DENSITIES OF METAMORPHIC ROCKS

Geophysics ◽  
1971 ◽  
Vol 36 (4) ◽  
pp. 690-694 ◽  
Author(s):  
Scott B. Smithson
Keyword(s):  
Metamorphic Rock ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Rock Density ◽  
Rock Types ◽  
Crystalline Crust ◽  
The Mean ◽  
Few Data

Although metamorphic rocks comprise a large part of the crystalline crust, relatively few data concerning metamorphic rock densities are available. In this paper, we present rock densities from seven different metamorphic terrains. Mean densities for rock types range from [Formula: see text] for biotite granite gneiss to [Formula: see text] for diopside granofels. Mean rock densities for metamorphic terrains range from 2.70 to [Formula: see text]. Rock density may decrease in the lower part of the upper crust. Most mean rock densities for metamorphic terrains fall between 2.70 and [Formula: see text]; the mean density of [Formula: see text] commonly used for the upper crystalline crust is too low.

Polymetamorphic greenschists with Al-rich green spinels (the Western Carpathian Mts.)

2013 ◽  
Vol 5 (2) ◽  
Author(s):  
Dušan Hovorka
Keyword(s):  
Thin Section ◽  
Special Interest ◽  
Present Author ◽  
Metamorphic Rock ◽  
Rock Type ◽  
Raw Material ◽  
Metamorphic Rocks ◽  
Material Type ◽  
Rock Types ◽  
Igcp Project

AbstractDuring the course of the UNESCO/IGCP project nr. 442 (1999–2001) the present author, along with several colleagues, has described rare raw material types, used in the Neolithic/Aeneolithic, for the construction of stone implements. A metamorphic rock-type (greenschist) containing a substantial amount of Al-rich green spinels, is of special interest. This raw material type is characterized in this contribution.The rocks, which are the object of the present study, are metamorphic rocks of the greenschist association (containing monoclinic as well as rhombic amphiboles, and Al-rich green spinels in a substantial (5–20 vol. %) amount). Accessory mineralsnot necessarily encountered in each thin section, are olivine, orthopyroxene, corundum, clinozoisite, muscovite, cordierite, various plagioclases (albite and anorthite included), phlogopite, ilmenite, magnetite and sphene. The results of microprobe analyses for individual rock-forming minerals are presented. The genesis of the described rock-types is complicated; they are product of three metamorphic events (M1, M2, M3).

ESTIMATION OF SOURCE PARAMETERS IN IBADAN, SOUTH – WESTERN NIGERIA USING DIGITIZED AEROMAGNETIC DATA

2018 ◽  
Vol 14 (2) ◽  
pp. 15-28
Author(s):  
A A ALABI ◽  
O OLOWOFELA
Keyword(s):  
Magnetic Susceptibility ◽  
Source Parameters ◽  
Granite Gneiss ◽  
Geological Structure ◽  
Magnetic Data ◽  
Susceptibility Map ◽  
Rock Types ◽  
Upward Continuation ◽  
Magnetic Basement ◽  
Local Wavenumber

Airborne magnetic data covering geographical latitudes of 7000‟N to 7030‟N and longitudes of 3 30′E to 4 00′E within Ibadan area were obtained from Nigeria Geology Survey Agency. The data were ana-lyzed to map the sub surface structure and the source parameters were deduced from the quantitative and qualitative interpretation of magnetic data. The upward continuation technique was used to de-emphasize short – wavelength anomaly while the depth to magnetic sources in the area was deter-mined using local wavenumber technique, the analytic signal was also employed to obtain the depths of the magnetic basement. Analysis involving the local wavenumber, upward continuation and appar-ent magnetic susceptibility techniques significantly improves the interpretation of magnetic data in terms of delineating the geological structure, source parameter and magnetic susceptibility within Iba-dan area.. These depth ranges from 0.607km to 2.48km. The apparent susceptibility map at the cut-off wavelength of 50 m ranges from -0.00012 to 0.00079 which agree with the susceptibility value of some rock types; granite gneiss, migmatite biotite gneiss, biotite muscovite granite, hornblende granite, quartz and schists. The result of the local wavenumber suggests variation along the profiles in the surface of magnetic basement across the study area.

