TY - JOUR
T1 - Geochronology and petrogenesis of Jurassic intraplate alkali basalts in the Junggar terrane, NW China
T2 - implication for low-volume basaltic volcanism
AU - Wang, Jian
AU - Su, Yuping
AU - Zheng, Jianping
AU - Gao, Shanlin
AU - Dai, Hongkun
AU - Ping, Xianquan
AU - Xiong, Qing
AU - Niyaz, Kahar
PY - 2019/1
Y1 - 2019/1
N2 - High-volume volcanic fields which are observed at continental intraplate setting are generally known as the large igneous provinces (LIPs), fed by hot and active plumes upwelling from the deep mantle. However, the source and mechanism of low-volume effusive volcanism within continental interiors remains poorly unknown. Here, we present a combined study of 40Ar/39Ar geochronology, mineral chemistry, whole-rock major and trace elements as well as Sr-Nd isotopes of Jurassic basalts from the Karamay area, Junggar terrane (NW China), aiming to determine their formation ages, constrain the petrogenesis and reveal their tectonic implications.New whole-rock 40Ar/39Ar dating yields consistent ages of 189.4–193.3 Ma for magma emplacement. The basalts exhibit a columnar joint structure and porphyritic texture with phenocryst minerals of olivine (Fo63–79), clinopyroxene (Wo39–46En38–47Fs12–22) and plagioclase (An25–54). They have SiO2 contents ranging from 45.0–51.8 wt% and belong to alkaline series (δ2.7–13.3, average of 5.0). The basalts are characterized by oceanic island basalt (OIB)-like trace element distribution patterns with enrichment in L-MREE, HFSE (e.g., Nb and Ta) and LILE (e.g., K, Sr and Ba), and slight depletion in HREE, relative to normal mid-ocean ridge basalt (N-MORB). Positive εNd(t) (+3.0), low to moderate 87Sr/86Sri (0.7048–0.7049) isotopic compositions, and trace element ratios (e.g., high Nb/U > 49.0 and Ce/Pb > 13.9) suggest that crust contamination was insignificant in the formation process. P–T estimates of major phenocryst minerals in these basalts reflect high crystallization temperatures (>1100 °C) but low pressures (<9.8 kbar). Geochemical features and REE modeling indicate that the basaltic magmas were likely derived by low degrees of partial melting (~5% – 10%) of an asthenospheric mantle source in the garnet stability field. Calculated lithospheric thickness and initial melting depths for the studied basalts are about 120 km and 180–200 km, respectively. Based on the available data and regional secular geological evolution, we suggest that decompression melting of upwelling asthenosphere triggered by small-scale removal of thickened lithospheric root could be a possible mechanism to explain Jurassic low-volume intraplate volcanism in the Junggar terrane.
AB - High-volume volcanic fields which are observed at continental intraplate setting are generally known as the large igneous provinces (LIPs), fed by hot and active plumes upwelling from the deep mantle. However, the source and mechanism of low-volume effusive volcanism within continental interiors remains poorly unknown. Here, we present a combined study of 40Ar/39Ar geochronology, mineral chemistry, whole-rock major and trace elements as well as Sr-Nd isotopes of Jurassic basalts from the Karamay area, Junggar terrane (NW China), aiming to determine their formation ages, constrain the petrogenesis and reveal their tectonic implications.New whole-rock 40Ar/39Ar dating yields consistent ages of 189.4–193.3 Ma for magma emplacement. The basalts exhibit a columnar joint structure and porphyritic texture with phenocryst minerals of olivine (Fo63–79), clinopyroxene (Wo39–46En38–47Fs12–22) and plagioclase (An25–54). They have SiO2 contents ranging from 45.0–51.8 wt% and belong to alkaline series (δ2.7–13.3, average of 5.0). The basalts are characterized by oceanic island basalt (OIB)-like trace element distribution patterns with enrichment in L-MREE, HFSE (e.g., Nb and Ta) and LILE (e.g., K, Sr and Ba), and slight depletion in HREE, relative to normal mid-ocean ridge basalt (N-MORB). Positive εNd(t) (+3.0), low to moderate 87Sr/86Sri (0.7048–0.7049) isotopic compositions, and trace element ratios (e.g., high Nb/U > 49.0 and Ce/Pb > 13.9) suggest that crust contamination was insignificant in the formation process. P–T estimates of major phenocryst minerals in these basalts reflect high crystallization temperatures (>1100 °C) but low pressures (<9.8 kbar). Geochemical features and REE modeling indicate that the basaltic magmas were likely derived by low degrees of partial melting (~5% – 10%) of an asthenospheric mantle source in the garnet stability field. Calculated lithospheric thickness and initial melting depths for the studied basalts are about 120 km and 180–200 km, respectively. Based on the available data and regional secular geological evolution, we suggest that decompression melting of upwelling asthenosphere triggered by small-scale removal of thickened lithospheric root could be a possible mechanism to explain Jurassic low-volume intraplate volcanism in the Junggar terrane.
KW - Junggar terrane
KW - Jurassic basalt
KW - ⁴⁰Ar/³⁹Ar dating
KW - Petrogenesis
KW - Low-volume basaltic volcanism
UR - http://www.scopus.com/inward/record.url?scp=85056770950&partnerID=8YFLogxK
U2 - 10.1016/j.lithos.2018.11.002
DO - 10.1016/j.lithos.2018.11.002
M3 - Article
AN - SCOPUS:85056770950
SN - 0024-4937
VL - 324-325
SP - 202
EP - 215
JO - Lithos
JF - Lithos
ER -