The Origin of Carbonatites from the eastern Armutlu Peninsula (NW Turkey)

2021 ◽  
pp. jgs2020-171
Author(s):  
Mutlu Özkan ◽  
Ömer Faruk Çelik ◽  
Andrea Marzoli ◽  
Rahmi Melih Çörtük ◽  
Mehmet Zeki Billor
Keyword(s):  
Continental Crust ◽  
Source Area ◽  
Field Studies ◽  
Mineral Chemistry ◽  
Geochemical Characteristics ◽  
Content Type ◽  
Neodymium Isotopes ◽  
Nw Turkey ◽  
Supplementary Material ◽  
Opaque Minerals

Unusual carbonate dykes, which have a thickness of up to 4 meters, crosscut the amphibolites from the high-grade metamorphic rocks in the Armutlu Peninsula (NW Turkey). They are described as carbonatites based on their petrographic, geochemical, and isotope-geochemical characteristics. The carbonatites, which show commonly equigranular texture, are composed of calcite and clinopyroxene with other minor phases of plagioclase, mica, garnet, K-feldspar, quartz, epidote, titanite, and opaque minerals. They contain abundant xenoliths of pyroxenite and amphibolite. Geochemical characteristics of the carbonatites are significantly different from those of mantle-derived carbonatites. They have remarkably low incompatible elements (e.g. Ba, Th, Nb) and total REE contents (11-91 ppm) compared to mantle-derived carbonatites. The high 87Sr/86Sr(i) (0.70797-0.70924) and low εNd(t) (-8.08 to -9.57) of the carbonatites confirm that they were derived from the continental crust rather than from a mantle source. Mica from carbonatite was dated by the 40Ar/39Ar method and yielded Late Jurassic – Early Cretaceous (148-137 Ma). This age is significantly younger from the age (Upper Triassic) of adjacent amphibolites. All data from field studies, as well as petrographic, geochemical and geochronological observations, suggest that these carbonatites were formed from the anatectic melting of a carbonated source area in the continental crust.Supplementary material: A complete description of the analytical methods (Whole rock chemistry, mineral chemistry, Strontium and Neodymium isotopes and 40Ar/39Ar measurements) and mineral chemistry and 40Ar-39Ar dating results are available at https://doi.org/ 10.6084/m9.figshare.12946955

Brittle–ductile fabrics and P–T conditions of deformation in the East Pernambuco shear zone (Borborema Province, NE Brazil)

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-109
Author(s):  
Paulo Castellan ◽  
Gustavo Viegas ◽  
Frederico M. Faleiros
Keyword(s):  
Shear Zone ◽  
Microstructural Analysis ◽  
Mineral Chemistry ◽  
Prism Slip ◽  
Content Type ◽  
Fine Grained ◽  
Brittle Ductile Transition ◽  
Epma Analysis ◽  
Borborema Province ◽  
Supplementary Material

Fabrics of the East Pernambuco shear zone (EPSZ) were studied via microstructural analysis, mineral chemistry and isochemical phase diagram modelling to constrain the pressure and temperature conditions of deformation during shearing. Granitic mylonites show fractured feldspar porphyroclasts embedded in a fine-grained, recrystallized quartzo-feldspathic matrix. These mylonites grade laterally into banded ultramylonites characterized by stretched feldspar clasts alternated with recrystallized quartz bands. Fractures in these ultramylonites are filled by phyllosilicates. The mineral chemistry of the feldspars points to systematic changes between porphyroclasts, grains within fractures and fine-grained mixtures. Quartz crystallographic fabrics in the mylonites suggest activation of prism slip, while the ultramylonites show the activation of both rhomb and basal slip systems. Thermodynamic modelling suggests that the mylonites were formed at 4.75 ± 0.25 kbar and 526 ± 9°C, while the ultramylonites yield conditions of 5.9 ± 1 kbar and 437 ± 17°C. These observations suggest that the EPSZ records a heterogeneous path of strain accommodation, marked by decreasing temperature from its western sector to its eastern termination. The differences in metamorphic conditions are consistent with a transitional, brittle–ductile strain regime. Such characteristics indicate that the EPSZ is a Neoproterozoic shear belt nucleated and heterogeneously exhumed at the brittle–ductile transition, possibly in an intracontinental setting.Supplementary Material: EPMA analysis of feldspars in Caruaru and Gravatá domains and T-X(O2) pseudosections are available at https://doi.org/10.6084/m9.figshare.c.5125957

