). Установлено, что породы имеют повышенный уровень концентрации Ag, Ве, LILe, LREE и высокозарядных элементов Zr, Hf, Nb, Tа. Спектры распределения REE, нормированных к хондриту, у базальтов, диабазов и анальцимовых долеритов имеют вид наклонных линии, расположенных между профилями OIB и EMORB. Трахиты отличаются небольшим Eu минимумом. Для риолитов и окварцованных трахитов характерны существенно больший Eu минимум и широкий диапазон содержаний REE. Предполагается, что исходный расплав основного состава образован при плавлении шпинелевых перидотитов, подвергался влиянию флюидной фазы и был обогащен компонентами континентальной коры и субконтинентальной литосферы. Эволюционные изменения расплава, на стадии образования трахитов и риолитов, включали такие процессы как фракционирование плагиоклаза, апатита, ильменита и частичное смешение с выплавками, образовавшимися при плавлении метаосадков. На основании геологических оценок сделано предположение, что полиметаллическое и AuAg оруденение ассоциирующее с вулканитами, образовано в результате взаимодействия остывающих субвулканических тел с захороненными, возможно минерализованными, вадозными и седиментационными водами с последующим выщелачиванием рудных компонентов из среднеюрской углерод содержащей терригенной черносланцевой толщи (механизм конвективной ячейки). In the central part of the North Caucasus, within the KestantyKhaznidon neoallochtonous zone, allocated in the southern part of the Scythian platform there are lava flows, sills, small stocks and dykes of volcanic rocks of the Khulam complex that are associated with goldsilver mineralization. The article considers the Mesozoic geological history of the region, the existing ideas about the geodynamic position and age of volcanics. Investigation of the most common rocks represented by alkaline and moderately alkaline basalt porphyrites, diabases, analcite dolerites, trachytes and trachiolites. A petrographic description of the rocks is briefly given and the results of their RFA, ICPMS analysis are presented, petrochemical and geochemical characteristics are considered. It was shown that the investigated rocks are high and moderatealumina, high and moderatetitanic, moderately and lowmagnesian formations, among which there are highpotassium and highsodium varieties and, therefore, their variable alkalinity (Na2O/K2O0.0377.0). It was established that rocks have an increased level of concentration of Ag, Ве, LILe, LREE and highly charged elements Zr, Hf, Nb, Tа. The distribution spectra of REE, normalized to chondritis in basalts, diabases, and analcimeic dolerites have the form of oblique lines located between the OIB and EMORB profiles. Trachyte is characterized by a small Eu minimum. Rhyolites and silicified trachytes are characterized by a significantly larger Eu minimum and a wide range of REE contents. It is assumed that the initial melt of the basic composition was formed during the spinel peridotite melting and it was influenced by the fluid phase, and was enriched by the components of the continental crust and subcontinental lithosphere. The evolutionary changes in the melt, at the formation stage of trachytes and rhyolites, included such processes as fractionation of plagioclase, apatite, ilmenite, and partial mixing with the melts formed during the melting of metasediments. Based on geological estimates, it has been suggested that polymetallic and AuAg mineralization associated with volcanics is formed as a result of the interaction of cooling subvolcanic bodies with buried, possibly mineralized, vadose and sedimentation waters, followed by leaching of ore components from Middle Jurassic carbon containing terrigenous black shale strata (mechanism of convective cells).

scholarly journals Flood basalts, rhyolites, and subsequent volcanism of the Columbia River magmatic province in eastern Oregon, USA

2021 ◽  
pp. 301-352
Author(s):  
Emily B. Cahoon† ◽  
Martin J. Streck† ◽  
Mark Ferns†
Keyword(s):  
Large Volume ◽  
Late Miocene ◽  
Middle Miocene ◽  
Volcanic Rocks ◽  
Columbia River ◽  
Flood Basalt ◽  
Lava Flows ◽  
Calc Alkaline ◽  
The North ◽  
High Lava Plains