scholarly journals Identifikasi Keterdapatan Mineral Radioaktif pada Urat-Urat Magnetit di Daerah Ella Ilir, Melawi, Kalimantan Barat

EKSPLORIUM ◽  
2019 ◽  
Vol 40 (1) ◽  
pp. 33
Author(s):  
Ngadenin Ngadenin ◽  
Frederikus Dian Indrastomo ◽  
Widodo Widodo ◽  
Kurnia Setiawan Widana
Keyword(s):  
Iron Ore ◽  
Biotite Granite ◽  
Ore Deposits ◽  
Geological Mapping ◽  
Granitic Rocks ◽  
Metamorphic Rocks ◽  
West Kalimantan ◽  
The North ◽  
Iron Ore Deposits ◽  
Radioactive Minerals

ABSTRAKElla Ilir secara administratif terletak di Kabupaten Melawi, Kalimantan Barat. Geologi regional daerah Ella Ilir tersusun atas batuan malihan berumur Trias–Karbon yang diterobos oleh batuan granitik berumur Yura dan Kapur. Keterdapatan mineral radioaktif di daerah tersebut terindikasi dari radioaktivitas urat-urat magnetit pada batuan malihan berumur Trias–Karbon dengan kisaran nilai 1.000 c/s hingga 15.000 c/s. Tujuan dari penelitian ini adalah menentukan jenis cebakan mineral bijih dan mengidentifikasi keterdapatan mineral radioaktif pada urat-urat bijih magnetit di daerah Ella Ilir. Metode yang digunakan adalah pemetaan geologi, pengukuran radioaktivitas, analisis kadar uranium, dan analisis mineragrafi beberapa sampel urat bijih magnetit. Litologi daerah penelitian tersusun oleh kuarsit biotit, metatuf, metabatulanau, metapelit, granit biotit, dan riolit. Sesar sinistral barat-timur dan sesar dekstral utara-selatan merupakan struktur sesar yang berkembang di daerah ini. Komposisi mineral urat-urat magnetit terdiri dari mineral-mineral bijih besi, sulfida, dan radioaktif. Mineral bijih besi terdiri dari magnetit, hematit, dan gutit. Mineral sulfida terdiri dari pirit, pirhotit, dan molibdenit sedangkan mineral radioaktif terdiri dari uraninit dan gumit. Keterdapatan urat-urat bijih magnetit dikontrol oleh litologi dan struktur geologi. Urat-urat magnetit pada metabatulanau berukuran tebal (1,5–5 m), mengisi rekahan-rekahan yang terdapat di sekitar zona sesar. Sementara itu, urat-urat magnetit pada metapelit berukuran tipis (milimetrik–sentimetrik), mengisi rekahan-rekahan yang sejajar dengan bidang sekistositas. Cebakan mineral bijih di daerah penelitian adalah cebakan bijih besi atau cebakan bijih magnetit berbentuk urat karena proses hidrotermal magmatik.ABSTRACTElla Ilir administratively located in Melawi Regency, West Kalimantan. Regional geology of Ella Ilir area is composed of metamorphic rocks in Triassic–Carboniferous age which are intruded by Jurassic and Cretaceous granitic rocks. Radioactive minerals occurences in the area are indicated by magnetite veins radioactivities on Triassic to Carboniferous metamorphic rocks whose values range from 1,000 c/s to 15,000 c/s. Goal of the study is to determine the type of ore mineral deposits and to identify the presence of radioactive mineral in magnetite veins in Ella Ilir area. The methods used are geological mapping, radioactivity measurements, analysis on uranium grades, and mineragraphy analysis of severe magnetite veins samples. Lithologies of the study area are composed by biotite quartzite, metatuff, metasilt, metapellite, biotite granite, and ryolite. The east-west sinistral fault and the north-south dextral fault are the developed fault structures in this area. Mineral composition of magnetite veins are consists of iron ore, sulfide, and radioactive minerals. Iron ore mineral consists of magnetite, hematit, and goetite. Sulfide minerals consist of pyrite, pirhotite, and molybdenite, while radioactive minerals consist of uraninite and gummite. The occurences of magnetite veins are controlled by lithology and geological structures. The magnetite veins in metasilt are thick (1.5–5 m), filled the fractures in the fault zone. Meanwhile, the magnetite veins in metapellite are thinner (milimetric–centimetric), filled the fractures that are parallel to the schistocity. The ore deposits in the study area are iron ore deposits or magnetite ore deposits formed by magmatic hydrothermal processes. 

