In this study, we present new U–Pb zircon ages and whole‐rock major and trace element data for the late Carboniferous–Middle Jurassic intrusive rocks in the Helong area, NE China. These data constrain the timing of tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime. U–Pb zircon dating indicates that the late Carboniferous–Middle Jurassic magmatic events in the Helong area can be subdivided into late Carboniferous, middle Permian, Early–Middle Triassic, Late Triassic, Early Jurassic, and early Middle Jurassic. The late Carboniferous granodiorites and middle Permian monzogranites belong to the calc‐alkaline series and have an affinity to I‐type granitoids, suggesting that they formed in a typical Andean‐type continental arc setting due to the southward subduction of the Paleo‐Asian oceanic plate beneath the NCC. The Middle Triassic granodiorites and monzogranites in the Helong area exhibit an affinity to adakitic rocks with their parental magma derived by the partial melting of thickened lower continental crust. The Late Triassic I‐type monzogranites and coeval ultramafic–mafic rocks constitute a bimodal igneous rock association, together with coeval A‐type granites and rhyolites, signifying an extensional environment. Combined with the absence of 240‐ to 225‐Ma sedimentation, the study area experienced a change from Early–Middle Triassic compression to Late Triassic extension related to the final closure of the Paleo‐Asian Ocean. The Early–early Middle Jurassic gabbros, diorites, granodiorites, and monzogranites are calc‐alkaline in nature and enriched in LREE and LILE but depleted in HREE and HFSE. Combined with the spatial variations in K contents of Early Jurassic igneous rocks in NE China from the continental margin to intracontinental region, and the presence of an Early Jurassic accretionary complex, we suggest that Early–early Middle Jurassic magmatism in the Helong area formed in an active continental margin setting related to the subduction of the Paleo‐Pacific Plate beneath Eurasia. We conclude that the tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime occurred in the Late Triassic–Early Jurassic.
In order to evaluate the sensitivity to alkali-saline land in the West of Jilin Province with the fragile eco-environmental problems, 6 395 cells had been divided with the help of the polygon over- laying method of GIS and 6 indexes were chosen. The degree of sensitivity had been divided into non-sensitivity, low-sensitivity, high-sensitivity and the highest-sensitivity. The AHP model was used to ascertain the weight of evaluating indexes, and the Fuzzy model was used to evaluate the level of sensitivity to alkali-saline land,which could supply the useful basis to the division of the sub areas and visualization of result by GIS technology. The result showed that the above methods could improve the precision of evaluation. The alkali-saline land in the West of Jilin Province is dominated by high-sensitivity. The low-sensitivity and the non-sensitivity were take second place, and the highest-sensitivity was the least.
Studying the driving factors and contributions of carbon emissions peak volume and time is essential for reducing the cumulative carbon emissions in developing countries with rapid economic development and increasing carbon emissions. Taking Jilin Province as a case study, four scenarios were set in this paper respectively: Business as Usual Scenario (BAU), Energy-Saving Scenario (ESS), Energy-Saving and Low-Carbon Scenario (ELS), and Low-Carbon Scenario (LCS). Furthermore, the carbon emissions were predicted according to the energy consumption based on the application of LEAP system. The research result showed that the peak time of carbon emissions would appear in 2045, 2040, 2035 and 2025 under the four different scenarios, respectively. The peak volumes would be 489.8 Mt, 395.2 Mt, 305.3 Mt and 233.6 Mt, respectively. The cumulative emissions by 2050 are respectively 15.632 Bt, 13.321 Bt, 10.971 Bt and 8.379 Bt. According to the forecasting, we analyzed the driving factors of and contributions to carbon emissions peak volume and time. On the premise of moderate economic growth, the “structural emission reduction”, namely the adjustment of industrial structure and energy structure, and “technology emission reduction”, namely the reduction of energy intensity and carbon emission coefficient could make the peak volume reduced by 20%–52% and cumulative carbon emissions (2050) reduced by 15%–46% on the basis of BAU. Meanwhile, controlling the industrial structure, energy structure and energy intensity could make carbon emissions reach the peak 5–20 years ahead of the time on the basis of BAU. Controlling GDP, industrial structure, energy structure, energy intensity and coefficient of carbon emissions is the feasible method to adjust the carbon emissions peak volume and time in order to reduce the cumulative emissions.
Plaques type level of characteristics of the landscape pattern for Changchun Lianhuashan tourist resort were studied.The result shows that field landscape accounts for the biggest area and plays an important role in landscape function which affected the material and energy flow of current region.The regional landscape patches has a state of aggregation distribution which has a very strong impact because of human activities.Therefore,positive development for local economy and protecting the local ecological environment form the harmonious development of society and the environment.The research results can provide theoretical basis for land planning and development of Lianhuashan region.It also has important practical significance for regional ecological environmental construction、protection and sustainable development of economy.
