Fuqin Zhang

SHRIMP U-Pb zircon geochronology and its implications on the Xilin Gol Complex, Inner Mongolia, China

The Xilin Gol Complex, consisting of deformed and metamorphosed rocks, was exposed as a large geological unit within the Central Asian Orogenic Belt, but its forming and subsequent deformed and metamorphic time has been an issue of little consensus. Petrographic analyses and SHRIMP dating on biotite-plagioclase gneiss, one of the major rocks within the Xilin Gol Complex, in southeast Xilinhot City, Inner Mongolia, China, where the Xilin Gol Complex was identified and named, yield its lower limit age of 437± 3 Ma (2σ) by its magmatic zircon SHRIMP U-Pb dating, and an upper limit age of 316 ± 3Ma (2σ), which was constrained by SHRIMP dating of magmatic zircons from adjacent undeformed garnet-bearing granite which intruded the Complex. The Complex was thus determined to be formed and subsequently deformed/metamorphosed from the late Ordovician-early Silurian to the mid-Carboniferous. Consequently, it is not the Precambrian terrane as previously considered by most geologists. More or less, the major rock — biotiteplagioclase gneiss within the Complex is more likely to be Paleozoic fore-arc turbidite formation before metamorphism and intensive deformation, in which the detrital zircons gave sporadic Precambrian ages as old as up to 3.1 Ga. The source of the turbidite formation is multiple, which may be derived either from the North China Craton, or from the South-Mongolia Micro-continent, or probably came from a potential and undiscoveredin situ terranes aged 600–800 Ma or even up to ca 3.1 Ga near the Complex.

Phanerozoic evolution of the Inner Mongolia–Daxinganling orogenic belt in North China: constraints from geochronology of ophiolites and associated formations

Abstract The Inner Mongolia–Daxinganling Orogenic Belt (IMDOB), located between the North China and South Mongolia Blocks, consists of several ENE–WSW- to NE–SW-trending zones including dismembered ophiolite blocks, metamorphic rocks and granitoids. Although numerous studies have been carried out on this belt, its tectonic evolution has been a subject of controversy, chiefly because of the lack of reliable geochronological data. Based on a synthesis of newly published geochronological data and our unpublished data for the IMDOB, we define two oceanic basins: Ondor Sum and Hegenshan. The former, probably the main one, was initiated during the Ordovician (>467 Ma) period, whereas the latter, representing a back-arc basin, opened on a pre-Permian basement at, or earlier than, Early Permian times (c. 295 Ma). These two oceanic basins were separated by a magmatic arc (Sunid–Baolidao), and were probably closed simultaneously when the final orogenesis of the IMDOB occurred during the Triassic period (240–220 Ma). Importantly, the Triassic timing of the final orogenesis of the IMDOB due north of the North China Craton is essentially coeval with that of the Qinling–Dabie–Su–Lu orogenic belt on the southern margin of the North China Craton. It is inferred that this two-sided subduction–collision scenario in the Triassic may have contributed to the Mesozoic lithospheric thinning event of the North China Craton, although the details are unclear.

Chromospheric activity on the RS CVn-type binary UX Arietis

High resolution spectroscopic observations of UX Ari made during three observing seasons in 2000 have been analyzed by means of the spectral subtraction technique. The information about chromospheric activity of UX Ari has been obtained from several optical chromospheric activity indicators such as the Hei D-3, Nai D-1, D-2, H-alpha, and CaII IRT lines. The results suggest the chromospheric activity of the system is associated with the cooler secondary. An orbital phase modulation of chromospheric emissions is found, and consequently the activity longitude area of the system is obtained, that corresponds to the phase interval near the second quadrature of the binary system. A are-like event is detected during our new observations, characterized by the dramatic increase in the Halpha and CaII IRT emission lines, that is confirmed by the emission of the Hei D-3 line and the filled-in cores of the Nai D-1, D-2 lines. It is found that the values of the EW8542/EW8498 ratio decrease when the activity of the system increases, especially when the are occurs. The small values of the EW8542/EW8498 ratio indicate that the CaII IRT emissions come from plage-like regions. The high activity level of UX Ari around the quadrature may originate with the coupling between the chromospheric activity of the secondary and the mass transfer activity of the two components.