The nature and origin of cratons constrained by their surface geology

2021 ◽  
Author(s):  
A.M. Celal Şengör ◽  
Nalan Lom ◽  
Ali Polat
Keyword(s):  
North China ◽  
Plate Boundary ◽  
Crustal Thickening ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Subsequent Removal ◽  
Total Removal ◽  
Common Misconception ◽  
Resistance To Deformation ◽  
Surface Geology

To the memory of Nicholas John (Nick) Archibald (1951−2014), master of cratonic geology. Cratons, defined by their resistance to deformation, are guardians of crustal and lithospheric material over billion-year time scales. Archean and Proterozoic rocks can be found in many places on earth, but not all of them represent cratonic areas. Some of these old terrains, inappropriately termed “cratons” by some, have been parts of mobile belts and have experienced widespread deformations in response to mantle-plume-generated thermal weakening, uplift and consequent extension and/or various plate boundary deformations well into the Phanerozoic. It is a common misconception that cratons consist only of metamorphosed crystalline rocks at their surface, as shown by the indiscriminate designation of them by many as “shields.” Our compilation shows that this conviction is not completely true. Some recent models argue that craton formation results from crustal thickening caused by shortening and subsequent removal of the upper crust by erosion. This process would expose a high-grade metamorphic crust at the surface, but greenschist-grade metamorphic rocks and even unmetamorphosed supracrustal sedimentary rocks are widespread on some cratonic surfaces today, showing that craton formation does not require total removal of the upper crust. Instead, the granulitization of the roots of arcs may have been responsible for weighing down the collided and thickened pieces and keeping their top surfaces usually near sea level. In this study, we review the nature and origin of cratons on four well-studied examples. The Superior Province (the Canadian Shield), the Barberton Mountain (Kaapvaal province, South Africa), and the Yilgarn province (Western Australia) show the diversity of rocks with different origin and metamorphic degree at their surface. These fairly extensive examples are chosen because they are typical. It would have been impractical to review the entire extant cratonic surfaces on earth today. We chose the inappropriately named North China “Craton” to discuss the requirements to be classified as a craton.

Metamorphic Rocks

2018 ◽  
Author(s):  
Alex Maltman
Keyword(s):  
Metamorphic Rock ◽  
Central Area ◽  
Tectonic Stress ◽  
Earth’S Crust ◽  
Metamorphic Rocks ◽  
Tectonic Plates ◽  
The Earth ◽  
Two Factors ◽  
Earth's Crust ◽  
Increased Pressure

We come now to the metamorphic rocks, the result of modifications to already existing rock. I’m well aware that this can all seem a bit mysterious. After all, no one has ever seen the changes take place; no one has ever witnessed a metamorphic rock form—the processes are imperceptibly slow, and they happen deep in the Earth’s crust, way out of sight. Why should these changes happen? Well, they are primarily driven by increases in pressure and temperature, so we begin with a look at these two factors. There are sites in the Earth’s crust where material becomes progressively buried. It happens, for example, where a tectonic plate is driving underneath another one, taking rocks ever deeper as it descends. It can happen in the central area of a plate that is stretching and sagging, allowing thick accumulations of sediment. It’s pretty self-evident that as buried material gets deeper, because of the growing weight of rocks above bearing down due to gravity, it becomes subjected to increasing burial pressure. Less intuitive, though, is the fact that this pressure acts on a volume of rock equally in all directions. Imagine a small volume of rock at depth. It’s bearing the weight of the rocks above it, and so it responds by trying to move downward and to spread out laterally. Of course, it can’t because it’s constrained all around by other volumes of rock that are trying to do exactly the same thing. And so the downward gravity is translated into an all-around pressure. It’s the same effect as diving down to the bottom of a swimming pool. You feel the increased pressure owing to the weight of water above, but you feel it equally in all directions. All-round pressure like this can cause things to change in volume, through changing their density, but it can’t change their shape. However, there can be another kind of pressure as well, and this does have direction, and it can cause change of shape. In the Earth, we call it tectonic stress. It comes about through heat-driven motions in the Earth, including the movement of tectonic plates.

