Jurassic Accretionary Complex Research Articles

Ulban Terrane (Zone) as Part of the Jurassic Accretionary Complex of the Sikhote-Alin Orogenic Belt

Ulban Terrane (Zone) as Part of the Jurassic Accretionary Complex of the Sikhote-Alin Orogenic Belt

УЛЬБАНСКИЙ ТЕРРЕЙН (ЗОНА) КАК ЧАСТЬ ЮРСКОГО АККРЕЦИОННОГО КОМПЛЕКСА СИХОТЭ-АЛИНСКОГО ОРОГЕННОГО ПОЯСА

New data are reported on the age of Triassic-Jurassic cherts replaced up the section by siliceous mudstones, and then by mudstones, which together with basalts form thin (up to hundreds of meters) plates and lenses that pinch out along the strike at different levels of the multi-kilometer terrigenous section of the Ulban terrane (zone). In the Nimelen subzone (the Albazino gold deposit area), their time interval of formation is Norian-Early Toarcian and that of host terrigenous deposits is Pliensbachian-Bathonian. In the Mewachan subzone, cherts and siliceous–clayey rocks are Middle Triassic-Callovian in age and terrigenous rocks are Middle-Late Jurassic (including Tithonian). A comparison of deposits of the Ulban terrane with deposits of the Samarka terrane which are well-studied and similar in age and composition allows us to consider the Ulban terrane (zone) as part of the Jurassic accretionary complex of the Sikhote-Alin orogenic belt. There are also sufficient indications to believe that its structural features are consistent with the subduction model. The basis for this is that the Triassic-Jurassic cherts and siliceous–clayey rocks accumulated for about 45 million years at a rate of about 1.8 m/million years characteristic for the oceanic plate sedimentary cover. At the same time, a gradual transition from cherts to mudstones is observed evidencing the movement of the oceanic plate into the subduction zone. The inclusion of its fragments in the terrigenous section is the result of their being detached in the trench and under the overhanging slab. Tectono-stratigraphic columns of the subzones of the Ulban terrane and a scheme of zoning of the Jurassic accretionary prism have been compiled with four structural-age levels along its entire length.

Petrogenesis of Jurassic granitic plutons in the Yanbian area, NE China: Implications for the subduction history of the Paleo-Pacific Plate

It is widely accepted that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent began during the early Mesozoic; however, the details of the subduction process remain uncertain. This paper presents new zircon U–Pb–Hf and whole-rock geochemical data for Jurassic intrusive rocks from the Yanbian area of NE China to provide a better understanding of the subduction history of the Paleo-Pacific Plate. Zircon U–Pb dating results reveal that three stages of Jurassic magmatism are recorded in the Yanbian area, namely, Early Jurassic (188–179 Ma), Middle Jurassic (172–163 Ma), and Late Jurassic (158–156 Ma). Early Jurassic intrusive rocks from the Yanbian area are predominantly calc-alkaline gabbro, gabbro-diorite, quartz monzonite, granodiorite, and syenogranite. These geochemical features and rock associations are indicative of formation in an active continental margin setting related to the initial subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The Early Jurassic granitoids were formed mainly by the partial melting of heterogeneous lower crust. The Middle Jurassic granitoids are geochemically similar to adakites and have εHf(t) values of + 2.0 to + 10.1. These rocks are inferred to have been derived from magmas generated by the partial melting of thickened juvenile lower-crustal material. Their formation was related to the subduction of the Paleo-Pacific Plate. Late Jurassic adakites in the Yanbian area formed in a compressional tectonic setting. Their negative εHf(t) values (−17.2 to − 8.6) and TDM2 ages (2025–1552 Ma) indicate that the primary magma was derived from the partial melting of ancient continental crust. Combining our data with the distribution of Late Jurassic igneous rocks in the NE Asian continental margin and the northward migration of Jurassic accretionary complexes along the margin, we conclude that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent during the Late Jurassic–earliest Early Cretaceous had a low angle of obliquity.

