Geochemistry of picrites and associated lavas of a Devonian island arc in the northern Junggar terrane, Xinjiang (NW China): Implications for petrogenesis, arc mantle sources and tectonic setting
Geochemistry of picrites and associated lavas of a Devonian island arc in the northern Junggar terrane, Xinjiang (NW China): Implications for petrogenesis, arc mantle sources and tectonic setting
复制标题
新疆准噶尔地体北部泥盆纪岛弧的苦味岩和相关熔岩的地球化学：对岩石成因、弧地幔来源和构造环境的影响
DOI：
10.1016/j.lithos.2008.05.013
复制
发表时间：
2008-10
期刊：
影响因子：
3.5
通讯作者：
张招崇
中科院分区：
文献类型：
--
作者：
张招崇
中国笔下的新疆准噶尔地体毗邻西伯利亚克拉通和哈萨克斯坦地块。在准噶尔地体的泥盆纪弧形中发现了一系列近100米厚的高镁熔岩流。高斑岩型高镁熔岩产于中泥盆统北塔山组下部，上覆玄武岩和安山岩。根据化学成分和斑晶含量，将高镁熔岩分为苦味岩类和蓝晶石类。前者以大量橄榄石斑晶(Fo 79-82)和少量单斜辉石(En44-50Fs1-10Wo44-48)和稀有铬尖晶石为特征，其Cr#(Cr/Cr+Al)值在0.63~0.86之间，而单斜辉石斑晶则以单斜辉石为主。苦苦岩和钾长花岗岩中的基质由斜长石、单斜辉石和钛磁铁矿组成。玻璃不被保存，但存在少量金属硫化物。根据橄榄石-熔融平衡，原始岩浆中的氧化镁含量约为9wt%，高镁熔岩中含有堆积的橄榄石(苦橄岩)和单斜辉石+橄榄石(安山岩)。所有熔岩具有相似的原始地幔归一化微量元素模式，以Nb、Ta和Ti负异常为特征，这是岛弧火山岩的典型特征。这些关系表明，岩套是同岩浆的。苦苦岩和玄武岩的Zr/Nb比值(23~66)与MORb相似(10~66)，表明苦苦岩的来源类似于MORb。苦橄岩具有轻微的轻稀土富集型式，(La/Yb)n为1.6~3.5，(La/Sm)n为1.2~2.1。玄武岩的(La/Yb)n为1.2~5.7，(La/Sm)n为0.8~2.5；安山岩为轻度LREE富集型，(La/Yb)n为2.8~9.1，(La/Sm)n为1.7~2.9。所有岩石的稀土配分模式均未显示Eu异常。岩石具有相似的(87Sr/86Sr)t(0.7033~0.7043，t=385M a)和εNd(T)值(6.47.3)，与现代岛弧场重叠。因此，原生岩浆很可能是在N-MORB型地幔中产生的，由于增加了来自蚀变俯冲洋壳的流体成分，因此原生岩浆最有可能产生于N-MORB型地幔，其高的锶/钕和低的Th/Yb比值表明。REE模拟表明，原生岩浆来源于石榴石-尖晶石过渡带地幔。
The Junggar terrane in China's Xinjiang Province sits adjacent to the Siberian craton and Kazakhstan block. A nearly 100-m thick series of high-Mg lava flows is found in a Devonian arc in the Junggar terrane. The highly porphyritic high-Mg lavas are stratigraphically in the lower part of the Middle Devonian Beitashan Formation, and are overlain by basalts and andesites. Based on the chemistry and phenocryst contents, the high-Mg lavas are classified into picrites and ankaramites. The former are characterized by a large amount of olivine phenocrysts (Fo 79–82) with minor clinopyroxene (En44–50Fs1–10Wo44–48) and rare chrome spinel with Cr# (Cr/Cr+Al) values between 0.63 and 0.86, whereas clinopyroxene phenocrysts are dominant in ankaramite. The groundmass in the picrites and ankaramites consists of plagioclase, clinopyroxene, and Ti-magnetite. Glass is not preserved, but minor metal sulfides are present. Based on olivine-melt equilibrium, the primitive magmas had approximately 9 wt.% MgO, and the high-Mg lavas contain accumulated olivine (picrites) and clinopyroxene+olivine (ankaramites). All lavas have similar primitive mantle normalized trace element patterns, characterized by negative Nb, Ta and Ti anomalies, as typical for island arc volcanic rocks. These relationships suggest that the rock suites are co-magmatic. The Zr/Nb ratios (23–66) of the picrites and basalts resemble MORBs (10–66), suggesting MORB-like sources for the picrites. The picritic rocks have slightly LREE-enriched patterns with (La/Yb)nranging from 1.6 to 3.5 and (La/Sm)nfrom 1.2 to 2.1. In contrast, basaltic rocks have flat to slightly LREE-enriched patterns with (La/Yb)nranging from 1.2 to 5.7 and (La/Sm)nfrom 0.8 to 2.5, whereas andesitic rocks have modestly LREE-enriched patterns with (La/Yb)nranging from 2.8 to 9.1 and (La/Sm)nfrom 1.7 to 2.9. The REE patterns for all rocks do not exhibit Eu anomalies. The rocks have similar (87Sr/86Sr)t(0.7033–0.7043, t=385 Ma) and εNd(t) values (6.4–7.3), overlapping with the present day island arc field. Consequently, primary magmas were most likely generated in N-MORB-type mantle, which was modified by the addition of a fluid component derived from altered subducted oceanic crust as indicated by elevated Sr/Nd and low Th/Yb ratios. REE modelling suggests that the primary magmas were derived from garnet–spinel transition zone mantle.
登录
查看更多内容
影响因子：
3.5
作者：
S. Eggins
通讯作者：
S. Eggins
DOI：
--
发表时间：
1983
期刊：
--
影响因子：
--
作者：
Kg Nickel
通讯作者：
Kg Nickel
影响因子：
3.9
作者：
G. Chai;A. J. Naldrett
通讯作者：
G. Chai;A. J. Naldrett
影响因子：
3.5
作者：
R. T. Helz;C. Thornber
通讯作者：
R. T. Helz;C. Thornber
影响因子：
3.5
作者：
W. Ramsay;A. Crawford;J. Foden
通讯作者：
W. Ramsay;A. Crawford;J. Foden