Evaluation and forecast of human impacts based on land use changes using multi-temporal satellite imagery and GIS: A case study on Zanjan,Iran

Land use and land cover changes due to human activities in a time sequence. Detection of such changes may help decision makers and planners to understand the factors in land use and land cover change in order to take effective and useful measures. Remote sensing and GIS techniques may be used as efficient tools to detect and assess land use change.     

Models on Snowball Earth and Cambrian explosion: A synopsis

During the late Proterozoic from 1000 to 542 Ma, the Earth is thought to have been frozen at least during two times: in the Sturtian (715–680 Ma) and in the Marinoan (680–635 Ma) global glaciations. Following the Marinoan Snowball Earth, large multi-cellular animals of the Ediacara fauna flourished as a prelude to the Phanerozoic world. Here we summarize the most popular models on the cause and cessation of Snowball Earth. Episodic decrease of greenhouse gas occurs through the effect of erosion and weathering promoted by either mountain building or by an increase in the coastlines during the break-up of supercontinents. Effects on the globe caused by true polar wander, eruption of voluminous flood basalts, or dramatic reduction in planetary obliquity can also lead to ice ages and mass extinction. A radically revised concept based on Earth's magnetic intensity has also been proposed, which explains the true polar wander through a quasi-polar dynamo model. The ‘switch-on’ and ‘switch-off’ of the Earth's strong dynamo can lead to the onset and disappearance of the Snowball Earth. The galactic model infers that gamma ray burst associated with starburst creates huge amounts of clouds which would cut off sun rays and freeze the Earth.The Snowball Earth event is considered to have exerted a significant control on the subsequent revolutionary changes in the evolution of life forms. Although according to the biological clock, extensive re-organisation of genome is thought to have been completed by around 900 Ma, the evolution of modern life in Cambrian occurred only after the geochemical bridge was in place with elevated oxygen and nutrient levels in lakes that developed within continental rifts where the hydrothermal system in the granitic basement created the chemical environment enriched in Ca²⁺, Fe²⁺, V, Mo, HCO₃, phosphate and other elements required for building the skeleton and bone of the first modern animals. With cosmic radiation exerting a significant control on the mutation, the Neoproterozoic Earth history illustrates the possible link from Galaxy to the genome level.     

Petrology, geochemistry and paleogeographic reconstruction of the East Sulawesi Ophiolite, Indonesia

The East Sulawesi Ophiolite (ESO) is tectonically dismembered and widely distributed in Central and East Sulawesi. It comprises, from base to top, residual mantle peridotite and mafic–ultramafic cumulate through layered to isotropic gabbro, to sheeted dolerites and basaltic volcanic rocks. Residual peridotite is dominantly spinel lherzolite intercalated with harzburgite and dunite. Ultramafic rocks from different locations display significant differences in rock composition and mineral. However, the clinopyroxene of peridotite displays REE pattern similarities with those of mid-ocean ridge (MOR) origin, rather than those of suprasubduction zone (SSZ) origin. The gabbroic unit consists of massive gabbro, layered gabbro, mafic and ultramafic cumulate and anorthosite. The observed crystallization sequence of gabbroic unit, which is olivine→(spinel)→plagioclase→clinopyroxene→(orthopyroxene)→(hornblende), and the mineral chemistry data indicate that the ESO gabbro has similarities with MOR setting.Major and trace element geochemistry of basalt and dolerite suggests MOR, oceanic plateau and minor SSZ origins. A possible oceanic plateau origin is supported by the following: (i) the 15-km thickness is comparable with the thickness of oceanic plateau rather than normal oceanic lithosphere; (ii) there are no or only minor olivine phenocrysts in the basalt; and (iii) predominance of aphyric texture in the basalts. The REE pattern of ESO basalt exhibits N-MORB-like signatures. However, a negative Nb anomaly in the trace element spider diagram may be attributed to mantle heterogeneity of an OPB source.The geochemical variations and disparities for both peridotite and basalt and the noncogenetic relationship between crust and mantle sections in several locations suggest that the ESO may have been formed at one tectonic setting and was later overprinted by magmatism in different environments through its birth to emplacement. A possible Cretaceous origin of an oceanic plateau component of the ESO is indicated on the basis of calculated paleopositions using plate trajectory analyses together with previously published paleolatitude data. The ESO can be traced back to the proximity of the presently active region of the SW Pacific Superplume.     

