Re-Os geochronology, O isotopes and mineral geochemistry of the Neoproterozoic Songshugou ultramafic massif in the Qinling Orogenic Belt, China
Re-Os geochronology, O isotopes and mineral geochemistry of the Neoproterozoic Songshugou ultramafic massif in the Qinling Orogenic Belt, China
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秦岭造山带新元古代松树沟超镁铁质岩体Re-Os年代学、O同位素及矿物地球化学
DOI：
10.1016/j.gr.2018.12.016
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发表时间：
2019-06
影响因子：
6.1
通讯作者：
Xiaoming Liu
中科院分区：
文献类型：
--
作者：
Shengsi Sun;Yunpeng Dong;Yali Sun;Chao Cheng;Xiaoxiao Huang;Xiaoming Liu
秦岭造山带是中国地块南北沿商丹缝合带俯冲碰撞形成的。位于商丹缝合带北侧的松树沟超镁铁质地块，为研究商丹大洋岩石圈扩张和俯冲过程中的地幔起源和演化过程提供了重要的信息。超大型地块由方辉橄榄岩、粗粒和细粒二辉橄榄岩组成。方辉橄榄岩中的尖晶石具有较低的Cr#和较高的Mg#值，表明其起源于大洋洋脊橄榄岩，而粗粒和细粒英安岩中的尖晶石则因其系统的较高的Cr#和较低的Mg#数而被认为是熔岩反应的结果。尖晶石中的低二氧化钛(主要是b0.4wt%)和橄榄石中的高Fo(90-92)也表明了英安岩中的这种熔岩反应。由于其在地幔中的相对均质性，氧同位素组成是反映松树沟超镁铁质岩石成因和构造环境的灵敏指标。根据26个岩石样品中橄榄石的氧同位素分析，松树沟超镁铁质地块中大多数方辉橄榄岩的δ~(18)O值较低，为4.54~5.30‰，表明橄榄石与N-MORB岩浆平衡，形成于大洋中脊环境。粗粒和细粒英安岩的橄榄石δ18O值分别略高，分别为4.69-6.00‰和5.00-6.11‰，表明它们可能受到了与俯冲有关的博尼质熔岩反应的改造。橄榄石的δ~(18)O值从方辉橄榄岩到粗粒橄榄岩和细粒橄榄岩系统地递增，表明熔岩反应增强。方辉橄榄岩到纯橄榄岩的Os浓度、187Re/188Os和187Os/188Os比值的下降表明，俯冲带熔体富含187Os，为熔岩反应创造了熔体通道。结合高温韧性变形微构造，这些同位素和矿物地球化学特征表明，方辉橄榄岩代表了大洋中脊或俯冲带部分熔融后的地幔残留物，而方辉橄榄岩可能是在俯冲带中的波尼质熔体与方辉橄榄岩反应的结果。Re-Os年代学给出的最大亏损模式年龄(TRD)为805 Ma，限制了大洋地幔方辉橄榄岩的最小形成年龄。8个全岩和铬铁矿样品的Re-Os等时线年龄为500±120 Ma，制约了熔岩反应的时间。结合区域地质和我们以往的研究，松树沟超镁铁质岩石最好起源于805 Ma之前的大洋中脊，并在约500 Ma的SSZ受到博尼质熔体渗流的影响。这种从扩张到俯冲的长期构造过程可能意味着在劳亚大陆(例如，北中国地块)和冈瓦那(例如，南半球)之间存在一个巨大的泛特提斯洋
The Qinling Orogenic Belt was formed by subduction and collision between the North and South China Blocks.along the Shangdan suture. The Songshugou ultramafic massif located on the northern side of the Shangdan suture.provides essential insights into the mantle origin and evolutionary processes during spreading and subduction.of the Shangdan oceanic lithosphere. The ultramaficmassif comprises harzburgite, coarse- and fine-grained.dunites. The spinels fromharzburgite exhibit low Cr# and highMg# numbers, suggesting amid-ocean ridge peridotite.origin, whereas spinels from both coarse- and fine-grained dunites are indicated as resulted from meltrock.reaction due to their systematic higher Cr# and lowMg# numbers. This melt-rock reaction in the dunites is.also indicated by the lowTiO2 (mostly b0.4wt%) in the spinel and high Fo (90–92) in olivines. Due to its relatively.homogeneous nature in the mantle, oxygen isotopic composition is a sensitive indicator for the petrogenesis and.tectonic setting of the Songshugou ultramafic rocks. Based on in-situ oxygen isotope analyses of olivines from.twenty-six rock samples, most harzburgites from the Songshugou ultramafic massif show low δ18O values of.4.54–5.30‰, suggesting the olivines are equilibrium with N-MORB magmas and originally formed in a midocean.ridge setting. The coarse- and fine-grained dunites exhibit slightly higher olivine δ18O values of.4.69–6.00‰ and 5.00–6.11‰, respectively, suggesting they may have been modified by subduction-related.boninitic melt-rock reaction. The δ18O values of olivines systematically increasing from the harzburgites, to.coarse-grained dunites and fine-grained dunites may suggest enhancing of melt-rock reaction. The decreasing.of Os concentration, 187Re/188Os and 187Os/188Os ratios from harzburgite to dunite suggest an 187Os-enriched,.subduction zone melt was responsible for creating the melt channel for melt-rock reactions. Together with the.high-temperature ductile deformation microstructures, these isotopic and mineral geochemical features suggest.that the harzburgites represent mantle residues after partial melting at mid-ocean ridge or supra-subduction.zone, while the dunites were probably resulted from reactions between boninitic melt and harzburgites in a.supra-subduction zone. Re-Os geochronology yields a maximum Re depletion model age (TRD) of 805 Ma,.constraining the minimum formation age of the harzburgites derived from oceanic mantle. Eight samples of.whole rock and chromite yield a Re-Os isochron age of 500±120Ma, constraining the timing ofmelt-rock reactions..Combined with the regional geology and our previous investigations, the Songshugou ultramafic rocks favors.amantle origin atmid-ocean ridge before 805 Ma, and weremodified by boniniticmelt percolations in a SSZ.setting at ca. 500 Ma. This long-term tectonic process from spreading to subduction might imply a huge Pan-.Tethyan ocean between the Laurasia (e.g., North China Block) and Gondwana (e.g., South C
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影响因子：
14.9
作者：
S. Shirey;R. Walker
通讯作者：
S. Shirey;R. Walker
影响因子：
--
作者：
D. Stakes;H. Taylor
通讯作者：
D. Stakes;H. Taylor
中国大别—苏鲁超高压变质带橄榄岩年龄和起源的真实证据
影响因子：
3.9
作者：
高山;于日东;Igor S. Puchtel;Richard J. Walker;金振民;袁洪林;Roberta L. Rudnick;刘勇胜
通讯作者：
刘勇胜
影响因子：
5.8
作者：
Daniel C. Pope;S. Willett
通讯作者：
Daniel C. Pope;S. Willett
影响因子：
3.5
作者：
I. Uysal;E. Ersoy;O. Karslı;Y. Dilek;M. B. Sadiklar;C. Ottley;M. Tiepolo;T. Meisel
通讯作者：
I. Uysal;E. Ersoy;O. Karslı;Y. Dilek;M. B. Sadiklar;C. Ottley;M. Tiepolo;T. Meisel