Nature of a flood-basalt-magma reservoir based on the compositional variation in a single flood-basalt flow and its feeder dike in the Mesozoic Hartford Basin, Connecticut
Nature of a flood-basalt-magma reservoir based on the compositional variation in a single flood-basalt flow and its feeder dike in the Mesozoic Hartford Basin, Connecticut
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基于康涅狄格州中生代哈特福德盆地单一溢流玄武岩流及其支脉岩成分变化的溢流玄武岩岩浆储层性质
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发表时间：
1998
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影响因子：
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通讯作者：
A. Philpotts
中科院分区：
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作者：
A. Philpotts
摘要康涅狄格州和马萨诸塞州哈特福德盆地、庞培盆地和迪尔菲尔德盆地中生代霍利奥克玄武岩的侵蚀遗迹表明，原始流量大于1200 km ~ 3。其补给岩墙宽约50 m，长约160 km，可通过2 km的中生代沉积物向下追溯，由于与盆地形成有关的断层作用，还可通过另外6 km的古生代变质岩向下追溯。化学配置文件通过远端和近端部分的流量，并通过在2，4和8公里的深度的岩墙提供连续的样品，在这一次喷发事件的岩浆上升。水流和岩脉的成分有限，表明深度处有橄榄石、普通辉石和斜长石饱和。该流动主要由在钙钛矿反应点的液体组成。岩脉成分可以建模为该液体与高达24%的斜长石、普通辉石和橄榄石晶体的混合物。岩脉组成表明这些矿物在3.8千巴的平衡。这一压力相当于12.2公里的深度，据信这是当时地壳中脆性/韧性转变的深度。这种过渡似乎是唯一合理的障碍，可能会导致岩浆在中地壳水平的积水。霍利奥克液体被解释为已从致密的晶体糊状物分离后，在这个中地壳水库的岩浆结晶30%。玄武岩的喷发耗尽了分离液体的供应，当剩余的晶体糊状物开始在岩脉中上升时，岩浆柱的平均密度增加，直到它与侵入地壳的平均密度相匹配，喷发结束。通过类比地表凝固的霍利奥克流中发生的分异，估计中地壳岩浆库的体积至少为12 000立方公里。这个岩浆房中的岩浆一定来自更深的岩浆房，因为它太分散了，不可能直接来自地幔源。
Abstract The erosional remains of the Mesozoic Holyoke basalt in the Hartford, Pomperaug, and Deerfield basins of Connecticut and Massachusetts indicate an original flow volume of >1200 km3. Its feeder dike, which is about 50 m wide and 160 km long, can be traced down through 2 km of Mesozoic sediments and, as a result of faulting associated with basin formation, through an additional 6 km of Paleozoic metamorphic rocks. Chemical profiles through the distal and proximal parts of the flow and through the dike at depths of 2, 4, and 8 km provide sequential samples of the magma that rose during this one eruptive event. The flow and dike have restricted compositions that indicate saturation with olivine, augite, and plagioclase at depth. The flow consisted largely of a liquid at the pigeonite reaction point. Dike compositions can be modeled as mixtures of this liquid with up to 24% crystals of plagioclase, augite, and olivine. The dike compositions indicate equilibration with these minerals at 3.8 kbar. This pressure corresponds to a depth of 12.2 km, which is believed to have been the depth of the brittle/ductile transition in the crust at the time. This transition appears to be the only reasonable barrier that could have caused ponding of the magma at the mid-crustal level. The Holyoke liquid is interpreted to have segregated from a compacting crystal mush following 30% crystallization of the magma in this mid-crustal reservoir. Eruption of the basalt exhausted the supply of segregated liquid, and when the remaining crystal mush began to rise in the dike, the average density of the magma column increased until it matched the average density of the intruded crust, and the eruption ended. By analogy with the differentiation that took place in the solidifying Holyoke flow on the surface, the mid-crustal magma reservoir is estimated to have had a volume of at least 12,000 km3. The magma in this chamber must have come from a still deeper chamber, because it was too fractionated to have come directly from a mantle source.