Compositional variations of basaltic glasses from the Mid-Cayman Rise spreading center
Compositional variations of basaltic glasses from the Mid-Cayman Rise spreading center
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中开曼海隆扩张中心玄武岩玻璃的成分变化
DOI：
10.1029/94jb02777
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发表时间：
1995
影响因子：
--
通讯作者：
J. Meen
中科院分区：
文献类型：
--
作者：
D. Elthon;D. Ross;J. Meen
中开曼隆起（MCR）扩展中心的玄武岩玻璃具有显著的成分范围，从7.7%到5.4% MgO。这些玻璃的主要元素和微量元素含量的定义明确的趋势是一致的，它们的发展高达50%的结晶的母岩浆只有一个小范围的成分变化。计算的液体下降线和原始MCR玻璃的1 atm相平衡研究以及岩相学关系表明，橄榄石和斜长石（±尖晶石）在低压下从MCR液体中结晶，直到残余液体具有<6.3%的MgO，此时单斜辉石与橄榄石和斜长石一起沿着结晶。然而，MCR玻璃中的CaO与MgO的变化清楚地表明，单斜辉石+橄榄石+斜长石结晶发生在整个套件中，而不仅仅是在最进化的一端。在MCR玻璃中，与在1个大气压的实验研究中的6.3%相比，在7.7% MgO处开始出现斜辉石饱和，这归因于在6.6千巴的压力下的结晶，其中最原始的MCR玻璃预期与橄榄石、斜长石和斜辉石共饱和。MCR玻璃中的主要元素和微量元素的变化是一致的提取的橄榄石辉长岩堆在成分上类似于相对简单的MCR辉长岩。尽管MCR玻璃的潜在原生岩浆成分范围很大，但该套玻璃可能是由未贫化地幔10-12%部分熔融或先前贫化地幔3-6%熔融产生的所有单个熔融部分的积累而产生的。
Basaltic glasses from the Mid-Cayman Rise (MCR) spreading center have a significant range of compositions, from 7.7% to 5.4% MgO. Well-defined trends in the major element and trace element contents of these glasses are consistent with their development by up to 50% crystallization of parental magmas with only a small range of compositional variability. Calculated liquid lines of descent and 1 atm phase equilibria studies of primitive MCR glasses, as well as petrographic relations, indicate that olivine and plagioclase (±spinel) crystallize from MCR liquids at low pressures until the residual liquid has <6.3% MgO at which point clinopyroxene crystallizes along with olivine and plagioclase. The CaO versus MgO variations in MCR glasses, however, clearly indicate that clinopyroxene + olivine + plagioclase crystallization has occurred throughout this suite, not just at the most evolved end. The onset of clino-pyroxene saturation at ∼7.7% MgO in the MCR glasses, compared to at 6.3% in 1 atm experimental studies, is attributed to crystallization at ∼6 kbar of pressure where the most primitive MCR glasses are expected to be cosaturated with olivine, plagioclase, and clino-pyroxene. The major element and trace element variations in the MCR glasses are consistent with the extraction of olivine gabbro cumulates similar in composition to the relatively simple MCR gabbroic rocks. Although there is a significant range in the compositions of potential primary magmas for the MCR glasses, the suite could have been produced by the accumulation of all individual melt fractions produced by 10–12% fractional melting of undepleted mantle or 3–6% melting of previously depleted mantle.