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2022 ◽  
Author(s):  
John P. Craddock ◽  
David H. Malone ◽  
Alex Konstantinou ◽  
John Spruell ◽  
Ryan Porter

ABSTRACT We report the results of 167 calcite twinning strain analyses (131 limestones and 36 calcite veins, n = 7368 twin measurements)t from the Teton–Gros Ventre (west; n = 21), Wind River (n = 43), Beartooth (n = 32), Bighorn (n = 32), and Black Hills (east; n = 11) Laramide uplifts. Country rock limestones record only a layer-parallel shortening (LPS) strain fabric in many orientations across the region. Synorogenic veins record both vein-parallel shortening (VPS) and vein-normal shortening (VNS) fabrics in many orientations. Twinning strain overprints were not observed in the limestone or vein samples in the supracrustal sedimentary veneer (i.e., drape folds), thereby suggesting that the deformation and uplift of Archean crystalline rocks that form Laramide structures were dominated by offset on faults in the Archean crystalline basement and associated shortening in the midcrust. The twinning strains in the pre-Sevier Jurassic Sundance Formation, in the frontal Prospect thrust of the Sevier belt, and in the distal (eastern) foreland preserve an LPS oriented approximately E-W. This LPS fabric is rotated in unique orientations in Laramide uplifts, suggesting that all but the Bighorn Mountains were uplifted by oblique-slip faults. Detailed field and twinning strain studies of drape folds identified second-order complexities, including: layer-parallel slip through the fold axis (Clarks Fork anticline), attenuation of the sedimentary section and fold axis rotation (Rattlesnake Mountain), rotation of the fold axis and LPS fabric (Derby Dome), and vertical rotations of the LPS fabric about a horizontal axis with 35% attenuation of the sedimentary section (eastern Bighorns). Regional cross sections (E-W) across the Laramide province have an excess of sedimentary veneer rocks that balance with displacement on a detachment at 30 km depth and perhaps along the Moho discontinuity at 40 km depth. Crustal volumes in the Wyoming Province balance when deformation in the western hinterland is included.


2022 ◽  
Author(s):  
Ravi Jonnalagadda ◽  
Ram Raj Mathur

Abstract Geophysical methods have extensively been used in exploration of Lamproite bodies. Lamproites are significant source rocks of primary diamond deposits other than Kimberlites. The Eastern Dharwar Craton is unique in the way that it hosts numerous Precambrian Lamproites confined to the crescent-shaped Paleo-Mesoproterozoic Cuddapah Basin and its north-western and north-eastern margins. In the present study electrical method was used as a tool for delineation of Lamproite bodies in contrast with country rocks in Gundrapally, Vattikode and Marepally regions in parts of the North Eastern Dharwar Craton in Telangana State, India. The electrical profiling method was conducted in different direction to identify the variation of the lithology of the area due to the anisotropic nature and smaller size of the 2-D intrusive bodies adopting the Wenner electrode configuration. The electrical properties of the Lamproites tended to change with their composition due to weathering and the presence of Olivine and K-Al rich composition. The electrical response on the Lamproite pipes is shows a decrease in resistivity concerning the country-rock in the area.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. K. Fitzgerald ◽  
J. D. L. White

AbstractMaar-diatreme volcanoes are the second-most common type on land, occurring in volcanic fields within all major tectonic environments. Their deposits typically contain an abundance of lithic fragments quarried from the substrate, and many contain large, deep-sourced lithic fragments that were erupted to the surface. Primary volcaniclastic deposits fill the diatreme structure formed during eruption. There is negligible inelastic deformation of diatreme-adjacent country rock, indicating that country rock is removed to create the diatreme structures, either by being shifting downward below observable levels, ejected upward to contribute to surficial deposits, or dissolved and hidden in magma erupted or intruded at depth. No previous study has systematically reviewed and analysed the reported lithic fragments of maar-diatreme systems. We present a comprehensive compilation from published work of lithic characteristics in maar ejecta rings and in diatreme deposits of both common and kimberlite maar-diatremes. For maar-diatremes and their tephra ring deposits, we find no correlations among lithic clast sizes, shapes, depositional sites, and excavation depths. This is difficult to reconcile with models involving systematic diatreme deepening coupled with tephra-ring growth, but consistent with those involving chaotic explosions and mixing. Larger amounts of data are needed to further examine how these types of volcanoes operate.


Author(s):  
Franz Weis ◽  
Valentin R. Troll ◽  
Erik Jonsson ◽  
Karin Högdahl ◽  
Chris Harris ◽  
...  

