Late Carboniferous TTG magmatic event in the Hegenshan suture zone:zircon U- Pb geochronology and geochemical constraints from the Huduge trondhjemite
Author NameAffiliationE-mail
WANG Jinfang College of the Earth Sciences, Heibei GEO University, Shijiazhuang, Hebei, 050031 
LI Yingjie College of the Earth Sciences, Heibei GEO University, Shijiazhuang, Hebei, 050031  
LI Hongyang College of the Earth Sciences, Heibei GEO University, Shijiazhuang, Hebei, 050031  
DONG Peipei College of the Earth Sciences, Heibei GEO University, Shijiazhuang, Hebei, 050031  
Abstract:The TTG magmatic event was an important geological process for the juvenile crustal growth. The Huduge trondhjemite is located in the Meilaotewula SSZ type ophiolite of the Hegenshan suture zone in the Xi Ujimqin Banner of Inner Mongolia. We present results of field geological survey, petrology, geochemistry and zircon U Pb geochronology to discuss the petrogenesis, tectonic setting, the TTG magmatic event and the final closure time subduction process of the Erenhot Hegenshan ocean basin(EHOB) of the Paleo Asian Ocean (PAO). Petrogeochemical studies show that the Huduge pluton has high SiO 2 (66. 27%~71. 59%), Al 2O 3 (15. 23%~15. 94%), Na 2O (4. 13%~6. 59%), Sr (196. 60×10 -6~465. 40×10 -6) and low K 2O (1. 72%~2. 53%), Y (5. 70×10 -6~12. 63×10 -6) contents, is enriched in Ba, Sr large ion lithophile elements and LREE, and depleted in Nb, Ta, Ti, P high field strength elements and HREE. There is no pronounced Eu anomaly. The lithological and geochemical characteristics show that the Huduge pluton belongs to tonalite trondhjemite granodiorite (TTG) assemblages dominated by trondhjemite. The geochemical characteristics of the TTG assemblages are similar to those of high SiO 2 adakites except for the relatively low Sr, Mg, Ni, Cr content. The TTGwas probably formed in island arc setting of oceanic subduction zone and comprises of island arcmagmatic rocks. It is inferred that the TTG might have been derived from the dehydration melting of the subducted oceanic crust. The zircon U Pb LA ICP MS dating provides two formation ages: 306. 3 ±1. 9 Ma and 315. 5±1. 9 Ma, indicating that the pluton was emplaced in the Late Carboniferous, reflecting the TTG magmatism and juvenile crustal growth events of oceanic subduction zone in the Hegenshan suture zone during the Late Carboniferous. Based on the petrotectonic assemblage of the fore arc basalts, high Mg andesite/high Mg diorite, high SiO 2 adakites, TTG and Nb enriched basalt/gabbro in the Meilaotewula Gaolihan ophiolite TTG belt, itis suggested that while the EHOB of the PAO may have been in the ocean continent transition process of oceanic subduction, TTG magmatism and juvenile crustal growth occurred in the Late Carboniferous.
keywords:Late Carboniferous  ocean continent transition  Hegenshan suture- zone
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