Vertical differentiation of land cover in the central Himalayas

Characterized by obvious altitudinal variation, habitat complexity, and diversity in land cover, the Mt. Qomolangma region within the central Himalayas is one of the most sensitive areas to climate change in the world. At the same time, because the Mt. Qomolangma region possesses the most complete natural vertical spectrum in the world, it is also an ideal place to study the vertical structure of alpine land cover. In this study, land cover data for 2010 along with digital elevation model data were used to define three methods for dividing the northern and southern slopes in the Mt. Qomolangma region, i.e., the ridgeline method, the sample transect method, and the sector method. The altitudinal distributions of different land cover types were then investigated for both the northern and southern slopes of the Mt. Qomolangma region by using the above three division methods along with Arc GIS and MATLAB tools. The results indicate that the land cover in the study region was characterized by obviously vertical zonation with the south-six and north-four pattern of vertical spectrum that reflected both the natural vertical structure of vegetation and the effects of human activities. From low to high elevation, the main land cover types were forests, grasslands, sparse vegetation, bare land, and glacier/snow cover. The compositions and distributions of land cover types differed significantly between the northern and southern slopes; the southern slope exhibited more complex land cover distributions with wider elevation ranges than the northern slope. The area proportion of each land cover type also varied with elevation. Accordingly, the vertical distribution patterns of different land cover types on the southern and northern slopes could be divided into four categories, with glaciers/snow cover, sparse vegetation, and grasslands conforming to unimodal distributions. The distribution of bare land followed a unimodal pattern on the southern slope but a bimodal pattern on the northern slope. Finally, the use of different slope division methods produced similar vertical belt structures on the southern slope but different ones on the northern slope. Among the three division methods, the sector method was better to reflect the natural distribution pattern of land cover.     

Orbital imprint on Holocene palaeohydrological variations in west‐central Europe as reflected by lake‐level changes at Cerin (Jura Mountains,eastern France)

This paper presents a lake‐level record for the Holocene at Lake Cerin (Jura Mountains, eastern France). It is based on a range of sedimentological techniques validated in previous studies, with a combination of systematic lithostratigraphic investigations of the infillings accumulated in the lacustrine basin, and sediment analyses of two selected cores. The chronology is based on 10 radiocarbon dates and pollen stratigraphy. On a millennial scale, the Cerin lake‐level record shows three distinct successive phases characterised by higher lake‐level conditions until ca. 9000 cal. a BP, followed by a maximal lowering at ca. 9000–8500 cal. a BP, and a progressive rise until the present. This rise was punctuated by centennial‐scale fluctuations, with major events around 4000, 2800 and after 1500 cal. a BP. Considered on a multimillennial scale, the general pattern of palaeohydrological changes reconstructed at Cerin reflects the impact of orbitally driven summer insolation. This is in agreement with other regional and extra‐regional palaeoclimatic records, although every record shows peculiarities in timing and shape depending on the proxy used for reconstruction. In this general context, centennial to multicentennial oscillations appear to have been second‐order events in comparison with the major influence of the orbital factor. Copyright © 2011 John Wiley & Sons, Ltd.     

First evidence for episodic flooding events in the arid interior of central Saudi Arabia over the last 60 ka

Although evidence for Quaternary environmental changes in the Arabian Peninsula is now growing, research has mostly been conducted in the United Arab Emirates (UAE) and in the Sultanate of Oman. There have been virtually no recent studies in Saudi Arabia, especially in the central region such as around Al‐Quwaiayh. In this area there are a series of outwash plains developed along the eastern edge of the Arabian Shield that formed in the late Quaternary. Four sedimentary sections, which are representative of the deposits that have accumulated, have been studied and five luminescence ages obtained. These are the first luminescence ages acquired from Quaternary sediments in central Saudi Arabia. The preserved fluvial deposits in the study area have formed during humid events at ca. 54 ka, ca. 39 ka and ca. 0.8 ka. In more recent times aeolian sands have been encroaching on to the distal parts of the outwash plains. Copyright © 2008 John Wiley & Sons, Ltd.     

