福建大田中山地带火炬松林分结构分析

研究分析了福建大田中山地带营造的30a生2种类型火炬松林的林分结构,结果表明:经营密度较高的A类林:林层结构简单,树种单一,为单层林,种群结构极不均匀,幼苗、幼树较少,种群呈衰老趋势,相对直径为1.0时,对应的株数累积百分比为69.78%。中径木占99.7%、中径木占绝对多数,大径木极少。经营密度较低(900株/hm2)的B类林:乔木层仍以火炬松占优势,但林下分布有甜槠等阔叶树,郁闭度0.4左右,初步形成异龄针阔混交林。种群出现Ⅲ级阔叶幼树,Ⅰ、Ⅱ级幼苗较多,种群处于恢复相对稳定阶段。相对直径为1.0时,对应的株数累计占比为59.78%。B类林中径木、大径木分别占69.67%和30.33%,有大径木273株/hm2。林分结构比较合理,可以培育火炬松大径木材。建议在中山地带营造火炬松林应及时进行林分密度调控,在培育火炬松大径材的同时,维持物种多样性,增强林分的生态功能。

找准定位调结构 培育产业促发展——对宜昌中山地带农业发展的调查与思考

文章先对中山地带进行了界定,进而对宜昌中山地带的分布及其农业发展现状进行了综合分析,对制约宜昌中山地带农业发展的各种因素做了剖析,并在此基础上,提出了促进宜昌中山地带农业发展的对策与建议。

巴中中山引种藏柏试验初报

巴中中山引种藏柏试验初报温跃明（巴中县林业局）藏柏（Ｃｕｐｒｅｓｓｕｓｔｏｒｕｉｏｓａ）原产西藏东南的墨脱、林芝、米林，沿雅鲁藏布江及其支流易贡茂布和西巴霞曲流域，以及印度北部、不丹、尼泊尔等地，原产地海拔２０００ｍ～２５００ｍ，多属河谷地带。藏柏在...

Digital Spectra and Analysis of Altitudinal Belts in Tianshan Mountains, China

Based on the framework of the geo-info spectra of montane altitudinal belts, this paper firstly reviews six classification systems for the spectra of mountain altitudinal belts in China and considers that detailed regional study of altitudinal belts is the key for reaching standardization and systemization of mountain altitudinal belts. Only can this further identify and resolve problems with the study of altitudinal belts. The factors forming the spectra of altitudinal belts are analyzed in the Tianshan Mountains of China, and a digital altitudinal belt system is constructed for the northern flank, southern flank, the heartland, and Ili valley in the west. The characteristics of each belt are revealed with a summarization of the pattern of areal differentiation of altitudinal belts.

Neogene coupling between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China

Based on the sedimentary and subsiding features of Kuqa foreland basin, this paper presents the following characteristics of Neogene coupling relationship between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China: (1) The Southern Tien Shan Orogen underwent Neogene uplifting of 4 km in height and the Kuqa Basin underwent Neogene subsidence of 4?6 km in depth accordingly beginning in 25 Ma; (2) The Southern Tien Shan Orogen moved continuously toward the Kuqa Basin, with largest structural shortening rate of greater than 53.7%, and the north boundary of the Kuqa Basin retreated continuously southward accordingly since the Miocene; (3) There are two subsidence centers with high subsiding rates and large subsiding extent, located in the eastern and western Kuqa Basin respectively, with the subsiding maximizing in the deposition period of Kuqa Formation.

Forming Proterozoic basement within eastern Central Asian Orogenic Belt:Evidence from zircon U-Pb-Hf-O isotopes

As part of the mosaic of micro-continents within the Central Asian Orogenic Belt(CAOB), the Xing’anAirgin Sum Block(XAB) features increasingly-recognized Meso-Neoproterozoic geological records. However, the origin, temporal-spatial distribution of ancient materials, and their roles in crust evolution remain to debate. This paper presents an integrated study of zircon U-Pb ages and Hf-O isotopes for Mesoproterozoic and Paleozoic granites from the Erenhot region of central Inner Mongolia, along eastern CAOB. The intrusion of 1450 Ma syenogranite denotes that the Precambrian basement of XAB extends from Sonid Zuoqi westward to Erenhot. The 384 and 281 Ma monzogranites containing Mesoproterozoic xenocrystic zircons possess Proterozoic-dominant two-stage Hf model ages, further suggesting the wide existence of Proterozoic crust beneath western XAB. Cyclic Proterozoic crustal growth and reworking seem to show close linkages with the orogenesis during relevant supercontinent cycles. 1450-1360 Ma juvenile crustal growth at Erenhot and synchronous ancient crust reworking at Sonid Zuoqi and Abagaqi were likely resulted from retreating subduction involved in Columbia breakup, while 1.2-1.0 Ga reworking and 0.9-0.7 Ga growth events within the Erenhot basement might respond to assembly and breakup of Rodinia, respectively. Besides, our work confirms that reworking of Neoproterozoic crust played important roles during Paleozoic multi-stage accretion of CAOB.