Neoproterozoic zircon inheritance in eastern North China craton (China) Mesozoic igneous rocks: derivation from the Yangtze craton and tectonic implications

We propose that inherited Neoproterozoic zircons in Mesozoic igneous rocks from the eastern portion of the North China craton (NCC) were initially derived from the Yangtze/South China block, rather than from the NCC itself. The mechanism that introduced these zircons into the NCC was likely tectonic underplating during Triassic continental subduction/collision of the Yangtze block beneath the NCC. The addition of abundant crustal materials represented by the exotic zircons, probably along the Moho or weak interfaces within the NCC crust, led to the crustal thickening of the NCC. These sialic materials contributed significantly to the Mesozoic igneous rocks, either as source rocks or as contaminants of magmas generated during an extensional environment following crustal thickening. Crustal thickening was spatially linked to lithospheric thinning, with both occurring mainly in the eastern segment of the NCC, suggestive of an intrinsic relationship between thickening and thinning events during Mesozoic evolution of the NCC.

Oxygen and hydrogen isotopic compositions of coexistent minerals of the Tasigake alkali granite pluton, northern Xinjiang: constraints upon the cause of18OD depletion and the18O/16O exchange kinetics

Oxygen and hydrogen isotopic compositions have been determined of three coexistent mineral triplets of alkali feldspar, quartz, arfvedsonite of 11 samples collected from the Tasigake alkali granite pluton, Ulungur River region, northern Xinjiang. Isotopic exchange with meteoric water during subsolidus cooling caused strong18O-D depletion and the remarkable nonequilibrium18O/16O relation between coexistent minerals.18O/16O exchange kinetic effects of the three minerals are simultaneously and consistently modelled. Exsolution and microtextural reorganization of alkali feldspar, and infiltration of water have been mutually facilitated by each other. Shallow intrusion, and circulation of meteoric water throughout the pluton cool it effectively. As a result, the “heat engine” is rapidly extinguished, and the nonequilibrium18O/16O relation is frosen.

Mesozoic Multi-phase Magmatism and Gold Mineralization in the Early Precambrian North China Craton, Eastern Hebei Province, China: SHRIMP Zircon U-Pb Evidence

The early Precambrian North China craton (NCC) in eastern Hebei Province (also known as the Jidong area) was intruded by granitic batholiths and plutons spatially associated with gold deposits. No consensus has been reached regarding timing and tectonic setting of the gold deposits, chiefly due to the lack of reliable geochronological data. The gold deposits in the district are localized by NE-striking faults within granite plutons and/or nearby Archean amphibolites, as well as in Proterozoic sedimentary rocks. Gold mineralizations in the area are characterized by quartz (± albite) veinand sulfide-disseminated styles; both types of ores have relatively low sulfide contents (<10 vol%) and similar sulfide mineral assemblages dominated by pyrite + chalcopyrite + pyrrhotite + galena + sphalerite, locally with molybdenite, tellurides, and bismuthinoids. The alterations around the gold lodes include K-feldspathization, sericitization, silicification, chloritization, and sulfidation. Previous fluid inclusion data from all the deposits of the district show that the mineralizing fluids are characterized by relatively high salinities (3 to 17 wt% NaCl equiv.), H2O-CO2 ± CH4, N2 solutions, with CO2 contents in the inclusions ranging from 5 to 40 mol%. Fluid inclusion homogenization temperatures are between 240 and 400°C, and estimates of the trapping pressures vary significantly from 0.5 to 3.7 kbar. Stable isotope (O, H, S, C, and Pb) data from these deposits indicate a major magmatic component in the mineralizing fluids and the ore-forming materials, with a partial contribution by Archean host rocks, suggesting that these deposits are basically intrusion-related. SHRIMP zircon U-Pb geochronology of the gold-hosting granitic intrusions, in combination with previous Ar-Ar and Rb-Sr dates on hydrothermal minerals (e.g., sericite), indicates that there was no Archean gold mineralization, but instead suggests that at least three episodes of granitic magmatism and associated gold mineralization took place during the Mesozoic. The first episode occurred in the Late Triassic at ∼222 Ma, with emplacement of the Dushan granite batholith (223 ± 2 Ma), Sanjia granite porphyry (222 ± 4 Ma), and the Baizhangzi granite (222 ± 3 Ma). This episode of magmatism and gold mineralization was coeval with collision of the NCC with the South Mongolian block in the north along the Solonker suture and with the Yangtze craton in the south along the Dabie-Sulu suture. The second episode took place in the Early Jurassic, with emplacement of the Qingshankou granite (199 ± 2 Ma), and the third episode occurred in the Middle Jurassic, with intrusion of the Yuerya (∼ 175 Ma) and Niuxinshan (172 ± 2 Ma) and granites. These two events are about 25 and 45 Ma later than the collision of the NCC with other continental blocks in a post-collisional environment.