Assessment of diversity, distribution, conservation status and preparation of management plan for medicinal plants in the catchment area of parbati hydroelectric project stage — III in Northwestern Himalaya

The developmental activities, particularly the construction of hydroelectric projects are causing a great loss of biodiversity in the Indian Himalayan Region. The Himachal Pradesh, a part of IHR is well known for the development of hydroelectric projects. The Parbati H.E. Project is amongst the major projects of the State. The different stages of the project are all causing loss of biodiversity of the area. Stage III of the Parbati H.E. Project is a run of the river scheme on the Sainj River downstream of Power House of Parbati H.E. Project Stage II. The project shall utilize regulated discharge of Parbati H.E. Project Stage II and inflow of River Sainj for power generation, and has been contemplated as a peaking station operating in tandem with Stage II. The present study has been undertaken to see the impact of hydroelectric project on the biodiversity, particularly on medicinal plants. A total of 104 species of medicinal plants, belonging to different life forms, i.e., trees (23 spp.), shrubs (22 spp.), herbs (57 spp.) and ferns (2 spp.) were recorded. The species have been analyzed and studied for their distribution, classification, altitudinal zones, part (s) used, indigenous uses, nativity, endemism and rarity. DDifferent parts of these species, such as whole plants, roots (including rhizomes and tubers), leaves, flowers, fruits, seeds, stems, barks, spikes, nuts and insect galls are used by the inhabitants for curing various diseases and ailments. 30 species are native to the Himalayan region, 9 species native to the Himalayan region and adjacent countries also and 65 species are non-natives. 9 species are near endemics. Considering the whole Himalaya as a biogeographic unit (sensu lato), the near endemics are endemic to the Himalaya. Among these species, Zanthoxylum armatum is categorized as Endangered and Valeriana wallichii as Vulnerable. Hedychium spicatum, Rhus javanica, Berberis lycium, Thalictrum foliolossum, Salvia lanata, Rubia cordifolia and Bergenia ligulata may be considered as threatened species due to their over exploitation for trade. 90 species are propagated by seeds, 8 species by seeds and rhizomes/roots/tubers, 4 species by seeds and cuttings, and 2 species by sori. A management plan for the cultivation and conservation of the medicinal plants in the dam submergence area, and the commercially viable medicinal plants with high value in the catchment area is suggested.     

Timing relationships between pegmatite emplacement,metamorphism and deformation during the intra‐plate Alice Springs Orogeny,central Australia

In the Harts Range (central Australia), the upper amphibolite facies to lower granulite facies, c. 480–460 Ma Harts Range Metamorphic Complex (HRMC), and the upper amphibolite facies, c. 340–320 Ma Entia Gneiss Complex are cut by numerous, generally peraluminous pegmatites and their deformed equivalents. The pegmatites have previously been interpreted as locally derived partial melts. However, SHRIMP U–Pb monazite and zircon dating of 29 pegmatites or their deformed equivalents, predominantly from the HRMC, reveal that they were emplaced episodically throughout almost the entire duration of the polyphase, c. 450–300 Ma intra‐plate Alice Springs Orogeny. Episodes of pegmatite intrusion correlate with the age of major Alice Springs‐age structures and with deposition of syn‐orogenic sedimentary rocks in the adjacent Centralian Superbasin. Similar Alice Springs ages have not been obtained from anatectic country rocks in the HRMC, suggesting that the pegmatites were not locally derived. Instead, they are interpreted as highly fractionated granites, and imply that much larger parental Alice Springs‐age granites exist at depth. The mechanism to allow repeated felsic magmatism in an intraplate setting, where all exposed rock types had a previous high‐temperature history, is enigmatic. However, we suggest that episodic underthrusting and dehydration of unmetamorphosed Centralian Superbasin sedimentary rocks allowed crustal fertility to maintained over a c. 140 Ma interval during the intra‐plate Alice Springs Orogeny.     

