Forest biodiversity assessment in Peruvian Andean Montane cloud forest

Cloud forests are unusual and fragile habitats, being one of the least studied and least understood ecosystems. The tropical Andean dominion is considered one of the most significant places in the world as regards biological diversity, with a very high level of endemism. The biodiversity was analysed in an isolated remnant area of a tropical montane cloud forest known as the "Bosque de Neblina de Cuyas", in the North of the Peruvian Andean range. Composition, structure and dead wood were measured or estimated. The values obtained were compared with other cloud forests. The study revealed a high level of forest biodiversity, although the level of biodiversity differs from one area to another: in the inner areas, where human pressure is almost inexistent, the biodiversity values increase. The high species richness and the low dominance among species bear testimony to this montane cloud forest as a real enclave of biodiversity.     

罗布泊腾龙台地第四系含钾盐类矿物赋存特征分析

罗布泊腾龙台地第四系盐类矿物中部分地段含钾,局部已达工业品位.本文从含钾盐类矿物的主要赋存层位及分布特征入手,在大量观察钻孔岩心和薄片、样品测试基础上,对第四纪含盐系,尤其是含钾盐类矿物赋存特征和分布进行分析,初步总结了3种成矿模式,从沉积时代学角度分析了今后固体钾盐找矿方向.     

Comparing predicted and observed ground motions from subduction earthquakes in the Lesser Antilles

This brief article presents a quantitative analysis of the ability of eight published empirical ground-motion prediction equations (GMPEs) for subduction earthquakes (interface and intraslab) to estimate observed earthquake ground motions on the islands of the Lesser Antilles (specifically Guadeloupe, Martinique, Trinidad, and Dominica). In total, over 300 records from 22 earthquakes from various seismic networks are used within the analysis. It is found that most of the GMPEs tested perform poorly, which is mainly due to a larger variability in the observed ground motions than predicted by the GMPEs, although two recent GMPEs derived using Japanese strong-motion data provide reasonably good predictions. Analyzing separately the interface and intraslab events does not significant modify the results. Therefore, it is concluded that seismic hazard assessments for this region should use a variety of GMPEs in order to capture this large epistemic uncertainty in earthquake ground-motion prediction for the Lesser Antilles.     

2008年唐古拉山北5.5(M_S)级地震烈度考察

2008年6月10日唐古拉山北唐古拉兵站附近发生了5.5(M_S)级地震,根据地震烈度考察,宏观震中位于唐古拉兵站和青藏铁路777号桥附近,震中烈度为Ⅵ度,Ⅵ度区的面积3245km~2,呈椭圆形,长轴为北北东向,短轴为北西西向.现场调查和震源机制解表明本次地震的发震构造为北北东向的温泉断裂.     

Mineralogical feature and geological significance of muscovites from the Longyuanba Indosinian and Yanshannian two-mica granites in the eastern Nanling Range

Emplacement P-T condition estimations using granites are important for understanding metamorphic and erosional processes of orogenic belt.Granites are widespread in South China and a majority of them are peraluminous.Particularly,over 91%of the Indosinian granites exposed in the region are peraluminous in composition.It is extremely hard to determine the pressure of intrusion of these peraluminous granites due to the absence of amphibole,a good mineral barometer commonly identified in metaluminous granites.Muscovite is a common mineral in peraluminous granites,certain kind of it could be used as a mineral barometer to constrain the emplacement pressure of peraluminous granites.In this paper,results of petrographic and geochemical studies of muscovites from the Indosinian and early Yanshanian two-mica granites at the Longyuanba in the eastern Nanling Range are reported.Based on petrographic studies,the primary muscovite can be discriminated from the secondary muscovites.Muscovites from the Indosinian two-mica granites are enriched in Ti,Al,Mg,and Na,and depleted in Fe and Mn.Geochemically,these muscovites were considered as primary,whereas those from the Yanshanian two-mica granites fall into the area of secondary muscovite on discrimination diagrams.Barometer estimations show that pressures calculated for primary muscovites are accurate,but those calculated for secondary muscovites are overestimated.The average pressure of emplacement of the Longyuanba Indosinian two-mica granites is 5.9 kbar,corresponding to~19 km in depth,suggesting that the Indosinian granitic magmas were probably generated by partial melting of a thickened crust root in a compressional tectonic setting.     

