scholarly journals Geochemistry of Late Triassic pelitic rocks in the NE part of Songpan-Ganzi Basin, western China: Implications for source weathering, provenance and tectonic setting

2012 ◽  
Vol 3 (5) ◽  
pp. 647-660 ◽  
Author(s):  
Yan Tang ◽  
Longkang Sang ◽  
Yanming Yuan ◽  
Yunpeng Zhang ◽  
Yunlong Yang
Keyword(s):  
Tectonic Setting ◽  
Western China ◽  
Late Triassic ◽  
Pelitic Rocks

Mineral ages and zircon Hf isotopic composition of the Andong ultramafic complex: implications for the evolution of Mesozoic subduction system and subcontinental lithospheric mantle beneath SE Korea

2013 ◽  
Vol 151 (5) ◽  
pp. 765-776 ◽  
Author(s):  
GI YOUNG JEONG ◽  
CHANG-SIK CHEONG ◽  
KEEWOOK YI ◽  
JEONGMIN KIM ◽  
NAMHOON KIM ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Eastern China ◽  
Mantle Xenoliths ◽  
Late Triassic ◽  
Magmatic Differentiation ◽  
Suprasubduction Zone ◽  
Ultramafic Complex ◽  
Yeongnam Massif ◽  
Subduction System

AbstractThe Phanerozoic subduction system of the Korean peninsula is considered to have been activated by at least Middle Permian time. The geochemically arc-like Andong ultramafic complex (AUC) occurring along the border between the Precambrian Yeongnam massif and the Cretaceous Gyeongsang back-arc basin provides a rare opportunity for direct study of the pre-Cretaceous mantle wedge lying above the subduction zone. The tightly constrained SHRIMP U–Pb age of zircons extracted from orthopyroxenite specimens (222.1±1.0 Ma) is indistinguishable from the Ar/Ar age of coexisting phlogopite (220±6 Ma). These ages represent the timing of suprasubduction zone magmatism likely in response to the sinking of cold and dense oceanic lithosphere and the resultant extensional strain regime in a nascent arc environment. The nearly coeval occurrence of a syenite-gabbro-monzonite suite in the SW Yeongnam massif also suggests an extensional tectonic setting along the continental margin side during Late Triassic time. The relatively enriched ɛHf range of dated zircons (+6.2 to −0.6 at 222 Ma) is in contrast to previously reported primitive Sr–Nd–Hf isotopic features of Cenozoic mantle xenoliths from Korea and eastern China. This enrichment is not ascribed to contamination by the hypothetical Palaeozoic crust beneath SE Korea, but is instead attributable to metasomatism of the lithospheric mantle during the earlier subduction of the palaeo-Pacific plate. Most AUC zircons show a restricted core-to-rim spread of ɛHf values, but some grains testify to the operation of open-system processes during magmatic differentiation.

The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

2021 ◽  
Author(s):  
Banafsheh Vahdati ◽  
Seyed Ahmad Mazaheri
Keyword(s):  
Subduction Zones ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Late Triassic ◽  
Common Belief ◽  
Thrust Tectonics ◽  
Wide Range ◽  
Lree Enrichment ◽  
Granitoid Rocks

<p>Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO<sub>2</sub>: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na<sub>2</sub>O and K<sub>2</sub>O show a positive correlation with silica while Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO, Fe<sub>2</sub>O<sub>3</sub>, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.</p>

scholarly journals Emplacement mechanism of Late Triassic granitic Dushan pluton, North China and its tectonic implications

2020 ◽  
Author(s):  
Huabiao Qiu ◽  
Wei Lin ◽  
Yan Chen ◽  
Michel Faure
Keyword(s):  
Solid State ◽  
North China ◽  
Tectonic Setting ◽  
Late Triassic ◽  
Gravity Modeling ◽  
Magnetic Fabrics ◽  
Southeastern Margin ◽  
Emplacement Mechanism ◽  
Southwestern Margin ◽  
Magnetic Lineations

