Crustal differentiation due to partial melting of granitic rocks in an active continental margin, the Ryoke Belt, Southwest Japan

AbstractThe eastern Kii Peninsula exhibits a variety of rock outcrops, fossils, and other geological features that illustrate the formation history of the Japanese Islands. This work aims to describe the geotourism potential of the region based on the significant rock exposures, and sets out the basis for establishing geosites in this region in the future. Geologically important sites have been selected, together with places of unique history and culture within the northern part of the eastern Kii Peninsula, including the Ise and Toba areas. The results of this study include a detailed description of the geology and history of the region, together with an evaluation of the relative value of each selected locality as a geosite. Proper development and promotion of the proposed sites would make the sites available for education and tourism, and provide opportunities for suitable development and the popularization of geological knowledge.

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Tectono-stratigraphy and low-grade metamorphism of Late Permian and Early Jurassic accretionary complexes within the Kurosegawa belt, Southwest Japan: Implications for mechanisms of crustal displacement within active continental margin

Tectonophysics ◽

10.1016/j.tecto.2013.02.006 ◽

2013 ◽

Vol 592 ◽

pp. 80-93 ◽

Cited By ~ 10

Author(s):

Hidetoshi Hara ◽

Toshiyuki Kurihara ◽

Hiroshi Mori

Keyword(s):

Continental Margin ◽

Active Continental Margin ◽

Early Jurassic ◽

Low Grade ◽

Late Permian ◽

Southwest Japan ◽

Grade Metamorphism

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Age and tectonic setting of the Nesåa Batholith: implications for Ordovician arc development in the Caledonides of Central Norway

Geological Magazine ◽

10.1017/s0016756803008069 ◽

2003 ◽

Vol 140 (5) ◽

pp. 573-594 ◽

Cited By ~ 14

Author(s):

G. B. MEYER ◽

T. GRENNE ◽

R. B. PEDERSEN

Keyword(s):

Rare Earth ◽

Partial Melting ◽

Continental Margin ◽

Tectonic Setting ◽

Active Continental Margin ◽

Shear Zones ◽

Late Ordovician ◽

Magma Ascent ◽

Middle Ordovician ◽

Laurentian Margin

New U–Pb zircon dating yields a crystallization age of 458±3 Ma for the largely gabbroic Grøndalsfjell Intrusive Complex in the Gjersvik Nappe of the Caledonian Upper Allochthon in Scandinavia. This is identical, within error, to the age of the adjacent Møklevatnet Complex that is dominated by quartz monzodiorite (456±2 Ma), and the two intrusive suites may be regarded as members of a composite intrusion here referred to as the Nesåa Batholith. Mafic members of this calc-alkaline batholith are characterized by slightly positive εNd–εSr values, marked enrichment of the light rare earth elements and high Th/Yb ratios suggestive of a subduction-modified mantle source. The I-type granitoids have similar isotope values and highly fractionated rare earth element patterns, and are interpreted as products from partial melting of garnet-bearing mafic rocks. The Nesåa Batholith intruded a previously deformed, 483 Ma or older, metavolcanic sequence of oceanic arc affinity. The margins of the pluton show evidence for synkinematic emplacement, which is tentatively interpreted in terms of magma ascent controlled by deep-seated shear zones. Further uplift and exhumation of the crystallized plutons was followed by rapid deposition of batholith-derived conglomerates and arkoses in a marginal basin represented by the Limingen Group. The age of the Nesåa Batholith fills the gap in reported ages for Caledonian magmatism, between the Early to Middle Ordovician, oceanic to continental margin type, arc sequences of Laurentian palaeotectonic affinity, and the Late Ordovician–Early Silurian batholith complexes of interpreted Laurentian margin affinity. It is interpreted as an early phase of the more extensive plutonism recorded in the Bindal Batholith of the Uppermost Allochthon to the west. Our model implies that the Early Ordovician oceanic arc sequences of the Gjersvik Nappe were deformed and accreted on to Laurentian margin lithologies prior to Late Ordovician times. This composite crustal assemblage was the source for the voluminous quartz monzodioritic intrusions of the Nesåa Batholith, which formed by partial melting due to ponding of subduction-related mantle derived mafic magmas either within or at the base of the active continental margin.