Soil respiration under three different land use types in a tropical mountain region of China

Soil respiration (SR) Wis one of the largest contributors of terrestrial CO_2 to the atmosphere.Environmental as well as physicochemical parameters influence SR and thus, different land use practices impact the emissions of soil CO_2. In this study, we measured SR, bi-monthly, over a one-year period in a terrace tea plantation, a forest tea plantation and a secondary forest, in a subtropical mountain area in Xishuangbanna, China. Along with the measurement of SR rates, soil characteristics for each of the land use systems were investigated. Soil respiration rates in the different land use systems did not differ significantly during the dry season, ranging from2.7±0.2 μmol m^(-2) s^(-1) to 2.8±0.2 μmol m^(-2) s^(-1). During the wet season, however, SR rates were significantly larger in the terrace tea plantation(5.4±0.5 μmol m^(-2)s^(-1)) and secondary forest(4.9±0.4 μmol m^(-2)s^(-1)) than in the forest tea plantation(3.7±0.2 μmol m^(-2) s^(-1)).This resulted in significantly larger annual soil CO_2 emissions from the terrace tea and secondary forest,than from the forest tea plantation. It is likely that these differences in the SR rates are due to the 0.5times lower soil organic carbon concentrations in thetop mineral soil in the forest tea plantation, compared to the terrace tea plantation and secondary forest.Furthermore, we suggest that the lower sensitivity to temperature variation in the forest tea soil is a result of the lower soil organic carbon concentrations. The higher SR rates in the terrace tea plantation were partly due to weeding events, which caused CO_2 emission peaks that contributed almost 10% to the annual CO_2 flux. Our findings suggest that moving away from heavily managed tea plantations towards low-input forest tea can reduce the soil CO_2 emissions from these systems. However, our study is a casestudy and further investigations and upscaling are necessary to show if these findings hold true at a landscape level.

Research on the Relationship between Active Faults and Earthquakes in the Junction Area of the China North-South Seismic Belt and Central Orogenic Belt Based on GIS

Research on the relationship between faults and seismicity in the junction area of China's north-south seismic belt and central orogenic belt based on the Geography Information System (GIS) has been done.For each of the 16 faults in this area,we build a 25km buffer zone and use overlay analysis to investigate the seismicity and its characteristics on each fault.The results unveil the main seismic faults as follows:the western segment of the northern-edge of the west Qinling fault,the southwestern segment of the Lixian-Luojiabao fault,the southeastern segment of the Lintan-Dangchang fault,the southwestern segment of the Wenxian fault,the Huya fault,and the Xueshan fault.The most active faults are the Huya and Xueshan faults,then the Tazang fault,the Lixian-Luojiabao fault and the northern piedmont of the Guanggaishan-Dieshan fault.The research zone can be divided into four areas according to focal depth,which gets deeper from north to south.The profile of focal depth indicates the geometry and mechanical property of faults,and further reveals the movement model of eastward extrusion of the Tibetan plateau and southeastward escape of masses,thus providing basis for the protection against earthquakes and hazard mitigation in this area.

Spatial Distribution Characteristic of the b-value in Dabie-Sulu and Its Adjacent Areas

The Tanlu （Tancheng-Lujiang） fault is one of the major structures in eastern China, which cuts across different blocks and controls the tectonic activity. Using the seismic data from the China Earthquake Networks Center, we investigate the spatial variations of the b-value in the Dabie-Sulu （Jiangsu-Shandong） organic belt by calculating the b-value of each grid （1~ xl~） from 1970 to 2010. The study shows that： the b-value is smaller in the Tanlu fault and its adjacent area, which might suggest that the major earthquake recurrence period is relatively long due to the lower frequency of small earthquake activity. In both sides of Tanlu fault, the b-value is higher at the edge of Sulu block and the eastern part of Dabie orogenic belt. The b values are higher in North China central orogenic belt, and small earthquake activity which occurred along the central orogenic belt is frequent. Additionally, combined with geological and geophysical study, we find that the b-value has a certain correspondence relationship with the lithologic distribution, which informs us that seismic activity features are closely related to the inhomogeneous media in the crust.

