Episodic crustal anatexis and the formation of Paiku composite leucogranitic pluton in the Malashan Gneiss Dome, Southern Tibet

Abstract

The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite, two-mica granite and garnet-bearing leucogranite. Zircon U-Pb dating yields that (1) tourmaline leucogranite formed at 28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma; (2) two-mica granite formed at 19.8±0.5 Ma; (3) both types of leucogranite contain inherited zircon grains with an age peak at ~480 Ma. These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions. As compared to the two-mica granites, the tourmaline ones have higher initial Sr and zircon Hf isotope compositions, indicating that they were derived from different source rocks combined with different melting reactions. Combined with available literature data, it is suggested that anatexis at ~35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System (STDS), and led to the tectonic transition from compressive shortening to extension. Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt. Crustal anatexis at ~28 Ma and ~20 Ma represent large-scale melting reactions associated with the movement of the STDS.Himalayan orogenic belt, Northern Himalayan Gneiss Domes, leucogranite, crustal anatexis, tectonic transition Citation:Gao L E, Zeng L S, Hou K J, et al. Episodic crustal anatexis and the formation of Paiku composite leucogranitic pluton in the Malashan Gneiss Dome, Southern Tibet.

Tectonic evolution of the middle crust in southern Tibet from structural and kinematic studies in the Lhagoi Kangri gneiss dome

“…Structural, kinematic, and deformation temperature analyses in the LKD indicate that the rocks underwent a sequence of events that is generally consistent with the histories reported from six previously studied domes ( Fig. 1; Lee et al, 2000Lee et al, , 2004Aoya et al, 2006;Quigley et al, 2006;Larson et al, 2010;King et al, 2011;Gao et al, 2013).…”

“…At least 15 domes have been identified along the North Himalayan antiform (e.g., Burg et al, 1984;Debon et al, 1986;Watts et al, 2005), and six of these domes have been studied in detail. Of the six previously studied domes, Changgo (Larson et al, 2010) Malashan (Aoya et al, 2005;Kawakami et al, 2007;Gao et al, 2013;Gao and Zeng, 2014), Yardoi (Aikman et al, 2008;Zeng et al, 2009Zeng et al, , 2011Zeng et al, , 2014, and Mabja-Sakya (Zhang et al, 2004;Lee et al, 2006;Lee and Whitehouse, 2007) contain granite bodies with Eocene to Miocene (35-10 Ma) U/Pb zircon ages, whereas Kangmar (Schärer et al, 1986;Lee et al, 2000) and Kampa (Quigley et al, 2008) contain only granitic gneiss with Neoproterozoic to Cambrian (560-500 Ma) U/Pb zircon ages. Granitic gneiss with Neoproterozoic to Cambrian age is also reported in Mabja-Sakya (Lee and Whitehouse, 2007) and Yardoi (e.g., Zeng et al, 2009).…”

Eocene magmatism in the Tethyan Himalaya, southern Tibet

“…These two belts are separated by the Southern Tibetan Detachment System (STDS) (Caby et al 1983;Burg et al 1984;Burchfiel et al 1992;Hodges et al 1992;Carosi et al 1998;Searle et al 1999;Searle & Godin 2003;Zhang et al 2012). Studies on the formation age and geochemical and isotopic characteristics of these Cenozoic granites have already revealed substantial along-strike differences and demonstrated high heterogeneities in the trace elements as well as isotopic compositions even within single granitic plutons or plugs (Le Fort 1981;Debon et al 1986;Schärer et al 1986;Deniel et al 1987;Le Fort et al 1987;France -Lanord & Le Fort 1988;; Barbey et al 1995;Guillot & Le Fort 1995;Harrison et al 1997Harrison et al , 1999Searle et al 1997;Prince et al 2001;Yang & Jin 2001;Zhang et al 2004a, b;Aoya et al 2005;Searle & Szulc 2005;Gao et al 2009Gao et al , 2013Zeng et al 2009Zeng et al , 2011King et al 2011;Gao & Zeng 2014). One of the unresolved questions with regard to the petrogenesis of these leucogranites is whether differentiation of more primitive granitic melts could produce leucogranites and such heterogeneities as mentioned above.…”

Eocene magmatism from the Liemai intrusion in the Eastern Tethyan Himalayan Belt and tectonic implications

“…It is generally accepted that the High Himalayan leucogranites were derived from metamorphic mudstones of the High Himalayan Crystallization System (HHCS) (Harris & Inger, 1992; Harrison et al 1999; Guo & Li, 2007; Huang et al 2013), whereas the source of the Tethyan Himalaya leucogranite (THL) remains controversial. The source may be similar to the Miocene leucogranites (Zhang et al 2004, 2005; Liao et al 2007; Yu et al 2011; Gao et al 2013).…”