Reaction Between Mid-Ocean Ridge Basalt and Lower Oceanic Crust: An Experimental Study
Reaction Between Mid-Ocean Ridge Basalt and Lower Oceanic Crust: An Experimental Study
复制标题
大洋中脊玄武岩与下洋地壳之间的反应：一项实验研究
DOI：
10.1029/2019gc008368
复制
发表时间：
2019
影响因子：
3.5
通讯作者：
Lissenberg Johan C
中科院分区：
文献类型：
--
作者：
Yang Alex;ra Yang;Wang Chunguang;Liang Yan;Lissenberg Johan C
大洋中脊玄武岩(MORB)与下洋壳结晶碎屑的反应解释了MORB和下洋壳矿物的化学变化。尽管如此，这种反应在实验上很少被研究。我们通过实验研究了熔融的MORB与沸石在0.5 Gpa下发生熔融-粉化相互作用的机理和化学后果。等温实验表明，熔体随着斜长石和橄榄石的溶解渗入到沸石中。与未反应熔体相比，反应熔体具有较高的MgO和Al_2O_3含量，较低的TiO_2和Na_2O含量，结晶出更原始的橄榄石和斜长石，表明熔体粉碎反应可能导致高铝玄武岩的形成。由反应引起的熔体组成变化也显著影响MORB分馏的计算压力，这表明只有在可以排除反应的情况下，MORB分馏的主要元素气压计才能可靠地使用。反应后，沸石中含有橄榄石和斜长石包裹体，斜方辉石含有部分吸收的橄榄石和斜长石包裹体，表明熔体-泥浆相互作用是通过溶解-再沉淀机制进行的。单斜辉石具有高的Mg#(>；83)和高的Na2O和TiO2含量，橄榄石具有不同于分离结晶模型的Fo和Ni相关性，这为岩石记录中熔融反应的影响提供了可测试的参数。通过与下洋壳和层状侵入体样品的对比，我们认为在大洋和大陆岩浆系统中，熔浆反应在结晶岩浆中的岩浆输送过程中都起着重要的作用。
Reaction between mid‐ocean ridge basalt (MORB) and crystal mush in the lower oceanic crust has been invoked to explain chemical variations of both MORB and minerals in the lower oceanic crust. Nonetheless, such reactions have been little studied experimentally. We conducted experiments to investigate the mechanisms and chemical consequences of melt‐mush interaction by reacting molten MORB with troctolite at 0.5 GPa. Isothermal experiments demonstrate that melt infiltrates into troctolite with dissolution of plagioclase and olivine. The reacted melts have higher MgO and Al2O3and lower TiO2and Na2O contents and crystallize more primitive olivine and plagioclase compared to those crystallized from the unreacted melts, suggesting melt‐mush reaction could result in the formation of high‐Al basalt. The melt compositional variations induced by reaction also significantly affect the calculated pressures for MORB fractionation, indicating that major element‐based barometers for MORB fractionation can only be used reliably if reaction can be ruled out. After reaction, the troctolite contains olivine with plagioclase inclusions and poikilitic clinopyroxene with partially resorbed olivine and plagioclase chadacrysts, indicating that melt‐mush interaction occurs through dissolution‐reprecipitation mechanisms. Clinopyroxene has high Mg# (>83) and elevated Na2O and TiO2contents, and olivine has different Fo versus Ni correlations from fractional crystallization models, which provide testable parameters for the effect of melt‐mush reaction in the rock record. By comparison with samples from lower oceanic crust and layered intrusions, we propose that melt‐mush reaction plays an important role during magma transport in the crystal mush in both oceanic and continental magma systems.