Coexistence of abyssal and ultra-depleted SSZ type mantle peridotites in a Neo-Tethyan Ophiolite in SW Turkey: Constraints from mineral composition, whole-rock geochemistry (major–trace–REE–PGE), and Re–Os isotope systematics
Coexistence of abyssal and ultra-depleted SSZ type mantle peridotites in a Neo-Tethyan Ophiolite in SW Turkey: Constraints from mineral composition, whole-rock geochemistry (major–trace–REE–PGE), and Re–Os isotope systematics
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DOI：
10.1016/j.lithos.2011.11.009
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发表时间：
2012-02
期刊：
影响因子：
3.5
通讯作者：
I. Uysal;E. Ersoy;O. Karslı;Y. Dilek;M. B. Sadiklar;C. Ottley;M. Tiepolo;T. Meisel
中科院分区：
文献类型：
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作者：
I. Uysal;E. Ersoy;O. Karslı;Y. Dilek;M. B. Sadiklar;C. Ottley;M. Tiepolo;T. Meisel
本文报道了土耳其西南部Muğla地区白垩系新特提斯蛇绿岩上地幔橄榄岩的稀土元素（REE）、铂族元素（PGE）和Re-Os同位素等全岩主微量元素化学数据。我们还报道了这些橄榄岩的大量矿物化学数据，以便更好地约束它们的岩石成因和形成的构造环境。Muğla橄榄岩主要由铅辉锌矿、贫辉锌矿和暗锰矿组成。Cpx-harzburgites的特点是其平均CaO （2.27wt）较高。wt %)、氧化铝(2.07。%)、REE （53ppb）和187os /188Os(i)比值在0.12497 ~ 0.12858之间变化。它们含有富铝辉石，共存尖晶石的Cr含量较低（Cr#= 13-22）。相比之下，贫化的哈尔茨布尔岩和泥质岩的平均CaO （0.58wt）较低。wt %)、氧化铝(0.42。%)和REE （1.24ppb）值。斜斜辉石贫铝，与高铬尖晶石共存（Cr#= 33-83）。187os /188Os(i)比值在0.12078 ~ 0.12588之间，与cpx-harzburgites相比更不具有放射性。矿物化学、全岩示踪和PGE资料表明，Muğla橄榄岩的形成不能用单期熔融事件来解释；要解释它们的地球化学特征，至少需要两个阶段的熔融和再成矿过程。cpx-哈兹伯尔土的微量元素组成可以通过原始地幔源高达~ 10-16%的封闭系统动态熔融来模拟，而枯竭的哈兹伯尔土和dunites的微量元素组成可以通过已经枯竭（~16%）的地幔的~ 10-16%的开放系统熔融来再现。这些模式表明，cpx-哈兹伯尔岩是发生在洋中脊（MOR）环境中的第一阶段熔融和低程度熔融岩相互作用的产物。亏缺的哈尔茨伯基岩和泥质岩是在俯冲带环境下发生的第二阶段熔融作用和再成矿作用的产物。Muğla橄榄岩的Re-Os同位素系统给出了~250Ma、~400Ma和~750Ma的模式年龄群，它们可能分别记录了新特提斯海洋、Rheic海洋和原特提斯海洋的地球动力学演化相关的主要构造事件。此外，bb0 - 1000Ma模式年龄可以解释为原始特提斯进化之前的古代融化事件的结果。
We present new, whole-rock major and trace element chemistry, including rare earth elements (REE), platinum-group elements (PGE), and Re–Os isotope data from the upper mantle peridotites of a Cretaceous Neo-Tethyan ophiolite in the Muğla area in SW Turkey. We also report extensive mineral chemistry data for these peridotites in order to better constrain their petrogenesis and tectonic environment of formation. The Muğla peridotites consist mainly of cpx-harzburgite, depleted harzburgite, and dunite. Cpx-harzburgites are characterized by their higher average CaO (2.27wt.%), Al2O3(2.07wt.%), REE (53ppb), and187Os/188Os(i)ratios varying between 0.12497 and 0.12858. They contain Al-rich pyroxene with lower Cr content of coexisting spinel (Cr#=13–22). In contrast, the depleted harzburgites and dunites are characterized by their lower average CaO (0.58wt.%), Al2O3(0.42wt.%), and REE (1.24ppb) values. Their clinopyroxenes are Al-poor and coexist with high-Cr spinel (Cr#=33–83). The187Os/188Os(i)ratios are in the range of 0.12078–0.12588 and are more unradiogenic compared to those of the cpx-harzburgites. Mineral chemistry and whole rock trace and PGE data indicate that formation of the Muğla peridotites cannot be explained by a single stage melting event; at least two-stages of melting and refertilization processes are needed to explain their geochemical characteristics. Trace element compositions of the cpx-harzburgites can be modeled by up to ~10–16% closed-system dynamic melting of a primitive mantle source, whereas those of the depleted harzburgites and dunites can be reproduced by ~10–16% open-system melting of an already depleted (~16%) mantle. These models indicate that the cpx-harzburgites are the products of first-stage melting and low-degrees of melt–rock interaction that occurred in a mid-ocean ridge (MOR) environment. However, the depleted harzburgites and dunites are the product of second-stage melting and related refertilization which took place in a supra subduction zone (SSZ) environment. The Re–Os isotope systematics of the Muğla peridotites gives model age clusters of ~250Ma, ~400Ma and ~750Ma that may record major tectonic events associated with the geodynamic evolution of the Neo-Tethyan, Rheic, and Proto-Tethyan oceans, respectively. Furthermore, >1000Ma model ages can be interpreted as a result of an ancient melting event before the Proto-Tethys evolution.