Large-scale early cretaceous lower-crust melting derived adakitic rocks in NE China: implications for convergent bidirectional subduction and slab rollback

2019 ◽  
Vol 62 (18) ◽  
pp. 2324-2343 ◽  
Author(s):  
Dian Ji ◽  
Huichuan Liu ◽  
Yinglei Li
Keyword(s):  
Early Cretaceous ◽  
Lower Crust ◽  
Large Scale ◽  
Ne China ◽  
Adakitic Rocks ◽  
Slab Rollback

scholarly journals Petrogenesis of the Early Cretaceous Aolunhua Adakitic Monzogranite Porphyries, Southern Great Xing’an Range, NE China: Implication for Geodynamic Setting of Mo Mineralization

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 332
Author(s):  
Xiaohu He ◽  
Shucheng Tan ◽  
Zheng Liu ◽  
Zhongjie Bai ◽  
Xuance Wang ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Early Cretaceous ◽  
Lower Crust ◽  
Evolutionary History ◽  
Ne China ◽  
Lower Continental Crust ◽  
Adakitic Rocks ◽  
Great Xing’An Range ◽  
Mafic Lower Crust

This paper reports on whole-rock major- and trace-elemental and Sr–Nd isotopic compositions of the Aolunhua adakitic monzogranite porphyries from the Xilamulun district in the southern Great Xing’an Range, Northeast (NE) China. The high-K calc-alkaline Aolunhua monzogranite porphyries are characterized by high Sr/Y ratios (34.59–91.02), Sr (362–809 ppm), and low Y contents (7.66–10.5 ppm), respectively. These rocks also show slightly enriched Sr and Nd isotopes ((87Sr/86Sr)i = 0.7051–0.7058; εNd(t) = −2.98–0.92), with young two-stage model ages (T2DM = 0.84–1.16 Ga). Such a signature indicates that these rocks were most likely formed by partial melting of juvenile mafic lower crust. Based on equilibrium melting and batch-melting equations, we performed incompatible trace elements modeling. Low FeOT/(FeOT + MgO) values indirectly reflect these adakitic rocks were derived from an oxidizing source related to magnesian granitoids. The decreasing content of TiO2, Fe2O3, Nb/Ta ratio, and moderately negative Eu anomalies suggest that minimal fractionation of Fe–Ti oxides and plagioclase may have occurred in their evolutionary history. The result shows that the Aolunhua adakitic porphyries and coeval adakitic intrusive rocks in this area had not experienced extensive fractional crystallization and were derived from 20%–40% partial melting of lower continental crust, which was composed of ~25%–40% and 5%–20% garnet-bearing amphibolite, respectively. Integrating with rock assemblages and regional tectonic evolutionary history in this regime, high (Sm/Yb)SN (SN—source normalized data, normalized to mafic lower continental crust with Yb = 1.5 ppm and Sm/Yb = 1.87 for continental adakite) and low YbSN ratios suggest that these rocks were generated in an extensional environment related to lithospheric delamination without crustal thickening. The collision between North China and Siberian cratons around 160 Ma blocked the westward movement of the lithosphere as a result of the subduction of Pacific plate, which then led to lithospheric delamination induced by asthenospheric upwelling and underplating. Subsequently, partial melting of mafic lower crust caused by mantle upwelling resulted in the Early Cretaceous magmatic activities of adakitic rocks and associated Mo mineralization in the southern Great Xing’an Range.

MESOZOIC Mo MINERALIZATION IN NORTHEASTERN CHINA DID NOT REQUIRE REGIONAL-SCALE PRE-ENRICHMENT

2021 ◽  
Author(s):  
Qihai Shu ◽  
Massimo Chiaradia
Keyword(s):  
Lower Crust ◽  
Large Scale ◽  
Source Region ◽  
Regional Scale ◽  
Northeastern China ◽  
Magma Source ◽  
Oceanic Plate ◽  
Ne China ◽  
Cretaceous Deposits ◽  
Regional Compression

