Research Field : Precambrian Geology and Supercontinent Evolution
The reconstruction of supercontinent, especially Rodina supercontinent, has received many attentions in last decades. The assembly and breakup of Rodinia are generally evidenced by many aspects, such as igneous and sedimentary rocks.
(1) Low-δ18O magma has profound implications on geological and climate evolution. We firstly report Neoproterozoic moderately 18O depleted zircons from the central part of the Cathaysia Block in South China. The similarity in low-δ18O magmatism between northwest India, Madagascar, and South China suggests close connections in the Rodinia supercontinent during the middle Neoproterozoic.
(2) Synthetic studies of the petrology, mineralogy, geochemistry, geochronology and isotopic geology have been carried on the Precambrian sedimentary sequences and igneous rocks from eastern Jiangnan Orogen. The presence of a back-arc basin system at ca. 860-820 Ma within the south-eastern margin of the Yangtze block also indicates that Rodinia assembly was not completed until ca. 820 Ma, with the South China block possibly acting as a connection between a Neoproterozoic Andean-type active continental margin and Grenvillian belts on the paleo–western margin of the Rodinia supercontinent.
(3) Besides, zircons from conglomerates can provide valuable information for crustal evolution. Based on comparisons of detrital zircon U–Pb age spectrums and Hf isotopic characters with worldwide continents, we propose that the early Neoproterozoic sediments at the southeastern margin of the Yangtze Block have close affinities with those from the India and East Antarctica, which matches a northwestern margin position for the SCB in the configuration of supercontinent Rodinia.
Precambrian geology in South China has also been hot-debated in recent years. We, our group, have gained some achievements in the following:
(1) We have proposed the Yangtze Block was not unified and witnessed heterogenous crustal evolution before Neoproterozoic, based on petrogenesis, geochemical modelling and data compilation. We also highlight the crucial role of Neoproterozoic intra-arc thrust belt on western Yangtze Block in driving endogenic recycling and contributing to magma diversity during continental arc evolution.
(2) High-Mg tonalites in the southern part of the ca. 830 Ma Dongma Pluton, northern Guangxi Province of South China, indicates the existence of Neoproterozoic subduction-related metasomatism in the western part of the Jiangnan Orogen. Furthermore, two episodes of Neoproterozoic mafic magmatism in the western segment of the Jiangnan Orogen shed light on the magma source transition from lithospheric mantle to depleted asthenospheric mantle.
(3) The Mesozoic granites in the middle Nanling area are characterized with more depleted zircon Hf and whole rock Nd isotopic compositions than granitoids in the western and eastern Nanling area, South China. We speculate the middle Nanling area was a sutural zone of Yangtze and Cathaysia block during the Neoproterozoic time, with more Neoproterozoic juvenile crustal materials (e.g., arc-magmatic rocks).
(4) Ophiolites can provide crucial constraints on the history of continental convergence. We focused on the South Anhui ophiolite and the Northeast Jiangxi ophiolite from eastern segment of the Jiangnan Orogen within the South China Block. The formations of these ophiolites record orogenic processes from the subduction of oceanic crust (early stage) to back-arc extension (late stage) and finally the closure of back-arc basins in South China from Mesoproterozoic to Neoproterozoic.
(5) A study on tectonic evolution and source analysis of Precambrian sedimentary strata in the northern margin of Yangtze block is important to decipher the history of Yangtze Block, and it revealed the early accretion in the periphery of continent.
(6) Moreover, owing to the improvement of the experimental petrology and phase equilibria modeling methods in recent decades, we used these powerful tools on Precambrian rock to explore the evidence of buried geological events.
Research Field: Genesis of Granite and Related Rocks
The Earth distinguishes from other planets by the existence of massive granitoids and continental crust, while granitoids occupy a significant position in the spectrum of continent. Thus, investigating the petrogenesis of granite and the formation of granitic plutons/batholiths plays a crucial role in understanding the formation and evolution of continents, and it is what we have been devoted to.