ABSTRACT The Miocene Columbia River Basalt Group (CRBG) is the youngest and smallest continental flood basalt province on Earth. This flood basalt province is a succession of compositionally diverse volcanic rocks that record the passage of the Yellowstone plume beneath eastern Oregon. The compositionally and texturally varied suite of volcanic rocks are considered part of the La Grande–Owyhee eruptive axis (LOEA), an ~300-km-long, north-northwest–trending, Middle Miocene to Pliocene volcanic belt that extends along the eastern margin of the Columbia River flood basalt province. Volcanic rocks erupted from and preserved within the LOEA form an important regional stratigraphic link between the flood basalt–dominated Columbia Plateau to the north, the north and bimodal basalt-rhyolite volcanic fields of the Snake River Plain to the east, the Owyhee Plateau to the south, and the High Lava Plains to the south and east; the latter two have time transgressive rhyolite centers that young to the east and west, respectively. This field-trip guide details a four-day geologic excursion that will explore the stratigraphic and geochemical relationships among mafic rocks of the CRBG and coeval and compositionally diverse silicic rocks associated with the early trace of the Yellowstone plume and High Lava Plains in eastern Oregon. The trip on Day 1 begins in Portland then traverses across the western axis of the Blue Mountains, highlighting exposures of the widespread, Middle Miocene Dinner Creek Welded Tuff and aspects of the Picture Gorge Basalt lava flows and northwest-striking feeder dikes situated in the central part of the CRBG province. Travel on Day 2 progresses eastward toward the eastern margin of the LOEA, examining a transition linking the Columbia River Basalt province with a northwestward-younging magmatic trend of silicic volcanism of the High Lava Plains in eastern Oregon. Initial field stops on Day 2 focus on the volcanic stratigraphy northeast of the town of Burns, which includes regionally extensive Middle to Late Miocene ash-flow tuffs and lava flows assigned to the Strawberry Volcanics. Subsequent stops on Day 2 examine key outcrops demonstrating the intercalated nature of Middle Miocene tholeiitic CRBG flood basalts, temporally coeval prominent ash-flow tuffs, and “Snake River–type” large-volume rhyolite lava flows cropping out along the Malheur River. The Day 3 field route navigates to southern parts of the LOEA, where CRBG rocks are associated in space and time with lesser known and more complex silicic volcanic stratigraphy forming Middle Miocene, large-volume, bimodal basalt-rhyolite vent complexes. Key stops will provide a broad overview of the structure and stratigraphy of the Middle Miocene Mahogany Mountain caldera and of the significance of intercalated sedimentary beds and Middle to Late Miocene calc-alkaline lava flows of the Owyhee basalt. Initial stops on Day 4 will highlight exposures of Middle to Late Miocene silicic ash-flow tuffs, rhyolite domes, and calc-alkaline lava flows overlying the CRBG across the northern and central parts of the LOEA. The later stops on Day 4 examine more silicic lava flows and breccias that are overlain by early CRBG-related rhyolite eruptions. The return route to Portland on Day 4 traverses the Columbia River gorge westward from Baker City. The return route between Baker and Portland on Day 4 follows the Columbia River gorge and passes prominent basalt outcrops of large volume tholeiitic flood lavas of the Grande Ronde, Wanapum, and Saddle Mountains Formations of the CRBG. These sequences of basaltic and basaltic andesite lavas are typical of the well-studied flood basalt dominated Columbia Plateau, and interbedded silicic and calc-alkaline lavas are conspicuously absent. Correlation between the far-traveled CRBG lavas and calcalkaline and silicic lavas considered during the excursion relies on geochemical fingerprinting and dating of the mafic flows and dating of sparse intercalated ashes.