Eruption history, petrogeochemistry, and geodynamic background of Tengchong volcanoes in Yunnan Province, SW China

2020 ◽  
pp. SP510-2020-45
Author(s):  
Hongmei Yu ◽  
Bo Zhao ◽  
Zhengquan Chen ◽  
Haiquan Wei ◽  
Wenjian Yang ◽  
...  
Keyword(s):  
Yunnan Province ◽  
Volcanic Rocks ◽  
Evolutionary Process ◽  
Source Area ◽  
Volcanic Field ◽  
Indian Plate ◽  
Eurasian Plate ◽  
Content Type ◽  
Supplementary Material ◽  
Eruption History

AbstractThe Tengchong Volcanic Field (TVF) is one of the youngest volcanic areas in China, and located in the southwestern part of Yunnan Province, China, adjacent to the collision zone between the Indian Plate and Eurasian Plate. This paper summarizes the results of previous research on the eruption history, petrochemistry, and geodynamic background of the TVF and presents a detailed analysis of the available data. Eruptions took place from the Pliocene to the Holocene and were divided into five stages. The composition of the magma went through two cycles: the N2-Q1 P-Q2 P volcanic rocks went through the evolutionary process from basalt to dacite and the Q3 P-Qh magma evolved from trachybasalt to trachyte. The evolution of magma is mainly related to the crystallisation and separation of pyroxene and ilmenite. The mantle source area of the TVF volcanic rocks was caused by the mixing between the MORB-source mantle and the eastern Indian continental margin sediments (EIS) to different degree. Geophysical data also showed that the Indian Plate has been subducted under the TVF area. There are also magma chambers in the crust within a depth of 25 km in the TVF that are replenished by mantle magma.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5227663

scholarly journals Rift-related magmatism influences petroleum system development in the NE Irish Rockall Basin, offshore Ireland

2020 ◽  
Vol 26 (4) ◽  
pp. 511-524
Author(s):  
Christopher A.-L. Jackson ◽  
Craig Magee ◽  
Carl Jacquemyn
Keyword(s):  
Deep Water ◽  
System Development ◽  
Source Area ◽  
Sedimentary Basins ◽  
Reservoir Quality ◽  
Content Type ◽  
The Poor ◽  
Supplementary Material ◽  
Break Up ◽  
Upper Paleocene

Large volumes of hydrocarbons reside in volcanically influenced sedimentary basins. Despite having a good conceptual understanding of how magmatism impacts the petroleum systems of such basins, we still lack detailed case studies documenting precisely how intrusive magmatism influences, for example, trap development and reservoir quality. Here we combine 3D seismic reflection, borehole, petrographical and palaeothermometric data to document the geology of borehole 5/22-1, NE Irish Rockall Basin, offshore western Ireland. This borehole (Errigal) tested a four-way dip closure that formed to accommodate emplacement of a Paleocene–Eocene igneous sill-complex during continental break-up in the North Atlantic. Two water-bearing turbidite-sandstone-bearing intervals occur in the Upper Paleocene; the lowermost contains thin (c. 5 m), quartzose-feldspathic sandstones of good reservoir quality, whereas the upper is dominated by poor-quality volcaniclastic sandstones. Palaeothermometric data provide evidence of anomalously high temperatures in the Paleocene–Eocene succession, suggesting the poor reservoir quality within the target interval is likely to reflect sill-induced heating, fluid flow, and related diagenesis. The poor reservoir quality is also probably the result of the primary composition of the reservoir, which is dominated by volcanic grains and related clays derived from an igneous-rock-dominated, sediment source area. Errigal appeared to fail due to a lack of hydrocarbon charge: that is, the low bulk permeability of the heavily intruded Cretaceous mudstone succession may have impeded the vertical migration of sub-Cretaceous-sourced hydrocarbons into supra-Cretaceous reservoirs. Break-up-related magmatism did, however, drive the formation of a large structural closure, with data from Errigal at least proving high-quality, Upper Paleocene deep-water reservoirs. Future exploration targets in the NE Irish Rockall Basin include: (i) stratigraphically trapped Paleocene–Eocene deep-water sandstones that onlap the flanks of intrusion-induced forced folds; (ii) structurally trapped, intra-Cretaceous, deep-water sandstones incorporated within intrusion-induced forced folds; and (iii) more conventional, Mesozoic fault-block traps underlying the heavily intruded Cretaceous succession (e.g. Dooish). Similar plays may exist on other continental margins influenced by break-up magmatism.Supplementary material: Borehole-related reports, and litho- and composite logs are available at https://doi.org/10.6084/m9.figshare.c.4803267