Abstract Northeastern China is one of the richest Mo-mineralized regions in China, with 95 Mesozoic Mo-bearing deposits and a total metal resource of >12.2 Mt Mo. The reasons behind the large-scale Mesozoic Mo mineralization in NE China remain unclear, and whether or not there was any regional-scale pre-enrichment of the source region (e.g., a Mo-rich lower crust) is still a matter of debate. In this study, whole-rock Nd and zircon Hf isotope compositions of the intrusions related to the Mo mineralization have been compiled. The results show that the isotopic compositions are highly heterogeneous among these deposits with different ages and Mo tonnages, indicating that Mo-related magmas could be derived from either ancient lower crust or relatively juvenile lower crust or via mixing of mantle-derived magmas with varying proportions of crustal melts. This suggests that different magmas, independently from their sources, can produce Mo mineralization in NE China, and, therefore, that there was probably not an unusually Mo rich basement underlying NE China. In addition, Monte Carlo simulations have been carried out to explore the magmatic processes potentially associated with the formation of magmatic-hydrothermal (porphyry- or skarn-type) Mo deposits. The results reveal that a variably large magma volume (e.g., >150 km3) was required to provide enough Mo metal to form the large (>0.1 Mt Mo) deposits. In NE China, the Jurassic Mo deposits are much more abundant and larger than the Triassic and Cretaceous deposits, which could be attributed to the specific Jurassic tectonic regime. In the Jurassic, the subduction of the Paleo-Pacific oceanic plate led to regional compression, which favors accumulation of larger amounts of magmas at depth, ultimately resulting in larger Mo deposit formation. In this study, we highlight the importance of magma volume, rather than magma source, in the formation of the Mesozoic Mo deposits in NE China.

scholarly journals Petrogenesis and Geodynamic Implications of Miocene Felsic Magmatic Rocks in the Wuyu Basin, Southern Gangdese Belt, Qinghai-Tibet Plateau

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 655
Author(s):  
Hanzhi Chen ◽  
Mingcai Hou ◽  
Fuhao Xiong ◽  
Hongwei Tang ◽  
Gangqiang Shao
Keyword(s):  
Lower Crust ◽  
Volcanic Rocks ◽  
Tibet Plateau ◽  
Southern Tibet ◽  
Mixed Product ◽  
Good Opportunity ◽  
Magmatic Rocks ◽  
Adakitic Rocks ◽  
Felsic Volcanic ◽  
Qinghai Tibet Plateau

Miocene felsic magmatic rocks with high Sr/Y ratios are widely distributed throughout the Gangdese belt of southern Tibet. These provide a good opportunity to explore the magmatic process and deep dynamic mechanisms that occurred after collision between the Indo and the Asian plates. In this paper, felsic volcanic rocks from the Zongdangcun Formation in the Wuyu Basin in the central part of the southern Gangdese belt are used to disclose their origin. Zircon U-Pb geochronology analysis shows that the felsic magmatism occurred at ca. 10.3 ± 0.2 Ma, indicating that the Zongdangcun Formation formed during the Miocene. Most of these felsic magmatic rocks plot in the rhyolite area in the TAS diagram. The rhyolite specimens from the Zongdangcun Formation have the characteristics of high SiO2 (>64%), K2O, SiO2, and Sr contents, a low Y content and a high Sr/Y ratio, and the rocks are rich in LREE and depleted in HREE, showing geochemical affinity to adakitic rocks. The rocks have an enriched Sr-Nd isotopic composition (εNd(t) = −6.76 to −6.68, (87Sr/86Sr)i = 0.7082–0.7088), which is similar to the mixed product of the juvenile Lhasa lower continental crust and the ancient Indian crust. The Hf isotopes of zircon define a wide compositional range (εHf(t) = −4.19 to 6.72) with predominant enriched signatures. The Miocene-aged crustal thickness in southern Tibet, calculated on the basis of the Sr/Y and (La/Yb)N ratios was approximately 60–80 km, which is consistent with the thickening of the Qinghai-Tibet Plateau. The origin of Miocene felsic magmatic rocks with high Sr/Y ratios in the middle section of the Gangdese belt likely involved a partial melting of the thickened lower crust, essentially formed by the lower crust of the Lhasa block, with minor contribution from the ancient Indian crust. After comprehensively analyzing the post-collisional high Sr/Y magmatic rocks (33–8 Ma) collected from the southern margin of the Gangdese belt, we propose that the front edge tearing and segmented subduction of the Indian continental slab may be the major factor driving the east-west trending compositional changes of the Miocene adakitic rocks in southern Tibet.

