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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Quaternary basaltic volcanism in the Golden Trout Volcanic Field, southern Sierra Nevada, California
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Quaternary basaltic volcanism in the Golden Trout Volcanic Field, southern Sierra Nevada, California

机译：加利福尼亚内华达州南部金鳟火山场中的第四纪玄武质火山活动

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摘要

The Golden Trout Volcanic Field (GTVF) produced the only Quaternary eruptions of mafic magma within the southern Sierra Nevada block. Approximately 38 x 10(6) m(3) of basalt, trachy-basalt, basaltic trachy-andesite, and basaltic andesite (50.1-56.1% SiO2, 1.1-1.9% K2O, and 5.4-9.1% MgO) was erupted from four vents within a similar to 10 km(2) portion of the GTVF, which also includes rhyolite domes that are not considered in this study. The vents include, from oldest to youngest: Little Whitney Cone, South Fork Cone, Tunnel Cone, and unglaciated Groundhog Cone. Little Whitney Cone is a 120 m-high pile of olivine-CPX-phyric scoria produced during a Strombolian-style eruption overlying two columnar jointed lava flows. Tunnel Cone formed through a Hawaiian-style eruption along a 400 m-long north-south trending fissure that excavated at least three 2565 m-wide craters. Crater walls up to 12 m high are composed of plagioclase-olivine-phyric spatter-fed flows that dip radially away from the crater center and crumble to form Tunnel Cone's steep unconsolidated flanks. South Fork Cone is a 170 m-high pile of plagioclase-olivine-phyric scoria that formed during Strombolian to violent Strombolian eruptions. South Fork Cone overlies the South Fork Cone lava, a 9.5 km-long flow (similar to 12 x 10(6) km(3)) that reached the Kern River Canyon to the west. Scoria and airfall deposits originating from South Fork Cone are located up to 2 km from the vent. Groundhog Cone is a 140 m-tall cinder and spatter cone breached on the north flank by a 13 x 10(6) m(3) lava flow that partially buried the South Fork Cone lava and extends 7.5 km west to Kern River Canyon. Incompatible trace element concentrations and ratios show vent specific trends but are unsystematic when plotted in terms of all mafic GTVF vents, implying that GTVF basalts were derived from a lithospheric mantle source and ascended through thick granitic Sierra Nevada crust as discrete batches that underwent different degrees of crustal contamination, differentiation, and magma mixing. Clinopyroxene-liquid thermobarometry calculations of the oldest and most primitive GTVF sample indicate that most clinopyroxene crystals record nucleation conditions of 1172-1196 degrees C and 896-1115 MPa. These pressures correspond to depths equivalent to, or up to 10 km shallower than, the Moho in this region. Deposits from the oldest GTVF vents are more primitive and homogeneous in terms of major and trace element concentrations, phenocryst textures and compositions, and their general absence of crustal xenoliths and xenocrysts compared to younger eruptive products. The eruption rate of the GTVF (similar to 0.05 km(3)/Myr) is two orders of magnitude less than neighboring and contemporaneous Big Pine and Coso volcanic fields to the north and east, respectively. We interpret these differences to result from a relative lack of strain in the GTVF region of the southern Sierra Nevada block, which limits magma accumulation and ascent. (C) 2017 Elsevier B.V. All rights reserved.
机译：金鳟鳟火山场（GTVF）在内华达山脉南部地块内唯一发生了镁铁质岩浆的第四纪喷发。从四个喷口中喷出了约38 x 10（6）m（3）的玄武岩，曲折玄武岩，玄武质曲奇安山岩和玄武质安山岩（50.1-56.1％SiO2、1.1-1.9％K2O和5.4-9.1％MgO）排气口与GTVF的10 km（2）部分相似，其中还包括流纹岩穹顶，本研究中未考虑。通风孔包括从最老到最小的通风孔：小惠特尼圆锥形，南叉圆锥形，隧道圆锥形和不结冰的土拨鼠圆锥形。小惠特尼圆锥体是在两条柱状节理熔岩流上空的斯特伦波斯式喷发过程中产生的120 m高的橄榄石-CPX-苦渣。隧道锥体是通过沿400 m长的南北向裂缝形成的夏威夷式喷发而形成的，该裂缝至少挖出了3个2565 m宽的陨石坑。高达12 m高的火山口壁由斜长石-橄榄石-物理飞溅的水流组成，这些水流沿径向远离火山口中心倾斜并破碎，形成了Tunnel Cone陡峭的未固结侧翼。南叉锥是在Strombolian到猛烈的Strombolian喷发期间形成的170 m高的斜长石-橄榄石-灰质鳞屑。南叉锥熔岩覆盖南叉锥熔岩，长9.5公里（约12 x 10（6）km（3）），流向西部的克恩河峡谷。来自南叉锥的Scoria和空降沉积物位于距通风口最多2公里处。土拨鼠锥是一个140米高的煤渣和飞溅锥，在北侧被13 x 10（6）m（3）的熔岩流破坏，该熔岩流部分掩埋了南叉锥熔岩，并向西延伸7.5公里到克恩河峡谷。不相容的痕量元素浓度和比例显示出出气孔的特定趋势，但按所有镁铁质GTVF出气孔进行绘制时，是不系统的，这意味着GTVF玄武岩是从岩石圈地幔源中提取的，并通过内华达山脉厚厚的地壳以不同的程度经历了不同的批次而上升。地壳污染，分化和岩浆混合。对最古老和最原始的GTVF样品进行的斜辉石-液体热压法计算表明，大多数斜辉石晶体记录的成核条件为1172-1196摄氏度和896-1115 MPa。这些压力对应的深度等于或小于该地区莫霍面的深度10 km。与较年轻的喷发产品相比，从主要和微量元素浓度，隐晶构造和组成以及它们普遍不存在地壳异石和异晶的角度来看，最古老的GTVF喷口的沉积物更为原始和均质。 GTVF的喷发率（约0.05 km（3）/ Myr）比北部和东部的毗邻和同期大松和科索火山场小两个数量级。我们将这些差异解释为内华达山脉南段GTVF区域相对缺乏应变所致，这限制了岩浆的堆积和上升。 （C）2017 Elsevier B.V.保留所有权利。

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