Looking beneath the Stawell and Bendigo zones in Victoria,Australia: a view through the granite window

Abstract

Information, mainly from the granitic and silicic volcanic rocks in the Stawell, Bendigo and Melbourne structural zones in the state of Victoria, shows that the sources of both the S- and I-type rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with the sources of similar granitic rocks in the Melbourne Zone, consistent with the absence of the mainly Proterozoic Selwyn Block beneath most of the SBZ. Below a mid-crustal décollement in the SBZ, the crust is evidently highly variable and possibly includes thinned Proterozoic crust. There is geochronological evidence for ca 400 and ca 370?Ma granulite-grade metamorphic events here, and, after this double bout of metamorphism, and depletion in the silicic melt component, the constituents of the entire deep crust of the SBZ would have densities similar to those of overlying, much lower-grade Cambrian metabasaltic to boninitic rocks. Thus, granitic magmas may have formed here by partial melting of a variety of rock types, probably with back-arc affinities, with ages that may extend back to the Proterozoic. Therefore, the basement of the SBZ is unlikely to consist solely of thick ocean-floor rocks, as in some current interpretations.

1. KEY POINTS

2. The sources of the Devonian granitic rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with those of the Melbourne Zone granites.

3. Two Devonian granulite-facies events left the melt-depleted deep SBZ crust with densities similar to those of overlying Cambrian metabasaltic rocks.

4. The SBZ Devonian granitic magmas probably formed by partial melting of heterogeneous Proterozoic to Cambrian arc-related crust, below the mid-crustal décollement.

     

Eocene migmatite formation and diachronous burial revealed by petrochronology in NW Himalaya,Zanskar

In this contribution, we highlight the importance of in-situ monazite geochronology linked to P−T modelling for identification of timescales of metamorphic processes. Barrovian-type micaschists, migmatites and augengneiss from the Gumburanjun dome in the southeastern extremity of the Gianbul dome, NW Himalaya, have been studied in order to correlate the early stages of Himalayan metamorphism at different crustal levels and infer the timing of anatexis. P−T−t paths are constrained through combined pseudosection modelling and in-situ and in-mount monazite and xenotime laser ablation–split-stream inductively coupled plasma-mass spectrometry. Petrography and garnet zoning combined with pseudosection modelling show that garnet-staurolite schists record burial from ~530 to 560°C and 5.5 kbar to ~630 to 660°C and 7 kbar; staurolite-kyanite schists from ~530 to 560°C and 5 kbar to ~670 to 680°C and 7−9 kbar; and garnet-kyanite migmatites from 540−570°C and 5 kbar to ~680 to 750°C and 7−10 kbar, probably also to >750°C and >9 kbar above the muscovite stability field. The decompression paths of garnet-staurolite schists indicate cooling on decompression, while garnet rim chemistry and local sillimanite growth point to a stage of re-equilibration at ~600 to 670°C and 4−6 kbar in some of the staurolite-kyanite schists, and at ~670 to 700°C and 6 kbar in garnet-kyanite migmatites. Some of the staurolite-kyanite schists and garnet-kyanite migmatites also contain andalusite or andalusite-cordierite. Monazite and xenotime were analysed in thin sections in garnet, staurolite and kyanite, and in the matrix; and in mounts. BSE images and compositional maps of monazite (xenotime was too small) show variable internal structures from homogeneous through patchy zoning with embayed to sharp boundaries. Two groups of samples can be identified on the basis of the presence or absence of c. 44 − 37 Ma ages. The first group of samples—two garnet-staurolite schists—recorded only c. 31 − 27 Ma ages in porphyroblasts and no c. 40 Ma ages. The second group (samples of staurolite-kyanite schist, garnet-kyanite migmatites, augengneiss) have both the older, c. 44 − 37 Ma monazite ages in porphyroblasts and younger ages down to c. 22 Ma. These significantly different ranges of ages from porphyroblasts of 44−37 Ma, and 31−27 Ma, are interpreted as the duration of prograde P−T paths in Eocene and Oligocene, and indicate diachronous two-stage burial of rocks. Early migmatization occurred at 38 Ma. The c. 29 Ma is interpreted as the time when rocks from the lower and middle crustal levels were partially exhumed and came in to contact with rocks that were downgoing at this time. Localized monazite recrystallization is as young as 26−24 Ma. The youngest ages of 23−22 Ma are related to leucogranite emplacement.     