AbstractThe origin of Kiruna-type iron oxide–apatite ores is controversial, and debate presently centres on a ‘magmatic’ versus a ‘hydrothermal’ mode of formation. To complement recent investigations on the Grängesberg iron oxide–apatite ore deposit in the northwestern part of the Palaeoproterozoic Bergslagen ore province in central Sweden, we investigated the oxygen isotope composition of the host rocks of this large iron oxide–apatite ore body. As the metavolcanic and metagranitoid country rocks around the Grängesberg ore body either pre-date or are coeval with ore formation, they would be expected to record an extensive isotopic imprint if the ore body had formed by large-scale hydrothermal processes involving an externally sourced fluid. A direct magmatic formation process, in turn, would have produced localized alteration only, concentrated on the immediate vicinity of the ore body. Here, we test these two hypotheses by assessing the oxygen isotope variations in the host rocks around the main Grängesberg iron oxide–apatite ore body. We analysed oxygen isotopes in quartz from metavolcanic (n = 17) and metagranitoid host rocks (n = 14) from the vicinity of the ore body, and up to 2 km distance along and across the strike of the ore body. Remarkably, we find no significant variation in δ18O values with distance from the ore body, or any deviations in country rock δ18O from common magmatic and/or regional values. Only two samples show shifts to values more negative than the common magmatic range, indicating highly localized hydrothermal overprint only. As a large-scale, low-temperature hydrothermal origin of the ore body through voluminous fluid percolation would be expected to have left a distinct imprint on the oxygen isotope values of the country rocks, our results are more consistent with an ortho-magmatic origin for the Grängesberg iron oxide–apatite ore.


2021 ◽  
Author(s):  
◽  
Tadiwos Chernet

<p>The Taupo Pumice Formation is a product of the Taupo eruption of about 1800a, and consists of three phreatomagmatic ash deposits, two plinian pumice deposits and a major low-aspect ratio and low grade (unwelded) ignimbrite which covered most part of the central North Island of New Zealand. The vent area for the eruption is located at Horomatangi Reefs in Lake Taupo. Lithics in the phreatoplinian ash deposits are negligible in quantity, but the plinian pumice deposits contain 5-10% lithics by volume in most near-vent sections. Lithics in the plinian pumice deposits are dominantly banded and spherulitic rhyolite with minor welded tuff, dacite and andesite. The ground layer which forms the base of the ignimbrite unit consists of dominantly lithics and crystals and is formed by the gravitational sedimentation of the 'heavies' from the strongly fluidized head of the pyroclastic flow. Lithic blocks in the ground layer are dominantly banded and spherulitic phenocryst-poor rhyolite, welded tuff with minor dacite and andesite. Near-vent exposures of the ground layer contain boulders upto 2 m in diameter. Friable blocks of hydrothermally altered rhyolite, welded tuff and lake sediments are found fractured but are preserved intact after transportation. This shows that the fluid/pyroclastic particle mixture provided enough support to carry such blocks upto a distance of 10 km from the vent. The rhyolite blocks are subdivided into hypersthene rhyolite, hypersthene-hornblende rhyolite and biotite-bearing rhyolite on the basis of the dominant ferromagnesian phenocryst assamblage. Hypersthene is the dominant ferromagnesian phenocryst in most of the rhyolite blocks in the ground layer and forms the major ferromagnesian crystal of the Taupo Sub-group tephra. The rhyolite blocks have similar whole rock chemistry to the Taupo Sub-group tephra and are probably derived from lava extrusions associated with the tephra eruptions from the Taupo Volcanic Centre in the last 10 ka. Older rhyolite domes and flows in the area are probably represented by the intensely hydrothermally altered rhyolite blocks in the ground layer. The dacite blocks contain hypersthene and augite as a major ferromagnesian phenocryst. Whole rock major and trace element analyses shows that the dacite blocks are distinct from the Tauhara dacites and from the dacites of Tongariro Volcanic Centre. The occurrence of dacite inclusions in significant quantity in the Taupo Pumice Formation indicates the presence of other dacite flows near the vent area. Four types of andesite blocks; hornblende andesite, plagioclase-pyroxene andesite, pyroxene andesite and olivine andesite occur as lithic blocks in the ground layer. The andesites are petrographically distinct from those encountered in deep drillholes at Wairakei (Waiora Valley Andesites), and are different from the Rolles Peak andesite in having lower Sr content. The andesite blocks show similar major and trace element content to those from the Tongariro Volcanic Centre. The roundness of the andesite blocks indicates that the blocks were transported as alluvium or lahars in to the lake basin before being incorporated into the pyroclastic flow. Two types of welded ignimbrite blocks are described. The lithic-crystal rich ignimbrite is correlated with a post-Whakamaru Group Ignimbrite (ca. 100 ka ignimbrite erupted from Taupo Volcanic Centre) which crops out to the north of Lake Taupo. The crystal rich ignimbrite is tentatively correlated with the Whakamaru Group Ignimbrites. The lake sediment boulders, pumiceous mudstone and siltstone in the ground layer probably correlate to the Huka Group sediments or younger Holocene sediments in the lake basin. A comparative mineral chemistry study of the lithic blocks was done. A change in chemistry of individual mineral species was found to accompany the variation in wholerock major element constituents in the different types of lithics. The large quantity of lithic blocks in the ground layer suggests extensive vent widening at the begining of the ignimbrite eruption. A simple model of flaring and collapse of the vent area caused by the down ward movement of the fragmentation surface is presented to explain the origin of the lithic blocks in the ground layer. The lithics in the Taupo Pumice Formation are therfore produced by the disruption of the country rock around the vent during the explosion and primary xenoliths from depths of magma generation were not found. Stratigraphic relations suggest that the most important depth of incorporation of lithics is within the post-Whakamaru Group Ignimbrite volcanics and volcaniclastic sedimentary units.</p>