Neogene volcanism on the eastside of Mount Diablo, Contra Costa County, California

2021 ◽  
Author(s):  
Raymond Sullivan ◽  
Ryan P. Fay ◽  
Carl Schaefer ◽  
Alan Deino ◽  
Stephen W. Edwards
Keyword(s):  
Middle Eocene ◽  
Volcanic Rocks ◽  
Calc Alkaline ◽  
Stream Channels ◽  
California Coast ◽  
Late Pliocene ◽  
The North ◽  
Great Valley Group ◽  
California Coast Ranges ◽  
Great Valley

ABSTRACT Two spatially separated areas of Neogene volcanic rocks are located on the northeast limb of the Mount Diablo anticline. The southernmost outcrops of volcanics are 6 km east of the summit of Mount Diablo in the Marsh Creek area and consist of ~12 hypabyssal dacite intrusions dated at ca. 7.8–7.5 Ma, which were intruded into the Great Valley Group of Late Cretaceous age. The intrusions occur in the vicinity of the Clayton and Diablo faults. The rocks are predominantly calc-alkaline plagioclase biotite dacites, but one is a tholeiitic plagioclase andesite. Mercury mineralization was likely concomitant with emplacement of these late Miocene intrusions. The northern most outcrops of Neogene volcanic rocks occur ~15 km to the north of Mount Diablo in the Concord Naval Weapons Station and the Los Medanos Hills and are probably parts of a single andesite flow. A magnetometer survey indicates that the flow originated from a feeder dike along the Clayton fault. The lava flow is flat-lying and occu pies ancient stream channels across an erosional surface of tilted Markley Sandstone of middle Eocene age. New radiometric dates of the flow yield an age of 5.8–5.5 Ma, but due to alteration the age should be used with caution. The flow is a calc-alkaline andesite rich in clinopyroxene and plagioclase. What appear to be uplifted erosional remnants of the flow can be traced northeastward in the Los Medanos Hills across a surface of tilted Cenozoic rocks that eventually rest on formations as young as the Lawlor Tuff dated at 4.865 ± 0.011 Ma. This stratigraphic relationship suggests that the andesite flow is probably late Pliocene in age and was impacted by the more recent uplift of the Los Medanos Hills but postdates the regional folding and faulting of the rocks of Mount Diablo. In terms of timing, location, and composition, the evidence suggests these two areas of dacitic and andesitic volcanics fit into a series of migrating volcanic centers in the California Coast Ranges that erupted following the northward passage of the Mendocino Triple Junction.

scholarly journals Local neotectonic restructuring in the North Caucasus orogene

2019 ◽  
pp. 3-12
Author(s):  
S. A. Nesmeyanov ◽  
O. A. Voeykova
Keyword(s):  
Structural Changes ◽  
Volcanic Rocks ◽  
Structural Rearrangement ◽  
Stone Tools ◽  
Initial Distribution ◽  
Total Thickness ◽  
North Caucasus ◽  
The Caucasus ◽  
The North ◽  
Transportation Distance

Cases of regional neotectonic restructuring are well known in the Caucasus. Detailed geotectonic zoning and identification of local structural changes are required for the engineering geological and paleoecological studies. The Baksan River valley was studied in the North Caucasus as an example of such a restructuring. The problem about the number of Quaternary volcanogenic strata and their role in structural rearrangement is considered. The Pliocene – Plio-Pleistocene volcanogenic strata cloak-like covered the Nizhnechegemsky district before the first reconstruction. Zayuksky graben (with an amplitude of 200 m) was formed in the end of Plio-Pleistocene; and a part of Pliocene- Plio-Pleistocene volcanogenic strata sank into it. Two layers with a total thickness of more than 100 m were deposited in the resulting trough. The upper strata (baxangess) contain redeposited boulder-pebbly volcanogenic material. Colluvial, subaquatic-deltoid and lacustrian facies are registered. The orographic depression in Zayuksky graben was completely filled before Eopleistocene as a result of next restructuring. The Baksan River began to form a wide well-terraced valley without any significant left tributaries there. The baxangess strata contain pebble of liparite lavas and obsidians. This pebble was used by the Paleolithic man for making stone tools. Poor roundness of pebble indicates its short transportation distance. Contradictory ideas about the initial distribution of parental volcanic rocks are considered. It is concluded on the acuteness of identifying such neotectonic rearrangements for the analysis of various paleogeographic and paleoecological changes.

scholarly journals Lithostratigraphy, geology and geochemistry of the volcanic rocks of the Maligât Formation and associated intrusions on Disko and Nuussuaq, Paleocene of West Greenland