Large areal extent of ultrahigh-pressure metamorphism in the Sulu ultrahigh-pressure terrane of East China: new implications from coesite and omphacite inclusions in zircon of granitic gneiss

Coesite and omphacite inclusions have been identified for the first time as minute inclusions in zircon from amphibolite-facies granitic orthogneiss in the Sulu ultrahigh-pressure (UHP) metamorphic terrane of eastern China by Raman spectroscopy and microprobe analyses. The occurrences of these minerals in the voluminous granitic gneiss of Sulu support a regional and pervasive UHP metamorphic event that predated regional amphibolitic retrogression. Taking into account the widespread discoveries of coesite in other lithologies, we thus conclude that a substantial crustal component in the Sulu UHP metamorphic terrane appears to have shared a common history of Triassic subduction to mantle depths and later exhumation.     

含柯石英锆石的SHRIMP U-Pb定年:胶东印支期超高压变质作用的证据

苏鲁超高压变质带的形成时代究竟是印支期还是新元古代争议始终很大。对山东胶南地区超高压变质带中超镁铁岩和榴辉岩的锆石激光拉曼、阴极发光和离子探针原位定年的研究获得超高压变质作用发生的时代为印支期。其中超镁铁岩含柯石英锆石的年龄为221±12Ma,该深成岩侵位时代为新元古代(581±44Ma)。此外,锆石中另有约400Ma年龄记录,可能代表岩石形成后另有一期热事件。榴辉岩的下交点年龄为228±29 Ma,与超镁铁岩含柯石英锆石年龄一致,代表超高压变质时代;上交点为中元古代(1821±19Ma),代表原岩年龄,后者与其片麻岩围岩时代相一致,说明榴辉岩是原位俯冲。     

Identification of Lower Pleistocene widespread tephras associated with large caldera-forming eruptions in the Tohoku area,north-east Japan

Tephra fingerprinting techniques contributing to volcanology and palaeoenvironmental studies have been developed using a combination of laser-ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). In particular, femtosecond LA-ICP-MS can determine major- and trace element abundances in individual glass shards. On the basis of the major oxide and trace element composition of the glass shards, using those methods, we re-examined the identification of four lower Pleistocene tephras originating from north-east Japan. All trace element abundances exhibited the typical pattern of tephras from the Hokkaido–Tohoku area, and major element concentrations were distinct. As a result, we re-examined the correlation of the widespread Tmg-R4 tephra (2.0 Ma), and newly defined the widespread Kd44-Naka tephra (1.968–1.781 Ma), both originating from the Sengan geothermal region. Furthermore, we re-examined identifications of Sr-Asn-Kd8 (1.219 Ma) and Sr-Kc-U8 (0.922–0.910 Ma) in central Japan, both derived from the Aizu volcanic region. The extensive distributions of the former two tephras suggest the occurrence of two large caldera-forming eruptions (Volcanic Explosivity Index 7) during a short period. Also, the distributions and volumes of the latter two tephras are broader and larger than those previously assumed. The results provide insight into large volcanic eruption history and terrestrial and marine palaeoenvironmental history.     

Role of tonalite-trodhjemite-granite (TTG) crust subduction on the mechanism of supercontinent breakup

The tonalite-trondhjemite-granite (TTG) crust has been considered to be buoyant and hence impossible to be subducted into the deep mantle. However, recent studies on the juvenile arc in the western Pacific region indicate that immature island arcs subduct into the deep mantle in most cases, except in the case of parallel arc collision. Moreover, sediment trapped subduction and tectonic erosion are also common. This has important implications in evaluating the role of TTG crust in the deep mantle and probably on the bottom of the mantle. Because the TTG crust is enriched in K, U and Th, ca. 20 times more than that of CI chondrite, the accumulated TTG on the Core Mantle Boundary (CMB) would have played a critical role to initiate plumes or superplumes radiating from the thermal boundary layer, particularly after 2.0 Ga, related to the origin of superplume-supercontinent cycle. This is because selective subduction of oceanic lithosphere including sediment-trapped subduction, tectonic erosion and arc- and microcontinent-subduction proceeded under the supercontinent before the final amalgamation ca. 200-300 million years after the formation of the nuclei. We speculate the mechanism of superplume evolution through the subduction of TTG-crust and propose that this process might have played a dominant role in supercontinent breakup.     

