Petrography and geochemistry of alkaline rocks from Michni (Warsak) area, NW Himalayas, Pakistan: Insights into petrogenesis and tectonic setting

Mineralogy and geochemistry of calc-alkaline magmatic rocks from the Mansehra Granitic Complex, NW Himalaya, Pakistan: insights into petrogenesis and tectonic setting

300 MW Baspa II — India's largest private hydroelectric facility on top of a rock avalanche-dammed palaeo-lake (NW Himalaya): Regional geology, tectonic setting and seismicity

The comments of Roser and Korsch (1984) are related to two aspects: (1) their apparent inability to reproduce the results of the discriminant scores as given in table 9 of my paper (Bhatia 1983) and (2) the effect of grain size on the composition of clastic sedimentary rocks. The apparent discrepancy in the discriminant scores is due to their error in calculation. Roser and Korsch (1984) calculated the discriminant scores using the volatile-free averages of the published sandstone suites tabulated in tables 5-8 of my paper. However, the discriminant functions that I developed are based on the actual (non volatilefree) analyses of the sandstone suites of eastern Australia. Thus, the discriminant scores on the published averages given in table 9 of my paper were also calculated using the actual analyses and not the volatile-free analyses. This is mentioned in the text of my paper (Bhatia 1983 p. 620): "Discriminant scores for averages of the published analyses were calculated using the unstandardized function coefficients of table 3 and the actual abundance of element oxide in the average" [italics added]. The actual average chemical analyses and the calculation of the discriminant scores for three of the suites on which significant apparent discrepancies exist are presented in table 1 as examples. In the three cases presented (Aure Trough, Santa Ynez, and the Rhyolitic Sand suites), all the scores agree with those given in Bhatia (1983) and differ significantly from those calculated by Roser and Korsch (1984). The incomplete published analyses certainly posed some problem. Due to the im-

This paper documents the geochemistry of clastic sedimentary rocks from the Upper Carboniferous Zongwulong Group in the Zongwulong structural belt of the Qaidam Basin, NW China, in order to trace the sources of the sediments and to understand their tectonic settings at the time of deposition of the Zongwulong Group. Although the major elements differ among different samples, their low mean chemical index of alteration (mean CIA = 51.04–64.79), plagioclase index of alteration (mean PIA = 51.41–69.54), and relatively high mean index of compositional variability (mean ICV = 1.18–1.56) indicate relatively low maturity and weak to moderate chemical weathering of their source. The Zr/Sc-Th/Sc diagram and relatively high mean ICV suggest that all sediments of Zongwulong Group have undergone no significant sediment recycling. All samples yield relatively high Al2O3/TiO2 ratios (16–27), strong LREE/HREE differentiation (mean LaN/YbN = 10.83–12.66), and obvious negative Eu anomalies (mean Eu/Eu* = 0.61–0.79). Combined with characteristic ratios (La/Sc, Th/Sc, Cr/Th, and Th/Co) and the provenance discriminant diagrams (Al2O3-(CaO* + Na2O)-K2O and Ni-TiO2), these results indicate felsic source rocks. Combined with the findings of previous studies, the representative values (La, Ce, ΣREE, V, Rb/Sr, Eu/Eu*, La/Sc, Th/Sc, and Zr/Th) and tectonic setting discriminants (SiO2-K2O/Na2O, Fe2O3 + MgO-Al2O3/SiO2, La/Sc-Ti/Zr, and Th-Sc-Zr/10) indicate that the Zongwulong Group sediments were deposited in a back-arc extensional basin behind the active continental margin-continental island arc tectonic setting.

Pan-African Magmatism, and Sedimentation in the NW Himalaya

Provenance, Tectonic Settings and Depositional Environmental Records of the Cambrian Wuliuan (Miaolingian) Kunzam La (Parahio) Formation in the Sumna Valley, Spiti, NW Himalaya

Manganese and ferromanganese ores from different tectonic settings in the NW Himalayas, Pakistan

The metasedimentary rocks along the Kullu-Rohtang Pass-Sissu section, NW Himalaya, have been analysed geochemically to characterise the composition of their provenance. The studies carried out suggest that, the source for these rocks is mainly of felsic nature, remarkably similar in composition to average Phanerozoic upper continental crust. The deposition of the sediments took place in an oxidising environment, and in a tectonic setting that spans from active to passive continental margins.

Geochemical evidence for the provenance, tectonic settings and depositional environment during the Cambrian Series 2-Wuliuan (Miaolingian) from the Kunzam La Formation in the Sumna Valley, Spiti, NW Himalaya

Mansehra Granite (MG) is massive and sheared which contains light-gray to jet-black schistosed and light-gray micaceous quartzite restites.The later possess relatively higher quartz as compared with mica contents whereas the former has predominant quartz and feldspar.Enclosure of apatite and zircon in micas and absence of sillimanite in schistosed and non-foliated facies suggest that these rocks are restite in nature.Presence of abundant and larger mica flakes at contact of restites with MG indicates exposure of these flakes at relatively higher temperature of granitic melt (623.7-886.6 °C) particularly at their margins.However, central part of restites remained unaffected due lesser impact of elevated temperature.Schistose and surmicaceous restites show crenulation cleavage and preserve structural antiquity during amalgamation in felsic melt.Geochemically, restites and Tanawal Formation indicate calc-alkaline to high K calc-alkaline domain with orogenic syn-collisional settings.Geochemical characteristics and modal mineralogy of restites and Tanawal Formation are similar.This study suggests that former has been derived from the later and their field relationships and geochemical signatures provide credible evidence in favour of S-type trait of Mansehra Granite.In geochemical diagrams, MG portrayed calc-alkaline, peraluminous S-type nature and its magma was generated from heterogeneous Tanawal Formation via fractional crystallization.