We present in situ trace element and Nd isotopic data of apatites from metamorphosed and metasomatized (i.e., altered) and unaltered granitoids in the Songnen and Jiamusi massifs in the eastern Central Asian Orogenic Belt, with the aim of fingerprinting granitoid petrogenesis, including both the magmatic and post-magmatic evolution processes. Apatites from altered granitoids (AG) and unaltered granitoids (UG) are characterized by distinct textures and geochemical compositions. Apatites from AG have irregular rim overgrowths and complex internal textures, along with low contents of rare earth elements (REEs), suggesting the re-precipitation of apatite during epidote crystallization and/or leaching of REEs from apatite by metasomatic fluids. εNd(t) values of the these apatites are decoupled from zircon εHf(t) values for most samples, which can be attributed to the higher mobility of Nd as compared to Sm in certain fluids. Apatites from UG are of igneous origin based on their homogeneous or concentric zoned textures and coupled Nd-Hf isotopic compositions. Trace element variations in igneous apatite are controlled primarily by the geochemical composition of the parental melt, fractional crystallization of other REE-bearing minerals, and changes in partition coefficients. Sr contents and Eu/Eu* values of apatites from UG correlate with whole-rock Sr and SiO2 contents, highlighting the effects of plagioclase fractionation during magma evolution. Apatites from UG can be subdivided into four groups based on REE contents. Group 1 apatites have REE patterns similar to the host granitoids, but are slightly enriched in middle REEs, reflecting the influence of the parental melt composition and REE partitioning. Group 2 apatites exhibit strong light REE depletions, whereas Group 3 apatites are depleted in middle and heavy REEs, indicative of the crystallization of epidote-group minerals and hornblende before and/or during apatite crystallization, respectively. Group 4 apatites are depleted in heavy REEs, but enriched in Sr, which are features of adakites. Some unusual geochemical features of the apatites, including the REE patterns, Sr contents, Eu anomalies, and Nd isotopic compositions, indicate that inherited apatites are likely to retain the geochemical features of their parental magmas, and thus provide a record of small-scale crustal assimilation during magma evolution that is not evident from the whole-rock geochemistry.
Abstract Substantial Phanerozoic crustal growth and reworking in the eastern Central Asian Orogenic Belt has partly obscured the Precambrian geological record. Accurate identification of such Precambrian magmatism and its petrogenesis is paramount to unveiling the early crustal evolution of the eastern Central Asian Orogenic Belt. Two outcrops of Neoarchean and Paleoproterozoic magmatism in the Longjiang area of NE China, eastern Central Asian Orogenic Belt, were recently discovered. The Kaoquantun outcrop consists of monzogranites that yield a zircon 207Pb/206Pb age of 2568 ± 8 Ma and are similar to peraluminous A1-type granites. They were derived from the partial melting of a hybrid crustal source comprising newly accreted Mesoarchean crust and abundant supracrustal metapelites in a post-collisional extensional setting. Such metapelites were initially part of the upper crust but were buried in the middle–lower crust due to crustal thickening prior to ca. 2.6 Ga. In the Zhanbeitun outcrop, basaltic andesites overlie monzogranites, and both have been intruded by syenogranites. The monzogranites and syenogranites yield zircon 207Pb/206Pb ages of 1881 ± 10 Ma and 1843 ± 3 Ma, respectively, whereas the basaltic andesites are inferred to have formed at 1.88–1.84 Ga. The 1.88 Ga monzogranites have relatively enriched zircon Hf-O isotopic compositions and were derived from a hybrid melt of mafic rocks in the lower crust and ancient metabasalts that had undergone low-temperature alteration at supracrustal depths. The 1.88–1.84 Ga basaltic andesites are Nb-rich and were generated by the partial melting of a mantle wedge that was metasomatized by subduction-derived fluids, recycled sediments, and slab-derived melts. The 1.84 Ga syenogranites are peraluminous and K-rich, and record a profound mixing and assimilation process involving melts derived from supracrustal sediments and the lower crust. Three stages of Paleoproterozoic magmatism emerged from subduction-related crustal thickening, slab breakoff, and collision, respectively. The zircon Hf isotopic data further indicate that the eastern Central Asian Orogenic Belt underwent at least one stage of proto-crustal growth at ca. 3.0 Ga, followed by multiple phases of crustal reworking during the Neoarchean and Paleoproterozoic, with dominant involvement of supracrustal components.
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