Sugarloaf Mountain,central Arizona,USA: A small-scale example of Miocene basalt-rhyolite magma mixing to yield andesitic magmas

Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2–49.1?wt.% SiO₂; 6.7–7.7?wt.% MgO) and overlying andesite and dacite lavas (61.4–63.9?wt.% SiO₂; 3.5–4.7?wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo_76-86) and clinopyroxene (～Fs_9-18Wo_35-44) coexisting with Na-plagioclase (An_48-28Or_1.4–7), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts.Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their ～61 to 64?wt.% SiO₂ is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77–105 in andesites vs 114–166?ppm in basalts; Zr 149–173 vs 183–237; Nb 21–25 vs 34–42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well ? although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8–16?km and 850° to 980?°C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing ‘collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (～20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances.     

某地平板玻璃原料用石英砂的提纯研究

某地石英矿砂通过磁选分离法、稀酸浸泡法处理后，矿砂不同程度地降低了铁、铝、钙镁的含量；采用磁选分离 稀酸浸泡法联合处理后，使该地石英砂的化学成分达到了优质的生产平板玻璃用硅质原料的国家标准。     

粉石英在蓄电池胶壳中的应用

本文着重介绍了粉石英的工艺矿物特性以及其在蓄电池胶壳中的应用效果,证明了粉石英用作蓄电池胶壳的填料,能够改善混炼工艺、提高产品质量、增加填充量、降低生产成本,是一种理想的橡胶填料。     

一种新的储层孔隙成因类型--石英溶解型次生孔隙

石英作为碎屑岩储层中的一种难溶组分,普遍认为它和次生孔隙的形成关系不十分密切。研究认为泌阳凹陷核桃园组储层中的碎屑石英颗粒存在明显的溶解现象,并形成以石英直接溶解型孔隙为主的储集空间特征。石英颗粒被溶解的部分在薄片中所占的范围为 2 %～ 7%者常见,高者达 8%以上,在总孔隙中所占的相对含量也多数在10 %～ 35 %之间,早成岩B期是其最主要形成期。石英溶解型次生孔隙的大量存在为碎屑岩储层中SiO₂ 胶结物及次生孔隙成因等问题的解释以及储层预测和评价提供了新的可能性。     

Mylonitization of Diorites in Jiangshao Fracture Belt,Zheijiang Province,China

Cahracteristics of progressive ductile deformation and remnant igneous fabrics indicate that the foliated diorites in the middle sector of the Jiangshao fracture belt in Zhuji County,Zhejiang,are mylonites deformed from diorites,The mylonitization occurres about 353-370Ma ago under a condition of 425-475℃and 3.8-4.6kb.herelation between the deformation and metamorphism was discussed based on petrographic evidence and mineral chemistry and assemblage,It is suggested that the deformation was responsible for the development of low-grade greenschist-facies metamorphism of mylonitic diorites by introducing fluid phase to accelerate metamorphic reaction and diffusion.     

西藏甲玛铜多金属矿区成矿斑岩的岩浆混合作用:石英及长石斑晶新证据

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金矿床石英中负价氮的发现及赋存状态探讨

利用ｘ光电子能谱测试，发现金矿床石英中有负价氮的存在。这种氮的结合能为３９８ｅＶ士，该结合能氮的化合物有多种，氦均为负价态，其中有Ｓｉ＿３Ｎ＿４Ｓｉ的ｘ光电子能谱有二个谱峰值：１０３．４ｅＶ和１０１．９ｅＶ，前者为ｓｉＯ＿２的结合能，后者为Ｓｉ＿３Ｎ＿４的结合能。Ｎ和Ｓｉ的结合能均表明石英中有Ｓｉ＿３Ｎ＿４为负三价态。石英中负价Ｎ可能为替代氧的类质同象成分。     

福建云霄晶洞花岗岩及含石榴子石伟晶岩的硅氧同位素研究

在运用常规方法和激光烧蚀同位素分析方法分别对云霄晶洞花岗岩和伟晶岩(长石、石英和石榴子石)的硅、氧同位素组成进行研究的基础上,探讨了晶涧花岗岩及其含石榴子石伟晶岩的物质来源及形成条件.伟晶岩中的石英和长石的氧、硅同位素组成分别较之花岗岩中的石英和长石的氧、硅同位素组成,均未发生明显变化,表明二者岩浆来源一致.云霄县的乌...     

柴达木盆地北缘果可山石英闪长岩LA-ICP-MS锆石U-Pb定年及其成因

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