UHT sapphirine granulite metamorphism at 1.93–1.92 Ga caused by gabbronorite intrusions: Implications for tectonic evolution of the northern margin of the North China Craton
UHT sapphirine granulite metamorphism at 1.93–1.92 Ga caused by gabbronorite intrusions: Implications for tectonic evolution of the northern margin of the North China Craton
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DOI：
10.1016/j.precamres.2011.07.020
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发表时间：
2012-12
影响因子：
3.8
通讯作者：
Jing-hui Guo;P. Peng;Yi Chen;S. Jiao;B. Windley
中科院分区：
文献类型：
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作者：
Jing-hui Guo;P. Peng;Yi Chen;S. Jiao;B. Windley
蓝宝石麻粒岩产于古元古代孔兹拉特岩带中的大青山和济宁地区，将中国克拉通西部地块划分为北部的银山地块和南部的鄂尔多斯地块。大青山地区蓝宝石麻粒岩常与变质辉长闪长岩墙接触，具有因果关系。含蓝宝石岩石分为spinel–garnet–sillimanite–biotite–plagioclase–sapphirine片麻岩、超高温蓝宝石麻粒岩和尖晶石-石榴石麻粒岩。蓝宝石麻粒岩含有高达30%的蓝宝石、石榴石(30-50%)、尖晶石(5-15%)、硅线石(5-15%)、黑云母(10-20%)和斜长石(10-20%)，并含有少量的堇青石、金红石和钛铁矿，但不含石英和斜方辉石。整体化学成分表明，蓝宝石麻粒岩的SiO_2含量很低(39wt.%)，Al含量很高，XMG很低。黑云母的二氧化钛含量很高，达7.6wt.%。对蓝宝石麻粒岩进行了详细的岩石学研究，发现了5种矿物组合(M0-M4)：(1)石榴石核内矿物包裹体的组合(M0)；(2)以粗粒石榴石、蓝宝石、尖晶石、硅线石、黑云母和斜长石为代表的基质(峰)组合(M1)；(3)蓝宝石+斜长正长石(M2)；(4)尖晶石+斜长混合岩(M3)；(5)退变黑云母(M4)。NCKFMASH系统假剖面的P-T稳定场表明，大青山蓝宝石麻粒岩的超高温变质峰期温度为910-980℃(与孔兹岩700-820℃的区域变质峰温相比)。从矿物组合(M1-M4)的P-T稳定场推断的P-T路径表明，在UHT变质高峰期(M1)之后，经历了近等温减压(M2和M3)和后来的冷却(M4)。场关系和年代学数据表明，大青山地区蓝宝石麻粒岩超高温变质所需的高热流来自于同时代的∼1.93-1.92Ga辉长闪长岩侵入岩，这些侵入岩最有可能是由山脊俯冲产生的，这也是该地区地壳熔融形成富含石榴石的花岗岩的原因。
Sapphirine granulites occur in the Daqingshan and Jining areas in the Palaeoproterozoic Khondalite belt, which divides the Western Block of the North China Craton into the Yinshan block to the north and the Ordos block to the south. The sapphirine granulites in the Daqingshan area are always in contact with meta-gabbronorite dykes, implying a causal relationship. The sapphirine-bearing rocks are divided into spinel–garnet–sillimanite–biotite–plagioclase–sapphirine gneiss, UHT sapphirine granulite, and spinel–garnet granulite. The sapphirine granulite contains up to 30% sapphirine, garnet (30–50%), spinel (5–15%), sillimanite (5–15%), biotite (10–20%) and plagioclase (10–20%) with minor cordierite, rutile and ilmenite, but without quartz and orthopyroxene. Bulk chemical compositions show that the sapphirine granulites have very low SiO2contents (39wt.%), high Al contents, and low XMg. Biotite contains very high TiO2contents up to 7.6wt.%. Detailed petrographic examination of the sapphirine granulites reveals five mineral assemblages (M0–M4): (1) an assemblage (M0) of mineral inclusions within garnet cores, (2) a matrix (peak) assemblage (M1) represented by coarse-grained garnet, sapphirine, spinel, sillimanite, biotite and plagioclase, (3) sapphirine+plagioclase symplectite (M2), (4) spinel+plagioclase symplectite (M3), and (5) retrogressive biotite (M4). The P–T stability field in the pseudosection of the NCKFMASH system indicates that the temperature of the peak UHT metamorphism of the Daqingshan sapphirine granulites is in the range 910–980°C (this compares with the peak regional metamorphic temperature of the khondalites of 700–820°C). The P–T path inferred from the P–T stability fields of the mineral assemblages (M1–M4) suggests that the peak UHT metamorphism (M1) was followed by nearly isothermal decompression (M2and M3) and later cooling (M4). Field relations and geochronological data suggest that the high-heat flow necessary for the UHT metamorphism of the sapphirine granulites from the Daqingshan area was provided by coeval ∼1.93–1.92Ga gabbronorite intrusions that were most probably generated by ridge subduction, which was also responsible for abundant garnet-rich granites by crust melting the area.