Petrology of ferroan alkali-calcic granites: Synorogenic high-temperature melting of undepleted felsic lower crust (Damara orogen, Namibia)
Petrology of ferroan alkali-calcic granites: Synorogenic high-temperature melting of undepleted felsic lower crust (Damara orogen, Namibia)
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铁碱钙花岗岩的岩石学：未贫化长英质下地壳的同生高温熔融（纳米比亚达马拉造山带）
DOI：
10.1016/j.lithos.2015.03.004
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发表时间：
2015
期刊：
影响因子：
3.5
通讯作者：
D. Garbe‐Schönberg
中科院分区：
文献类型：
--
作者：
J. Stammeier;Stefan Jung;R. Romer;J. Berndt;D. Garbe‐Schönberg
纳米比亚中央达马拉造山带的Bloedkoppie花岗岩的年龄为556 ± 4 Ma，是一种偏铝质至稍过铝质、碱钙质至钙碱性和铁质花岗岩。它的组成意味着在花岗岩形成过程中的高温、还原和无水条件。花岗岩是分馏的，但不均匀的放射性同位素数据（87 Sr/86 Sr（初始）：0.712至0.727; εNd（初始值）：206 Pb/204 Pb：17.30-17.72; 207 Pb/204 Pb：15.54-15.67; 208 Pb/204 Pb：37.80-38.23）也表明同化-分离结晶过程在花岗岩的形成中起了重要作用。最不演化样品的主量、微量元素组成、同位素数据和锆石U-Pb数据表明，烃源岩以钙为主。1.95来自下伏基底的古老长英质正片麻岩。锆石饱和温度和标准Qz-Ab-Or组成表明最低熔融P-T条件约为0.0001。860 °C，> 5 kbar且< 5 wt.%水最有可能的成岩模式涉及高温部分熔融的古元古代长英质源在下地壳约。区域高温变质作用第一次高峰期前10-20 Ma。来自岩石圈地幔的岩浆对下地壳的底侵作用可能为未贫化基底的熔融提供了热量，从而产生还原的无水熔体。
The 556 ± 4 Ma-old Bloedkoppie granite (Central Damara orogen, Namibia) is a metaluminous to slightly peraluminous, alkali-calcic to calc-alkalic and ferroan granite. Its composition implies high-temperature, reduced, and anhydrous conditions during granite formation. The granite is fractionated, but heterogeneous radiogenic isotope data (87Sr/86Sr(init.): 0.712 to 0.727; εNd(init.): − 7.2 to − 13.1;206Pb/204Pb: 17.30–17.72;207Pb/204Pb: 15.54–15.67;208Pb/204Pb: 37.80–38.23) indicate also that combined assimilation–fractional crystallization processes played an important role in the generation of the granite. Major and trace element compositions and isotope data of the least evolved samples and U–Pb data from zircon cores demonstrate that the source rocks are dominated by ca. 1.95 Ga old felsic orthogneisses from the underlying basement. Zircon saturation temperatures and normative Qz–Ab–Or compositions indicate minimum melting P–T conditions of ca. 860 °C at > 5 kbar and < 5 wt.% H2O. The most likely petrogenetic model involves high temperature partial melting of a Paleoproterozoic felsic source in the lower crust ca. 10–20 Ma before the first peak of regional high-temperature metamorphism. Underplating of the lower crust by magmas derived from the lithospheric mantle may have provided the heat for melting of the undepleted basement to produce reduced and anhydrous melts.