The granite-upper mantle connection in terrestrial planetary bodies: an anomaly to the current granite paradigm?

Granite formed in the terrestrial planets very soon after their accretion. The oldest granite-forming minerals (4.4 Ga zircon) and granite (4.0 Ga granodiorite) indicate conditions resembling the present-day ones, with the presence of oceans and external processes related to liquid water. As a result, the current granite paradigm states that granite is not issued directly from the melting of the mantle. However, a granite-upper mantle connection is well established from several pieces of evidence. Tiny micrometre- to millimetre-sized enclaves of granite-like glassy and crystalline materials in Earth's mantle rocks are known in oceanic and continental areas. Earth's mantle-forming minerals, such as olivine, pyroxene, and chromite, can contain silicic materials, either as glass inclusions or as crystallised products (quartz or tridymite, sanidine, K-feldspar, and/or plagioclase close to albite end-member). Importantly, the same evidence is amply found in some types of meteorites, whether they are primitive, such as ordinary chondrites, or differentiated, such as IIE irons, howardite–eucrite–diogenite (HED), and Martian shergottite–nakhlite–chassignite (SNC) achondrites. Although constituting apparently an anomaly, the granite-upper mantle connection can be reconciled with the current granite paradigm by recognising that the conditions prevailing in the formation of granite are not only necessarily crustal but can occur also at depths in mantle rocks. Unresolved problems to be explored further include whether tiny amounts of granitic material within terrestrial mantles may be hints of greater abundances and more direct mantle involvement, and what role can be played by granite trapped within the upper mantle in lithosphere buoyancy.     

Source regions of granites and their links to tectonic environment: examples from the western United States

This review, in honor of Ilmari Haapala's retirement, reflects on lessons learned from studies of three granitic systems in western North America: (1) Mesoproterozoic samples from west Texas and east New Mexico; (2) Laramide granitic systems associated with porphyry-copper deposits in Arizona; and (3) granites of the Colorado Mineral Belt. The studies elucidate relationships amongst tectonic setting, source material, and magma chemistry.

Mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions. The first suite, the “plutonic province”, is dominantly magnesian, calc-alkalic to alkali-calcic, and metaluminous. It has low K₂O/Na₂O and Rb/Sr, and Nd model ages of 1.56 to 1.40 Ga. The second suite, the “Panhandle igneous complex”, is magnesian, metaluminous, alkalic, and is part of the Mesoproterozoic belt of magmatism that extends from Finland to southwestern United States. Samples from the Panhandle igneous complex demonstrate three episodes of magmatism: the first pulse was intrusion of quartz monzonite at 1380 to 1370 Ma; the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 Ma. Both of these rock types are high-K to slightly ultra-high-K. The third pulse at 1338 to 1330 Ma was intrusion of ultra-high-K quartz syenite. Nd model ages (1.94 to 1.52 Ga) are distinct from those of the “plutonic province” and systematically older than crystallization ages, implying a substantial crustal input to the magmas.

At the Sierrita porphyry-copper deposit in the Mazatzal Province of southeastern Arizona, trace element, Sr, and Nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks (67 Ma) intruded by granodiorite and granite. Isotopic composition and chemical evolution are well correlated throughout the suite. Andesite has the least negative initial ε_Nd (−4.3) and lowest ⁸⁷Sr/⁸⁶Sr_i (0.7069). It is also the oldest and chemically most primitive, having low concentrations of Rb, SiO₂, and high concentrations of transition elements. These parameters change through the system to the youngest unit (granite), which has the most negative ε_Nd (−8.5), the highest ⁸⁷Sr/⁸⁶Sr_i (0.7092), and is chemically most evolved. Correlation between chemical and Nd isotopic evolution probably resulted from a continuous process of progressive assimilation, in which mafic magmas invade and incorporate continental crust. Deposits in Arizona with ε_Nd values more negative than the −8.5 of Sierrita lie in the older Yavapai province in the northwestern part of the state. The difference in the most negative epsilon Nd implies that Nd isotopic signature is sensitive to the age of the Precambrian domain.

The granites from the Colorado Mineral Belt were emplaced during the transition from Laramide convergence to mid-Tertiary extension. Three different groups of granites are recognized. The first is Laramide and was formed during assimilation-fractional crystallization involving lower crustal mafic source materials; the second and third groups are mid-Tertiary and represent intracrustal melting of heterogeneous sources. This change in source regions and melt regimes in transition from convergence to extension is fundamental to the Mesozoic and Cenozoic evolution of western North America.     

Granitic pegmatites: an assessment of current concepts and directions for the future

Although many explanations have been proposed for the internal zonation of granitic pegmatites, the most widely accepted model is attributed to R.H. Jahns. Jahns and Burnham [Jahns, R.H., Burnham, C.W., 1969. Experimental studies of pegmatite genesis: I. A model for the derivation and crystallization of granitic pegmatites. Econ. Geol. 64, 843–864] said that pegmatites owe their distinctive textural and zonal characteristics to the buoyant separation of aqueous vapor from silicate melt, giving rise to K-rich pegmatitic upper portions and Na-rich aplitic lower zones of individual pegmatites. Jahns and Tuttle [Janhs, R.H., Tuttle, O.F., 1963. Layered pegmatite–aplite intrusives. Spec. Pap.-Miner. Soc. Am. 1, 78–92] cited experiments as confirmation of this effect, but several experimental studies contradict the partitioning behavior that was the premise of Jahns' model. More recent work indicates that pegmatite-forming melts should cool quickly, or in any case, more quickly than crystallization can keep pace with. The distinctive textural and zonal features of pegmatites have been replicated in experiments that employ constitutional zone refining of melts that are substantially undercooled before crystallization commences. Melt boundary layers formed by this process would represent the last silicate liquids to crystallize in pegmatites, which explains the tendency in pegmatites for abrupt transitions from simple to evolved mineral and rock compositions. The sources of pegmatite-forming melts and of the causes of regional zonation within pegmatite groups represent important directions for future research.     

