A model involving amphibolite lower crust melting and subsequent melt extraction for leucogranite generation

In the southern Tibetan Plateau, leucogranites are dominantly distributed in the Himalayan orogenic belt with minor occurrences in the southern Lhasa subterrane. In this paper, we report the first Miocene Anglonggangri leucogranites in the northern Lhasa subterrane. This finding provides important constraints on both leucogranite petrogenesis and the tectono-magmatic evolution of the Lhasa terrane. The Anglonggangri leucogranites include biotite-muscovite granite and slightly younger garnet-muscovite granite and pegmatite. Zircon U-Pb and muscovite 40Ar-39Ar dating of these leucogranites yields Miocene ages of 11.1−10.2 Ma. The biotite-muscovite and garnet-muscovite granites are characterized by high SiO2 (72.3−74.4 wt%) and Al2O3 contents (14.4−15.4 wt%) and are peraluminous. The biotite-muscovite granite displays geochemical signatures with high Sr/Y (29.2−81.0) and (La/Yb)N (37.5−98.9) ratios, low Y (4.30−7.22 ppm) and Yb contents (0.26−0.47 ppm), low to moderate initial (87Sr/86Sr)i ratios (0.7085−0.7192), and moderate εNd(t) values (−10.17 to −6.94). Furthermore, they also exhibit radiogenic Pb isotope and variable zircon εHf(t) values (−9.6 to +4.4) with Proterozoic Nd (1.1−1.4 Ga) and Hf model ages (0.8−1.7 Ga). By comparison, the garnet-muscovite granite has lower CaO, MgO, TiO2, and total FeO contents and is enriched in Rb (380−466 ppm) and depleted in Sr (24.1−38.5 ppm) and Ba (30.7−58.6 ppm) and further characterized by a significant rare earth element (REE) tetrad effect and non-charge and radius-controlled (CHARAC) trace element behaviors. The garnet-muscovite granite shows a negative Eu anomaly and positive correlations among Sr and Eu, Sr and Ba, and Th and light rare earth elements (LREEs). Pegmatite comprising Nb-Ta oxides and cassiterite occurs in the garnet-muscovite granite. Geochronological and geochemical characteristics of the Anglonggangri leucogranites indicate that the magma of the biotite-muscovite granite was derived from partial melting of amphibolite lower crust contaminated with Proterozoic-Archean upper crustal materials. The garnet-muscovite granite was generated through melt extraction from the biotite-muscovite granite crystal mush. These results confirm that partial melting of the amphibolite lower crust not only occurred in the southern and central Lhasa subterranes but also in the northern Lhasa subterrane.

Detecting a Sinistral Transpressional Deformation Belt in the Zagros

The oblique collision between the northeastern margin of the Arabian platform and the Iranian microcontinent has led to transpressional deformation in the Zagros orogenic belt in the central part of the Alpine–Himalayan orogenic belt. Although previous articles have emphasized the dextral sense of shear in the Zagros orogenic belt, in this paper, using several indicators of kinematic shear sense upon field checking and microscopic thin-section studies, evidence of the development of a sinistral top-to-the NW deformation belt is presented. The mean attitudes of the foliations and lineations in this belt are 318°/55°NE and 19°/113°, respectively.

The geographical prerequisites for the identification and prevention of dangerous geomorphological processes in the mountain geosystems of the Alpine-Himalayan belt (on the example of the Major Caucasus of Azerbaijan)

Destructive natural phenomena are a serious, sometimes unsolvable, regional and local environmental and socioeconomic problem. This paper presents the results of a comprehensive analysis of materials from long-term geomorphological studies in the mountainous areas on the example of the Major Caucasus of Azerbaijan. The dangerous geomorphological processes on the example of the Major Caucasus of Azerbaijan were investigated in detail using large-scale maps, satellite imagery and aerial photography. Geomorphological maps were drawn (map of mudflow hazard and map of landslide hazard in the Azerbaijani part of the Major Caucasus). The research determined the dangerous zones where landslides could cover 65–70% of the total area and outlined the zones and regularities of spread of various types of mudflow origination sites. The analysis of the manifestations of most active (with catastrophic consequences) destructive natural processes and the morphotectonic structure of the studied area showed that the their occurrence and maximum intensity was confined to the weakest plexuses of mountains – intersections of faults and fractures of various directions and orders. A technique for assessing the eco-geomorphological risk to prevent dangerous natural phenomena was offered. The technique is based on the detection of zones with intensive geomorphological processes, which are often not dangerous separately, but could have catastrophic consequences together. The results obtained during the assessment of the effect of natural and man-caused factors on the stability of montane ecosystems may be used to forecast dangerous natural phenomena and to research geodynamical dangerous geomorphological process not only in Azerbaijan, but also in other regions of the Alpine-Himalayan orogenic belt. The obtained results can be used to plan and perform economic activities, determine and minimize the hazards and risks of occurrence of dangerous natural phenomena, and forecast such phenomena in the future.

The break-up of the Indian subcontinent from Gondwana: constrain by detrital zircon U-Pb dating of mid- Paleozoic-early Cenozoic strata in eastern Nepal

<p>The rifting and the amalgamation of earth landmass is a continuous process. The assembly of the Gondwana lasted from ~730 Ma to 500 Ma, and most of the mass is covered by glaciation at the southern hemisphere. Afterthought experienced multiple episodes of rifting and collision of small ribbon shape microcontinents. The extra-peninsular Gondwana sequence is discontinuous in the Himalayan orogenic belt while peninsular Gondwana sequence is broadly distributed in numerous intracratonic basins of peninsular India. The detrital zircon U-Pb ages from Permo-Carboniferous sequence peak at ~1164 with a subordinate peak at ~1305 Ma. This result emphasised that the sediments were mainly sourced from the Stenian magmatism in Albany-Fraser orogeny or the East Africa-Nibua and eastern coast of India, and southwest Australia. Also, the unit also contains sporadic volcanic unit (Baraha Volcanics). The Saptakoshi Formation, uncomfortably overlain the Khokha Diamictite, yield the peaks at ~522 Ma and 941 Ma with a younger peak at ~113 Ma with some older peaks at ~1811 and 1917 Ma. This younger detritus possibly sourced from the Rajhmahal basalt ~~115-120 Ma) while the remaining grains show a similar trend to the underlying Diamictite and overlying Tamrang Formation. Additionally, the Tamrang Formation have peaks at ~976 Ma, and 1716 Ma, identically identical to the Greater Himalayan sequence. The U-Pb age distribution of these three units coincide with the Tethys Himalaya further brings the possibility that either they share the same provenance or recycled from the Tethys Himalaya till Permian and onwards there was input from the Lhasa terrane, South Qiangtang terrane, and Indo China blocks.</p>

Ali Mehmet Celâl Şengör: A geologist who unravels the histories of continents and oceans

This special issue is dedicated to Ali Mehmet Celâl Şengör for his outstanding contributions to plate tectonics and history of geology. His studies have unraveled several mysteries on the origin and deformation of continents and formation of orogenic belts in many parts of the world. We received 22 articles for the special issue, 11 of which are published in this issue. The rest of the articles will be published in the next issue. The articles in this issue mainly focus on geological processes in the Alpine–Himalayan orogenic belt and on the history of the theory of plate tectonics.