<p>To better understand the Late Triassic tectonic setting in the northern North China Craton (NCC), a multidisciplinary investigation, including structural geology, geochronology, anisotropy of magnetic susceptibility (AMS) and gravity modeling, has been carried out in the Dushan pluton. The Dushan pluton consists of monzogranite and biotite-rich facies along the pluton margin without sharp contact between them. The granite varies southwestwards from isotropic texture to arcuate gneissic structures, with locally mylonitic structures. The intensity of solid-state deformation increases southwestwards across the pluton, leaving preserved magmatic fabrics in the northeastern part. The compatible outward dipping magmatic and solid-state magnetic fabrics, together with mesoscopic fabrics, define an elliptic dome-like pattern with a NE-SW oriented long axis, despite the fabrics dip inwards in the southeastern margin of the pluton. Combining gravity modeling, the Dushan pluton presents an overall tabular or tongue-like shape with a northeastern root. The magnetic lineations nearly strike NE-SW, concordant with the stretching lineations observed in the mylonitic zones. We propose the emplacement mode that the Dushan pluton emplaced southwards through the feeder zone in its northeast, beginning probably with a sill. The later successive magma batches may laterally and upwardly inflate, deform and even recrystallize the former cool-down magma. This inflation forms an arcuate, gneissic to mylonitic foliation in the southwestern margin. The Dushan pluton is considered as typically post-tectonic in emplacement, recording a Late Triassic post-tectonic setting of the northern NCC.</p>

scholarly journals Metallogenic Epoch and Tectonic Setting of Saima Niobium Deposit in Fengcheng, Liaoning Province, NE China

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 80 ◽  
Author(s):  
Nan Ju ◽  
Yun-Sheng Ren ◽  
Sen Zhang ◽  
Zhong-Wei Bi ◽  
Lei Shi ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Nepheline Syenite ◽  
Large Scale ◽  
Tectonic Setting ◽  
Liaoning Province ◽  
Late Triassic ◽  
Ne China ◽  
The North ◽  
Heavy Rare Earth Elements

The Saima deposit is a newly discovered niobium deposit which is located in the eastern of Liaoning Province, NE China. Its mineralization age and geochemical characteristics are firstly reported in this study. The Nb orebodies are hosted by the grey–brown to grass-green aegirine nepheline syenite. Detailed petrographical studies show that the syenite consists of orthoclase (~50%), nepheline (~30%), biotite (~15%) and minor arfvedsonite (~3%) and aegirine (~2%), with weak hydrothermal alteration dominated by silicification. In situ LA-ICP-MS zircon U-Pb dating indicates that the aegirine nepheline syenite was emplaced in the Late Triassic (229.5 ± 2.2 Ma), which is spatially, temporally and genetically related to Nb mineralization. These aegirine nepheline syenites have SiO2 contents in the range of 55.86–63.80 wt. %, low TiO2 contents of 0.36–0.64 wt. %, P2O5 contents of 0.04–0.11 wt. % and Al2O3 contents of more than 15 wt. %. They are characterized by relatively high (K2O + Na2O) values of 9.72–15.51 wt. %, K2O/Na2O ratios of 2.42–3.64 wt. % and Rittmann indexes (σ = [ω(K2O + Na2O)]2/[ω(SiO2 − 43)]) of 6.84–17.10, belonging to the high-K peralkaline, metaluminous type. These syenites are enriched in large ion lithophile elements (LILEs, e.g., Cs, Rb and Ba) and light rare earth elements (LREEs) and relatively depleted in high field strength elements (HFSEs, e.g., Nb, Zr and Ti) and heavy rare earth elements (HREEs), with transitional elements showing an obvious W-shaped distribution pattern. Based on these geochronological and geochemical features, we propose that the ore-forming intrusion associated with the Nb mineralization was formed under post-collision continental-rift setting, which is consistent with the tectonic regime of post-collision between the North China Craton and Paleo-Asian oceanic plate during the age in Ma for Indosinian (257–205 Ma). Intensive magmatic and metallogenic events resulted from partial melting of lithospheric mantle occurred during the post-collisional rifting, resulting in the development of large-scale Cu–Mo mineralization and rare earth deposits in the eastern part of Liaoning Province.