2021 ◽  
Author(s):  
◽  
Tadiwos Chernet

<p>The Taupo Pumice Formation is a product of the Taupo eruption of about 1800a, and consists of three phreatomagmatic ash deposits, two plinian pumice deposits and a major low-aspect ratio and low grade (unwelded) ignimbrite which covered most part of the central North Island of New Zealand. The vent area for the eruption is located at Horomatangi Reefs in Lake Taupo. Lithics in the phreatoplinian ash deposits are negligible in quantity, but the plinian pumice deposits contain 5-10% lithics by volume in most near-vent sections. Lithics in the plinian pumice deposits are dominantly banded and spherulitic rhyolite with minor welded tuff, dacite and andesite. The ground layer which forms the base of the ignimbrite unit consists of dominantly lithics and crystals and is formed by the gravitational sedimentation of the 'heavies' from the strongly fluidized head of the pyroclastic flow. Lithic blocks in the ground layer are dominantly banded and spherulitic phenocryst-poor rhyolite, welded tuff with minor dacite and andesite. Near-vent exposures of the ground layer contain boulders upto 2 m in diameter. Friable blocks of hydrothermally altered rhyolite, welded tuff and lake sediments are found fractured but are preserved intact after transportation. This shows that the fluid/pyroclastic particle mixture provided enough support to carry such blocks upto a distance of 10 km from the vent. The rhyolite blocks are subdivided into hypersthene rhyolite, hypersthene-hornblende rhyolite and biotite-bearing rhyolite on the basis of the dominant ferromagnesian phenocryst assamblage. Hypersthene is the dominant ferromagnesian phenocryst in most of the rhyolite blocks in the ground layer and forms the major ferromagnesian crystal of the Taupo Sub-group tephra. The rhyolite blocks have similar whole rock chemistry to the Taupo Sub-group tephra and are probably derived from lava extrusions associated with the tephra eruptions from the Taupo Volcanic Centre in the last 10 ka. Older rhyolite domes and flows in the area are probably represented by the intensely hydrothermally altered rhyolite blocks in the ground layer. The dacite blocks contain hypersthene and augite as a major ferromagnesian phenocryst. Whole rock major and trace element analyses shows that the dacite blocks are distinct from the Tauhara dacites and from the dacites of Tongariro Volcanic Centre. The occurrence of dacite inclusions in significant quantity in the Taupo Pumice Formation indicates the presence of other dacite flows near the vent area. Four types of andesite blocks; hornblende andesite, plagioclase-pyroxene andesite, pyroxene andesite and olivine andesite occur as lithic blocks in the ground layer. The andesites are petrographically distinct from those encountered in deep drillholes at Wairakei (Waiora Valley Andesites), and are different from the Rolles Peak andesite in having lower Sr content. The andesite blocks show similar major and trace element content to those from the Tongariro Volcanic Centre. The roundness of the andesite blocks indicates that the blocks were transported as alluvium or lahars in to the lake basin before being incorporated into the pyroclastic flow. Two types of welded ignimbrite blocks are described. The lithic-crystal rich ignimbrite is correlated with a post-Whakamaru Group Ignimbrite (ca. 100 ka ignimbrite erupted from Taupo Volcanic Centre) which crops out to the north of Lake Taupo. The crystal rich ignimbrite is tentatively correlated with the Whakamaru Group Ignimbrites. The lake sediment boulders, pumiceous mudstone and siltstone in the ground layer probably correlate to the Huka Group sediments or younger Holocene sediments in the lake basin. A comparative mineral chemistry study of the lithic blocks was done. A change in chemistry of individual mineral species was found to accompany the variation in wholerock major element constituents in the different types of lithics. The large quantity of lithic blocks in the ground layer suggests extensive vent widening at the begining of the ignimbrite eruption. A simple model of flaring and collapse of the vent area caused by the down ward movement of the fragmentation surface is presented to explain the origin of the lithic blocks in the ground layer. The lithics in the Taupo Pumice Formation are therfore produced by the disruption of the country rock around the vent during the explosion and primary xenoliths from depths of magma generation were not found. Stratigraphic relations suggest that the most important depth of incorporation of lithics is within the post-Whakamaru Group Ignimbrite volcanics and volcaniclastic sedimentary units.</p>