Holocene fire and vegetation dynamics in a montane forest, North Cascade Range, Washington, USA

We reconstructed a 10,500-yr fire and vegetation history of a montane site in the North Cascade Range, Washington State based on lake sediment charcoal, macrofossil and pollen records. High-resolution sampling and abundant macrofossils made it possible to analyze relationships between fire and vegetation. During the early Holocene (> 10,500 to ca. 8000 cal yr BP) forests were subalpine woodlands dominated by Pinus contorta. Around 8000 cal yr BP, P. contorta sharply declined in the macrofossil record. Shade tolerant, mesic species first appeared ca. 4500 cal yr BP. Cupressus nootkatensis appeared most recently at 2000 cal yr BP. Fire frequency varies throughout the record, with significantly shorter mean fire return intervals in the early Holocene than the mid and late Holocene. Charcoal peaks are significantly correlated with an initial increase in macrofossil accumulation rates followed by a decrease, likely corresponding to tree mortality following fire. Climate appears to be a key driver in vegetation and fire regimes over millennial time scales. Fire and other disturbances altered forest vegetation at shorter time scales, and vegetation may have mediated local fire regimes. For example, dominance of P. contorta in the early Holocene forests may have been reinforced by its susceptibility to frequent, stand-replacing fire events.     

Recognition of Early Paleozoic Magmatisms in the Supposed Proterozoic Basements of Zhalantun, Great Xing’an Range, NE China

The Zhalantun terrane from the Xing'an massif, northeast China, was used to be considered as Proterozoic basements. However, amounts of detrital zircon ages from the meta-sedimentary rocks deny the existence of Precambrian basements recently. Notably, magmatic rocks were barely reported to limit the exact ages of the Zhalantun basements. In this study, we collected rhyolite, gabbro and quartz diorite for zircon in-situ U-Pb isotopic dating, which yield crystallization ages of ～505 Ma, ～447 Ma and ～125 Ma, respectively. Muscovite schist and siltstone define maximum depositional ages of ～499 Ma and ～489 Ma, respectively. Additionally, these dated supracrustal rocks and plutons also yield ancient detrital/xenocryst zircon ages of ～600–1000 Ma, ～1600–2220 Ma, ～2400 Ma, ～2600–2860 Ma. Based on the whole-rock major and trace element compositions, the ～505 Ma rhyolites display high SiO_2 and alkaline contents, low Fe_2O_3T, TiO_2 and Al_2O_3, and relatively high Mg O and Mg#, which exhibit calc-alkaline characteristics. These rhyolites yield fractionated REE patterns and negative Nb, Ta, Ti, Sr, P and Eu anomalies and positive Zr anomalies. The geochemistry, petrology and Lu-Hf isotopes imply that rhyolites were derived from the partial melting of continental basalt induced by upwelling of sub-arc mantle magmas, and then experienced fractional crystallization of plagioclase, which points to a continental arc regime. The ～447 Ma gabbros exhibit low Si O2 and alkaline contents, high Fe2 O3 T, Ti O2, Mg O and Mg#. They show minor depletions of La and Ce, flat MREE and HREE patterns, and negative Nb, Ta, Zr and Hf anomalies. Both sub-arc mantle and N-MORB-like mantle were involved in the formation of the gabbros, indicative of a probable back-arc basin tectonic setting. Given that, the previously believed Proterozoic supracrustal rocks and several plutons from the Zhalantun Precambrian basements were proved to be Paleozoic to Mesozoic rocks, among which these Paleozoic magmatic rocks were generally related to subduction regime. So far, none Proterozoic rocks have been identified from the Zhalantun Precambrian basement, though some ～600–3210 Ma ancient detrital/xenocryst zircons were reported. Combined with ancient zircon ages and newly reported ～2.5 Ga and ～1.8 Ga granites from the south of the Zhalantun, therefore, the Precambrian rocks probably once exposed in the Zhalantun while they were re-worked and consumed during later long tectonic evolutionary history, resulting in absence of Precambrian rocks in the Zhalantun.     

Metallogenesis and hydrothermal evolution of Middle Jurassic porphyry Mo deposits in the southern Zhangguangcai Range,NE China: evidence from fluid inclusions,H–O–S isotopes,and Re–Os geochronology

A major metallogenic belt with substantial resources of gold, lead, zinc, copper, and molybdenum is present in the southern Zhangguangcai Range, NE China. Several large porphyry Mo deposits are located in this belt, as for example at Jidetun, Fu’anpu, and Daheishan. Five molybdenite samples from the Jidetun deposit yielded an Re–Os isochron age of 168.6 ± 2.1 Ma (mean standard weighted deviation = 0.20), and this is consistent with the Re–Os isochron ages of the other Mo deposits in the southern Zhangguangcai Range, giving a Middle Jurassic age for metallogenesis. The Jidetun, Fu’anpu, and Daheishan deposits all tend to have weakly enriched ³⁴S values of 0.80‰–3.20‰ and relatively low Re contents ranging from 3.073 to 43.567 ppm, which indicates the ore-forming materials were derived mainly from granitic magmas that had an origin in the mixture of crust and mantle. Three stages of mineralization can be identified in the deposits at Jidetun, Fu’anpu, and Daheishan. The original ore-forming fluids in stage I were characterized by high-temperature magmatic hydrothermal fluids that were most likely derived by exsolution from the Middle Jurassic ore-bearing magmas. However, two different fluid systems, NaCl–H₂O–CO₂ fluids and NaCl–H₂O fluids, were widespread in stage I of porphyry Mo deposits in the southern Zhangguangcai Range. Taking into account the regional geological characteristics and tectonic setting, we suggest that two different emplacement modes of the ore-bearing magmas explain the different fluid systems in stage I: the first magmas were emplaced along the contact zones between the strata and earlier granitoids, whereas the second magmas were emplaced entirely within the earlier granitoid intrusions. The stage II and III fluids were characterized by relatively lower temperatures and low H–O isotopic values, indicating a gradual evolution from magmatic to meteoric sources.     

