Cenozoic K-rich adakitic volcanic rocks in the Hohxil area, northern Tibet: Lower-crustal melting in an intracontinental setting

Research Article| June 01, 2005 Cenozoic K-rich adakitic volcanic rocks in the Hohxil area, northern Tibet: Lower-crustal melting in an intracontinental setting Qiang Wang; Qiang Wang 1Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People's Republic of China Search for other works by this author on: GSW Google Scholar Frank McDermott; Frank McDermott 2Department of Geology, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Ji-feng Xu; Ji-feng Xu 3Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People's Republic of China Search for other works by this author on: GSW Google Scholar Hervé Bellon; Hervé Bellon 4Laboratoire de Géochronologie et UA 1278, Université de Bretagne Occidentale, 29287 Brest, France Search for other works by this author on: GSW Google Scholar Ying-tang Zhu Ying-tang Zhu 5Academy of Geological Survey of Qinghai Province, Xining 810012, People's Republic of China Search for other works by this author on: GSW Google Scholar Author and Article Information Qiang Wang 1Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People's Republic of China Frank McDermott 2Department of Geology, University College Dublin, Belfield, Dublin 4, Ireland Ji-feng Xu 3Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People's Republic of China Hervé Bellon 4Laboratoire de Géochronologie et UA 1278, Université de Bretagne Occidentale, 29287 Brest, France Ying-tang Zhu 5Academy of Geological Survey of Qinghai Province, Xining 810012, People's Republic of China Publisher: Geological Society of America Received: 13 Jan 2005 Revision Received: 05 Feb 2005 Accepted: 09 Feb 2005 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2005) 33 (6): 465–468. https://doi.org/10.1130/G21522.1 Article history Received: 13 Jan 2005 Revision Received: 05 Feb 2005 Accepted: 09 Feb 2005 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Qiang Wang, Frank McDermott, Ji-feng Xu, Hervé Bellon, Ying-tang Zhu; Cenozoic K-rich adakitic volcanic rocks in the Hohxil area, northern Tibet: Lower-crustal melting in an intracontinental setting. Geology 2005;; 33 (6): 465–468. doi: https://doi.org/10.1130/G21522.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract It is generally accepted that the Cenozoic potassic volcanic rocks of northern Tibet were derived from a lithospheric mantle source. Here we report new chronological, geochemical, and isotopic data for the Miocene (ca. 18–15 Ma) K-rich adakitic volcanic rocks from the Hohxil area of the Songpan-Ganzi block in northern Tibet. We contend that these rocks were generated by partial melting of the mafic lower crust, in an intracontinental setting unrelated to subduction of oceanic crust. The Hohxil rocks exhibit high Sr/Y and La/Yb ratios, high Sr and La contents, but low Yb and Y concentrations, similar to adakites formed by slab melting associated with subduction. However, their relatively low ε Nd values (−2.09 to −4.58); high 87Sr/86Sr (0.7072–0.7075), Th/U, Th/Ba, and Rb/Ba ratios; and distinctive potassium enrichments (K2O > Na2O) are very different from the composition of typical adakites. In addition, those K-rich adakitic rocks with the highest SiO2 contents (>61 wt%) exhibit the lowest 87Sr/86Sr ratios and highest ε Nd values and are the oldest Cenozoic volcanic rocks exposed in the Songpan-Ganzi block, suggesting that they were derived neither directly from a mantle source nor by differentiation of a shoshonitic magma. Taking into account the composition of lower-crustal mafic xenoliths in Tibet, as well as the tectonic and geophysical evidence, we conclude that the Hohxil adakitic magmas were produced by partial melting of amphibole-bearing eclogites with a K-rich mafic bulk composition, in the lower part (≥∼55 km) of the thickened northern Tibetan crust. Partial melting of the lower crust may have been triggered by dehydration release of fluids from sedimentary materials in the southward-subducted continental lithosphere. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.