Petrology and tectonic significance of metabasite slivers in the Lesser and Higher Himalayan domains of Sikkim,India

The metamorphic history of the Himalayas has been constrained mostly through studies of the ubiquitous metapelitic rocks. Non‐eclogitic metabasite rock lenses that occur intercalated with the metapelites have received little attention and it is not clear whether they share a common metamorphic history. This study reports the results of a petrological study of the metabasite lenses (dm³–m³) from the Lesser Himalayan (LH) and the Higher Himalayan (HH) domains in Sikkim. These have similar bulk chemical compositions and chemical affinities (sub‐alkaline tholeiitic basalts), with plagioclase and amphibole as the dominant mineralogical constituents. Garnet and clinopyroxene occur in some samples depending on small variations in bulk chemistry; and orthopyroxene is developed as a retrograde phase in some rocks. Minor phases are ilmenite, chlorite, titanite and rutile. The rocks were metamorphosed at similar conditions (～9–12 kbar, 800 °C). Minor differences in bulk chemical composition lead to different phase assemblages and mineral chemistry in adjacent metabasite lenses, a feature that is used to demonstrate that metamorphic conditions (peak P–T as well as retrograde P–T path) can be reliably retrieved through a combination of pseudosection analysis and kinetically constrained individual thermobarometry. The peak P–T conditions of the metabasites from this region are independent of the present geographic or tectonic (i.e. within the LH or HH) location of the samples and they differ from the conditions at which the regional metapelites (i.e. metapelites not immediately adjacent to the metabasite lenses) were metamorphosed. Metapelites that are immediately adjacent to the metabasite lenses differ in their appearance, phase assemblage and recorded P–T history from those of the regional metapelites, either because they were emplaced as slivers along with the metabasites, or because they were modified when they came in contact with the metabasites. The retrograde P–T paths of the LH and HH metabasites are different: the HH samples underwent steep decompression whereas the LH followed a more gentle exhumation path. The P–T conditions of peak metamorphism (9–12 kbar, 800 °C) are commensurate with a thermal perturbation at the base of a crust of average thickness and may be the signature of a widespread (samples found across different regions in the Himalaya) and long‐lasting (e.g. homogeneous garnet compositions) crustal underplating event that occurred during the early stages (?subduction) of the Himalayan orogeny, or earlier if the metamorphism was pre‐Himalayan.     

渤海湾中部中、新生代构造演化与潜山的形成

渤海湾盆地是华北克拉通东部的晚中—新生代断陷盆地,其东部为西太平洋活动大陆边缘,经历了多期不同性质的构造运动叠加。目前对渤海湾地区中—新生代的构造期次划分及各期次构造运动的应力状态的认识仍存在较大的争议。潜山是盆地沉积之前就已形成的基岩古地貌山,后被新地层覆盖而成,潜山内幕所保留的先存断裂及潜山与上覆盖层之间的接触关系为研究盆地构造运动提供了依据。本文以渤中19-6潜山构造为例,基于三维地震资料的精细解释、结合相干剖面及钻井资料进行系统构造解析,建立渤中19-6潜山构造演化新模型,并探讨了华北克拉通东缘的区域构造演化。研究结果表明:(1)渤中19-6潜山构造西部以一系列S-N向雁列式正断层为界,断层东侧为隆起的渤中19-6潜山构造,西侧为低洼的沙南凹陷。古潜山最早形成于晚三叠世,早白垩世形成如今以S-N向正断层为界的东隆西降的潜山构造格局;(2)渤中19-6潜山构造西部边界S-N向断裂以及上覆地层中存在的E-W向断裂为两侧大型走滑带间雁列式断裂构造,是该潜山构造储层形成的重要控制因素;(3)该潜山受华北板块与扬子板块剪刀式闭合碰撞和古太平洋板块NNW向俯冲的多重影响,中生代以来,共经历了印支早期挤压隆起、印支晚期伸展改造、燕山早期左行压扭改造、燕山中期左行伸展改造、燕山晚期左行压扭改造、喜山期右行伸展埋藏6个阶段的发育演化。