Premium
Zircon U–Pb Geochronology and Geochemistry of the Early Cretaceous Volcanic Rocks from the Manitu Formation in the Hongol Area, Northeastern Inner Mongolia
Author(s) -
ZHANG Xiangxin,
SU Zhen,
GAO Yongfeng
Publication year - 2017
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13362
Subject(s) - zircon , geology , geochemistry , geochronology , petrogenesis , volcanic rock , lithophile , cretaceous , volcano , partial melting , crust , mantle (geology) , paleontology
We undertook zircon U–Pb dating and geochemical analyses of volcanic rocks from the Manitu Formation in the Hongol area, northeastern Inner Mongolia, to determine their age, petrogenesis and sources, which are important for understanding the Late Mesozoic tectonic evolution of the Great Xing'an Range. The volcanic rocks of the Manitu Formation from the Hongol area consist primarily of trachyandesite, based on their chemical compositions. The zircons from two of these trachyandesites are euhedral–subhedral in shape, display clear oscillatory growth zoning and have high Th/U ratios (0.31–1.15), indicating a magmatic origin. The results of LA‐ICP‐MS zircon U–Pb dating indicate that the volcanic rocks from the Manitu Formation in the Hongol area formed during the early Early Cretaceous with ages of 138.9–140.5 Ma. The volcanic rocks are high in alkali (Na 2 O + K 2 O = 6.22–8.26 wt%), potassium (K 2 O = 2.49–4.58 wt%) and aluminium (Al 2 O 3 = 14.27–15.88 wt%), whereas they are low in iron (total Fe 2 O 3 = 3.76–6.53 wt%) and titanium (TiO 2 = 1.02–1.61 wt%). These volcanic rocks are obviously enriched in large ion lithophile elements, such as Rb, Ba, Th and U, and light rare earth elements, and are depleted in high field strength elements, such as Nb, Ta and Ti with pronounced negative anomalies. Their Sr–Nd–Pb isotopic compositions show positive ∊ Nd ( t ) (+0.16‰ to+1.64‰) and low T DM ( t ) (694–767 Ma). The geochemical characteristics of these volcanic rocks suggest that they belong to a shoshonitic series and were likely generated from the partial melting of an enriched lithospheric mantle that was metasomatised by fluids released from a subducted slab during the closure of the Mongol–Okhotsk Ocean. Elemental and isotopic features reveal that fractional crystallization with the removal of ferromagnesian minerals, plagioclase, ilmenite, magnetite and apatite played an important role during the evolution of the magma. These shoshonitic rocks were produced by the partial melting of the enriched lithospheric mantle in an extensional regime, which resulted from the gravitational collapse following the final closure of the Mongol–Okhotsk Ocean in the Middle–Late Jurassic.