scholarly journals Petrology of the metamorphic rocks (gravels) from Bhajanpur area in Panchagarh District, Bangladesh

1970 ◽  
Vol 5 ◽  
pp. 91-96
Author(s):  
Md Rahat Hossain ◽  
Ismail Hossain ◽  
ASM Zahid Hossain ◽  
Prodip Kumar Biswas
Keyword(s):  
Key Words ◽  
Metamorphic Rock ◽  
Metamorphic Rocks ◽  
Mica Schist ◽  
Mineral Assemblages ◽  
Temperature Ranges ◽  
Garnet Zone ◽  
Opaque Minerals ◽  
Mineralogical Compositions ◽  
Chlorite Schist

The present study deals with petrology of the detrital gravelly rocks from Bhajanpur area, Panchagarh, Bangladesh. The results of detailed petrography of gravelly rocks indicate the presence of quartz (monocrystalline and polycrystalline quartz), K-feldspar, plagioclase, chlorite, muscovite and biotite as major mineralogical compositions. Other minor minerals are garnet, kyanite, graphite and opaque minerals. Based on definitive mineral assemblages, blueschist and greenschist facies sequences are recognized. Correspondingly, index minerals provide chlorite zone, biotite zone, garnet zone, kyanite zone, and graphite zone. The P-T conditions of the studied rocks demonstrate the possible temperature ranges 300-550°C and pressure ranges 2-10 kbar. Most common varieties of metamorphic rocks in the study area are garnet mica schist, chlorite schist, gneiss and few quartzites. Characteristics of garnet mica schist and chlorite schist are equivalent with the lesser Himalayan metamorphic rock sequence in Sikkim area, whereas gneiss from Bhajanpur area has similar precursor as Darjeeling gneiss. Therefore, the sources of detrital metamorphic rocks in Bhajanpur area obviously come from the lesser Himalayan sequence in Sikkim and Darjeeling areas, India. Key words: Petrology; metamorphic rocks; gravels; P-T conditions; Panchagarh; lesser Himalayan sequence DOI: 10.3329/jles.v5i0.7357 J. Life Earth Sci., Vol. 5: 91-96, 2010

The Mid-Atlantic Ridge near 45° N. XII. Coercivity, secondary magnetization, polarity, and thermal stability of dredge samples

1970 ◽  
Vol 7 (6) ◽  
pp. 1499-1514 ◽  
Author(s):  
J. K. Park ◽  
E. Irving
Keyword(s):  
Coercive Force ◽  
Empirical Relationship ◽  
Blocking Temperature ◽  
Lower Intensity ◽  
Volcanic Zone ◽  
Rock Types ◽  
Mid Atlantic Ridge ◽  
The Mean ◽  
Force Range ◽  
Thermal Stability Of