The earliest Jurassic A-type granite in the Nanling Range of southeastern South China: petrogenesis and geological implications

The tectonic transition from the palaeo-Tethyan to palaeo-Pacific dynamic domains in the South China Block (SCB) is still a matter of debate. The A-type granites collected from the southeastern SCB offered an opportunity to illustrate this tectonic transition. This article records a set of petrographic, geochronological, and geochemical data for the Wengong granitic pluton from the eastern Nanling Range. LA-ICP-MS zircon U–Pb dating shows a crystallization age of 196.9 ± 4.4 Ma with ε_Hf(t) values ranging from +2.1 to +7.7. The samples have high SiO₂, Zr+Nb+Ce+Y, FeOt/MgO, Ga/Al, and Y/Nb and are depleted in Nb–Ta, Zr–Hf, Ba, Sr, Ti, and Eu, similar to those of the A₂-type granite. Their initial ⁸⁷Sr/⁸⁶Sr ratios range from 0.70885 to 0.70983 and the ε_Nd(t) values range from ?2.9 to ?1.1, close to those of the Early Palaeozoic mafic rocks in the southeastern SCB. The Wengong A₂-type granite was derived from partial melting of the mafic rocks underplated into the lower crust during the Early Palaeozoic.

The Mesozoic A-type granites in the southeastern SCB can be subdivided into 229–215 Ma (Late Triassic), 197–152 Ma (Jurassic), and 135–92 Ma (Cretaceous). They differ in geochemical and spatial distribution characteristics. The Late Triassic A-type granites were formed in the post-collision extensional setting associated with the palaeo-Tethyan dynamic domain, whereas the Cretaceous A-type granites were under the control of the palaeo-Pacific dynamic domain. The A-type granites were hardly exposed during the Late Triassic–Early Jurassic and Late Jurassic–Early Cretaceous. The Jurassic A-type granites were formed in the intra-plate extensional setting, a response to the tectonic transition from the palaeo-Tethyan to palaeo-Pacific dynamic domains. Thus, the occurrence of the Wengong A₂-type granite indicates that this tectonic transition possibly initiated at the earliest Early Jurassic.     

Preservation and exhumation history of the Harizha-Halongxiuma mining area in the East Kunlun Range,Northeastern Tibetan Plateau,China

The extent to which ore bodies are preserved in orogenic belts remains a poorly understood area of ore deposit research. Using zircon and apatite fission track analysis together with apatite (U-Th)/He dating we constrained the erosion history of the ore bodies in the Harizha–Halongxiuma mining area of the East Kunlun Range, Northern Tibetan Plateau, China. Apatite fission-track ages range from 114 ± 8 to 87 ± 6 Ma, with mean track lengths varying from 11.4 ± 1.9 to 12.9 ± 2.0 μm. Zircon fission-track ages vary from 205 ± 14 to 142 ± 7 Ma. In addition, apatite (U–Th)/He dating yielded ages of 60–56 Ma. The thermal history of Jiapigou was modelled based on the apatite fission-track data, including ages and track lengths, with constraints of zircon fission-track ages and (U-Th)/He ages. The exhumation history of the Harizha–Halongxiuma mining area was reconstructed with these age data, revealing that since the early Mesozoic the area has undergone three cooling stages: (1) rapid cooling from 175 ± 30 Ma to 100 ± 10 Ma with a cooling rate and inferred exhumation of 2.0 ± 0.8 °C/Myr and 4.3 ± 1.7 km, respectively; (2) a relatively stable stage from 100 ± 10 Ma to 40 ± 10 Ma with a cooling rate and inferred exhumation of 0.3 ± 0.1 °C/Myr and 0.5 ± 0.2 km, respectively; and (3) rapid cooling since 40 ± 10 Ma with a cooling rate and inferred exhumation of 1.2 ± 0.6 °C/Myr and 1.4 ± 0.4 km, respectively. This exhumation history is consistent with the subduction process of Pacific plate and the strike slip movements of Dunmi fault. The total exhumation after main mineralization is calculated to be 7.6 ± 3.2 km, suggesting that ore bodies in the Harizha–Halongxiuma mining area remain partially preserved.