Constraints on the formation of the giant Daheishan porphyry Mo deposit (NE China) from whole-rock and accessory mineral geochemistry

2021 ◽  
Author(s):  
Kai Xing ◽  
Qihai Shu ◽  
David R Lentz
Keyword(s):  
High Water ◽  
Accessory Mineral ◽  
Ne China ◽  
Accessory Minerals ◽  
Slab Rollback ◽  
Continental Arc ◽  
Arc Setting ◽  
Porphyry Mo Deposit ◽  
T Values ◽  
Water Contents

Abstract There are more than 90 porphyry (or skarn) Mo deposits in northeastern China with Jurassic or Cretaceous ages. These are thought to have formed mainly in a continental arc setting related to the subduction of the Paleo-Pacific oceanic plate in the Jurassic and subsequent slab rollback in the early Cretaceous. The Jurassic Daheishan porphyry Mo deposit is one of the largest Mo deposits in NE China, which contains 1.09 Mt Mo with an average Mo grade of 0.07%. To better understand the factors that could have controlled Mo mineralization at Daheishan, and potentially in other similar porphyry Mo deposits in NE China, the geochemical and isotopic compositions of the ore-related granite porphyry and biotite granodiorite, and the magmatic accessory minerals apatite, titanite and zircon from the Daheishan intrusions, were investigated so as to evaluate the potential roles that magma oxidation states, water contents, sulfur and metal concentrations could have played in the formation of the deposit. Magmatic apatite and titanite from the causative intrusions show similar εNd(t) values from -1.1 to 1.4, corresponding to TDM2 ages ranging from 1040 to 840 Ma, which could be accounted for by a mixing model through the interaction of mantle-derived basaltic melts with the Precambrian lower crust. The Ce and Eu anomalies of the magmatic accessory minerals have been used as proxies for magma redox state, and the results suggest that the ore-forming magmas are highly oxidized, with an estimated ΔFMQ range of + 1.8 to + 4.1 (+2.7 in average). This is also consistent with the high whole-rock Fe2O3/FeO ratios (1.3–26.4). The Daheishan intrusions display negligible Eu anomalies (Eu/Eu* = 0.7–1.1) and have relatively high Sr/Y ratios (40–94) with adakitic signatures; they also have relatively high Sr/Y ratios in apatite and titanite. These suggest that the fractionation of amphibole rather than plagioclase is dominant during the crystallization of the ore-related magmas, which further indicates a high magmatic water content (e.g., >5 wt%). The magmatic sulfur concentrations were calculated using available partitioning models for apatite from granitoids, and the results (9–125 ppm) are indistinguishable from other mineralized, subeconomic and barren intrusions. Furthermore, Monte Carlo modelling has been conducted to simulate the magmatic processes associated with the formation of the Daheishan Mo deposit, and the result reveals that a magma volume of ∼280 km3 with ∼10 ppm Mo was required to form the Mo ores containing 1.09 Mt Mo in Daheishan. The present study suggests that a relatively large volume of parental magmas with high oxygen fugacities and high water contents is essential for the generation of a giant porphyry Mo deposit like Daheishan, whereas a specific magma composition (e.g., with unusually high Mo and/or S concentrations), might be less critical.

Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

2021 ◽  
pp. 1-22
Author(s):  
Jia-Hao Jing ◽  
Hao Yang ◽  
Wen-Chun Ge ◽  
Yu Dong ◽  
Zheng Ji ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Ne China ◽  
Asthenospheric Mantle ◽  
High K ◽  
Wide Range ◽  
Great Xing’An Range ◽  
Subducting Slab

Abstract Late Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.

Sign in / Sign up

Export Citation Format

Share Document