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Formation of a Late Cretaceous continental margin arc and an Early Cenozoic back-arc basin in the Kyrenia Range, northern Cyprus related to S-Neotethyan subduction

10.5194/egusphere-egu2020-7260 ◽

2020 ◽

Author(s):

Guohui Chen ◽

Alastair Robertson

Keyword(s):

Continental Margin ◽

Late Cretaceous ◽

Active Continental Margin ◽

Granitic Rocks ◽

Arc Magmatism ◽

Marginal Basin ◽

Thrust Sheets ◽

Basin Formation ◽

Se Turkey ◽

Early Cenozoic

<p>Field, geochemical and geochronological research on Late Cretaceous and Early Cenozoic volcanic rocks in Kyrenia Range provide constraints on the tectono-magmatic evolution of the northerly, active continental margin of the Southern Neotethys. Field mapping in the western Kyrenia Range demonstrates that frontal (southerly) thrust sheets are dominated by felsic volcanogenic rocks. U-Pb zircon dating indicates that the felsic volcanics erupted at 72.9 &#177; 1.0 Ma (Late Campanian). These volcanics are interpreted as the products of sub-aqueous continental margin arc volcanism based on geochemical evidence. The exposed arc volcanics are somewhat younger than arc-derived volcaniclastic sediments in W Cyprus (80.1 &#177; 1.1 Ma), and are also younger than arc-related granitic rocks (88-82 Ma) cutting the Tauride active continental margin (Malatya-Keban platform) in SE Turkey. Structurally higher (more northerly) imbricate thrust sheets include Late Cretaceous (Maastrichtian) and Early Cenozoic basalts that are underlain by a Mesozoic continental carbonate platform (metamorphosed), and interbedded with pelagic and redeposited carbonates that formed in an active continental margin setting. The basalts have within-plate geochemical characteristics, although with a variable subduction influence in some areas (e.g., western Kyrenia Range) that could be either be contemporaneous or inherited from Late Cretaceous (c. 70-80 Ma) subduction. Modern and ancient comparisons (e.g., Tyrrhenian Sea) suggest that the basaltic rocks represent incipient, extensional marginal basin formation. Integration with comparable evidence of continental margin arc magmatism in SE Turkey and elsewhere provides a picture of arc magmatism and marginal basin formation along an active continental margin, prior to collision during the Miocene.</p>

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Nature and origin of the volcanic ash beds near the Permian–Triassic boundary in South China: new data and their geological implications

Geological Magazine ◽

10.1017/s001675681900133x ◽

2019 ◽

Vol 157 (4) ◽

pp. 677-689 ◽

Cited By ~ 3

Author(s):

Binsong Zheng ◽

Chuanlong Mou ◽

Renjie Zhou ◽

Xiuping Wang ◽

Zhaohui Xiao ◽

...

Keyword(s):

Trace Element ◽

Continental Margin ◽

South China ◽

Volcanic Ash ◽

Active Continental Margin ◽

Main Body ◽

Early Triassic ◽

Late Permian ◽

Triassic Boundary ◽

Permian Triassic Boundary

AbstractPermian–Triassic boundary (PTB) volcanic ash beds are widely distributed in South China and were proposed to have a connection with the PTB mass extinction and the assemblage of Pangea. However, their source and tectonic affinity have been highly debated. We present zircon U–Pb ages, trace-element and Hf isotopic data on three new-found PTB volcanic ash beds in the western Hubei area, South China. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons yields ages of 252.2 ± 3.6 Ma, 251.6 ± 4.9 Ma and 250.4 ± 2.4 Ma for these three volcanic ash beds. Zircons of age c. 240–270 Ma zircons have negative εHf(t) values (–18.17 to –3.91) and Mesoproterozoic–Palaeoproterozoic two-stage Hf model ages (THf2) (1.33–2.23 Ga). Integrated with other PTB ash beds in South China, zircon trace-element signatures and Hf isotopes indicate that they were likely sourced from intermediate to felsic volcanic centres along the Simao–Indochina convergent continental margin. The Qinling convergent continental margin might be another possible source but needs further investigation. Our data support the model that strong convergent margin volcanism took place around South China during late Permian – Early Triassic time, especially in the Simao–Indochina active continental margin and possibly the Qinling active continental margin. These volcanisms overlap temporally with the PTB biocrisis triggered by the Siberian Large Igneous Province. In addition, our data argue that the South China Craton and the Simao–Indochina block had not been amalgamated with the main body of Pangea by late Permian – Early Triassic time.

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