scholarly journals The Almacık mafic-ultramafic complex: exhumed Sakarya subcrustal mantle adjacent to the İstanbul Zone, NW Turkey

2012 ◽  
Vol 150 (2) ◽  
pp. 254-282 ◽  
Author(s):  
ERDİN BOZKURT ◽  
JOHN A. WINCHESTER ◽  
MUHARREM SATıR ◽  
QUENTIN G. CROWLEY ◽  
CHRISTIAN J. OTTLEY
Keyword(s):  
Active Continental Margin ◽  
Late Result ◽  
Ultramafic Rocks ◽  
High Grade ◽  
Calc Alkaline ◽  
The North ◽  
Rock Types ◽  
Mafic Complex ◽  
Nw Turkey ◽  
Northwestern Turkey

AbstractThe Almacık Mountains in northwestern Turkey expose an upper-amphibolite-facies complex consisting of alternating ultramafic (harzburgitic and websteritic) and mafic (metagabbroic) rock types. In the eastern part of this complex are island arc meta-tholeiites and transitional to calc-alkaline metabasites that are chemically quite similar to those of the Permo-Triassic Çele mafic complex north of Bolu, and this suggests an equivalence. However, much of the section exposes structurally deeper and chemically different mafic and ultramafic rocks, which have no equivalent in the Çele mafic complex, and isotopic dating has suggested that these rocks also formed during the Permian period and underwent Triassic and Jurassic metamorphism. Furthermore, sparse inherited ages, unlike those from İstanbul Zone granitoids, suggest a link with North African-derived Armorican-type basement (and hence the Sakarya Zone), rather than Amazonia-derived Avalonian basement. Alternating mafic and ultramafic rocks suggest structural repetition, supported by the exposure of discrete high-strain zones or poorly exposed shattered rock west of each outcrop of ultramafic rocks. The high grade of metamorphism, and the absence of either extrusive lavas or sheeted dyke rocks, suggests that the Almacık complex was not an ophiolite, but formed instead as subcontinental lower crust and subjacent mantle. Dominantly calc-alkaline geochemistry suggests that it formed the basement to an active continental margin bounding the north side of the Sakarya Continent, with S-dipping subduction of Palaeotethys. The Almacık complex was uplifted as a late result of compression against the southern margin of the İstanbul Zone in the Jurassic period. Lack of coeval high-grade metamorphism in the İstanbul Zone indicates that the latter was overthrust southwards over the Sakarya margin, and that there was therefore a change of subduction polarity in the Triassic period. The evidence further casts doubt on the existence of a Mesozoic Intra-Pontide Ocean in northwestern Turkey and suggests that the latest Permian magmatism, with subsequent Triassic and Jurassic metamorphism, was instead related to the closure of the Palaeotethyan Ocean.

Evidence for early fluid channelization, Pikwitonei granulite domain, Manitoba, Canada

1992 ◽  
Vol 29 (8) ◽  
pp. 1701-1716 ◽  
Author(s):  
Julie K. Vry ◽  
Philip E. Brown
Keyword(s):  
Carbon Isotope ◽  
Fluid Inclusions ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Garnet Growth ◽  
High Grade ◽  
Low Oxygen ◽  
The North ◽  
Rock Types ◽  
Lake Region

The results of field mapping and carbon isotope and phase equilibria studies suggest that two different, locally controlled fluid regimes existed during at least the early phases of high-grade metamorphism in the north Cauchon Lake region, Pikwitonei granulite domain, Manitoba, Canada. During the prograde stages of high-grade "anticlockwise" regional metamorphism, rocks already metamorphosed to at least sillimanite grade were thermally metamorphosed at temperatures near 900 °C by the intrusion of a charnockitic magma. It is likely that this magma released an oxidizing, CO2-bearing, probably CO2-rich fluid phase while the region was still at relatively shallow depths. Fluid migration was channelized along the intrusive contact, and local fluid buffering characterized many of the country rocks. The light carbon isotope values of graphites (gr) and CO2 in cordierites (crd) in pelitic lithologies (δ13Cgr = −41.8 to −30.4; δ13Ccrd = −31.8 to −34.9), and the low oxygen fugacities in many samples rule out infiltration of these units by large amounts of an externally derived CO2-rich fluid phase. Texturally early CO2-rich fluid inclusions occur in the cores of garnets in a variety of rock types along the intrusive contact. These fluid inclusions were probably trapped during early garnet growth at high temperatures and relatively low pressures, and appear to have undergone limited or no subsequent reequilibration. They do not appear to provide direct information about the highest regional metamorphic temperature and pressure conditions to have affected the region (750 °C and 7 kbar (1 kbar = 100 MPa)) but may instead retain evidence of the prograde metamorphic path. These studies demonstrate the importance of local controls on the sources, compositions, timing, and transport of metamorphic fluids in the north Cauchon Lake region.

