Petrology of the hilina formation, Kilauea volcano, Hawaii
Petrology of the hilina formation, Kilauea volcano, Hawaii
复制标题
夏威夷基拉韦厄火山希利纳地层的岩石学
DOI：
10.1007/bf02600364
复制
发表时间：
1980
期刊：
影响因子：
--
通讯作者：
Michael O. Garcia
中科院分区：
文献类型：
--
作者：
R. Easton;Michael O. Garcia
希利纳地层由基拉韦厄火山暴露的最古老的熔岩流和凝灰岩组成。这些岩石仅暴露在基拉韦厄火山南侧悬崖上较年轻的普纳组熔岩的基普卡中。在当地，帕哈拉组的凝灰岩和水流将下面的希利纳组岩石与上覆的普纳组岩石分开。从帕哈拉地层底部收集的木炭得出的 C14 年龄为 22.800±340 年 B.P.它定义了希利纳地层的最小年龄。希利纳组熔岩在广阔的区域内喷发，可能起源于山顶区域和两个裂谷带。希利纳组包含橄榄石控制熔岩和分化熔岩（使用 Wright，1971 年的术语）。希利纳组橄榄石控制的熔岩在矿物学和地球化学上与较年轻的橄榄石控制的基拉韦厄熔岩有区别。较年轻的熔岩通常含有离散的低钙辉石颗粒。更高的玻璃含量、更高的 K2O/P2O5 比率和更低的总铁含量。马努纳罗亚熔岩也存在类似的地球化学趋势，并且可能是夏威夷盾状火山早期熔岩的典型。尽管有这些相似之处，但希利纳组（以及所有基拉韦厄火山）熔岩的 TiO2 和 CaO 含量高于莫纳罗亚熔岩，而 SiO2 和 Al2O3 含量较低。这些差异已经存在了三万多年。因此，基拉韦厄较古老的熔岩在成分上不太可能与先前提出的最近的莫纳罗亚熔岩相似。来自希利纳组熔岩地层序列的熔岩中 K2O、TiO2、Na2 和 Zr 含量是可变的。这些变化可用于将序列细分为地球化学组。这些组不是岩浆批次。相反，它们代表了不同批次的熔岩，其成分可能已通过晶体分馏和岩浆混合而改变。
The Hilina Formation comprises the oldest sequence of lava flows and tuffs exposed on Kilauea Volcano. These rocks are only exposed in kipukas in younger Puna Formation lavas along cliffs on the south flank of Kilauea Volcano. Locally, tuffs and flows of the Pahala Formation separate the underlying Hilina Formation rocks rom the overlying Puna Formation rocks. Charcoal collected from the base of the Pahala Formation yielded a C14 age of 22.800±340 years B.P. which defines a minimum age for the Hilina Formation. Hilina Formation lavas crop out over a wide region and probably originated from the summit area and from both rift zones.The Hilina Formation contains both olivine-controlled and differentiated lavas (using the terminology ofWright, 1971). The olivine-controlled lavas of the Hilina Formation are distinguishable mineralogically and geochemically from younger olivine-controlled Kilauea lavas. The younger lavas generally contain discrete low-calcium pyroxene grains. greater glass contents, higher K2O/P2O5 ratios and lower total iron contents. Similar geochemical trends prevail for Manuna Loa lavas, and may typify the early lavas of Hawaiian shield volcanoes. Despite these similarities, the Hilina Formation (and all Kilauea) lavas have higher TiO2 and CaO, and lower SiO2 and Al2O3 contents than Mauna Loa Lavas. These differences have existed for over 30,000 years. Therefore, it is unlikely that the older lavas of Kilauea are compositionally similar to recent Mauna Loa lavas as was previously suggested.K2O, TiO2, Na2 and Zr contents of lavas from a stratigraphic sequence of Hilina Formation lavas are variable. These variations may be utilized to subdivide the sequence into geochemical groups. These groups are not magma batches. Rather, they represent lavas from batches whose compositions may have been modified by crystal fractionation and magma mixing.