Early Mesozoic granitoids from SW Vietnam and SE Cambodia – an example of the southeastern extension of the Southeast Asian granite belt

2020 ◽  
Author(s):  
Anh Nong ◽  
Christoph Hauzenberger ◽  
Daniela Gallhofer ◽  
Sang Dinh
Keyword(s):  
Large Scale ◽  
Early Stage ◽  
Tectonic Setting ◽  
Biotite Granite ◽  
Coarse Grained ◽  
Late Triassic ◽  
Late Paleozoic ◽  
Western Boundary ◽  
Early Mesozoic ◽  
Granite Belt

<p>Early Mesozoic magmatism in Indochina and its vicinities in Sundaland (SE Asia) has been usually ascribed to be in connection with one of three approximately coeval tectonic regimes: 1) the Indochina-Sibumasu amalgamation leading to the closure of the Paleotethys during the Late Paleozoic – Early Mesozoic forming the Thai-Malaysia tin-bearing granite belt, 2) the Indochina-South China amalgamation along the northern boundary of Indochina closing another branch of the Paleotethys during Late Paleozoic – Triassic times, and 3) the early stage of an active margin with subduction of the Paleo-Pacific plate during Triassic-Jurassic times.</p><p>Scattered granitic plutons (185–210 Ma) located in southern Cambodia and some islands in southernmost Vietnam are distributed along the N-S Rach Gia-Nam Can fault which is a large-scale fault active during the Early Mesozoic. The studied rocks can be distinguished based on petrological features: weakly foliated biotite-rich granite (Hon Khoai Island, SW Vietnam), biotite-tourmaline-bearing granite (Hon Da Bac Island, SW Vietnam), and coarse-grained biotite granite (Tamao, SE Cambodia). The Honkhoai granites are a range of dark to light coloured granites due to a variation in biotite content and display a foliation. They usually contain amphibole, ilmenite, and monazite. The Hondabac granites comprise dark-colored granodiorites and granites with biotite, tourmaline, ilmenite, apatite, fluorite, epidote, and subordinate titanite. The Tamao granites are mainly composed of biotite aggregates with sporadic muscovite and accessory phases such as ilmenite, apatite, and fluorite.</p><p>Zircon U-Pb ages yield 189 ± 1 to 206 ± 2 Ma for the Honkhoai rocks, 192 ± 1 to 202 ± 1 Ma for the Hondabac rocks, and 189 ± 2 Ma for the Tamao rocks. Apparently, these Late Triassic - Early Jurassic granitoids are chronologically consistent with all three tectonic events. However, geographical and geochemical arguments favor a connection to the Thai-Malaysia tin-bearing granites. Similarities include high silica content and predominantly high-K to calc-alkaline affinities. Trace element composition is characterized by enrichments in Cs, Rb, Th, U, and Pb, and depletion in Ba, Sr, Nb, P, and Ti. All analyzed rock samples show (La/Yb)n values of 4.05–17.27 and negative Eu anomalies (Eu/Eu*=0.15–0.65). The whole-rock and biotite chemistry point to an arc-related tectonic setting for the Hondabac rock, while the Honkhoai and Tamao rocks are ambiguous in the tectonic regime but likely close to syn-collision and within-plate field, respectively. Geobarometry of the Honkhoai rocks using the Al-in-amphibole geobarometer yields crystallization pressure up to 3 kbar.</p><p>We conclude that the studied rocks formed during the closure of the Palaeotethys along the western boundary of the Indochina block, particularly similar to the Thai-Malaysia granite belt. Hence, the Sukhothai-Chantaburi Terrane may be extended southeastward as far as to the Hon Khoai Island (Southernmost Vietnam).</p>

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