Age and geological context of the Barby Formation, a key volcanic unit in the Mesoproterozoic Sinclair Supergroup of southern Namibia

2019 ◽  
Vol 122 (4) ◽  
pp. 519-540
Author(s):  
T. Malobela ◽  
B. Mapani ◽  
M. Harris ◽  
D.H. Cornell ◽  
A. Karlsson ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Inductively Coupled Plasma ◽  
Cell Mass ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Granite Gneiss ◽  
Crustal Material ◽  
Calc Alkaline ◽  
Inductively Coupled ◽  
Rock Types

Abstract Volcanic and sedimentary rocks of the Sinclair Supergroup occur in the Konkiep Terrane of Southern Namibia. Three volcanic and sedimentary cycles are recognised. In this work we describe and date volcanic rocks of the Barby Formation, a key unit in the Sinclair area. The coeval Spes Bona Syenite and the Tiras Granite Gneiss are also described and dated. The rock types in the Barby Formation are rhyolites, basaltic trachyandesites, trachybasalts and trachydacites as well as volcanoclastic rocks. The rocks are largely undeformed and partly altered by deuteric and contact metamorphic processes but not regionally metamorphosed. Our samples represent both the calc-alkaline and alkaline trends documented in previous work. U-Pb ion probe and laser ablation inductively coupled plasma (LA-ICP) multicollector mass spectrometer Lu-Hf microbeam analyses were made of zircon and baddeleyite grains from four samples. A felsic tuff sample from the base of the Barby Formation has a 207Pb/206Pb zircon age of 1214 ± 5 Ma (2σ). A rhomb porphyry sample from the top of an 8.5 km-thick stratigraphic section gives a 207Pb/206Pb baddeleyite age of 1217 ± 2 Ma. The Spes Bona Syenite which intrudes the top of the Barby Formation has a 207Pb/206Pb baddeleyite age of 1217 ± 3 Ma and an indistinguishable LA-ICP collision cell mass spectrometer Rb-Sr biotite isochron age of 1238 ± 20 Ma, showing that there was no >350°C regional metamorphic event. Multi-element diagrams for the calc-alkaline samples show a dominant signature of reworked crust which is superimposed on a possible subduction signature. However the alkaline samples contain clear subduction signatures which are not seen in the underlying 1.37 Ga Kumbis rhyolite. The Barby Formation samples and coeval Spes Bona Syenite have Lu-Hf crustal residence ages between 1682 and 1873 Ma, suggesting that both of these units formed from a mixture of juvenile mantle-derived and older crustal material. The Barby Formation is considered to have originated due to a subduction event which took place during the assembly of the Rodinia supercontinent. The duration of the Barby magmatic episode is constrained to a maximum 9 m.y. period between 1219 and 1210 Ma, and during this period the Konkiep Terrane was an active continental margin. The 1204 ± 9 Ma Tiras Granite Gneiss is slightly younger than the Barby Formation and intruded across the Lord Hills Shear Zone, which is the suture between the hardly metamorphosed Konkiep Terrane and the highly metamorphosed Grunau Terrane of the Namaqua-Natal Province. Its intrusion reflects the end of subduction-related volcanism, due to the collision of Namaqua terranes with the Konkiep Terrane.

Geochemical signatures of recent bar deposits in the Tista river, Bangladesh: Implications to provenance, paleoweathering and tectonics

2020 ◽  
Vol 60 ◽  
pp. 1-20
Author(s):  
Pradip Kumar Biswas ◽  
M. Shafiqul Alam ◽  
A.S.M. Mehedi Hasan ◽  
Syed Samsuddin Ahmed ◽  
Mohammad Nazim Zaman
Keyword(s):  
Chemical Weathering ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Granulite Facies ◽  
Depositional Environments ◽  
Source Rocks ◽  
Low Grade ◽  
Geochemical Composition ◽  
The North ◽  
Rock Types

