Zircon trace element, U-Pb age, and Lu-Hf isotope composition were determined for two eclogite samples from the Xinxian ultrahigh-pressure (UHP) unit in the western Dabie orogen to constrain its exhumation processes. Cathodoluminescence imaging reveals that most zircons are metamorphic, while some have inherited magmatic cores in one sample. The magmatic cores have high Th/U and Lu/Hf ratios, high trace element contents, and a clear negative Eu anomaly, consistent with their igneous genesis. They yield an upper intercept age of Ma and a positive εHf(t) value of 8.0, arguing for reworking of early Mesoproterozoic crust during the middle Neoproterozoic in the western Dabie orogen. The metamorphic zircons contain mineral inclusions of garnet, omphacite, rutile, and quartz. They are characterized by low Nb, Ta, Y, and heavy rare earth elements (HREE) contents, a nearly flat HREE pattern, and an insignificant negative Eu anomaly. These indicate that the metamorphic zircons formed under high-pressure (HP) quartz eclogite-facies metamorphic conditions. The metamorphic zircons in the two samples have Ti-in-zircon temperatures of and C, respectively, suggesting that they formed in different HP eclogite-facies metamorphic stages. The metamorphic zircons in the two samples yield weighted mean U-Pb ages of and Ma, which may date the initial exhumation to ∼90 km and ∼700°C and a subsequent HP quartz eclogite-facies retrogression at ∼50 km and ∼600°C for ultrahigh-pressure (UHP) rocks in the western Dabie orogen. This yields a maximum exhumation and average cooling rates of ∼0.33 cm/yr and 8°C/Ma, respectively. Based on the published Rb-Sr and Ar-Ar ages of ∼212 Ma for the UHP rocks in the area, the subsequent stage of exhumation of UHP rocks has a maximum exhumation and average cooling rates of 0.67 cm/yr and 65°C/Ma, respectively. This two-stage cooling process may be common for HP-UHP metamorphic terranes in continental collision zones.
The KEDA® circulating fluidized-bed (KEDA®CFB) gasifier is a high-temperature air-blown circulating fluidized bed developed by KEDA (ANHUI) Clean Energy Co., Ltd to produce clean industrial gas. This project describes the design and the initial operating results of using low-rank coal to produce industrial fuel gas in a 65MWth KEDA®CFB industrial-scale plant with a feeding rate of 13 ton/hr. The gasification process was carried out at an ambient pressure and temperatures at 980 ± 10 °C. A long-term stable operation was achieved for more than 20 days. Cold gas efficiency could reach 73% with a gas high heating value of 5.89MJ/Nm3 at a steam-to-coal ratio of 0.38 and an equivalence ratio of 0.3. During the stable operation, it was also observed that the operational bed temperature has to be kept under the residual ash fusion temperatures (AFTs) to avoid aggregation and defluidization.
Both oceanic and continental HP rocks are juxtaposed in the Huwan shear zone in the western Dabie orogen, and thus provide a window for testing the buoyancy-driven exhumation of dense oceanic HP rocks. The HP metamorphic age of the continental rocks in this zone has not been well constrained, and hence it is not known if they are of the same age as the exhumation of the HP oceanic rocks. In situ laser ablation (multiple collector) inductively coupled plasma mass spectrometry (LA-(MC-)ICP-MS), U–Pb, trace element and Hf isotope analyses were made on zircon in a granitic gneiss and two eclogites from the Huwan shear zone. U–Pb age and trace element analysis of residual magmatic zircon in an eclogite constrain its protolith formation at 411 ± 4 Ma. The zircon in this sample displays εHf (t) values of +6.1 to +14.4. The positive εHf (t) values up to +14.4 suggest that the protolith was derived from a relatively depleted mantle source, most likely Palaeotethyan oceanic crust. A granitic gneiss and the other eclogite yield protolith U–Pb ages of 738 ± 6 and 700 ± 14 Ma, respectively, which are both the Neoproterozoic basement rocks of the Yangtze Block. The zircon in the granitic gneiss has low εHf (t) values of −14.2 to −10.5 and old TDM2 ages of 2528–2298 Ma, suggesting reworking of Palaeoproterozoic crust during the Neoproterozoic. The zircon in the eclogite has εHf (t) values of −1.0 to +7.4 and TDM1 ages of 1294–966 Ma, implying prompt reworking of juvenile crust during its protolith formation. Metamorphic zircon in both eclogite samples displays low Th/U ratios, trace element concentrations, relatively flat heavy rare earth element patterns, weak negative Eu anomalies and low 176Lu/177Hf ratios. All these features suggest that the metamorphic zircon formed in the presence of garnet but in the absence of feldspar, and thus under eclogite facies conditions. The metamorphic zircon yields U–Pb ages of 310 ± 3 and 306 ± 7 Ma. Therefore, both the oceanic- and continental-type eclogites share the same episode of Carboniferous eclogite facies metamorphism. This suggests that high-pressure continental-type metamorphic rocks might have played a key role in the exhumation and preservation of oceanic-type eclogites through buoyancy-driven uplift.
Change detection based on remote sensing images plays an important role in the field of remote sensing analysis, and it has been widely used in many areas, such as resources monitoring, urban planning, disaster assessment, etc. In recent years, it has aroused widespread interest due to the explosive development of artificial intelligence (AI) technology, and change detection algorithms based on deep learning frameworks have made it possible to detect more delicate changes (such as the alteration of small buildings) with the help of huge amounts of remote sensing data, especially high-resolution (HR) data. Although there are many methods, we still lack a deep review of the recent progress concerning the latest deep learning methods in change detection. To this end, the main purpose of this paper is to provide a review of the available deep learning-based change detection algorithms using HR remote sensing images. The paper first describes the change detection framework and classifies the methods from the perspective of the deep network architectures adopted. Then, we review the latest progress in the application of deep learning in various granularity structures for change detection. Further, the paper provides a summary of HR datasets derived from different sensors, along with information related to change detection, for the potential use of researchers. Simultaneously, representative evaluation metrics for this task are investigated. Finally, a conclusion of the challenges for change detection using HR remote sensing images, which must be dealt with in order to improve the model’s performance, is presented. In addition, we put forward promising directions for future research in this area.
In this paper, we report U-Pb age and Hf isotope composition of hydrothermal zircons from a quartz vein within an UHP eclogite outcrop from the Hong’an area, western Dabie orogen. These data are used to decipher the age, formation conditions and source of fluid flow during the exhumation of UHP rock. Zircons from the vein have perfect euhedral shape, oscillatory zoning or weak zoning, and very low Th/U ratios (0.03―0.07), indicating that they precipitated from the aqueous fluid responsible for the vein formation. The weighted mean 206Pb/238U age of 224.7 ± 1.3 Ma of these zircons is taken as the best estimated age of the quartz vein formation, and records aqueous fluid flow during the early exhumation stage of the UHP rocks. The zircons in the quartz vein show low Lu/Hf ratios and have similar Hf compositions to those in the host eclogite, indicating an internal source and small-scale fluid transport for veining. Therefore, the Hf isotope composition of hydrothermal zircon from quartz vein can constrain on the nature, forming condition, and origin of high-pressure metamorphic fluids.
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