(1) The A-type granites in the Mesozoic granitic belt have more depleted Nd-Hf isotopic composition than that of contemporaneous I- and S- type granites. The distribution of the A-type granites may be along the Neoproterozoic amalgamation belt of the Yangtze and Cathaysia Block, where have more juvenile material than the source of the I- and S-type granites. Thus, the generation of Mesozoic granites in Nanling area more likely support the source controlled model.
(2) Southern China experienced extensive, episodic, Mesozoic granitic magmatism and W–Sn polymetallic mineralization, making this area an ideal natural laboratory for the study of granitic magmatism and related metallogenesis. We proposed a deep crustal hot zone (DCHZ) to account for these granitoids within the Jiuling composite batholith, which has not previously been recognized beneath the South China Block.
(3) The coupling and decoupling relationship between mantle- and crust-derived magmatism at different stages of subduction-suture zone is explored through the petrogenesis research on Neoproterozoic high-Mg tonalite and the discussion on the magma source melting progress of mafic-ultramafic rocks from northern Guangxi.
(4) The magmatic evolution of Permian mafic-felsic volcanic rocks from Tu Le Basin of northern Vietnam is studied to explore the episodic evolution and eruption of volcanic rocks under the extension background related to mantle plume as well as the coupling relationship between mantle- and crust-derived magmatism.
(5) By combining mineral assemblage, field relationship, and thermodynamic modeling data with observations of zircon internal structures, we infer that anatexis occurred via partial melting of Neoproterozoic metasedimentary rocks, immediately following amphibolite-facies regional metamorphism at ca. 442 Ma for the granitic rocks in the northern Wuyi Mountains of southern Jiangxi Province. Three types of zircon grains/domains in the analyzed samples were identified, relating to anatectic melt migration, extraction, and eventual crystallization. Large variations in zircon Hf isotopic compositions and homogenization trends indicate that melting was heterogeneous, and homogenization of the anatectic melt occurred later.
(6) Based on the field work, petrography, geochemistry and numerical simulation, we regard the Oligocene (ca. 30 Ma) Gangdese leucogranite in southern Tibet as the latest product of fractional crystallization from coeval host granitoids which derived from the anatexis of juvenile lower crust. This work also stresses the crucial role of water-present melting and delamination in the formation of continental crust. The first report of Oligocene Gangdese leucogranites, along with compilations of synchronous high Sr/Y Gangdese granitoids and Himalayan leucogranites, indicate the existence of diverse sources, generations and evolutions of granitic magmatism in southern Tibet may be resulted from partial melting of local deep crustal materials.
(7) U-Pd-Hf data imply the existence of a Paleoproterozoic basement and suggest that the late Mesozoic continental arc magmatism in the Eastern Cathaysia Blok was most likely developed on and contaminated by the basement.
(8) Numerical simulations show great potential for intrusive magmas to generate large amounts of CO2. Geological big data implies a close relationship between magmatism and climate change.
Research Field: Isotope Geochemistry
Stable isotope geochemistry has the potential to be powerful tracers in a variety of geological settings. The principal focus of our research has been the use of stable isotope systematics to understand the evolution of continental crust and ore formation, with a special interest in the interactions among them over geological time.
The current projects including:
1) iron isotope systematics, studying its fractionation mechanisms in high-silica igneous rocks and using it to trace compositional differentiation magmatic orogens;
2) magnesium isotope systematics, understanding its fractionation behaviors in felsic magmatism and tracing the recycling of supracrustal materials during oceanic subduction at convergent margin;
3) sulfer isotope systematics, developing and optimizing analytical methods and applying it to track ore-forming processes.
The tools that we use include multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS, for Fe and Mg isotopes) and secondary ion mass spectrometry (SIMS, for S isotopes).