L'érosion chimique et l'érosion mécanique à long terme du substrat granitique (Vendée,France)

We calculate the chemical depletion fraction of the granitic bedrock by analysing the rock-soil enrichment of zirconium. In Vendée (France), chemical weathering rates account for 26% of the denudation rates. Such a chemical depletion fraction characterizes temperate regimes. It is three times lower than that of humid tropical regimes. To cite this article: J.-C. Maurin et al., C. R. Geoscience 337 (2005).     

沽源—多伦盆地火山岩类和花岗岩类同位素地质年代学及铀成矿条件研究

本文对沽源-多伦盆地火山岩类和花岗岩类进行了同位素地质年代学和铀成矿条件的系统研究。确定了该区张家口组、花吉营组火山岩类均属早白至世产物,其形成年龄为125—135Ma。指出本区花岗岩浆活动有前海西期、海西期、印支期和燕山期,不存在文献中提到的自北而南分布的3条东西向海酉期花岗岩浆活动带。本文还指出该区区域铀成矿作用具有多期次的特点,同一矿床铀成矿作用的叠加是形成富铀矿体的前提。该区火山岩类钠含量较低,对铀成矿不利。然而,在不利的地质背景中局部存在利于铀成矿的地段和岩性,应作为今后重点的找矿对象。     

花岗岩残积土中人工挖孔桩流泥施工病害及防治

探讨龙岗岩残积土中人工挖孔桩的流泥施工病害产生机制,模拟模型及防治措施,并介绍一个典型的工程实例。     

Interaction of rock and atmosphere: patinas on Mediterranean monuments

 This paper analyzes – chemically, mineralogically, and petrolographically – the patinas developed on several Mediterranean monuments made with different stones (siliceous and carbonatic) in order to establish their origin and their evolution under the present environmental conditions, and to evaluate the environmental parameters controling their development. Most of the patinas show a common sequence of layers, which, from the outer to the inner zone, are: (1) present bioactivity and/or biological remains, (2) gypsum-rich patina, and (3) calcitic brown to orange patina. Each one may exhibit different fabrics (from micritic to stromatolitic) and may be more or less continuous and homogeneous. The main mineral components are calcite and gypsum, but Ca-oxalates and Ca-phosphates have also been found associated to biological structures, as well as quartz and clays. The different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem to be related to the biological activity, facilitating the growth of different organisms and leading to the development of a deposit with distinct characteristics (fabric, texture, porosity, etc.). The gypsum-rich patina has been interpreted as a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the atmospheric dust. The mineralogy and texture of the patina is independent of the nature of the underlying rock and only in few cases a micritization process has been observed as interaction between patina and rock. Recently, the penetration of endolithic microflora produced drillings and the development of a fissuration system parallel to the surface, and thus the detachment of the crust from the rock and even flackening of the rock itself has been observed. Consequently, under the present climatic conditions in the Mediterranean basin, erosion is a more active process than deposition, and the crusts and patinas show a tendency to disappear from the surface of the monuments. Received: 3 November 1996 · Accepted: 10 September 1997     

内蒙古额仁陶勒盖花岗岩成因与银矿床的形成

对额仁陶勒盖花岗岩的地质学、地球化学的研究表明，它为岩浆成因，是壳幔混合源岩浆演化的产物；岩体在成岩过程中发生了强烈的结晶分异作用，导致岩浆后期及期后热液中银的富集，银矿床与石英斑岩（花岗岩结晶分异的产物）在地质及地球化学诸多方面存在着显著的成因联系。     

花岗岩岩相学特征及岩石可锯性研究

花岗岩岩石中矿物的成分、结构、构造类型和矿物力学性质是制约岩石可锯性的主要因素。花岗岩岩石中石英矿物多（岩石偏酸性）、颗粒结晶粗大，矿物裂理和解理发育差，岩石呈致密块状构造，则可锯性差，反之则可锯性好。并以四川红系列花岗岩石材加工为例，说明了花岗岩岩相学特征对岩石可锯性影响的程度。从而，为花岗岩石材开发过程中，如何选择金刚石锯片提供科学参考资料     

新疆阿拉套山花岗岩类高εNd值的成因探讨

新疆阿拉套山广泛出露的华力西期花岗岩类的一般岩石学和地球化学性质可与我国以及世界上大部分地区出露的花岗岩相类比,但其ε_Nd(t)高,为+2.2-+3.2,其中一部分花岗岩的⁸⁷Sr/⁸⁶Sr(t)也高,可达0.715.这可能是壳幔物质AFC式混合的结果,也可能是准噶尔地块及其两缘特殊地质环境的反映。