Petrography and geochemical composition of sediments is a sensitive indicator which archives the signature of a previous record of a source rock and depositional environments in a basin.  This study deals with the elemental geochemistry of recent bar deposits of the Tista river in the north western part of Bangladesh to evaluate their provenance, paleoweathering and tectonic setting. Petrographically, the sediments are rich in quartz (70%), whereas feldspar and lithic fragments are found about 8% and 3%, respectively. The geochemical composition of the samples exhibits dominantly quartzose litharenites with low grade sedimentary and metasedimentary lithics, low feldspar indicates tectonic provenance field of recycled orogeny. Discrimination functions revels that the sediments of the Tista river are the derivation of active continental margin. The analyses also reflect that the sediments are dominantly a mixture of felsic (e.g., granitic/Gneiss, quartzite, amphibolite, granulite facies rock types) and some of mafic source (e.g., alkali-basalt/greenschist facies). It may occur, since 60% of the sedimentary flux carried out by the river from low-grade metamorphic rock and the rest from high-grade rock (in the west and north Sikkim Himalaya respectively). The weathering indices highlight that the source rocks have not undergone significant chemical weathering. The immature sorting status and petrographic evidences indicate that the sediments deposited in the Tista river basin are simply the product of mechanically weathered rocks.

scholarly journals Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)

2020 ◽  
Vol 12 (1) ◽  
pp. 764-790
Author(s):  
Amin Allah Kamali ◽  
Mohsen Moayyed ◽  
Nasir Amel ◽  
Fadaeian Mohammad ◽  
Marco Brenna ◽  
...  
Keyword(s):  
Active Continental Margin ◽  
Mineral Chemistry ◽  
Quartz Diorite ◽  
Alkaline Magmatism ◽  
Porphyry Deposit ◽  
Average Percentage ◽  
The North ◽  
Northwestern Iran ◽  
Subduction System ◽  
Late Stages

AbstractThe Sungun copper–molybdenum porphyry deposit is located in the north of Varzaghan, northwestern Iran. The Sungun quartz-monzonite is the oldest mineralized intrusive body in the region and was emplaced during the Early Miocene. Eight categories of the late and unmineralized dykes, which include quartz diorite, gabbrodiorite, diorite, dacite, microdiorite and lamprophyre (LAM), intrude the ore deposit. The main mineral phases in the dykes include plagioclase, amphibole and biotite, with minor quartz and apatite and secondary chlorite, epidote, muscovite and sericite. The composition of plagioclase in the quartz diorite dykes (DK1a, DK1b and DK1c) varies from albite-oligoclase to andesine and oligoclase to andesine; in the diorite, it varies from andesine to labradorite; in the LAM, from albite to oligoclase; and in the microdiorite (MDI), it occurs as albite. Amphibole compositions are consistent with classification as hornblende or calcic amphibole. Based on their AlIV value (less than 1.5), amphibole compositions are consistent with an active continental margin affinity. The average percentage of pistacite (Ps) in epidotes formed from alteration of plagioclase and ferromagnesian minerals is 27–23% and 25–30%, respectively. Thermobarometric studies based on amphibole and biotite indicate approximate dyke crystallization temperature of 850–750℃, pressure of 231–336 MPa and high fO2 (>nickel-nickel-oxide buffer). The range of mineral compositions in the postmineralization dyke suite is consistent with a genetic relationship with the subduction of the Neotethys oceanic crust beneath the continental crust of the northwest part of the Central Iranian Structural Zone. Despite the change from calc-alkaline to alkaline magmatism, the dykes are likely related to the late stages of magmatic activity in the subduction system that also generated the porphyry deposit.

The Metasomatized Mantle beneath the North Atlantic Craton: Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada)

2019 ◽  
Vol 60 (10) ◽  
pp. 1991-2024 ◽  
Author(s):  
M G Kopylova ◽  
E Tso ◽  
F Ma ◽  
J Liu ◽  
D G Pearson
Keyword(s):  
North Atlantic ◽  
Thermal State ◽  
Mineral Chemistry ◽  
Mantle Metasomatism ◽  
Labrador Sea ◽  
The North ◽  
Rock Types ◽  
History Of ◽  
The North Atlantic ◽  
North Atlantic Craton

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as <1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as <1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

scholarly journals Ore-Bearing Magmatic Systems with Complex Sn–Au–Ag Mineralization in the North-Eastern Verkhoyansk–Kolyma Orogenic Belt, Russia

