Per
mian basalts distribute at least 250,000 k
m2, and underlie the southwest Tari
m Basin in Xinjiang Uygur Autono
mous region, northwest China. This vast accu
mulation of basalt is the
main part of the Tari
m Large Igneous Province (LIP). The basaltic units in the Lower Per
mian Kupukuzi
man and Kaipaizileike For
mations in the Keping area, Tari
m Basin; were the best exposure of the Per
mian basalt sequence in the basin. LA-ICP-MS U-Pb dating of zircon fro
m the basal basaltic unit in the section gives an age of 291.9 卤 2.2 Ma (MSWD = 0.30,
m>nm> = 17); this age, co
mbined with previously published geochronological data, indicates that the basalts in the Tari
m Basin were e
mplaced between 292 Ma and 272 Ma, with about 90%of the basalts being e
mplaced between 292 and 287 Ma. Basalts fro
m the Keping area have high FeOT (10.8-18.6 wt.%), low Mg#s (0.26-0.60), and exhibit pri
mitive
mantle nor
malized patterns with positive Pb, P and Ti but negative Zr, Y and Ta ano
malies.
The basalts from both formations have similar 206Pb/204Pb (18.192-18.934), 207Pb/204Pb (15.555-15.598) and 208Pb/204Pb (38.643-38.793) ratios. The basalts also have high m>蔚m>Sr(m>tm>) (45.7-62.1), low m>蔚m>Nd(m>tm>) (鈭?.6 to 鈭?.2) and low zircon m>蔚m>Hf(m>tm>) (鈭?.84 to 鈭?.65) values. These characteristics are typical of alkali basalts and suggest that the basalts within the Tarim Basin were derived from an OIB-type mantle source and interacted with enriched mantle (EMI-type) before emplacement. Rare earth element systematics indicate that the parental melts for the basalts were high-degree partial melts derived from garnet lherzolite mantle at the base of the lithosphere. Prior to emplacement, the Tarim Permian Basalts (TPB) underwent fractional crystallization and assimilated crustal material; the basalts were finally emplaced during crustal extension in an intra-plate setting. The wide distribution, deep source and high degree partial melting of the TPB was consistent with a mantle plume origin. The TPB and other coeval igneous rocks in the Tarim Basin constitute a Permian LIP formed by a mantle plume in a similar fashion to the plume-related Emeishan LIP in southwest China.