Occurrence of manganese ores in different tectonic settings in the NW Himalayas, Pakistan

Granitoid rocks in Myanmar occur in three north–south-trending linear belts (Khin Zaw 1990) (Fig. 18.1b) over a distance of more than 1500 km from Kachin State in the north through Mogok, Mandalay, Taungoo and Mon State to the Tanintharyi Region in the south. This chapter describes a suite of granitoid rocks exposed at the Mawpalaw Taung area, covering about 141.44 km2 in the Thanbyuzayat Township, Mon State, southern Myanmar (Fig. 18.1a), not described previously. The area is located within latitudes 15° 45′ N to 15° 53′ N and longitudes 97° 45′ E to 97° 51′ 30′′ E and lies about 80 km south of Mawlamyine. The aim of this chapter is to describe the petrology, geochemistry and geochronology of these granitoid rocks and their associated mineralization in the Mawpalaw Taung area and to discuss their petrogenesis and tectonic setting. Fig. 18.1. ( a ) Location map of the Mawpalaw Taung area, Thanbyuzayat Township, southern Myanmar and ( b ) the Granitoid Belt of Khin Zaw (1990). The Mawpalaw Taung area lies within the Shan–Tanintharyi Block (Maung Thein & Ba Than Haq 1969) in the northern Tanintharyi Hill Range, and forms a part of the Slate Belt of Mitchell et al. (2012). It also is a section of the Southeast Asian tin–tungsten belt, stretching from southern Yunnan in the north through eastern Myanmar, Thailand and the Malay Peninsula to the Indonesian Tin Islands (Maung Thein 1973; Mitchell 1977; Cobbing et al. 1992; Schwartz et al. 1995). The area lies within the Western Granite Province of Southeast Asia (Cobbing et al. 1992) (Fig. 18.1) and the Central Granitoid Belt of Myanmar (Khin Zaw 1990). The general structural trend of this part of the Slate Belt (Mitchell et al. 2012) is NNW–SSE aligned. The metasediments and igneous rocks lie between parallel …

The geochemistry of the basic volcanic rocks at the south margin of the Qinling orogenic belt (SMQOB) suggests that they were formed in an intraplate tectonic setting. The REE distribution patterns show these rocks are strongly enriched in LREE with high ∑REE, and their trace elements geochemistry is similar to that of continental flood basalt. All the above evidence suggests that the Caledonian basic volcanic rocks in the SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting. The characteristics of regional geology and geochemistry indicate that there was an intraplate spreading-rift tectonic setting between the South Qinling block and the Yangtze block in the Caledonian epoch. The dynamic spreading in this district began in the Early Caledonian and then the intraplate spreadinginitial rifts were formed in the Late Caledonian. As a result of spreading of the Tethys and geodynamic processes in deep mantle, the Mianlue-Huashan oceanic basin was formed between the Qinling block and the Yangtze block in Devonian, and the Qinling microplate was separated from the northern part of the Yangtze plate.

Geochemistry of rocks (Late Cretaceous) in the Anambra Basin, SE Nigeria: insights into provenance, tectonic setting, and other palaeo-conditions

To the south of Manzhouli, Hulunbuir, Inner Mongolia, experienced a tectonic regime transformation from compression to extension in the mid‐Mesozoic. Based on systematic research of the volcanics, petrology, volcanic facies, chronology and geochemistry of rocks in the Buridun area, two stages of volcanics are identified. The first stage named the trachyte series was formed in the late Middle Jurassic (167–163 Ma), its eruption rhythm is pyroxene trachyandesite–trachyandesite–trachyte, and its origin rock is basic volcanics from thickened lower crust, with a tectonic setting in the collision orogeny after the closure of the Mongolia Okhotsk Ocean (MOO). The second stage is a bimodal volcanic rock, formed in the early Late Jurassic (163–160 Ma). The eruption rhythm of basic volcanics in this stage is basaltic andesite–basalt–olivine basalt, which comes from the metasomatized lithospheric mantle, the acidic volcanics of which being characterized by the eruption rhythm of sedimentary‐explosive‐overflow facies, which came from the partial melting of newly formed lower crust, and this shows the characteristics of A‐type granite; the tectonic setting is extension of the lithosphere after collision and closure of the MOO. The changes in the formation age and tectonic setting of the two stages of volcanics demonstrate that the transition time from the compressive system to the extensional system south of Manzhouli is about 163 Ma.