The mean coercivities of natural (n.r.m.), anhysteretic (a.r.m.), and isothermal (i.r.m.) remanent magnetization in 34 samples of submarine basalt from the Mid-Atlantic Ridge are 270, 250, and 370 oersteds respectively, showing their magnetization to be stable. The spectra of coercive force of n.r.m. and a.r.m. of these basalts are similar, although, because of small secondary components, there are small differences in the low coercive force range (0 to 100 Oe). The magnitude and sign of these differences are used to derive an empirical relationship between coercivity and the magnitude of secondary components, and to infer the polarity of primary components. The inferred polarities of samples from within the Median Valley of the Ridge are all normal, whereas both normal and reversed polarities are found from the adjacent mountains and plateaus. Experiments show that warming specimens from the Median Valley to 100 °C for 90 h causes the production of a new component with a lower intensity, and higher blocking temperature, but with the same direction as the original natural remanence. Similar effects may occur in the axial volcanic zone, and may have caused the decrease in intensity with distance from the axis. The magnetic properties of various other rock types from the Mid-Atlantic Ridge are also described.

scholarly journals Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

2010 ◽  
Vol 105 (5) ◽  
pp. 233-250 ◽  
Author(s):  
Michio TAGIRI ◽  
Shingo TAKIGUCHI ◽  
Chika ISHIDA ◽  
Takaaki NOGUCHI ◽  
Makoto KIMURA ◽  
...  
Keyword(s):  
Tien Shan ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
T Path

scholarly journals Epidemiology of primary and secondary headaches in a Brazilian tertiary-care center

2006 ◽  
Vol 64 (1) ◽  
pp. 41-44 ◽  
Author(s):  
André Carvalho Felício ◽  
Denis Bernardi Bichuetti ◽  
William Adolfo Celso dos Santos ◽  
Clecio de Oliveira Godeiro Junior ◽  
Luis Fabiano Marin ◽  
...  
Keyword(s):  
Care Center ◽  
Tertiary Care ◽  
Population Sample ◽  
Tension Type Headache ◽  
Hypnic Headache ◽  
Secondary Headaches ◽  
The Mean ◽  
Headache Clinic ◽  
Type Headache ◽  
Few Data

OBJECTIVE: To analyze the demographic features of the population sample, the time of headache complaint until first consultation and the diagnosis of primary and secondary headaches. METHOD: 3328 patients were analyzed retrospectively and divided according to gender, age, race, school instruction, onset of headache until first consultation and diagnosis(ICHD-II, 2004). RESULTS: Sex ratio (Female/Male) was 4:1, and the mean age was 40.7±15 years, without statistical differences between sexes. Approximately 65% of the patients were white and 55% had less than eight years of school instruction. Headache complaint until first consultation ranged from 1 to 5 years in 32.99% patients. The most prevalent diagnosis were migraine (37.98%), tension-type headache-TTH (22.65%) and cluster headache (2.73%). CONCLUSION: There are few data on epidemiological features of headache clinic populations, mainly in developing countries. According to the literature, migraine was more frequent than TTH. It is noteworthy the low school instruction of this sample and time patient spent to seek for specialized attention. Hypnic headache syndrome was seen with an unusual frequency.

Chemical composition of Archean Pontiac metasediments, southwestern Abitibi Belt, Superior Province

1984 ◽  
Vol 21 (6) ◽  
pp. 727-731 ◽  
Author(s):  
Osamu Ujike
Keyword(s):  
Chemical Composition ◽  
Chemical Data ◽  
Superior Province ◽  
Upper Crust ◽  
The Mean

Three mica schists from the Pontiac Group have a La/Yb ratio of ~19, a La content of ~32 ppm, and a Th content of ~6 ppm. These values are higher than those of the average Archean upper crust (La/Yb, ~7; La, ~13 ppm; Th, ~3.5 ppm) and the mean compositions of Blake River (La/Yb, ~2.6 (184 analyses); La, ~10 ppm (184 analyses); Th, ~1.3 ppm (143 analyses)) and other subalkalic volcanic groups in the Kirkland Lake–Noranda region. Hence it is unlikely that the latter are exclusive sources of Pontiac detritus. The chemical data reveal that Timiskaming-type alkalic rocks (La/Yb, ~ 45; La, ~95 ppm; Th, ~21 ppm (means of 29 analyses)) are likely contributors to Pontiac metasediments. However, the Timiskaming Group itself is generally considered to be younger than the Pontiac Group. This implies the presence of an undetected or unpreserved terrane characterized by Timiskaming-type alkalic rocks.

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