Zircon U–Pb ages and Lu–Hf isotopes of metagranitoids from the Subansiri region, Eastern Himalaya: implications for crustal evolution along the northern Indian passive margin in the early Paleozoic

2018 ◽  
Vol 481 (1) ◽  
pp. 299-318 ◽  
Author(s):  
R. K. Bikramaditya ◽  
A. Krishnakanta Singh ◽  
Sun-Lin Chung ◽  
Rajesh Sharma ◽  
Hao-Yang Lee
Keyword(s):  
Experimental Period ◽  
Mineral Chemistry ◽  
Hf Isotope ◽  
Passive Margin ◽  
Hf Isotopes ◽  
Eastern Himalaya ◽  
Geochemical Data ◽  
Early Paleozoic ◽  
Content Type ◽  
Supplementary Material

AbstractWe studied the zircon U–Pb ages, Hf isotopes, and whole-rock and mineral chemistry of metagranitoids from the Subansiri region of the Eastern Himalaya to constrain their emplacement age, origin and geodynamic evolution. The investigated metagranitoids have high SiO2, Na2O + K2O, Rb, Zr and low Fe2O3, Nb, Ga/Al ratios with fractionated rare earth element patterns [(Ce/Yb)N = 6.46–42.15] and strong negative Eu anomalies (Eu/Eu* = 0.16–0.44). They are peraluminous (molar A/CNK = 1.04–1.27) and calc-alkaline in nature, with normative corundum (1.04–3.61) and relatively high FeOt/MgO ratios in biotite (c. 3.38), indicating their affinity with S-type granites. The time of emplacement of the Subansiri metagranitoids is constrained by zircon U–Pb ages between 516 and 486 Ma. The zircon grains have negative εHf(t) values ranging from −1.4 to −12.7 and yield crustal Hf model ages from 1.5 to 2.2 Ga, suggesting the occurrence of a major crustal growth event in the Proterozoic and re-melting of the crust during the early Paleozoic. The geochemical data in conjunction with the U–Pb ages and Hf isotope data suggest that the Subansiri metagranitoids were produced by partial melting of older metasedimentary rocks in the Indian passive margin.Supplementary material: Hf isotope results for the Mud Tank zircon standard acquired during the experimental period are available at https://doi.org/10.6084/m9.figshare.c.4299830

scholarly journals Nature of the Cuvier Abyssal Plain crust, offshore NW Australia

2021 ◽  
pp. jgs2020-172
Author(s):  
Matthew T. Reeve ◽  
Craig Magee ◽  
Ian D. Bastow ◽  
Carl McDermott ◽  
Christopher A.-L. Jackson ◽  
...  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Seismic Reflection ◽  
Abyssal Plain ◽  
Magnetic Data ◽  
Borehole Data ◽  
Seismic Reflection Data ◽  
Content Type ◽  
Supplementary Material ◽  
Nw Australia

Magnetic stripes have long been assumed to be indicative of oceanic crust. However, continental crust heavily intruded by magma can also record magnetic stripes. We re-evaluate the nature of the Cuvier Abyssal Plain (CAP), offshore NW Australia, which hosts magnetic stripes and has previously been defined as oceanic crust. We show that chemical data from a basalt within the CAP, previously described as an enriched mid-ocean ridge basalt, could equally be interpreted to contain evidence of contamination by continental material. We also recognize seaward-dipping reflector sequences in seismic reflection data across the CAP. Borehole data from overlying sedimentary rocks suggests that these seaward-dipping reflectors were emplaced in a shallow water (<200 m depth) or subaerial environment. Our results indicate that the CAP may not be unambiguous oceanic crust, but may instead consist of a spectrum of heavily intruded continental crust through to fully oceanic crust. If the CAP represents such a continent–ocean transition zone, then the adjacent unambiguous oceanic crust would be located >500 km further offshore NW Australia than currently thought. This would impact plate tectonic reconstructions, as well as heat flow and basin modelling studies. Our work also supports the growing consensus that magnetic stripes cannot, by themselves, be used to determine crustal affinity.Supplementary material: Enlarged and uninterpreted versions of the magnetic data and seismic reflection lines are available at https://doi.org/10.6084/m9.figshare.c.5332172