Early Permian rhyolite within a Jurassic accretionary complex in the NorthKitakami Belt and its attribution

Early Permian rhyolite within a Jurassic accretionary complex in the NorthKitakami Belt and its attribution

Detrital zircon U–Pb ages of the Miocene clastic sedimentary succession in the Shidara Basin, central Japan: Implications for provenance changes and timing of collision between the Izu–Ogasawara and Honshu arcs

• Zircon U–Pb dating revealed provenance change in the middle of Miocene succession. • Deposition of Miocene strata was associated with the initial collision of two arcs. • Collision between the two arcs was initiated at around 17.4 ± 0.4 Ma. Collision of the Izu–Ogasawara and Honshu arcs occurred during the Miocene. The Miocene Hokusetsu Subgroup in the western part of the Izu collision zone is considered to be a key formation that might record the timing of the initial collision. To clarify the timing, we conducted provenance analysis based on detrital zircon U–Pb ages of the Hokusetsu Subgroup. Zircon ages show a Late Cretaceous peak in the strata below the Umedaira Sandstone Member and a peak around 100 Ma in the lower Umedaira Sandstone Member. Furthermore, the proportions of Jurassic to Proterozoic ages increase in the upper part of the sandstone member and the overlying horizons. The zircon ages and the petrographical characteristics of detritus suggest that the formations below the lower Umedaira Sandstone Member were derived from the Ryoke Plutonic Rocks, but the formations above the upper Umedaira Sandstone Member were derived from a Jurassic accretionary complex. Deposition of the Umedaira Sandstone Member suggests uplift of the provenance areas, which are inferred to have been the 100 Ma Ryoke Plutonic Rocks to the northeast and east of the Shidara Basin and Jurassic accretionary complexes farther to the northeast and east. The provenance change during deposition of the Umedaira Sandstone Member was caused by collision of the Izu–Ogasawara and Honshu arcs. Therefore, the collision is considered to have begun around 17.4 ±0.7 Ma constrained by depositional age of the Umedaira Sandstone Member.

СТРУКТУРНАЯ ПОЗИЦИЯ, ПЕТРОГЕОХИМИЧЕСКАЯ И ПЕТРОПАЛЕОМАГНИТНАЯ ХАРАКТЕРИСТИКА ВУЛКАНИТОВ НИЛАНСКОГО ТЕРРЕЙНА (ЗОНА СОЧЛЕНЕНИЯ МОНГОЛО-ОХОТСКОГО И СИХОТЭ-АЛИНЬСКОГО ОРОГЕНОВ) И ГЕОДИНАМИЧЕСКИЕ ВЫВОДЫ

The paper presents the results of structural, geochemical, magnetic and paleomagnetic studies on Mesozoic rocks of the Nilan terrane, which from the north flank on the Paleozoic rocks of the Paukan block (52.0°N, 135.6°E). Jurassic and Triassic (?) multiple disturbance deposits of the terrane were found to be fragments of the Middle-Late Jurassic accretionary complex with accumulations of older oceanic rocks varying in thickness and the oceanic plate with completely destroyed stratigraphy. Basic and intermediate volcanic rocks hosted within Jurassic and Triassic (?) sedimentary rocks of the terrane are of oceanic origin. Based on geochemical and paleomagnetic data, it is assumed that the volcanic rocks formed near the equator in geodynamic settings of mid-ocean ridge and intraplate ocean islands.

Metamorphic Ages of the Jurassic Accretionary Complexes in the Kanto Mountains, Central Japan, Determined by K–Ar Dating of Illite: Implications for the Tectonic Relationship between the Chichibu and Sanbagawa Belts

To determine the metamorphic ages of the accretionary complexes in the Northern Chichibu Belt in SW Japan, K–Ar dating was conducted using weakly metamorphosed sedimentary rocks collected from the Kanto Mountains, Central Japan. Whole-rock ages were obtained for chert and red shale samples, and the mineral ages of fine-grained illite with a grain size of less than 4 μm were obtained for chert, red shale, mudstone, acidic tuff, and basic tuff. The K–Ar ages of chert and red shale presented large variations, with systematically older ages compared to those of mudstone and tuff in the same strata. The influence of submarine hydrothermal activities on chert and red shale before subduction is a possible cause of this deviation. The illite samples, which were fractionated into four grain-size classes using a suspension method, yielded older ages and higher illite crystallinity (i.e., smaller values of Kübler’s crystallinity index) for larger grain-size classes. The peak metamorphic ages were determined from the K–Ar ages of the 3–4 μm class illite in mudstone and tuff. The Late Jurassic to the Earliest Cretaceous accretionary complex of the lowest structural unit (Kashiwagi Unit) was dated within a small range between 117–110 Ma, which is distinctly older than the K–Ar ages of white mica reported from the Sanbagawa Belt. The peak metamorphic age of acidic tuff (113 Ma) at the type locality of the Mikabu Greenstones indicates that the subducted Mikabu seamount is a constituent of the Kashiwagi Unit. The peak metamorphic ages of the Manba and Kamiyoshida Units were obtained as 132–107 Ma and 163–144 Ma, respectively. Major structural discontinuity is suggested within the Middle Jurassic accretionary complexes.