2018 ◽  
Vol 40 ◽  
pp. 1-239 ◽  
Author(s):  
Asger Ken Pedersen ◽  
Lotte Melchior Larsen ◽  
Gunver Krarup Pedersen
Keyword(s):  
Basaltic Andesite ◽  
Volcanic Rocks ◽  
Middle Part ◽  
Lava Flows ◽  
Lake Basin ◽  
The North ◽  
Rock Types ◽  
Native Iron ◽  
North Eastern ◽  
Iron Bearing

The Paleocene volcanic rocks in the Nuussuaq Basin on Disko and Nuussuaq comprise the picritic Vaigat Formation (c. 62–61 Ma) and the overlying basaltic Maligât Formation (c. 60 Ma). The Maligât Formation is up to 2000 m thick on western Disko where the top of the formation is least eroded. The formation is divided into four members, the Rinks Dal, Nordfjord, Niaqussat and Sapernuvik members, which are formally defined here. On central and eastern Disko and Nuussuaq the Maligât Formation lavas are interbedded with fluvial and lacustrine sandstones and mudstones of the Atanikerluk Formation.The Rinks Dal Member is the lowest member and originally constituted around 61% by volume of the formation. It is divided into 12 informal units based on chemically recognisable oscillations in the fractionation state of the basalts. The oldest units are present on central and south Disko close to the Disko Gneiss Ridge. The younger lavas spread farther to the east, north and west, filled the Assoq Lake basin east of the ridge and gradually onlapped the shield of the earlier Vaigat Formation that rose to the north. Only the lavas of the upper Rinks Dal Member reached far into Nuussuaq. The lavas are generally not crustally contaminated and comprise evolved basalts with 4.4–9.2 wt% MgO and a few picrites. The most evolved basalts with 3.2–4.8 wt% TiO2 occur in the middle part of the member where they form the Akuarut unit. The Nordfjord Member originally constituted around 6% by volume of the formation. It is not subdivided because the lithological variability is local. The member is widespread but has its depocentre on north-western Disko where thicknesses reach 350 m and eruption sites, intermediate lavas and acid tuffs are present. Over most of the area the member consists of just a few lava flows with combined thicknesses of 30–100 m. The member has a very diverse lithology with rock types ranging from silicic basalt with 5.3–10.0 wt% MgO through magnesian basaltic andesite and andesite with 2.4–10.6 wt% MgO to dacite with 1.2–2.2 wt% MgO. Rhyolite with 0.2–1.2 wt% MgO and up to 77 wt% SiO2 occur in tuffs and conglomerate clasts. All rocks are crustally contaminated and some are native-iron-bearing. The Niaqussat Member originally constituted around 33% by volume of the formation. It is subdivided into three informal units. The member is widespread, but much of it has been removed by erosion. Lithologies in the lower unit range from silicic picrite with up to 15 wt% MgO to basalt with 6–12 wt% MgO and a few basaltic andesite flows. The middle and upper parts of the Niaqussat Member comprise more evolved basalts with respectively 6.1–7.2 wt% MgO and 4.9–6.4 wt% MgO. All rocks are crustally contaminated and a few lava flows are native-iron-bearing. The Sapernuvik Member comprises three uncontaminated basalt flows with 7.5–10.7 wt% MgO. It is only preserved in a small area on western Disko. Dyke systems with up to 80 km long dykes and subvolcanic intrusions associated with the Nordfjord and Niaqussat members occur on western and north-eastern Disko. The rocks are crustally contaminated and range from silicic basalt with 4–13 wt% MgO to magnesian andesite with 3–10 wt% MgO. They commonly form composite intrusions, some of which contain accumulations of native iron and sulfides. The contaminants are carbon- and sulfur-bearing sediments of the Nuussuaq Group. Major contamination mechanisms were mixing with partial melts from the sediment sidewall and xenoliths and selective exchange of some elements, including carbon and sulfur, between magma and sediment. Degrees of contamination vary from 2−5% in the basalts to 10−50% in the more silicic rocks. No rocks more evolved than basalt were produced by ordinary fractional crystallisation.

Sign in / Sign up

Export Citation Format

Share Document