scholarly journals A “coarse-grained” metabasite body newly found in the Sambagawa metamorphic rocks in Kumakogen Town, Ehime Prefecture, SW Japan

2019 ◽  
Vol 125 (6) ◽  
pp. 447-452
Author(s):  
Koki Nakata ◽  
Nao Kusuhashi ◽  
Satoshi Saito ◽  
Hiroaki Ohfuji ◽  
Masakazu Nara
Keyword(s):  
Coarse Grained ◽  
Metamorphic Rocks ◽  
Sw Japan

scholarly journals Metamorphic rocks and granitoids in the Aoyama area, Ryoke belt, SW Japan

2012 ◽  
Vol 118 (Supplement) ◽  
pp. S79-S89 ◽  
Author(s):  
Tetsuo Kawakami ◽  
Yoshiharu Nishioka
Keyword(s):  
Metamorphic Rocks ◽  
Sw Japan

scholarly journals Sedimentologic, Heavy Mineral and Provenance Studies of the Cretaceous Sediments in the Auchi Area of the Anambra Basin

2020 ◽  
Vol 24 (6) ◽  
pp. 955-959
Author(s):  
O.A. Ilegieuno ◽  
E.J. Ighodaro ◽  
R.O. Sunny
Keyword(s):  
Upper Cretaceous ◽  
Heavy Mineral ◽  
Coarse Grained ◽  
Metamorphic Rocks ◽  
Basement Complex ◽  
Provenance Studies ◽  
Anambra Basin ◽  
Edo State ◽  
Sand Particles ◽  
Cretaceous Deposits

The Upper Cretaceous Deposits of the Anambra Basin has a part of its sedimentary rock deposited in the Auchi area of Edo State. Geologic field and Sedimentological studies carried out on twenty eight (28) selected samples from a section of a road–cut show that the sediments range from fine through medium to coarse grained. Morphoscopic studies reveal subangular to subrounded outline of sand particles. These coupled with the  various colours observed in the sediment, ranging from whitish sand through yellowish brown, pink and reddish brown possibly indicate a non–marine environment and a fluviatile to deltaic environment of sedimentation is suggested. Heavy mineral assemblage made up mainly of opaque, andalusite, zircon, hornblend, sphene and epidote suggest derivation from the Precambrian Igneous and medium to high grade metamorphic rocks of the underlying Basement Complex of Nigeria. Keywords: Sedimentology, Cretaceous, Morphoscopic, Heavy Mineral, Provenance

Extensive normal faulting during exhumation revealed by the spatial variation of phengite K-Ar ages in the Sambagawa metamorphic rocks, central Shikoku, SW Japan

Island Arc ◽  
2015 ◽  
Vol 24 (2) ◽  
pp. 245-262 ◽  
Author(s):  
Toru Takeshita ◽  
Koshi Yagi ◽  
Chitaro Gouzu ◽  
Hironobu Hyodo ◽  
Tetsumaru Itaya
Keyword(s):  
Spatial Variation ◽  
Metamorphic Rocks ◽  
Normal Faulting ◽  
Sw Japan

Mineralogy

2003 ◽  
Author(s):  
Anthony S. R. Juo ◽  
Kathrin Franzluebbers
Keyword(s):  
Land Surface ◽  
Sedimentary Rock ◽  
Sedimentary Rocks ◽  
Volcanic Glass ◽  
Igneous Rocks ◽  
Coarse Grained ◽  
Metamorphic Rocks ◽  
Great Pressure ◽  
Rock Texture ◽  
Primary Minerals

Soils are weathering products of rocks and minerals. The rocks in Earth’s outer surface can be classified as igneous, sedimentary, or metamorphic rocks. Igneous rocks are formed from molten magma. They are composed of primary minerals, which are minerals that have not been altered chemically since they formed as molten lava solidified. Examples of primary minerals are the light-colored minerals quartz, muscovite, feldspars, and orthoclase, and the dark-colored minerals biotite, augite, and hornblende. In general, dark-colored minerals contain iron (Fe) and magnesium (Mg) and are more easily weathered than light-colored minerals. Coarse-grained igneous rocks, such as granite and diorite, contain mainly lightcolored minerals, while medium-grained igneous rocks such as gabbro, peridotite, and hornblendite are composed of dark-colored primary minerals. Rhyolite and andesite are medium-grained igneous rocks containing light-colored primary minerals. Basalt is dark-colored with an intermediate to fine rock texture, and basaltic volcanic glass has a fine texture. Examples of light-colored igneous rocks with a fine texture are felsite and obsidian. Sedimentary rocks are the most common type of rock, covering about 75% of Earth’s land surface. They are mainly composed of secondary minerals, which are minerals that are recrystallized products of the chemical breakdown and/or alteration of primary minerals. Sedimentary rocks form when weathering products from rocks are cemented or compacted. For example, quartz (SiO2) sand, a weathering product of granite, may become cemented into sandstone. Another common sedimentary rock is limestone. There are two types of limestone, namely, calcite (CaCO3), and dolomite (CaCO3.MgCO3). Clays may become cemented into a sedimentary rock, which is known as shale. A sedimentary rock with several dominant minerals is called a conglomerate, in which small stones with different mineralogy are cemented together. Metamorphic rocks are formed by the metamorphism of igneous or sedimentary rocks. Great pressure and high temperatures, caused by the shifting of continental plates, can compress, distort, and/or partially re-melt the original rocks. Igneous rocks are commonly modified to form schist and gneiss, in which light and dark minerals have been reoriented into bands. Sedimentary rocks, such as limestone and shale, may be metamorphosed to form marble and slate, respectively.

