Detrital heavy minerals constraints on the Triassic tectonic evolution of the West Qinling terrane, NW China: implications for understanding subduction of the Paleotethyan Ocean

We have examined the Triassic sediments in the west Qinling terrane, northeastern Tibet. These sediments consist mainly of flysch and shallow-sea and fluvial deposits with abundant lithic and heavy mineral detritus, sandwiched between and overlying Late Paleozoic and Early-Middle Triassic ophiolitic mélanges. Volcanic and metamorphic detritus dominates the lithic component of Lower Triassic sandstones accompanied by high Cr-spinel, pyroxene, and magnetite contents, indicating a mixed ophiolite and metamorphic source. Detrital mineral geochemistry further suggests that ophiolitic, high-grade metamorphic, basic, and intermediate-acidic igneous rocks must have been exposed and deeply eroded in their source area. Abundances of zircon, rutile, garnet, tourmaline, and epidote are greater in the Middle Triassic samples, and granitic and volcanic sources are the major contributors of detrital clasts. Considering these new observations on sedimentary petrography and detrital heavy mineral geochemistry, along with published data on paleocurrents, detrital zircon U-Pb ages, sedimentary facies, and regional magmatism, we suggest that these Triassic sediments represent the sedimentary fill of a forearc basin that overlies a late Paleozoic ophiolitic complex. A south-facing Andean-type convergent continental margin system developed along the southern margin of the North China block during the Triassic, in response to northward subduction of the Paleotethyan Ocean

Anatexis of former arc magmatic rocks during oceanic subduction: A case study from the North Wulan gneiss complex

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.gr.2018.04.016 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Migmatites are widespread in the North Wulan gneiss complex from the South Qilian–North Qaidam orogenic belt, but their petrogenesis and ages are poorly constrained. Here, an integrated study of petrography, whole-rock geochemistry, geochronology, zircon trace element and Hf isotope analysis deciphers the nature and timing of partial melting in migmatitic amphibole-biotite gneiss. Zircon U–Pb geochronology reveals that the protoliths crystallized at 506–494 Ma followed by metamorphism and anatexis at ca. 465 to 450 Ma. Hafnium isotope compositions of inherited cores and anatectic rims are very similar, suggesting that partial melting occurred in a relatively closed isotopic system and new zircon rims grew via dissolution–reprecipitation of pre-existing zircon cores. Anatexis occurred by water-fluxed melting of mafic-intermediate rocks through the breakdown of biotite and growth of peritectic amphibole. The protolith of the migmatites records Cambrian arc magmatism in an active continental margin, which was induced by northward subduction of the South Qilian ocean slab. Contemporary arc-like magmatism and high-temperature/low-pressure metamorphism in the region suggest that anatexis in the North Wulan gneiss complex likely took place in a continental arc setting, which reflects the reworking of former arc magmatic rocks in a late stage of oceanic subduction.National Natural Science Foundation of China [41372207, 41772228, 41272221]China Scholarship Council [201606690007]Key Program of the Ministry of Land and Resources of China [DD20160022, 12120115069401, 1212011120159

Hualong Complex, South Qilian terrane: U-Pb and Lu-Hf constraints on Neoproterozoic micro-continental fragments accreted to the northern Proto-Tethyan margin

The Neoproterozoic Hualong Complex dominates the South Qilian terrane. It contains mafic to felsic magmatic rocks, cherts and turbiditic sediments, some of which have been metamorphosed to amphibolite grade and is traditionally regarded as a pre-Cambrian micro-continental block rifted from the South China plate. New U-Pb geochronology of morphologically complex zircons sheds light on the history of the complex. Garnet-bearing amphibolite and quartzite have detrital zircon U-Pb main peak ages of 1.47-1.78. Ga with youngest U-Pb ages of 967. Ma and 964. Ma. They are intruded by Neoproterozoic orthogneisses that crystallized between ca. 850 and 940. Ma. Psammitic paragneisses are dominated by 940-780. Ma detrital zircon populations with a youngest U-Pb weighted mean age of 721. ±. 3. Ma and a main peak at 906. Ma. Metamorphic overgrowths on older zircons record amphibolite facies metamorphism of the Hualong Complex and correspond to the emplacement of the younger plutonic rocks during the Early Paleozoic northward subduction of Proto-Tethyan oceanic lithosphere. 426. Ma and 455. Ma detrital zircon populations that originated from synkinematic granitoids dominate quartz-mica schist. Negative to positive εHf(t) values for both 940-850Ma granitic orthogneisses and intruding 460-410Ma granites suggest a crustal-mantle mixture source. Hf TDM1 model ages and inherited zircon U-Pb ages are the same as those for garnet-bearing amphibolites and psammitic gneiss indicating that late magmatic rocks were formed by melting of the accreted Neoproterozoic rocks

Petrogenesis and geological significance of the Late Indosinian adakitic granites in the East Kunlun Orogen