Microseismic Concentration Zones before and after the February 12,2014 M_S 7.3 Yutian Earthquake and the Possible Indication of an Earthquake Risk Zone

Since 2001, there have occurred in succession the 2001 Kunlun Mountains M S8. 1earthquake,the 2008 Wenchuan M S8. 0 earthquake,the 2010 Yushu M S7. 1 earthquake and the 2012 Lushan M S7. 0 earthquake in the periphery of the Bayan Har block. By comparison of the characteristics of seismic strain release variations before and after the Kunlun Mountains M S8. 1 earthquake in the same time length in the geodynamical related regions,we found that the seismic strain release was obviously enhanced after the earthquake in the Longmenshan area,Batang area,and the NS-trending valleys at the west of the Hot Spring Basin. The Wenchuan earthquake occurred in the first area,and the Yushu earthquake is related to the second area. After the earthquake rupture occurred on the East Kunlun fault zone on the northern boundary of the Bayan Har Block,crustal materials on the south side of the fault zone migrated to the southeast,leading to a concentration of tectonic deformation in the Longmenshan thrust belt, e ventually rupturing on the Longmenshan thrust belt. This earthquake case illustrates that seismicity enhancement zones are possibly prone to long-term destructive earthquakes. After the M S7. 3 earthquake in Yutian,Xinjiang on February 12,2014,earthquake frequency and seismic strain release markedly increased in the junction area between the eastern Qilian Mountain tectonic belt and the Altun Tagh fault zone,where more attention should be paid to the long-term seismic risk.

Crustal accretion and reworking processes of micro-continental massifs within orogenic belt:A case study of the Erguna Massif,NE China

This paper summarizes the geochronological, geochemical and zircon Hf isotopic data for Mesozoic granitoids within the Erguna Massif, NE China, and discusses the spatial-temporal variation of zircon Hf isotopic compositions, with the aim of constraining the accretion and reworking processes of continental crust within the Erguna Massif, and shedding light on the crustal evolution of the eastern segment of the Central Asian Orogenic Belt. Based on the zircon U-Pb dating results, the Mesozoic granitic magmatisms within the Erguna Massif can be subdivided into five stages: Early-Middle Triassic(249–237 Ma), Late Triassic(229–201 Ma), Early-Middle Jurassic(199–171 Ma), Late Jurassic(155–149 Ma), and Early Cretaceous(145–125 Ma).The Triassic to Early-Middle Jurassic granitoids are mainly I-type granites and minor adakitic rocks, whereas the Late Jurassic to Early Cretaceous granitoids are mainly A-type granites. This change in magmatism is consistent with the southward subduction of the Mongol-Okhotsk oceanic plate and subsequent collision and crustal thickening, followed by post-collision extension. Zircon Hf isotopic data indicate that crustal accretion of the Erguna Massif occurred in the Mesoproterozoic and Neoproterozoic. ZirconεHf(t) values increase gradually over time, whereas two-stage model(TDM2) ages decrease throughout the Mesozoic. The latter result indicates a change in the source of granitic magmas from the melting of ancient crust to more juvenile crust. Zircon εHf(t)values also exhibit spatial variations, with values decreasing northwards, whereas TDM2 ages increase. This pattern suggests that,moving from south to north, there is an increasing component of ancient crustal material within the lower continental crust of the Erguna Massif. Even if at the same latitude, the zircon Hf isotopic compositions are also inconsistent. These results reveal lateral and vertical heterogeneities in the lower continental crust of the Erguna Massif during the Mesozoic, which we use as the basis of a structural and tectonic model for this region.

Mesozoic contraction deformation in the Yanshan and northern Taihang mountains and its implications to the destruction of the North China Craton

Mesozoic contraction deformation in the Yanshan and Taihang mountains is characterized by basement-involved thrust tectonics,basement-cored buckling anticlines and ductile thrust and nappe tectonics.Most of these deformations are orientated west-east,west-northwest and northeast to north-northeast.The contraction deformations began in the Permian,continued through the Triassic and Jurassic and terminated in the Early Cretaceous,and constitute an important part of the destruction of the North China Craton.It is estimated,from balanced cross-section reconstructions,that the north-south shortening of the central part of the Yanshan belt before 135 Ma was around 38%.The initial crust thickness,pre-dating the major contraction deformation in late Paleozoic and early Mesozoic,was estimated to be around 35 km based on paleogeographic characteristics.Assuming that the inferred depth of ductile thrusting deformation,20-25 km,was the crust thickness involved in the contraction deformation,and also assuming that the N-S contraction deformation was accommodated by vertical crust thickening,the thickness of the crust after the contraction deformation was expected to be around 47-50 km.This was the approximate crust thickness required for the eclogitization of the lower crust for delamination.The gravity potential accumulated by the isostatic uplift of the thickened crust,together with the decrease in crustal strength caused by the coeval magmatisms associated with the contraction deformation,led to the subsequent extensional collapse of the middle and upper crust although the regional stress regime associated with the plate interactions remained constant.It is inferred that the Mesozoic contraction deformations in the Yanshan and Taihang mountains were not only a significant tectonic process contributing to the destruction of the craton in middle and upper crust but also stimulated delamination at a deep level and the extension of the shallow crust.In other words,both the suspected delamination of the lower crust and upper mantle and the well constrained extension deformations of the shallow crust in the eastern North China Craton during the late Mesozoic are a consequence of crust thickening due to previous contractions.Extensional deformations could be expected to occur independently in the shallow crust,and are not necessarily associated with or responding to delamination at a deep level.