2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Lei Xu ◽  
Fengqiang Gong

In deep mining and excavation of tunnels with high geothermal, the surrounding rock is not only subjected to high ground stress but also subjected to high temperature. Temperature will change mechanical characteristics and energy storage capacity of rocks, as well as increase the destructiveness and randomness of rockburst. To reveal the mechanism of high-temperature strain burst in deep rock, the rockburst tests from uniaxial compression to three-dimensional compression were reviewed, and the research results of the minimum principal stress rapid unloading, true-triaxial loading with one free face, and dynamic disturbance triggered pre-heated granite rockburst simulation tests were focused on. According to the occurrence state of country rock for deep high-temperature and stress state in the whole process during excavation, six development directions for high-temperature strain rockburst simulation tests were proposed: (1) constructing the damage constitutive models of high-temperature rocks according to linear energy dissipation law; (2) developing the true triaxial rockburst simulation testing system accomplishing the function of “real-time high temperature + unloading + dynamic disturbance”; (3) considering the true triaxial rockburst simulation test after microwave irradiation; (4) developing the real-time high-temperature rockburst simulation testing device for large-size specimens and internal unloading; (5) focusing on the energy actuating mechanism for deep high-temperature rock failure via rockburst simulation tests; and (6) implementing the three-dimensional rockburst simulation test on the basis of deep in situ coring.


2021 ◽  
Author(s):  
Shuisheng Yu ◽  
Wancheng Zhu ◽  
Leilei Niu

Abstract The axial loading in rockbolts changes due to stress redistribution and rheology in the country rock mass. Such a change may lead to debonding at rockbolt to grout interface or rupture of the rockbolt. In this study, based on laboratory experiments, ultrasonic guided wave propagation in fully grouted rockbolt under different pull-out loads was investigated in order to examine the resultant debonding of rockbolt. The signals obtained from the ultrasonic monitoring during the pull-out test were processed using wavelet multi-scale analysis and frequency spectrum analysis, the signal amplitude and the amplitude ratio (Q) of low frequency to high frequency were defined to quantify the debonding of rockbolt. In addition to the laboratory test, numerical simulation on the effect of the embedment lengths on ultrasonic guided wave propagation in rockbolt was conducted by using a damage-based model, and the debonding between rockbolt and cement mortar was numerically examined. It was confirmed that the ultrasonic guided wave propagation in rockbolt was very sensitive to the debonding because of pull-out load, therefore, the critical bond length could be calculated based on the propagation of guided wave in the grouted rockbolt. In time domain, the signal amplitude in rockbolt increased with pull-out load from 0 kN to 100 kN until the completely debonding, thus quantifying the debonding under the different pull-out loads. In the frequency domain, as the Q value increased, the debonding length of rockbolt decreased exponentially. The numerical results confirmed that the guided wave propagation in the fully grouted rockbolt was effective in detecting and quantifying the debonding of rockbolt under pull-out load.


2021 ◽  
Vol 11 (4) ◽  
pp. 5361-5374
Author(s):  
Manaswini Tripathy ◽  
Mithunchandra Chaudhari

Music has proven to play a vital role in social and emotional development in teenagers and young adults. From contemplation, developing self-identity, understanding interpersonal relationships, and providing possibilities of experience mastery, agency, and self-control with the help of self-directed activities, music helps its audience develop in all aspects of life. In specific, Rock music, since its existence has been more than entertainment, artists expressed themselves and shared their opinions through their musical pieces. Infamous for promoting drugs and alcohol, Rock Music used its platform to enlighten the audience about taboo topics like racism, inequality, and other social issues. This research paper uses a qualitative methodology approach to understand Rock Music listeners’ points of view. Data was collected through ‘in-depth interviews’ of 15 participants hailing from different parts of the country. Rock Music has several positive effects on the listeners. Rock can elevate moods, induce emotions, helps the listeners be more productive and creative with their everyday work, and constantly motivate them to do better in every aspect of life. Rock provides a platform to express feelings and vent out all the angst, especially for those who otherwise do not voice their opinions because of their nature in general. Rock Music has been able to shape personalities, characteristics, and thought processes. Moreover, majorly, Rock Music helps people with anger management.


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