Reaction textures and metamorphic evolution of sapphirine–spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India

2014 ◽  
Vol 152 (2) ◽  
pp. 316-340 ◽  
Author(s):  
DIVYA PRAKASH ◽  
DEEPAK ◽  
PRAVEEN CHANDRA SINGH ◽  
CHANDRA KANT SINGH ◽  
SUPARNA TEWARI ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Coarse Grained ◽  
Eastern Ghats ◽  
Metamorphic Rocks ◽  
Mobile Belt ◽  
Granulite Facies Metamorphism ◽  
Facies Metamorphism ◽  
Isothermal Decompression ◽  
Eastern Ghats Mobile Belt ◽  
Prograde Path

AbstractThe Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine–spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine–spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd–Opx–Qtz–Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx–Crd–Kfs–Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c. 1000°C and c. 12 kbar were computed by isopleths of XMg in garnet and XAl in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P–T evolution. The P–T path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust.

40Ar/39Ar age constraints on the thermal history of the Archean Abitibi greenstone belt and the Pontiac Subprovince: implications for terrane collision, differential uplift, and overprinting of gold deposits

1992 ◽  
Vol 29 (7) ◽  
pp. 1389-1411 ◽  
Author(s):  
R. Feng ◽  
R. Kerrich ◽  
S. McBride ◽  
E. Farrar
Keyword(s):  
High Temperature ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Coarse Grained ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Thermal Activity ◽  
Thermal Event ◽  
Southern Volcanic Zone ◽  
Differential Uplift

40Ar/39Ar mineral age spectra of granitic and metamorphic rocks, in conjunction with existing conventional zircon geochronology, indicate that at least two major late Archean thermal events affected tectonic blocks of the Abitibi Southern Volcanic Zone (SVZ) and the juxtaposed Pontiac Subprovince. The earlier thermal activity (2690–2670 Ma) was accompanied by the intrusion of voluminous syntectonic plutons and caused low-pressure, greenschist-facies metamorphism in the SVZ and intermediate-pressure metamorphism in the Pontiac Subprovince. The second thermal event (2660–2630 Ma) was coeval with the emplacement of syncollisional, S-type garnet–muscovite granites in the Pontiac Subprovince and the higher grade Lacorne block of the Abitibi SVZ, and reset the K–Ar systems in preexisting rocks.Magmatic amphibole from the syntectonic Round Lake batholith (~2695 Ma U–Pb zircon age) of the Abitibi SVZ has a slightly disturbed Ar release spectrum with an upper plateau age of 2669 ± 6 Ma, signifying that the low-grade Round Lake block cooled through 500 °C at a slow rate. Amphiboles in syntectonic batholiths from the higher grade Lacorne block and the Pontiac Subprovince have substantially disturbed Ar release spectra, with high-temperature steps giving apparent ages of 2681 ± 4 to 2679 ± 4 Ma; these overlap zircon ages of 2690–2670 Ma, indicating relatively rapid cooling through the amphibole blocking temperature.Metamorphic rocks (amphibolites) from the Lacorne block and the Pontiac Subprovince contain amphiboles with substantially disturbed 40Ar/39Ar release spectra and higher temperature step ages of 2677 ± 6 to 2670 ± 5 Ma, representing the minimum formation age. Fine-grained muscovite and biotite (180–250 μm) from mica schists also have disturbed Ar release patterns, but much younger apparent ages at high-temperature release steps (2581–2523 Ma for muscovite, 2562–2455 Ma for biotite) than the amphiboles.Coarse-grained muscovites from pegmatites associated with syncollision, S-type garnet–muscovite granites (2644 ± 13 Ma) in the Lacorne block and Pontiac Subprpvince show undisturbed or slightly disturbed Ar release spectra and magmatic δ18Oquartz–muscovite = 1.8–3.5‰, with total integrated ages of 2615 ± 10 to 2594 ± 7 Ma (Lacorne) and 2572 ± 6 Ma (Pontiac), respectively, indicating different uplift rates for the two terranes. Amphiboles (~2680 Ma) from metamorphic rocks in the Lacorne block and Pontiac Subprovince and from the Round Lake batholith are disturbed, whereas coarse-grained muscovites from the pegmatites (2644 ± 13 Ma) are relatively undisturbed. This indicates that the disturbance of the amphiboles may have been caused by a thermal event that preceded or was coeval with the emplacement of the garnet–muscovite granite suite, rather than being a grain-size effect.These results are consistent with a model whereby early subduction of oceanic lithosphere beneath the Abitibi SVZ (2740–2680 Ma), and separately under the Pontiac Subprovince, was responsible for syntectonic batholiths and the first thermal event. Collision with the Abitibi SVZ and local underthrusting of the Pontiac Subprovince at about 2670–2630 Ma caused the second major thermal event and partial melting of the underthrust Pontiac-type metasediments to form the garnet–muscovite granites. Later differential uplift exposed the entire Pontiac Subprovince and the Lacorne block as a tectonic window of underthrust Pontiac in the Abitibi SVZ. Resetting of several isotopic systems, including apparent younger ages of gold mineralization, is probably related to this late collisional, tectonothermal overprinting event. Fluid and (or) thermal events at ≥275 °C influenced the Kirkland Lake – Cadillac fault down to 2513 ± 10 Ma, as indicated by a plateau age of postkinematic biotite in the fault. The fault was intermittently reactivated over a period of 440 Ma, from ~2690 Ma to ≤2250 Ma.

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