Post-collisional adakites in south Tibet: Products of partial melting of subduction-modified lower crust

Geochemical variations in Miocene adakitic rocks from the western and eastern Lhasa terrane: Implications for lower crustal flow beneath the Southern Tibetan Plateau

“…Sr and Nd isotopic compositions were measured using a Micromass Isoprobe multi-collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) and a Triton Thermal Ionization Mass Guo et al (2007) and Gao et al (2007a). The localities are as follows (from east to west): 1, Linzhi (Chung et al, 2003); 2, Jiama (Hou et al, 2004, the present study); 3, Qulong (Hou et al, 2004); 4, Lakang'e (Hou et al, 2004, the present study); 5, Nanmu (Hou et al, 2004); 6, Nemu (Hou et al, 2004, the present study); 7, Maquiang (Turner et al, 1996); 8, Xigaze (Chung et al, 2003); 9, Daggyaio Tso (Williams et al, 2004); 10, Manasarowar and Gegar (Miller et al, 1999); 11, Bangba (the present study); 12, Shiduo (Cai et al, 2005); 13, Shiquanhe (Guo et al, 2007); and 14, Ritu (Cai et al, 2005).…”

“…Miocene adakitic rocks in Southern Tibet are thought to have originated from a thickened lower crust (Cai et al, 2005;Chung et al, 2003Chung et al, , 2009Gao et al, 2007a;Guo et al, 2007;Hou et al, 2004;Jiang et al, 2006), meaning that their compositions reflect the geochemical characteristics of their lower crustal source(s). Here, we present new geochemical data and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb zircon age data for adakitic rocks in the Lhasa terrane, which, when combined with previous geochemical data, allows us to assess possible sources on both sides of the IYS.…”

“…Previous studies have shown that the adakitic rocks are K-rich, forming a 1000-km-long belt oriented sub-parallel to the IYS. The ages of the adakitic rocks range from 26.2 to 10 Ma (Cai et al, 2005;Chung et al, 2003Chung et al, , 2009Gao et al, 2007a;Guo et al, 2007;Hou et al, 2004;Xu et al, 2010;this study), within the range of the 22.5-12 Ma ages obtained for potassic-ultrapotassic igneous rocks in the Lhasa terrane (e.g., Ding et al, 2003;Gao et al, 2007b;Miller et al, 1999;Nomade et al, 2004;Williams et al, 2001Williams et al, , 2004Zhao et al, 2009), except for the 26.2 Ma age of adakitic rocks in Linzhi (Chung et al, 2003). Recently, Miocene adakitic dykes have been found on the southern side of the IYS, including the Mayum and Kuday dykes King et al, 2007) within the northern belt of the Tethyan Himalayan tectonic zone.…”

“…To identify spatial differences in geochemistry, adakitic rocks of the Lhasa terrane are divided into eastern and western groups, either side of the longitude of approximately 87°E (Fig. 1) (Guo et al, 2007;Hou et al, 2006;Xiao et al, 2007;Zhao et al, 2006Zhao et al, , 2009Zhou and Murphy, 2005).…”

“…The groundmasses of these porphyries consist mainly of plagioclase, alkali feldspar, biotite, quartz, zircon, Fe-Ti oxides, titanite, apatite, and glass. The petrographic characteristics of these adakitic rocks have been described by Hou et al (2004), Guo et al (2007), and Gao et al (2007aGao et al ( , 2007b. In the western Lhasa terrane, the adakitic rocks occur as erupted lavas or small intrusive bodies.…”