Indication for clockwise rotation in the Siang window south of the eastern Himalayan syntaxis and new geochronological constraints for the area

Abstract

Palaeomagnetic, rock magnetic and geochronological investigations were carried out on the Abor volcanics of Arunachal Pradesh, NE India. A Late Palaeozoic formation age for part of the Abor volcanics cannot be excluded based on K–Ar whole rock dating. Low-temperature thermochronometers – zircon (U–Th)/He and fission track analyses – yield a maximum burial temperature of c. 150–170 °C during Late Miocene. ZFT thermochronology of the Yinkiong and Miri Fms. indicates a post-Paleocene and post-Jurassic deposition age, respectively. This infers that the volcanic rocks intercalating or intruding them are not part of the Late Palaeozoic sequence but represent one or more, latest Cretaceous to Tertiary event(s). Therefore the Abor volcanics are connected to at least two separate events of volcanism. From palaeomagnetic sites, two characteristic magnetic remanence components were separated: a low-coercivity-component demagnetized below 20 mT and a high-coercivity-component demagnetized between 15 and 100 mT. Fold tests support a secondary origin of both components. Thermochronological and rock magnetic analyses indicate a low-grade overprint event between India–Asia collision and Miocene, which probably represents the time of remanence acquisition. The high-coercivity-component shows a trend of clockwise declinations, which is likely related to vertical-axis rotations of the eastern Himalayas due to eastward extrusion of the Tibetan Plateau.

Rock Magnetic, Petrography, and Geochemistry Studies of Lava at the Ijen Volcanic Complex (IVC), Banyuwangi, East Java, Indonesia

“…These results show that the samples have two phases of magnetic minerals. The presence of magnetite mineral (Fe-rich titanomagnetite) in the samples is supported by the high Tc (472-544 • C), whereas the presence of Ti-rich titanomagnetite is supported by the low Tc (<400 • C) [41]. This result can be caused by the temperature variation [31].…”

“…The saturation curves of the other samples were saturated in a field of 140-400 mT (Table 2). These results indicate that the magnetic minerals contained in the sample were predominately Fe-rich titanomagnetite and Ti-rich titanomagnetite series [32,41,42]. Figure 5 shows the thermomagnetic curve of some samples.…”

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya, Northeast India

“…Furthermore other basalt samples from the Abor volcanics yield K-Ar ages between 87.2 AE 1.3 and 24.9 AE 0.4 Ma which are interpreted as partly reset ages resulting from argon loss during the partial transformation of the analysed rocks (Liebke et al, 2011). Thus the age of the Abor volcanics is currently poorly constrained, with apparent K-Ar ages ranging from Late Carboniferous to Early Tertiary (Liebke et al, 2011). New isotopic data from mafic and felsic volcanics will lead to better understanding of the magmatism in the Siang window.…”

“…An Ar-Ar age of 1.68 Ga (mid Proterozoic) for the Dowar-khola volcanics (Takigami et al, 2002) and a Late Carboniferous whole rock K-Ar age (319 AE 15 Ma) for the Abor volcanics (Liebke et al, 2011) do not support the hypothesis of slab window volcanism and suggest that both were emplaced prior to the India-Asia collision. Furthermore other basalt samples from the Abor volcanics yield K-Ar ages between 87.2 AE 1.3 and 24.9 AE 0.4 Ma which are interpreted as partly reset ages resulting from argon loss during the partial transformation of the analysed rocks (Liebke et al, 2011). Thus the age of the Abor volcanics is currently poorly constrained, with apparent K-Ar ages ranging from Late Carboniferous to Early Tertiary (Liebke et al, 2011).…”

“…Although the mafic volcanic rocks have been the subject of intensive geological investigations (Jain and Thakur, 1978;Tripathi and Chowdhury, 1983;Talukdar and Majumdar, 1983;Chowdhury, 1984;Singh, 1993Singh, , 2006Singh, , 2007Acharyya, 1994;Bhat, 1984;Bhat and Ahmad, 1990;Sengupta et al, 1996;Liebke et al, 2011), the associated felsic volcanics have received little attention (Talukdar and Majumdar, 1983), and geochemical data have not been investigated. In order to address this gap in the data and implications for the tectonic significance of the Abor volcanics, this paper focuses on the petrological characteristics of the felsic volcanics to constrain the genesis of felsic magma at the Siang window.…”