U-Pb isotopic ages and provenance of some far travelled exotic pebbles from glaciogenic sediments of the Polonez Cove Formation (Oligocene, King George Island)

2020 ◽  
pp. jgs2020-113
Author(s):  
Jerzy Nawrocki ◽  
Magdalena Pańczyk ◽  
Krystian Wójcik ◽  
Andrzej Tatur
Keyword(s):  
Source Area ◽  
Crystalline Rocks ◽  
Substantial Part ◽  
King George Island ◽  
Pb Isotope ◽  
Content Type ◽  
Isotope Data ◽  
Supplementary Material ◽  
Glaciogenic Sediments ◽  
The Antarctic

Zircon grains from nine erratic pebbles of granite, granodiorite/tonalite and quartzite from the Polonez Cove Formation (southern King George Island) were studied for their U-Pb isotope ages and provenance. The calculated concordia ages of the studied pebbles are 108.79 ± 0.89 Ma, 119.7 ± 2.2 Ma, 178.6 ± 2.8 Ma, 180.7 ± 1.9 Ma, 207.4 ± 3.1 Ma, 231.1 ± 1.9 Ma, 1087.5 ± 4 Ma and 1833 ± 4 Ma. The source area of individual pebbles was analyzed and defined. Pebbles of crystalline rocks were derived from the Antarctic Peninsula, as well as from the Antarctic mainland. The erratic made of quartzite was eroded from the southernmost part of the Ellsworth Mountains (Linder Pak Member of Howard Nunatak Formation). Our isotope data analytically supports the earlier thesis that the Oligocene ice-sheet covered a substantial part of Antarctica and its nucleus was located in its central part.Supplementary material: The U-Pb isotope data (Table S1) are available at https://doi.org/10.6084/m9.figshare.c.5233335

Petrology of Precambrian metagranites and heavy mineral chemistry of the Olounou area within the Cameroon mineral belt (Ntem Complex, South Cameroon): relationships with the Fe-mineralization

2021 ◽  
pp. geochem2021-006
Author(s):  
Mboudou Germain Marie Monespérance ◽  
Owona Sebastien ◽  
Ndema Mbongue Jean Lavenir ◽  
Agyingi Christopher Mbaringong ◽  
Balla Ateba Christian ◽  
...  
Keyword(s):  
Iron Ore ◽  
Mineral Chemistry ◽  
Stream Sediments ◽  
Heavy Mineral ◽  
Hydrothermal Solutions ◽  
Content Type ◽  
Mineral Belt ◽  
Supplementary Material ◽  
Mineral Concentrations ◽  
Ore Exploration

The petrology of Achaean biotite- and amphibole-rich metagranites, the geochemistry of Fe-occurrences and heavy mineral concentrations in stream sediments from Olounou (Ntem complex) help to constrain their inter-relationships. These metagranites display granoblastic textures outlined by microcline, biotite, amphibole and oxides. Ilmenite (60 to 80%), zircon (15 to 20%) and rutile (1 to 2%) are the mineral fractions in pan concentrates. Two types of Fe-mineralization as silicified veins crosscut the above rocks: hematite± magnetite quartzites with primary hematite enclosing magnetite relicts contain high average Fe2O3 (69.05 wt %) and TiO2 (0.73wt %); banded magnetite-rich quartzites with magnetite partially replaced by hematite are characterized byFe2O3 (52.15 wt %), TiO2 (0.27 wt %), relatively high W (286 ppm) and Ni (108 ppm). Both types have Zn, Cu, Ga contents below 10 ppm, positive Eu anomalies, HREE enrichment over LREEs and low ∑REE (9.76 to 12.07). Iron and SiO2 were derived from weathering of Archean biotite and amphibole metagranites, deposited in existing Post-Archean intra-cratonic basins under greenschist facies and impacted by sub-marine hydrothermal solutions. These results are genetically comparable to other Precambrian BIFs and underline the iron potential of Olounou. They equally contribute to iron ore exploration in Cameroon and worldwide.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5426547