Granite subduction: Arc subduction, tectonic erosion and sediment subduction

Continental growth has been episodic, reflecting the episodic nature of mantle dynamics as well as surface dynamics of the Earth, the net result of which is exhibited by the present mantle with two huge reservoirs of TTG rocks, one on the surface continents and the other on the D″ layer on the Core-Mantle Boundary (CMB). During the early half of the Earth history, the felsic continental crust on the surface which formed in an intra-oceanic environment has mostly been subducted into the deep mantle, except in the rare case of parallel arc collision. The growth history of continental crust shows that with its simultaneous formation, a considerable amount must have also been subducted. Such ongoing subduction processes can be seen in the western Pacific region, through tectonic erosion, arc subduction, and sediment-trapped subduction.     

Micro-FTIR spectroscopic signatures of Bacterial lipids in Proterozoic microfossils

Precambrian microbial fossils show carbonaceous cellular structure, which often resemble in shape and size cyanobacteria and other prokaryotes. Morphological taxonomy of these minute, simple, and more or less degraded fossils is, however, often not enough to determine their precise phylogenetic positions. Here we report the results of micro-FTIR spectroscopic analyses of well-preserved microfossils in 850 Ma and 1900 Ma stromatolites, together with those of 8 species of extant prokaryotes and 5 of eukaryotes for comparison. These Proterozoic fossils have low CH₃/CH₂ absorbance ratios (R_3/2 < 0.5) of aliphatic CH moieties, suggesting selective preservation of long, straight, aliphatic carbon chains probably derived from bacterial membrane lipids. All the observed R_3/2 values of coccoids, filaments and amorphous organic matter resemble lipid fractions of extant Bacteria including cyanobacteria, but not Archaea. The results indicate that Proterozoic microfossils belong to Bacteria, which is consistent with the cyanobacterial origin inferred from morphology. Moreover, the R_3/2 value of fossilized cell would reflect chemical composition of its precursor membrane lipid, thus could be a useful new tracer for distinguishing Archaea, Bacteria and possibly Eucarya for fossilized and extant microorganisms.     

A possible anorthositic continent of early Mars and the role of planetary size for the inception of Earth-like life

The Moon has an anorthositic primordial continental crust. Recently anorthosite has also been discovered on the Martian surface. Although the occurrence of anorthosite is observed to be very limited in Earth's extant geological record,both lunar and Martian surface geology suggest that anorthosite may have comprised a primordial continent on the early Earth during the first 600 million years after its formation. We hypothesized that differences in the presence of an anorthositic continent on an Earthlike planet are due to planetary size. Earth likely lost its primordial anorthositic continent by tectonic erosion through subduction associated with a kind of proto-plate tectonics(PPT). In contrast, Mars and the Moon, as much smaller planetary bodies, did not lose much of their anorthositic continental crust because mantle convection had weakened and/or largely stopped, and with time, they had appropriately cooled down. Applying this same reasoning to a super-Earth exoplanet suggests that, while a primordial anorthositic continent may briefly form on its surface, such a continent will be likely transported into the deep mantle due to intense mantle convection immediately following its formation. The presence of a primordial continent on an Earth-like planet seems to be essential to whether the planet will be habitable to Earth-like life. The key role of the primordial continent is to provide the necessary and sufficient nutrients for the emergence and evolution of life. With the appearance of a "trinity" consisting of(1) an atmosphere,(2) an ocean, and(3) the primordial continental landmass, material circulation can be maintained to enable a "Habitable Trinity" environment that will permit the emergence of Earth-like life. Thus, with little likelihood of a persistent primordial continent, a super-Earth affords very little chance for Earth-like life to emerge.