Yunnan-III models for Evolutionary population synthesis

We build the Yunnan-III evolutionary population synthesis (EPS) models by using the stellar evolution code, BaSeL stellar spectra library and the initial mass functions (IMFs) of Kroupa and Salpeter, and present colours and integrated spectral energy distributions (ISEDs) of solar-metallicity stellar populations (SPs) in the range of 1Myr-15Gyr. The main characteristic of the Yunnan-III EPS models is the usage of a set of self-consistent solar-metallicity stellar evolutionary tracks (the masses of stars are from 0.1 to 100M⊙). This set of tracks is obtained by using the state-of-the-art code. code can evolve stellar models through thermally pulsing asymptotic giant branch (TP-AGB) phase for low- and intermediate-mass stars. By comparisons, we confirm that the inclusion of TP-AGB stars make the V K, V J and V R colours of SPs redder and the infrared flux larger at ages log(t/yr) > 7.6 (the differences reach the maximum at log(t/yr)�8.6, �0.5-0.2mag for colours, � 2 times for K band flux). We also find that the colour-evolution trends of Model with-TPAGB at intermediate and large ages are similar to those from the code, which employs the Padova-AGB stellar library, BaSeL spectral library and the Kroupa IMF. At last, we compare the colours with the other EPS models comprising TP-AGB stars (such as CB07, M05, V10 and POPSTAR), and find that the B V colour agrees with each other but the V K colour exists larger discrepancy among these EPS models (�1mag when 8< log(t/yr)< 9). The stellar evolutionary tracks, isochrones, colours and ISEDs can be obtained on request from the first author or from our website (http://www1.ynao.ac.cn/�zhangfh/). Using the isochrones, you can build your EPS models. Now the format of stellar evolutionary tracks is the same as that in the code, you can put them into the code and get the SP’s results. Moreover, the colours involving other passbands or on other systems (for example, HST F439W F555W colour on AB system) can also be obtained on request.

The impact of binary stars on the colors of high-redshift galaxies

Context: Evolutionary population synthesis (EPS) models play an important role in many studies on the formation and evolution of galaxies. Most EPS models are still poorly calibrated for certain stellar evolution stages, especially for the treatment of binary stars, which are very different from single stars.

Oxygen isotopic (17O-18O) heterogeneity in Archaean continental nucleus, North China Craton

The oxygen isotopic data for amphibolites from Archaean continental nucleus, North China Craton indicate that ( i ) the evolving lines structured by the data are parallel to the geoselenic evolving line, which means that the parent materials of these continental nucleus originated from solar matter; ( ii ) different intercepts for these evolving lines manifest that oxygen isotopic compositions of different continental nucleus are heterogeneous, which means that these continental nucleuses originated from different parent resources with different original compositions.

Evidence of Nd isotope for unhomogeneity and origin of upper mantle of North China platform

Based on isptopic age of Sm-Nd and its initial composition and its evolution obtained during the recent years of archean metamorphic magnesio-ferro the vocanics of upper mantle of the North China platform, it is concluded that the isotopic composition of Archean upper mantle of the North China platform is not homogeneous, and values of IND don not change regularly through the whole Archean; in contrast, they present obvious differences in different regions. All this demands that the unhomogeneity of Archean upper mantle of the North China platform inherits initial unhomogeneity of origin, and the origin of the North China platform should contribute to uneven accumulation of planetesimals.