Mantle Potential Temperature Estimates of Basalt from the East Taiwan Ophiolite

Abstract

The East Taiwan Ophiolite (ETO) is a fragment of the eastern-most South China Sea that was accreted to the Eurasian margin during the Pliocene and is a member of the Western Pacific and Cordilleran belt ophiolite group. Ophiolites from the Western Pacific and Cordilleran belt are typically subduction-related (i.e., supra-subduction or volcanic-arc) but the ETO is compositionally, isotopically and mineralogically similar to subduction-unrelated ophiolites. The primary melt compositions of ETO basaltic rocks were calculated and range from high-Mg basalt to picrite (i.e., MgO = 10 to 14 wt%). The mantle potential temperature (T P ) estimates are within the range of ambient mantle (1300 -1400°C) and other mid-ocean ridge ophiolites (i.e., Macquarie Island and Masirah) indicating that it is consistent with a mid-ocean ridge setting. Mantle potential temperature estimates for rocks from a mantle-plume-type ophiolite (i.e., 1620 -1630°C) are anomalously high whereas rocks from supra-subduction zone ophiolites show a wider range that extends from ambient (i.e., Troodos and Semail) T P to very high (i.e., Betts Cove and Bay of Islands) T P .

Mantle Potential Temperature Estimates and Primary Melt Compositions of the Low-Ti Emeishan Flood Basalt

“…The crystallization temperatures based on the primary melt compositions of the low-Ti basalt in this study are between 1,300 and 1,450 • C (oxidizing models = 1,315-1,410 • C; reducing models = 1,330-1,435 • C) and similar to the estimates using Al-in-olivine for komatiites and basalts from Gorgona, Baffin Island, SE Greenland and Madagascar but much higher than estimates (<1,300 • C) for mid-ocean ridge basalt (Coogan et al, 2014;Shellnutt and Hsieh, 2016). The Al-in-olivine thermometer method produced a range of crystallization temperatures from 1,188 ± 56 • C to 1,440 ± 63 • C (low-Ti picrites = 1249 ± 58 • C−1356 ± 61 • C) for all compositions of the ELIP picrites (Xu and Liu, 2016).…”

“…The olivine-liquid T P (vertical black lines) estimates for low-Ti Emeishan picrite using melt fractions of (F) of ≈0.35 and ≈0.2 (Tao et al, 2015). Crystallization and mantle potential temperature estimates (blue circles) of mid-ocean ridge (MOR) basalt are also shown (Shellnutt and Hsieh, 2016).…”

“…Ultramafic volcanic rocks are commonly found in the lower volcanic sequences of flood basalt provinces, generated by high degrees of melting under high mantle temperatures, and provide a clear record of the thermal regime (Herzberg and O'Hara, 2002;Kamenetsky et al, 2012). In cases where ultramafic volcanic rocks are unexposed or unidentified, mafic volcanic (basalt) rocks may also be able to help constrain the thermal regime, providing that they have not experienced pyroxene or plagioclase fractionation or were not derived from a volatilerich and/or pyroxenite source (Coltice et al, 2007;Herzberg et al, 2007;Herzberg and Gazel, 2009;Hole, 2015;Whalen et al, 2015;Shellnutt and Hsieh, 2016;Yeh and Shellnutt, 2016).…”

Ages of ophiolitic rocks along plate suture in Taiwan orogen: Fate of the South China Sea from subduction to collision

“…Petrological and geochemical studies suggest the ETO was formed in a deep-sea slow-spreading ridge (Jahn 1986;Chung and Sun 1992;Hsieh et al 2017). However, whether the ETO was generated from a ridge on the South China Sea (e.g., Chung and Sun 1992;Shellnutt and Hsieh 2016;Hsieh et al 2017) or the Philippine Sea Plate (e.g., Chang et al 2009;Huang et al 2018) remained an open question. The recipe is the crystallization age of the ophiolitic rocks since the neighboring South China Sea and the Philippine Sea Plate were formed at different time intervals (Oligo-Miocene, and Eocene or Cretaceous, respectively; Deschamps et al 2000;Sibuet et al 2002;Yeh et al 2010).…”

“…Therefore, the ophiolitic rocks in the Lichi Mélange might have been also originated from the South China Sea lithosphere considering the age of mid-ocean ridge basalt (Hsieh et al 2017) eruption. Prolonged magmatic activity in the mush zone in a slow-spreading ridge environment (Chung and Sun 1992;Shellnutt and Hsieh 2016) might be responsible for the slightly older gabbro crystallization ages from sample JW-02, and not consistent with upper-plate suprasubduction processes (Huang et al 2018). So far no Luzon forearc basement rocks have been documented via geochronological or petrological means within the Lichi Mélange, indicating that although the Lichi Mélange was formed during forearc basin closure through basement underthrusting/ subduction, the basement rocks (except arc volcanics) were not mixed with overlying sediments.…”