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 266
Author(s):  
Vera A. Trunilina ◽  
Andrei V. Prokopiev
Keyword(s):  
Active Continental Margin ◽  
Orogenic Belt ◽  
Crustal Extension ◽  
Margin Setting ◽  
The North ◽  
Magmatic Rocks ◽  
Isotopic Methods ◽  
North Eastern ◽  
Magmatic Stage ◽  
Mineral Compositions

This paper reports the results of a study of magmatic rocks with Sn–W–Au–Ag mineralization from the Kuranakh, Elikchan, and Istekh ore fields in the Northern batholith belt of the north-eastern Verkhoyansk–Kolyma orogenic belt in Eastern Russia. Using petrographic, mineralogical, geochemical, and isotopic methods, we determined the mineral compositions, petrochemistry, and geochemistry of magmatic rocks, the P–T conditions of their generation and crystallization, and their geodynamic affinity. The studied magmatic rocks have common geochemical characteristics that likely reflect the influence of fluids supplied from a long-lived, deep-seated mantle source. The ore fields are characterized by Sn–W–Au–Ag–Pb polygenetic mineralization. The magmatic and metallogenic evolution comprised five stages for the formation of magmatic rocks and ores. During the first stage (Berriasian–Barremian), arc-related magmatic rocks formed in an active continental margin setting and were associated with Au–Ag mineralization. The second, third, and fourth stages (Aptian–Campanian) took place in a crustal extension and rift setting, and were accompanied by Au–Ag and Sn–W mineralization. During the fifth (post-magmatic) stage, Sn–Ag–Sb and Pb–Ag mineralization occurred.

scholarly journals Segmentation and Holocene Behavior of the Middle Strand of the North Anatolian Fault (NW Turkey)

2021 ◽  
Author(s):  
Yacine Benjelloun ◽  
Julia De Sigoyer ◽  
Stéphane Garambois ◽  
Julien Carcaillet ◽  
Yann Klinger
Keyword(s):  
North Anatolian Fault ◽  
The North ◽  
Nw Turkey

Velocity changes across the Ganos segment of the North Anatolian Fault Zone in NW Turkey from systematic variations in body wave arrival times

2021 ◽  
Author(s):  
Esref Yalcinkaya ◽  
Marco Bohnhoff ◽  
Patricia Martinez-Garzon ◽  
Ethem Görgün ◽  
Ali Pınar ◽  
...  
Keyword(s):  
Body Wave ◽  
Waveform Analysis ◽  
Marmara Region ◽  
Rupture Directivity ◽  
Data Set ◽  
High Resolution Data ◽  
Arrival Times ◽  
The North ◽  
Nw Turkey ◽  
Geological Units

<p>Imaging and characterizing transform fault sections that are capable to produce large earthquakes is crucial for evaluating seismic hazard and subsequent risk for nearby population centers. The Marmara Fault near the megacity of Istanbul is one of the best defined seismic gaps in the world and its complexity is captured by seismological, geodetic and geological data. A local dense seismic array (MONGAN) provides a high resolution data set allowing to image the Ganos fault separating two different geological units in the western Marmara region. First results of the waveform analysis from this array present systematic early-phase arrivals at the seismic stations located on the northern block of the Ganos fault which comprises geological units including older and more compact materials than that of the southern block. This difference in the arrival times causes the earthquake epicenters to shift further north than the real locations. In this preliminary results, the early-arrivals will be evaluated according to source azimuths and distances, and possible earth models and wave paths will be discussed. The results have implications for rupture directivity during future earthquakes as input for hazard and risk models for the Marmara region.</p>

Felsic plutonic rocks from the southern portion of the New Caledonian Ultramafic Belt

1973 ◽  
Vol 110 (5) ◽  
pp. 431-446 ◽  
Author(s):  
K. A. Rodgers
Keyword(s):  
New Caledonia ◽  
Ultramafic Rocks ◽  
Calc Alkaline ◽  
Mafic Rocks ◽  
Alkaline Magma ◽  
Southwest Pacific ◽  
Plutonic Rocks

SummaryGranodiorite stocks were intruded into the alpine peridotites of southern New Caledonia in the Eocene following overthrusting of the ultramafics onto the sialic core of the island. Strong zoning, from mela-diorite to granodiorite, is developed in one pluton and is believed to be the result of assimilation of ultramafic and mafic rocks by the calc-alkaline magma. Evidence in favour of a consanguineous relationship between the felsic and ultramafic rocks is largely circumstantial. In their petrography, mineralogy and chemistry, the rocks show few differences from other felsic plutonics of Tertiary age in the southwest Pacific.

Sign in / Sign up

Export Citation Format

Share Document