Field excursion guide: Jurassic accretionary complex in the Kiryu and Ashikaga District, southwestern Ashio Mountains, central Japan

Field excursion guide: Jurassic accretionary complex in the Kiryu and Ashikaga District, southwestern Ashio Mountains, central Japan

Increased Terrigenous Supply to the Pelagic Panthalassa Superocean Across the Carnian Pluvial Episode: A Possible Link With Extensive Aridification in the Pangean Interior

In the Late Triassic, a global environmental change called the Carnian Pluvial Episode (CPE) emerged, causing major biological turnover. The CPE has been recognized by siliciclastic input to sedimentary basins, multiple carbon isotope perturbations, and climate proxies for humidification. The CPE is considered to have been associated with increased atmospheric pCO2 from eruptions of large igneous provinces. However, the nature of this global environmental perturbation on the continents is still not well understood. Here we present a geochemical analysis of a pelagic deep-sea bedded chert sequence across the CPE in the Jurassic accretionary complex of Mino terrane, central Japan. Fluctuations in terrigenous material supply were reconstructed using Principal Component Analysis of major element compositions. The first principal component positively correlates with elements enriched in clay minerals such as Al2O3, whereas it negatively correlates with CaO, P2O5, and MnO, derived from apatite and manganese. A sudden increase in terrigenous supply was detected around the Julian/Tuvalian boundary, suggesting that CPE-related siliciclastic input also occurred in the abyssal plain environment. The terrigenous supply returned to the pre-CPE state in the Tuvalian. Since the terrigenous material supplied to the abyssal plain is thought to be derived from eolian dust blown from continental arid regions, the increasing terrigenous supply detected in the pelagic deep-sea chert succession may indicate extensive aridification. This result seems to conflict with the common view of the CPE as a humidification event. This contradiction possibly suggests that the extensive aridification occurred within the interior of the supercontinent Pangea, while hydrological circulation enhanced on the coastal region during the CPE.

Castellation Incorporating Geology and Geography: Tenth–Sixteenth Century Castles on Chert of a Jurassic Accretionary Complex in Central Japan

Castellation Incorporating Geology and Geography: Tenth–Sixteenth Century Castles on Chert of a Jurassic Accretionary Complex in Central Japan

Pyroclastic dyke intruded into the Jurassic accretionary complex along the Sagami River, east of Mt. Otowa, Otsu City, Shiga Prefecture, Central Japan

Pyroclastic dyke intruded into the Jurassic accretionary complex along the Sagami River, east of Mt. Otowa, Otsu City, Shiga Prefecture, Central Japan

Conodont and radiolarian biostratigraphic age constraints on Carnian (Upper Triassic) chert-hosted stratiform manganese deposits from Panthalassa: Formation of deep-sea mineral resources during the Carnian pluvial episode

Numerous stratiform manganese deposits occur in the Permian to Jurassic bedded chert successions of the Jurassic accretionary complexes of the Chichibu, Mino–Tamba, and North Kitakami belts in Japan. These accretionary complexes consist of deep-sea sediments accumulated in a pelagic, open-ocean setting within the Panthalassa Ocean. Although the depositional ages and processes of the Permian and Jurassic manganese deposits in these accretionary complexes have been studied, the Triassic bedded chert-hosted stratiform manganese deposits are poorly understood. We investigated the occurrence and stratigraphic distribution of Triassic stratiform manganese deposits in Japan, constraining their ages by means of integrated conodont–radiolarian biostratigraphy. On the basis of the conodont and radiolarian biostratigraphies, the depositional age of the Triassic manganese deposits was constrained to the latest Julian to earliest Tuvalian (mid-Carnian). This age indicates that the formation of the Triassic manganese deposits occurred contemporaneously with the last eruptive phase of the Wrangellia Large Igneous Province (LIP) volcanism and subsequent changes in the deep-sea redox conditions in the Panthalassa Ocean during the Carnian pluvial episode (CPE). Therefore, these manganese deposits may have been formed with the hydrothermal activity associated with the eruption of the Wrangellia LIP and/or the subsequent changes in marine redox conditions in the CPE.