Volcano-sedimentary processes at Las Derrumbadas rhyolitic twin domes, Serdán-Oriental basin, Eastern Trans-Mexican Volcanic Belt

2021 ◽  
pp. SP520-2021-144
Author(s):  
Marie-Noëlle Guilbaud ◽  
Corentin Chédeville ◽  
Ángel Nahir Molina-Guadarrama ◽  
Julio Cesar Pineda-Serrano ◽  
Claus Siebe
Keyword(s):  
Volcanic Belt ◽  
Debris Avalanche ◽  
Density Currents ◽  
Content Type ◽  
Mexican Volcanic Belt ◽  
Wide Range ◽  
Eruptive Episode ◽  
Basin Floor ◽  
Supplementary Material ◽  
Trans Mexican Volcanic Belt

AbstractThe eruption of the ∼10 km3 rhyolitic Las Derrumbadas twin domes about 2000 yrs ago has generated a wide range of volcano-sedimentary deposits in the Serdán-Oriental lacustrine basin, Trans-Mexican Volcanic Belt. Some of these deposits have been quarried, creating excellent exposures. In this paper we describe the domes and related products and interpret their mode of formation, reconstructing the main phases of the eruption as well as syn-and-post eruptive erosional processes. After an initial phreatomagmatic phase that built a tuff ring, the domes grew as an upheaved plug lifting a thick sedimentary pile from the basin floor. During uplift, the domes collapsed repeatedly to form a first-generation of hetero-lithologic hummocky debris avalanche deposits. Subsequent dome growth produced a thick talus and pyroclastic density currents. Later, the hydrothermally-altered over-steepened dome peaks fell to generate 2nd generation, mono-lithologic avalanches. Subsequently, small domes grew in the collapse scars. From the end of the main eruptive episode onwards, heavy rains remobilized parts of the dome carapaces and talus, depositing lahar aprons. Las Derrumbadas domes are still an important source of sediments in the basin, and ongoing mass-wasting processes are associated with hazards that should be assessed, given their potential impact on nearby populations.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5752296

Jurassic–Cretaceous arc magmatism along the Shyok–Bangong Suture from NW Himalaya: Formation of the peri-Gondwana basement to the Ladakh Arc

2021 ◽  
pp. jgs2021-035
Author(s):  
Wanchese M. Saktura ◽  
Solomon Buckman ◽  
Allen P. Nutman ◽  
Renjie Zhou
Keyword(s):  
Late Cretaceous ◽  
Nw Himalaya ◽  
Content Type ◽  
Magmatic Arc ◽  
Basement Rocks ◽  
Ladakh Himalaya ◽  
Accreted Terranes ◽  
Volcaniclastic Rocks ◽  
Supplementary Material ◽  
Depositional Age

The Jurassic–Cretaceous Tsoltak Formation from the eastern borderlands of Ladakh Himalaya consists of conglomerates, sandstones and shales, and is intruded by norite sills. It is the oldest sequence of continent-derived sedimentary rocks within the Shyok Suture. It also represents a rare outcrop of the basement rocks to the voluminous Late Cretaceous–Eocene Ladakh Batholith. The Shyok Formation is a younger sequence of volcaniclastic rocks that overlie the Tsoltak Formation and record the Late Cretaceous closure of the Mesotethys Ocean. The petrogenesis of these formations, ophiolite-related harzburgites and norite sill is investigated through petrography, whole-rock geochemistry and U–Pb zircon geochronology. The youngest detrital zircon grains from the Tsoltak Formation indicate Early Cretaceous maximum depositional age and distinctly Gondwanan, Lhasa microcontinent-related provenance with no Eurasian input. The Shyok Formation has Late Cretaceous maximum depositional age and displays a distinct change in provenance to igneous detritus characteristic of the Jurassic–Cretaceous magmatic arc along the southern margin of Eurasia. This is interpreted as a sign of collision of the Lhasa microcontinent and the Shyok ophiolite with Eurasia along the once continuous Shyok–Bangong Suture. The accreted terranes became the new southernmost margin of Eurasia and the basement to the Trans-Himalayan Batholith associated with the India-Eurasia convergence.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5633162

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