Zircon U-Pb-Hf isotopes, bulk-rock geochemistry and Sr-Nd-Pb isotopes from late Neoproterozoic basement in the Mahneshan area, NW Iran: Implications for Ediacaran active continental margin along the northern Gondwana and constraints on the late Oligocene crustal anatexis

2018 ◽  
Vol 57 ◽  
pp. 48-76 ◽  
Author(s):  
Maryam Honarmand ◽  
Wenjiao Xiao ◽  
Ghasem Nabatian ◽  
Morgan L. Blades ◽  
Mozaniel C. dos Santos ◽  
...  
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Pb Isotopes ◽  
Hf Isotopes ◽  
Late Oligocene ◽  
Bulk Rock ◽  
Crustal Anatexis ◽  
Nw Iran ◽  
Late Neoproterozoic

scholarly journals Relationships between Alluvial Facies/Depositional Environments, Detrital Zircon U-Pb Geochronology, and Bulk-Rock Geochemistry in the Cretaceous Neungju Basin (Southwest Korea)

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1023
Author(s):  
Hyojong Lee ◽  
Min Gyu Kwon ◽  
Seungwon Shin ◽  
Hyeongseong Cho ◽  
Jong-Sun Kim ◽  
...  
Keyword(s):  
Continental Margin ◽  
Detrital Zircon ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Depositional Environments ◽  
Source Rocks ◽  
Bulk Rock ◽  
Zircon Age ◽  
Margin Setting ◽  
Weathering Intensity

Zircon U-Pb geochronology and bulk-rock geochemistry analyses were carried out to investigate their relationship with depositional environments of the non-marine Neungju Basin sediments in South Korea. The Neungju Basin was formed in an active continental margin setting during the Late Cretaceous with associated volcanism. Detrital zircon age distributions of the Neungju Basin reveal that the source rocks surrounding the basin supplied sediments into the basin from all directions, making different zircon age populations according to the depositional environments. Mudstone geochemistry with support of detrital zircon U-Pb age data reveals how the heterogeneity affects the geochemical characteristics of tectonic setting and weathering intensity. The sediments in the proximal (alluvial fan to sandflat) and distal (playa lake) environments differ compositionally because sediment mixing occurred exclusively in the distal environment. The proximal deposits show a passive margin signature, reflecting their derivation from the adjacent metamorphic and granitic basement rocks. The distal deposits properly indicate an active continental margin setting due to the additional supply of reworked volcaniclastic sediments. The proximal deposits indicate a minor degree of chemical weathering corresponding to fossil and sedimentological records of the basin, whereas the distal deposits show lower weathering intensity by reworking of unaltered volcaniclastic detritus from unstable volcanic and volcaniclastic terranes. Overall, this study highlights that compositional data obtained from a specific location and depositional environments may not describe the overall characteristic of the basin.

A newly discovered Late Cretaceous metamorphic belt along the active continental margin of the Neo-Tethys ocean

2021 ◽  
Author(s):  
Dan Wang ◽  
Fu-Lai Liu ◽  
Richard Palin ◽  
Jia-Min Wang ◽  
Mathias Wolf ◽  
...  
Keyword(s):  
Continental Margin ◽  
Late Cretaceous ◽  
Regional Scale ◽  
Active Continental Margin ◽  
Granulite Facies ◽  
High Grade ◽  
Crustal Anatexis ◽  
Metamorphic Belt ◽  
Granulite Facies Metamorphism ◽  
Tethys Ocean

High-grade metamorphic rocks and crustal melts provide crucial evidence for growth and differentiation of the continental crust, and are widespread in collisional orogens. However, their importance in the evolution of continental arcs remains poorly understood. Metamorphism and related anatexis in the preserved continental margin of the Neo-Tethys ocean serves as a key natural laboratory to investigate this process. Along the Neo-Tethyan arc margin, the Gaoligong shear zone, Yunnan region of China, is an important locality for linking Lhasa in the north with Sibumasu and Burma in the south. Here, Late Cretaceous granulite-facies metamorphism and crustal anatexis have been identified for the first time in the Gaoligong area. Zircon and monazite U-Pb dating indicates that S-type granites formed at 87−73 Ma, granites and buried pelitic sediments were simultaneously metamorphosed at 75−70 Ma during Neo-Tethyan subduction, and all lithologies were overprinted by a younger 40−30 Ma magmatic and strike-slip event related to India-Asia collision. Phase equilibria modeling of high-grade anatectic gneiss in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicates peak pressure-temperature (P−T) conditions of 780−800 °C and 6.5−7.5 kbar and defines a cooling and decompressional P−T path for the metapelites. This demonstrates that sediments within the Neo-Tethyan active continental arc were buried to >20 km depth at 75−70 Ma. In combination with the metamorphic record of the Lhasa, Burma, and Sibumasu blocks, an extensive Late Cretaceous metamorphic belt must have formed along the Neo-Tethyan subduction zone. This spatially correlates with coeval gabbro-diorite suites exposed in the Gangdese, Sibumasu and Burma terranes that were triggered by thinning of the lithospheric mantle. This prolonged Late Cretaceous mantle-derived magmatism and lithospheric thinning may have provided a regional-scale heat source for high-grade metamorphism and crustal anatexis along the active continental margin of the Neo-Tethys ocean.

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

2019 ◽  
Vol 157 (4) ◽  
pp. 677-689 ◽  
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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