Palaeozoic tectonic evolution of the Tianshan belt,NW China

The Chinese Tianshan belt is a major part of the southern Central Asian Orogenic Belt, extending westward to Kyrgyzstan and Kazakhstan. Its Paleozoic tectonic evolution, crucial for understanding the amalgamation of Central Asia, comprises two stages of subduction-collision. The first collisional stage built the Eo-Tianshan Mountains, before a Visean unconformity, in which all structures are verging north. It implied a southward subduction of the Central Tianshan Ocean beneath the Tarim active margin, that induced the Ordovician-Early Devonian Central Tianshan arc, to the south of which the South Tianshan back-arc basin opened. During the Late Devonian, the closure of this ocean led to a collision between Central Tianshan arc and the Kazakhstan-Yili-North Tianshan Block, and subsequently closure of the South Tianhan back-arc basin, producing two suture zones, namely the Central Tianshan and South Tianshan suture zones where ophiolitic melanges and HP metamorphic rocks were emplaced northward. The second stage included the Late Devonian-Carboniferous southward subduction of North Tianshan Ocean beneath the Eo-Tianshan active margin, underlined by the Yili-North Tianshan arc, leading to the collision between the Kazakhstan-Yili-NTS plate and an inferred Junggar Block at Late Carboniferous-Early Permian time. The North Tianshan Suture Zone underlines likely the last oceanic closure of Central Asia Orogenic Belt; all the oceanic domains were consumed before the Middle Permian. The amalgamated units were affected by a Permian major wrenching, dextral in the Tianshan. The correlation with the Kazakh and Kyrgyz Tianshan is clarified. The Kyrgyz South Tianshan is equivalent to the whole part of Chinese Tianshan （CTS and STS） located to the south of Narat Fault and Main Tianshan Shear Zone; the so-called Middle Tianshan thins out toward the east. The South Tianshan Suture of Kyrgyzstan correlates with the Central Tianshan Suture of Chinese Tianshan. The evolution of this southern domain remains similar from east （Gangou area） to west until the Talas-Ferghana Fault, which reflects the convergence history between the Kazakhstan and Tarim blocks.

Crustal structures of the Weihe graben and its surroundings from receiver functions

We use 15 seismic stations, crossing the Qinling orogen （QO）, Weihe graben （WG） and Ordos block （OB）, to study the crustal structures by receiver functions （RFs） methods. The results show quite a difference in crustal structures and materials of three tectonic units （orogenic belt, extentional basin and stable craton）. The average crustal thickness in the northern QO is 37.8 km, and Poisson ratio is 0.247, which indicates the increase of felsic materials in QO. In the southern OB, the average crustal thickness is 39.2 km and Poisson ratio is 0.265. Comparatively high value of Poisson ratio is related with old crystallized base in the lower crust and shallow sediments. The artificial RFs reveal that low-velocity and thick sediments have a significant ef fect on phases of the MohoroviEi6 discontinuity （Moho）. As a result, the Moho phases in WG are tangled. S-wave velocity （Vs） inversion shows that there are shallow sediment layers with 4-8 km＇s thickness and high velocity zones in the middle-lower crust in WG. Complex Moho structure and high velocity zone may have been induced by the activities of the Weihe faults series.

Methods and application of using detrital zircons to trace the provenance of loess

The composition of single-grain detrital zircons is an effective provenance indicator of loess,and sheds new light on dust formation and transportation.Here we review the features of detrital zircons and their use as a provenance indicator,including internal structure,trace element,U-Pb age spectrum and Hf isotopic compositions,and present a case study from the Horqin sandy land and its surrounding loess.The loess samples have detrital zircon age peaks in range of 2600-2300,2100-1600,and 600-100 Ma,of which the 2600-2300 Ma zircon grains mainly have positive Hf(t) values(3.4-8.7),the 2100-1600 Ma zircon grains mainly have negative Hf(t) values(10.1-6.8),and the 600-100 Ma zircon grains have a variable Hf(t) values ranging from 21 to 15.9.The detrital zircon signatures of the loess are similar to the Horqin sandy land,but clearly different from the Chinese Loess Plateau and central-western deserts,implying that the loess is transported mainly from the Horqin sandy land in the Last Glacial period.Comparing these with neighboring tectonic units,we found that zircon populations at 2600-2300,2100-1600,and 600-100 Ma with negative Hf(t) values may come from the northeast North China Craton(NCC),and those at 600-100 Ma with positive Hf(t) values may come from the east Central Asian Orogenic Belt(CAOB).It is estimated that the two sources contribute equally to the Horqin sandy land and the surrounding loess.