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Background: In 2009, residents of Lhasa city, Tibet Autonomous Region (TAR), China reported large numbers of mosquitoes and bites from these insects. It is unclear whether this was a new phenomenon, which species were involved, and whether these mosquitoes had established themselves in the local circumstances. Methods: The present study was undertaken in six urban sites of Chengguan district Lhasa city, Tibet. Adult mosquitoes were collected by bed net trap, labor hour method and light trap in August 2009 and August 2012. The trapped adult mosquitoes were initially counted and identified according to morphological criteria, and a proportion of mosquitoes were examined more closely using a multiplex PCR assay. Results: 907 mosquitoes of the Culex pipiens complex were collected in this study. Among them, 595 were females and 312 were males. There was no significant difference in mosquito density monitored by bed net trap and labor hour method in 2009 and 2012. Of 105 mosquitoes identified by multiplex PCR, 36 were pure mosquitoes (34.29%) while 69 were hybrids (65.71%). The same subspecies of Culex pipiens complex were observed by bed net trap, labor hour method and light trap in 2009 and 2012. Conclusion: The local Culex pipiens complex comprises the subspecies Cx. pipiens pipiens, Cx. pipiens pallens, Cx. pipiens quinquefasciatus and its hybrids. Mosquitoes in the Cx. pipiens complex, known to be, potentially, vectors of periodic filariasis and encephalitis, are now present from one season to the next, and appear to be established in Lhasa City, TAR. [ABSTRACT FROM AUTHOR]

The Xigaze ophiolite is located in the middle section of the Yarlung Zangbo River ophiolite belt and includes a well-preserved sequence section of seven ophiolite blocks. The relatively complete ophiolitic sequence sections are represented by Jiding, Dejixiang, Baigang, and Dazhuqu ophiolites and consist of three-four units. The complete ophiolite sequence in order from the bottom to top consists of mantle peridotite, cumulates, sheeted sill dike swarms, and basic lavas±radiolarian chert. These cumulates are absent in the remaining blocks of Dejixiang and Luqu. The age of radiolaria in the radiolarian chert is Late Jurassic-Cretaceous. The basalt and ultramafic rock of the ophiolite also are overlaid by Tertiary Liuqu conglomerate, which contains numerous pebble components of ophiolite, indicating that the Tethys Ocean began to close at the end of Cretaceous Period. The isotopic data of gabbro, diabase, and albite granite in the Xigaze ophiolite are approximately 126-139 Ma, which indicates that the ophiolite formed in the Early Cretaceous. The K-Ar age of amphibole in garnet amphibolite in the ophiolite mélange is 81 Ma, indicating that tectonic ophiolite emplacement occurred at the end of Late Cretaceous. Research in petrology, petrological chemistry, mineralogy, and geochemistry of volcanic rocks and dikes of the Xigaze ophiolite indicate the following characteristics: (1) They are mainly composed of basalt, basaltic andesite, dolerite, and diabase and are characterized by high TiO2 (0.7-1.47%), low MgO (mostly less than 8%), and low SiO2 (mostly less than 53%). (2) The volcanic rocks and dikes of the Xigaze ophiolite show light rare earth element (LREE)-depleted rare earth element (REE) patterns. (3) The spider diagrams of the volcanic rocks and dikes of the Xigaze ophiolite exhibit LILE depletion relative to high-field-strength element (HFSE) patterns with left oblique features. (4) No protogenetic olivine and clinoenstatite was detected. (5) Some dikes show low TiO2 and high MgO, in which a few of Cr-enriched spinels and a very few pseudomorphs of olivine, orthopyroxene can be seen. They show more distinctive affinity as boninitic rock and canbe classified to boninite series rock. The previously mentioned features of the volcanic rocks and dikes in the Xigaze ophiolite implies that these ophiolites formed in a mid-ocean ridge (MOR) in the earlier stage and than forearc extension of subduction initiation occurred once at the later stage of the evolution of the Xigaze ophiolite. The forearc extention caused further melting of the residue-depleted mantle, resulting in the formation of melts with lower TiO2 and higher MgO. These melts formed as dikes and intruded into the oceanic crust formed in the earlier stage, resulting in a close association of mid-ocean ridge basalt and the boninite rock of the Xigaze ophiolite. [ABSTRACT FROM AUTHOR]