Objective  The Indosinian collision process of the East Kunlun Orogenic Belt remains a subject of debate. The newly discovered Triassic adakitic granites in the Xiaonanchuan area of East Kunlun provide new geological evidence that constrains the evolution of collisional orogenesis.   Methods  This study conducted petrological, geochemical, zircon U-Pb, and Lu-Hf isotopic analyses of the Moshigou and Bentoushan granitic intrusions in the Xiaonanchuan area to investigate their petrogenesis and tectonic settings. By integrating previous research on magmatism and sedimentation during the late Indosinian period within the East Kunlun Orogenic Belt, a preliminary discussion was conducted on collisional orogensis process.   Results and Conclusion  The Moshigou intrusion consists of granodiorite and monzogranite with zircon U-Pb ages of 209–208 Ma. The Bentoushan intrusion is composed of granodiorite with zircon U-Pb ages of 201–200 Ma. These granitoids have high SiO2 and Al2O3 contents and are rich in sodium. They also have high Sr contents (398×10−6–613×10−6) and Sr/Y ratios (50–97) and are depleted in heavy rare earth elements without Eu anomalies, exhibiting typical geochemical characteristics of adakitic rocks. The Moshigou granitoids have negative whole-rock εNd(t) (−3.60 to −3.34) and variable zircon εHf(t) (−1.3 to +5.9), indicating their derivation from the partial melting of the thickened lower crust. The Bentoushan granitoids have negative whole-rock εNd(t) (−1.65 to −1.55) and positive zircon εHf(t) (+3.4 to +7.3), suggesting their origin from meta-basic rock-dominated thickened lower crust with eclogite residue. Significance These results suggest that they were formed in a post-collisional extension setting. A comprehensive analysis indicates that the East Kunlun Orogenic Belt was in the collision and post-collision stages during the Late Triassic. The post-collision stage can be further divided into two phases of magmatic activity: early and late phases of the Late Triassic

Cambrian intrusions along the North Qilian suture zone

Supplementary Table 1. LA-ICP-MS zircon U-Pb data for Cambrian intrusive rocks along the southern margin of North Qilian suture zone. Supplementary Table 2. SIMS zircon U-Pb data for Zhamashi gabbro. Supplementary Table 3. Zircon Lu-Hf isotopic data for Cambrian intrusive rocks along the southern margin of North Qilian suture zone. Supplementary Table 4. Whole-rock major (wt.%) and trace element (ppm) data for Cambrian intrusive rocks along the southern margin of North Qilian suture zone. Supplementary Table 5. Sr-Nd isotopic compositions for Cambrian intrusive rocks along the southern margin of North Qilian suture zone

Multiple subduction processes of the Proto-Tethyan Ocean: Evidences from Cambrian intrusions along the North Qilian suture zone

Supplementary Table 1. LA-ICP-MS zircon U-Pb data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 2. SIMS zircon U-Pb data for the Zhamashi gabbro. Supplementary Table 3. Zircon Lu-Hf isotopic data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 4. Whole-rock major (wt.%) and trace element (ppm) data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 5. Sr-Nd isotopic compositions for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone

Multiple subduction processes of the Proto-Tethyan Ocean: Evidences from Cambrian intrusions along the North Qilian suture zone

Supplementary Table 1. LA-ICP-MS zircon U-Pb data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 2. SIMS zircon U-Pb data for the Zhamashi gabbro. Supplementary Table 3. Zircon Lu-Hf isotopic data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 4. Whole-rock major (wt.%) and trace element (ppm) data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 5. Sr-Nd isotopic compositions for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone

Multiple subduction processes of the Proto-Tethyan Ocean: Evidences from Cambrian intrusions along the North Qilian suture zone

Supplementary Table 1. LA-ICP-MS zircon U-Pb data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 2. SIMS zircon U-Pb data for the Zhamashi gabbro. Supplementary Table 3. Zircon Lu-Hf isotopic data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 4. Whole-rock major (wt.%) and trace element (ppm) data for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone. Supplementary Table 5. Sr-Nd isotopic compositions for Cambrian intrusive rocks along the southern margin of the North Qilian suture zone

Cambrian intrusions along the North Qilian suture zone

Supplementary Table 1. LA-ICP-MS zircon U-Pb data for Cambrian intrusive rocks along the southern margin of North Qilian suture zone. Supplementary Table 2. SIMS zircon U-Pb data for Zhamashi gabbro. Supplementary Table 3. Zircon Lu-Hf isotopic data for Cambrian intrusive rocks along the southern margin of North Qilian suture zone. Supplementary Table 4. Whole-rock major (wt.%) and trace element (ppm) data for Cambrian intrusive rocks along the southern margin of North Qilian suture zone. Supplementary Table 5. Sr-Nd isotopic compositions for Cambrian intrusive rocks along the southern margin of North Qilian suture zone