Chronology, chemistry, and origin of trachytes from Hualalai Volcano, Hawaii
Chronology, chemistry, and origin of trachytes from Hualalai Volcano, Hawaii
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DOI：
10.1029/2003gc000560
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发表时间：
2003-09-18
影响因子：
3.5
通讯作者：
Sharp, WD
中科院分区：
文献类型：
--
作者：
Cousens, BL;Clague, DA;Sharp, WD
[1]华拉莱火山在夏威夷火山中是独一无二的，因为它拥有相对较高比例的演化粗面熔岩，这些熔岩是在火山活动的碱性后阶段开始喷发的。这些演化的熔岩提供了对岩浆来源、岩浆供应速率以及此时次火山岩浆管道系统演化的洞察。粗面岩熔岩暴露在Puu Wawaa浮石穹顶和Puu Anahulu Flow，作为火山南侧马尔斯的块体，以及在Hualalai西侧钻探的水井中的流动。新的40Ar/39Ar测年表明，Puu Wawaa和Puu Anahulu杂岩的年龄为114ka，与Waha Pele maar的一个区块的年龄为103ka，水井粗面岩的年龄范围为107~92ka，表明粗面岩火山作用的范围为20ka。Nd、Pb同位素组成与华拉莱较年轻的碱性玄武岩重叠，但与华拉莱拉斑玄武岩和太平洋中脊玄武岩不同，粗面岩与碱性母岩联系在一起，后者经历了广泛的结晶，产生了粗面岩残余岩浆。粗面岩中的锶、氧同位素比值均高于华拉莱碱性熔岩中的锶、氧同位素比值，这可以用浅层蚀变华拉莱屏蔽玄武岩的反应或同化作用来解释。粗面岩之间的主元素、微量元素和同位素变化与其从Puu Anahulu母岩分离结晶而来的演化一致。拉斑玄武岩火山作用结束(<；133ka)到粗面岩、碱性火山作用开始之间的短时间间隔，以及缺乏深源包体，形成了岩浆储集层，其中粗面岩在浅层(<；7公里)快速演化。尽管莫纳克亚和科哈拉火山产生了少量高度演化的熔岩，因为岩浆供应速度在屏蔽后阶段逐渐减少，但华拉莱的屏蔽后岩浆侵入率在粗面岩形成期间最低，并在较新的碱性玄武岩喷发期间增加。三个地区粗面岩之间微妙的稀土元素和放射性同位素差异表明，浅层岩浆储集层的顶板可能是不规则的，使得一些粗面岩可以独立于其他粗面岩演化。
[1] Hualalai Volcano is unique among Hawaiian volcanoes in that it possesses a relatively high proportion of evolved, trachytic lavas that were erupted at the beginning of the alkalic, postshield phase of volcanism. These evolved lavas yield insights into magma sources, magma supply rates, and the evolution of the subvolcanic magmatic plumbing system at this time. Trachyte lavas are exposed at the Puu Waawaa pumice dome and Puu Anahulu flow, as blocks in maars on the south flank of the volcano, and as flows in water wells drilled on the west flank of Hualalai. New 40Ar/39Ar dates show that the Puu Waawaa and Puu Anahulu complex is 114 ka, a block from the Waha Pele maar is 103 ka, and water well trachytes range from 107 to 92 ka in age, indicating a range for trachyte volcanism of 20 ka. Nd and Pb isotopic compositions overlap with younger alkalic basalts from Hualalai but are distinct from Hualalai tholeiitic basalts and Pacific mid-ocean ridge basalts, linking the trachytes to alkalic parental magmas that underwent extensive crystallization to yield trachytic residual magmas. Both Sr and O isotopic ratios are higher in the trachytes than in Hualalai alkalic lavas, which is best explained by reaction with, or assimilation of, altered Hualalai shield basalts at shallow depth. Major, trace element, and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a Puu Anahulu parent. The short time gap between the end of tholeiitic volcanism (< 133 ka) and the onset of trachytic, alkalic volcanism and the lack of deep-origin xenoliths place the magma reservoir within which the trachytes evolved rapidly at shallow (< 7 km) depth. Whereas Mauna Kea and Kohala volcanoes produced small volumes of highly evolved lavas as magma supply rates dwindled through the postshield stage, postshield magma intrusion rates at Hualalai were lowest during trachyte formation and increased through a more recent period of alkalic basalt eruptions. Subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three localities indicate that the roof of the shallow magma reservoir may have been irregular, allowing some trachytes to evolve independently from others.