The Sandvik peridotite, Gurskøy, Norway: Three billion years of mantle evolution in the Baltica lithosphere
The Sandvik peridotite, Gurskøy, Norway: Three billion years of mantle evolution in the Baltica lithosphere
复制标题
挪威古尔斯克山特维克橄榄岩：波罗的海岩石圈三十亿年的地幔演化
DOI：
10.1016/j.lithos.2008.08.007
复制
发表时间：
2009
期刊：
影响因子：
3.5
通讯作者：
C. Johnson
中科院分区：
文献类型：
--
作者：
T. Lapen;L. Medaris;B. Beard;C. Johnson
挪威西部片岩地区Gurskøy岛的Sandvik超镁铁质体是一个包含多变质矿物组合的地幔碎片，为研究次大陆岩石圈地幔对重复造山/岩浆事件的响应提供了独特的视角。山特维克橄榄岩体及其附近露头记录了4个共生阶段：1)ol+grt+opx（高ca）+cpx（低ca）的预溶斑岩碎屑，在1100 ~ 1200℃、6.5 ~ 7.0 GPa时达到平衡；(2)含ol+grt+spl+opx（低ca）+am（高al）的榴辉石，以及含opx+cpx+spl的辉石，与基体橄榄石在725℃和1.5 GPa条件下达到平衡；3) ol+spl+opx（低钙）+am（高铝）的成粒基质，温度700℃，GPa 1.0。附近的露头包含第四个组合，由ol+chl+opx+am组成。石榴石橄榄岩的Lu-Hf和Re-Os模型年龄表明熔体在3.3 Ga时枯竭[Beyer， e.e., Brueckner, h.k., Griffin， W.L， O'Reilly， S.Y, Graham， S., 2004]。挪威西部片麻岩地区元古代地壳中太古宙地幔碎片。地质32,609-612 .；Lapen, t.j., Medaris， L.G. Jr., Johnson, c.m.和Beard， b.l., 2005。波罗的海次大陆岩石圈太古代至中元古代演化：来自挪威Sandvik超镁铁质体Sm-Nd和Lu-Hf联合同位素分析的证据。矿物学与岩石学的贡献，150,131-145。]，标志着与对流地幔分离的时间。Sandvik岩体中石榴石橄榄岩和石榴石橄榄岩组成层的Lu-Hf全岩和矿物等时线年龄分别反映了~1.25 Ga和~1.18 Ga的冷却和侵位，而石榴石橄榄岩和石榴石橄榄岩组成层的Sm-Nd全岩和矿物年龄与~1.15 Ga的交代蚀变相一致[j]， Medaris， L.G. Jr., Johnson， C.M, and Beard， B.L., 2005。波罗的海次大陆岩石圈太古代至中元古代演化：来自挪威Sandvik超镁铁质体Sm-Nd和Lu-Hf联合同位素分析的证据。矿物学与岩石学的贡献[j]., 15(5): 131-145。等时线年龄可能记录了与1.25-1.00 Ga晚鄂西造山运动相关的岩石圈改造，代表了第1阶段矿物组合平衡的最年轻年龄。第2阶段榴辉岩组合的Sm-Nd等时线年龄为606±39 Ma，与大陆裂谷时期波罗的海与劳伦提亚之间Iapetus洋的打开或波罗的海与西伯利亚之间的伸展（Ægir海的打开）的部分再平衡相一致。因此，榴辉岩的年代将山特维克橄榄岩置于波罗的海和劳伦大陆之间志留纪缩短之前的最上层地幔。
The Sandvik ultramafic body, Island of Gurskøy, Western Gneiss Region, Norway, is a mantle fragment that contains polymetamorphic mineral assemblages and affords a unique view into the response of subcontinental lithospheric mantle to repeated orogenic/magmatic events. The Sandvik peridotite body and nearby outcrops record four paragenetic stages: 1) pre-exsolution porphyroclasts of ol+grt+opx (high-Ca )+cpx (low-Ca), which equilibrated at 1100–1200 °C and 6.5–7.0 GPa; 2) kelyphite containing ol+grt+spl+opx (low-Ca)+am (high-Al), as well as exsolved pyroxene containing opx+cpx+spl in equilibrium with matrix olivine, at 725 °C and 1.5 GPa; 3) granoblastic matrix of ol+spl+opx (low-Ca)+am (high-Al), at 700 °C and 1.0 GPa. A nearby outcrop contains a fourth assemblage consisting of ol+chl+opx+am. Lu–Hf and Re–Os model ages of garnet peridotite indicate melt depletion at 3.3 Ga [Beyer, E.E., Brueckner, H.K., Griffin, W.L., O'Reilly, S.Y., Graham, S., 2004. Archean mantle fragments in Proterozoic crust, Western Gneiss Region, Norway. Geology 32, 609–612.; Lapen, T.J., Medaris, L.G. Jr., Johnson, C.M., and Beard, B.L., 2005. Archean to Middle Proterozoic evolution of Baltica subcontinental lithosphere: evidence from combined Sm–Nd and Lu–Hf isotope analyses of the Sandvik ultramafic body, Norway. Contributions to Mineralogy and Petrology 150, 131–145.], marking the time of separation from the convecting mantle. Lu–Hf whole rock and mineral isochron ages of constituent garnet peridotite and garnet pyroxenite layers in the Sandvik body reflect cooling and emplacement at ~1.25 Ga and ~1.18 Ga, respectively, whereas Sm–Nd whole rock and mineral ages of the garnet pyroxenite layers and the garnet peridotite are consistent with metasomatic alteration at ~1.15 Ga [Lapen, T.J., Medaris, L.G. Jr., Johnson, C.M., and Beard, B.L., 2005. Archean to Middle Proterozoic evolution of Baltica subcontinental lithosphere: evidence from combined Sm–Nd and Lu–Hf isotope analyses of the Sandvik ultramafic body, Norway. Contributions to Mineralogy and Petrology 150, 131–145.]. The isochron ages likely record lithospheric modification associated with the 1.25–1.00 Ga Sveconorwegian orogeny and represent the youngest age of the Stage 1 mineral assemblage equilibration. A 606±39 Ma Sm–Nd isochron age of the Stage 2 kelyphite assemblage is consistent with partial re-equilibration of the porphyroclastic assemblage during continental rifting associated with opening of the Iapetus Ocean between Baltica and Laurentia at ~600 Ma, or extension between Baltica and Siberia that may have been associated with opening of the Ægir Sea. The age of kelyphite, therefore, places the Sandvik peridotite in the uppermost mantle prior to Silurian shortening between the Baltic and Laurentian continents.