Radiolarians from Jurassic accretionary complex of the Ashio belt in the Kiryu and Ashikaga District (Quadrangle series 1:50,000), central Japan

Radiolarians from Jurassic accretionary complex of the Ashio belt in the Kiryu and Ashikaga District (Quadrangle series 1:50,000), central Japan

Geochemical characteristics of basaltic rocks from the Omama Complex of Jurassic accretionary complex in the Ashio Mountains, central Japan

Geochemical characteristics of basaltic rocks from the Omama Complex of Jurassic accretionary complex in the Ashio Mountains, central Japan

Occurrence report of Triassic and Jurassic radiolarians from the Jurassic accretionary complexes of the Ashio belt in eastern Mt. Narukami, Ashio Mountains, central Japan

Occurrence report of Triassic and Jurassic radiolarians from the Jurassic accretionary complexes of the Ashio belt in eastern Mt. Narukami, Ashio Mountains, central Japan

Geology and correlation of Jurassic accretionary complex in the Ashio Mountains, central Japan: Investigation on the Kiryu and Ashikaga District (Quadrangle series 1:50,000)

Geology and correlation of Jurassic accretionary complex in the Ashio Mountains, central Japan: Investigation on the Kiryu and Ashikaga District (Quadrangle series 1:50,000)

Radiolarians and foraminifers from the Omama Complex of Jurassic accretionary complex in the Ashio Mountains, central Japan

Radiolarians and foraminifers from the Omama Complex of Jurassic accretionary complex in the Ashio Mountains, central Japan

Geochemical features and origin of basalt within the Jurassic accretionary complex in the southwestern margin of the North Kitakami Belt, Northeast Japan

Geochemical features and origin of basalt within the Jurassic accretionary complex in the southwestern margin of the North Kitakami Belt, Northeast Japan

Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif, Northeast Japan: New evidence for correlation with Southwest Japan

AbstractThe Kitakami Massif of the Tohoku district, Northeast Japan, consists mainly of the South Kitakami Belt (Silurian–Cretaceous forearc shallow‐marine sediments, granitoids, and forearc ophiolite) and the North Kitakami Belt (a Jurassic accretionary complex). The Nedamo Belt (a Carboniferous accretionary complex) occurs as a small unit between those two belts. An accretionary unit in the Nedamo Belt is lithologically divided into the Early Carboniferous Tsunatori Unit and the age‐unknown Takinosawa Unit. In order to constrain the accretionary age of the Takinosawa Unit, detrital zircon U–Pb dating was conducted. The new data revealed that the youngest cluster ages from sandstone and tuffaceous rock are 257–248 Ma and 288–281 Ma, respectively. The Early Triassic depositional age of the sandstone may correspond to a period of intense magmatic activity in the eastern margin of the paleo‐Asian continent. A 30–40 my interval between the youngest cluster ages of the sandstone and the tuffaceous rock can be explained by the absence of syn‐sedimentary zircon in the tuffaceous rock. The new detrital zircon data suggest that the Takinosawa Unit can be distinguished as an Early Triassic accretionary complex distinct from the Early Carboniferous Tsunatori Unit. This recognition establishes a long‐duration northeastward younging polarity of accretionary units, from the Carboniferous to Early Cretaceous, in the northern Kitakami Massif. Lithological features and detrital zircon spectra suggest that the Early Triassic Takinosawa Unit in the Nedamo Belt is comparable with the Hisone and Shingai units in the Kurosegawa Belt in Shikoku. The existence of this Early Triassic accretionary complex strongly supports a pre‐Jurassic geotectonic correlation and similarity between Southwest and Northeast Japan.

Radiolarians from Jurassic accretionary complex of the Chichibu belt in the western Akaishi Mountains and chert pebbles of the Miocene Wada Formation in Minami-Shinano, central Japan

Radiolarians from Jurassic accretionary complex of the Chichibu belt in the western Akaishi Mountains and chert pebbles of the Miocene Wada Formation in Minami-Shinano, central Japan