Mafic dikes are generally emplaced in extensional tectonic settings and provide key information regarding deep mantle processes and sources. The Bangong-Nujiang suture zone was formed by the collision of the Qiangtang and Lhasa terranes and experienced intense magmatism during the Early Cretaceous. However, the deep mantle processes and mechanisms involved in this magmatic flare-up (ca. 115 Ma) in the collisional belt remain controversial because of the lack of evidence for coeval mafic magmatism. Here, we present detailed petrological, geochronological, geochemical, and Sr-Nd- Hf-O isotope data for the newly discovered hypersthene-bearing mafic dikes in the Baingoin area in the middle-eastern parts of the Bangong-Nujiang suture zone, central Tibet. Secondary ion mass spectroscopy (SIMS) zircon U-Pb dating showed that the mafic dikes were emplaced during 120-115 Ma. These mafic rocks are characterized by variable MgO contents (2.7-5.2 wt%) and Mg# values (38.5-52.8), slight enrichment in light rare earth elements (REEs; [La/ Yb]N = 7.5-8.1), relatively flat heavy REE patterns ([Gd/Yb]N = 1.75-1.84), and negative Eu, Ta, Nb, and Ti anomalies. The dikes also have relatively low initial 87Sr/86Sr ratios 0.7060-0.7062) and negative εNd(t) (-2.2 to -1.6) and positive εHf(t) (+2.5 to +3.6) values, and variable zircon εHf(t) (-2.2 to +7.2) and slightly elevated zircon δ18O (5.6‰-7.0‰) values. These geochemical characteristics indicate that the mafic dikes were derived from an enriched lithospheric mantle source. However, compared with coeval magmatic rocks, the mafic dikes have relatively high εNd(t) and εHf(t) values, indicating that they contain a depleted mantle component. The mafic dikes contain clinopyroxene and orthopyroxene (i.e., hypersthene), indicative of derivation from a high-temperature magma source. Clinopyroxene-melt thermobarometry yielded a temperature range of 1167-1213 °C, further supporting the involvement of a high-temperature asthenospheric component. Therefore, we suggest that the parental magmas of the Nakoulai mafic dikes were probably generated by the interaction between the asthenospheric mantle and overlying metasomatized lithospheric mantle. Combined with data from nearby Cretaceous magmatic rocks and sedimentary rocks, we suggest that the mafic dikes were generated in a postcollisional setting caused by upwelling of asthenospheric mantle owing to slab breakoff beneath the Bangong-Nujiang suture zone. Slab breakoff played a key role in the crust-mantle interactions and the onset of the magmatic flare-up in the middle-eastern parts of the Bangong-Nujiang suture zone. [ABSTRACT FROM AUTHOR]

Accompanying Gondwana assembly, widespread but diachronous Ediacaran--early Paleozoic magmatism of uncertain origin occurred along the supercontinent's proto-Tethyan margin. We report new geochemical, isotopic, and geochronological data for Cambrian magmatic rocks (ca. 500 Ma) from the Gondwana-derived North Lhasa terrane, located in the present-day central Tibetan Plateau. The magmatic rocks are composed of basalts, gabbros, quartz monzonites, granitoids (with mafic microgranular enclaves), and rhyolites. Nd-Hf isotopic and whole-rock geochemical data indicate that these rocks were probably generated by mixing of mantle-derived mafic and crust-derived felsic melts. The mantle end-member volumes of mafic, intermediate, and felsic rocks are ~75%-100%, 50%-60%, and 0-30%, respectively. Integration of our new data with previous studies suggests that the North Lhasa terrane experienced long-term magmatism through the Ediacaran to Ordovician (ca. 572-483 Ma), with a magmatic flare-up at ca. 500 Ma. This magmatism, in combination with other Ediacaran--early Paleozoic magmatism along the proto-Tethyan margin, was related to an Andean-type arc, with the magmatic flare-up event related to detachment of the oceanic slab following collisional accretion of Asian microcontinental fragments to northern Gondwana. Diachroneity of the proto-Tethyan arc system along the northern Gondwanan margin (ca. 581-531 Ma along the Arabian margin and ca. 512--429 Ma along the Indian-Australian margin) may have been linked to orogenesis within Gondwana. The North Lhasa terrane was probably involved in both Arabian and Indian-Australian proto-Tethyan Andean-type orogens, based on its paleogeographic location at the northern end of the East African orogen. [ABSTRACT FROM AUTHOR]

The nature and timing of post-collisional crustal thickening and its link to surface uplift in the eastern Lhasa block of the southern Tibetan plateau remain controversial. Here we report on Cenozoic magmatism in the Wuyu area of the eastern Lhasa block. The Eocene (ca. 46 Ma) trachyandesites and trachydacites show slight fractionation of rare earth elements (REE), slightly negative Eu and Sr anomalies, and relatively homogeneous Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7050-0.7063, εNd(t) = -0.92 to -0.03, εHf(t) = +2.6 to +4.8). Previous studies have suggested Neo-Tethys oceanic slab break-off at 50-45 Ma; thus, the Wuyu Eocene magmatism could represent a magmatic response to this slab break-off and originate from relatively juvenile Lhasa crust. The Miocene (ca. 15-12 Ma) dacites and rhyolites have adakitic affinities, e.g., high Sr (average 588 ppm), Sr/Y (29-136), and La/ Yb (30--76) values, low Y (4-12 ppm) and Yb (0.4-0.9 ppm) contents, and variable Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7064-0.7142, εNd(t) = -11.7 to -3.7, εHf(t) = -3.2 to +4.5). Their more enriched Sr-Nd-Hf isotopes relative to the Eocene lavas indicate that they should be derived from mixed Lhasa lower crust comprising juvenile crust, ultrapotassic rocks, and probably Indian lower crustderived rocks. This study has also revealed the transformation from Eocene juvenile and thin crust with a thickness of <40 km to Miocene mixed and thickened crust with a thickness of >50 km. Combined with published tectonic data, we suggest that both lithospheric shortening and magma underplating contributed to eastern Lhasa block post-collisional crustal thickening. Given the spatial-temporal distribution of eastern Lhasa block magmatism and regional geology, we invoke a post-collisional tectonic model of steep subduction of the Indian plate and subsequent westward-propagating plate break-off beneath the eastern Lhasa block, which caused the surface uplift. [ABSTRACT FROM AUTHOR]