So far, we have obtained some achievements as following:
1) fractional crystallization is the dominant mechanism that controls Fe isotope fractionation in high-silica igneous rocks; 2) two standards for S isotope in-situ analysis have been developed (HTS4-6: chalcopyrite, YP136: pyrrhotite) and off-mount calibration of sulfur isotope determination has been established on SIMS.
Research Field: Big Data of Geoscience
The Early Paleozoic Wuyi-Yunkai orogen in southeast China is widely accepted as an intracontinental collision belt and has attracted significant attention in recent decades. Nevertheless, the tectonic driving mechanism for the formation of these granitic rocks is still puzzling. Integrating available data, we conclude that the Ordovician-Devonian granitic rocks in southeast China formed during the period from 452 Ma to 381 Ma, yielding an age peak at around 450–430 Ma. Ordovician rocks are generally distributed in a narrow NE trending belt within the Wuyi-Yunkai orogen, relatively to widely distributed Silurian-Devonian rocks. The Ordovician granitic rocks are mainly distributed in the Wuyi, Yunkai, and Wugongshan areas and exhibit gneissic structures. They were dominantly formed by crustal anatexis and could represent the reworking of Neoproterozoic supracrustal materials. The Silurian-Devonian granitic rocks were massive in structure and are mainly concentrated in the Xuefengshan and Nanling-Wanyangshan areas. They display higher εHf(t) and εNd(t) values and are less variable than the Ordovician granites, suggesting a relatively high contribution of juvenile crust. More importantly, the geochemistry shows a significant transition at ca. 435 Ma, coinciding with regional extension after 435 Ma. We suggest that there was a NE-trending continent-continent collision before 435 Ma and the subsequent increasing orogenic collapse led to the expansion of intracontinental crustal melting.
Big data analysis of magmatic rocks in South China and the relationship between volcanic rocks and intrusive rocks. Through field investigation, geochemical testing, big data analysis, modeling, numerical simulation and other methods, taking Mesozoic magmatic rocks in South China as an example, the formation and evolution of the crust are studied. Based on the big data model, it compares with the magmatic rocks in western North America, discusses the relationship between volcanic rocks and intrusive rocks, and provides theoretical and data support for predicting volcanic eruptions. Furthermore, we also work on Geological Big Data in terms of spatial and temporary distribution of Mesozoic granitoids and volcanic rocks, which helps us find out the relationship between Mesozoic magmatism and tectonic settings. We suggest that the formation of Mesozoic granitoids and volcanic rocks in SE China was related to multiple stages of subduction and roll-back of oceanic slab on the southeast margin of the South China Block.
The Archean crust was dominated by greenstones and granitic rocks such as TTGs (tonalite-trondhjemite-granodiorite), and they are critical for us to understand the process of continental evolution and the tectonic regime on the early Earth. Thus, what I'm working on is geological big data in terms of trace elements geochemistry of those Archean igneous rocks. Such work has shown that TTGs are probably formed by partial melting of hydrated basalt at high pressures, and there may be an extensive mantle overturn at 3.5-3.2 Ga. What else do those datas could tell us is still being researched. Besides, the investigation on pegmatitic lithium deposits in both Australia and Africa which is still going on could tell us about the features of lithium resources in these two continents, the relation between the formation of pegmatitic lithium deposits and the crustal evolution, and may help to solve other geological issues.
Liu, J.X., Wang, S., Wang, X.L., Du, D.H., Xing, G.F., Fu, J.M., Chen, X., Sun, Z.M., 2020. Refining the spatio-temporal distributions of Mesozoic granitoids and volcanic rocks in SE China. Journal of Asian Earth Sciences, doi: https://doi.org/10.1016/j.jseaes.2020.104503.
Huang, D.L., Wang, X.L., 2019. Reviews of geochronology, geochemistry, and geodynamic processes of Ordovician-Devonian granitic rocks in southeast China. Journal of Asian Earth Sciences 184: 104001. https://doi.org/10.1016/j.jseaes.2019.104001.