Devonian alkaline magmatism in South Qinling, China: evidence from the Taohekou Formation, Northern Daba Mountain

<p>The Langao area in South Qinling consists of a poorly dated sequence of volcano-sedimentary units (Taohekou Formation). This study focuses on volcanic edifice of Taohekou Formation. Detailed field mapping, section facies analysis, geochemistry, and Ar–Ar geochronology is presented here to develop a more accurate understanding of the tectonic evolution of the Qinling Orogen. Detailed field mapping and section facies analysis reveals the presence of a seamount volcanic edifice in western Xiaozhen area. Ar–Ar dating of alkaline basalts in the sequence indicates an Early Devonian magmatic age. Whole rock geochemistry of these alkaline basalts indicates that both potassic and sodic basalts were erupted respectively in the eastern and western areas. Both types of samples are typically characterized by high concentrations of TiO₂, Nb, Ta, and Zr. Ocean-island basalt (OIB)-like rare earth element distribution patterns, trace element spider diagrams, and similar Sr and Nd isotopic compositions (i.e. relatively low Sr and moderate Nd isotopic ratios) likely indicate that the samples were comagmatic but have experienced varying degrees of fractional crystallization. In addition, the samples appear to have all originated from the asthenospheric mantle and undergone mantle metasomatism, ultimately resulting in an OIB-type provenance. Most importantly, in combination with its regional tectonic evolution, the Taohekou Formation is constrained to a seamount environment. This formation does not represent a plume but, rather, an extensional fracture zone related to subduction. Thus, this geologic interpretation generates pivotal evidence for accurately investigating the properties and temporal constraints of the Mianlue oceanic basin.</p

Middle Triassic arc magmatism along the northeastern margin of the Tibet: U–Pb and Lu–Hf zircon characterization of the Gangcha complex in the West Qinling terrane, central China

<p>The tectonic setting of Mesozoic magmatic complexes in the northeastern margin of the Tibet plateau is disputed, and hence gives rise to uncertainty concerning the tectonic evolution of the northeastern Tibet Plateau and the timing of the closure of the Palaeo-Tethys ocean. The Gangcha complex is typical of these complexes, consisting of andesite, dacite, gabbro, gabbroic diorite, granodiorite, quartz diorite, and diorite with typical chemical traits of continental margin arc rocks. Andesite, gabbroic diorite, and mineralization-associated potassic-altered diorite yield weighted mean ²⁰⁶Pb/²³⁸U ages of 242.1 ± 1.2 Ma, 243.8 ± 1.0 Ma and 234.0 ± 0.6 Ma respectively. Zircon ϵ_Hf(t) for magmatic grains ranges from −3.5 to +5.7, interpreted to demonstrate that the Gangcha complex contains crustally contaminated mantle magmas. Inherited zircons in the complex yield similar U–Pb ages (777–310 Ma) to the A’nyemaqen composite ophiolite assemblage with ϵ_Hf(t) of −17.4 to +11.6. This suggests that components of this older ophiolite melted and contributed to the Gangcha complex magmas. Hence the Gangcha complex is considered to have formed as a continental margin arc in northeastern Tibet by northward subduction during consumption of the Palaeo-Tethys ocean. Regionally, it corresponds to the arc magmatism along the eastern and western Kunlun sutures to the west and the Mianlue suture to the east. </p

Additional file 1: of Amyloid-beta modulates microglial responses by binding to the triggering receptor expressed on myeloid cells 2 (TREM2)

Figure S1. Oligomeric Aβ1–42 specifically binds to TREM2. Figure S2. Oligomeric Aβ1–42 specifically activates TREM2 reporter cells. Figure S3. The number of microglia clustered around Aβ is decreased in Trem2-KO mice. (PDF 1369 kb