Late Paleozoic underplating in North Xinjiang: Evidence from shoshonites and adakites
Late Paleozoic underplating in North Xinjiang: Evidence from shoshonites and adakites
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DOI：
10.1016/j.gr.2009.03.001
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发表时间：
2009-10
影响因子：
6.1
通讯作者：
Zhenhua Zhao;Xiaolin Xiong;Qiang Wang;Z. Bai;Y. Qiao
中科院分区：
文献类型：
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作者：
Zhenhua Zhao;Xiaolin Xiong;Qiang Wang;Z. Bai;Y. Qiao
中国，新疆北部西天山伊什吉力克-阿吾拉勒山脉二叠系陆相火山岩地层中广泛分布着橄榄岩系列火山岩和埃达克岩。同位素测年得出二叠纪的年龄为280-250 Ma。SSVR以富碱、富钾、富铝(A/NKC=0.70~0.99，金属铝)和Fe_2O_3、GT、FeO为特征。富含LILE、高稀土含量和Eu/Eu⁎的SSVR在0.59~1.30之间。它们富LREE((La/Yb)N2.15-11.97)，亏损Nb、Ta、Ti(TnT负异常)。埃达克岩为偏铝至弱过铝(A/NKC=0.85~1.16)，属高SiO_2埃达克岩类型(HSA，SiO_2=62%~71%)。它们的特征是轻稀土元素含量较低，Σ含量较高((La/Yb)N13-35)。明显的Eu正异常(Eu/Eu⁎=1.0 2-1.2 7)、极低的Yb含量和明显的TnT负异常。SSVR具有与埃达克岩相似的εNd(T)(+1.28~+4.92)和(87Sr/86Sr)I(0.7041~0.7057)，其特征为εNd(T)=0.95至+5.69，(87Sr/86Sr)i=0.7050~0.7053。微量元素、稀土元素和锶/钕同位素组成表明，SSVR和埃达克岩具有与底侵地幔玄武岩物质有关的相似源区。岩浆底侵作用驱动的岩石圈伸展作用导致了SSVR和埃达克岩的产生。这种岩浆作用是二叠纪底侵作用的岩石学标志。明显增厚的地壳(62~52 Ma)、复杂的莫霍面、高热流(~100M W·m−~2)、广泛分布的现代富碱花岗岩、基性岩墙群(K-Ar年龄187~271m a，Ar-Ar年龄174~271m a，Rb-sr年龄255±28 Ma；εNd(T)+1.84~+10.1；(87Sr/86Sr)i0.7035和0.7065)，基性麻粒岩(SHRIMP U-Pb年龄268~279±5.6 Ma)为本区二叠纪底侵事件提供了进一步的证据。
Shoshonitic series volcanic rocks (SSVR) and adakites are widely distributed in the Permian terrestrial volcanic strata of the Yishijilike–Awulale range of west Tianshan, north Xinjiang, China. Isotopic dating yields Permian ages of 280–250 Ma. The SSVR include absarokite, shoshonite and banakite which are characterized by enrichment of alkalis, particularly in K, combined with lower Ti, higher Al (A/NKC=0.70–0.99, metaluminous) and Fe2O3>FeO. The SSVR that are rich in LILE with high REE contents and Eu/Eu⁎ range from 0.59 to 1.30. They are rich in LREE ((La/Yb)N2.15–11.97) and depleted in Nb, Ta and Ti (TNT negative anomalies). The adakites are metaluminous to weakly peraluminous (A/NKC=0.85-1.16) and belong to the high-SiO2type of adakite (HSA, SiO2=62%–71%). They are characterized by lower ΣREE with strong LREE enrichment ((La/Yb)N13–35). Pronounced positive Eu anomalies (Eu/Eu⁎=1.02–1.27), very low Yb contents and distinct TNT-negative anomalies are evident. The SSVR have εNd(t) (+1.28 to +4.92) and (87Sr/86Sr)i(0.7041–0.7057) that are similar to adakites in the regions which are characterized by εNd(t)=0.95 to +5.69 and (87Sr/86Sr)i=0.7050–0.7053. Trace element, REE and Sr/Nd isotopic compositions suggest that both SSVR and adakites possess similar source regions associated with underplated mantle-derived basaltic materials. Lithosphere extension driven by magmatic underplating was responsible for the generation of both the SSVR and adakites. This magmatism serves as a petrological indicator of underplating during the Permian. Obviously thickened crust (62–52 km), a complex Moho discontinuity, high heat flow (~100 mw·m−2), widespread contemporary alkali-rich granites, basic dike swarms (K–Ar ages of 187–271 Ma, Ar–Ar ages of 174–270 Ma and Rb–Sr ages of 255±28 Ma; εNd(t)+1.84 to +10.1; (87Sr/86Sr)i0.7035 and 0.7065), and basic granulites (SHRIMP U–Pb age of 268–279±5.6 Ma) provide additional evidences for the underplating event in this area during Permian.