2011

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Geochemistry, petrology and ore-bear of spilite keratophyre of foreac ophiolite complex
R. M. Yurkova, B.I. Voronin

Institute of Oil and Gas Problems RAS, str. Gubkin, 3; bivrmyrzb@mtu-net.ru

Spilite-keratophyre volcanoplutonic complex is a  part of the ophiolite association formed as a result of the mantle diapir lifting in forearc palaeozone [Yurkova, Voronin, 2006]. This complex is most fully presented and studied in detail in the Peninsula Schmidt (Sahalin.) where it is the upper part of forearc ophiolite association primitive paleoarc. The structure of the tectonic block spilite-keratophyre complex shown (Fig. 1).

Established that the contrast between the rock associations volcanoplutonic series and a set of sheet dyke complex of ophiolite are genetically related. This relationship is determined by the fact that the volcanic column, are built dyke complex. There are packages diabase halfdyke and dykes that are characteristic for the complex of parallel dykes forearc type. They served as conduits for the leads in the formation of magmatic lavas of basic composition. Automagmatic brecciation basic lavas, forming gialoklastite occurred as a result of enrichment by fluids of finite portions of the melt, rising by dyke channels. With the influence of partially oxidized fluids due to the formation of spilites sinmagmatic  (metagenesis) and autometamorfic stages of lavas change. Spilitization occurs in certain of the geodynamic regime, in particular tension crust over the Benioff zone. It is not fully complete due to violations of fluid-rock equilibrium due to changes in the geodynamic environment    tension by strike-slip fault. In the latter case, the active processes of acid magmatism and propylitization  basic rocks.  As part of pyroclastic rocks identified pyroxene diabase tuffs, explosive breccias and quartz keratophyres with inclusions of dyke rocks.

In the tuffs and  volcanic breccias of mixed composition fragments of quartz keratophyres and plagiogranites prevail over the rubble spilite. They also found fragments of silicified gabbro and metasomatic  diorite-plagiogranites. In the pyroclastic column observed near-fault lenses of serpentinite. Column includes subvolcanic bodies of quartz keratophyres dome, lenticular, obelisklike, acicular and other forms, which are widely manifested automagmatic brecciation.

Volcanics intrude keratophyre bodies quartz  with explosive breccias and tufolavas in marginal parts. The central parts of large laccolith bodies of up to 150 m are composed of porphyry plagiogranite. Most of the subvolcanic bodies is heterogeneous, patchy and band structure  formed due to the secondary transformations of rocks by fluids carrying silica, copper and iron, which has affected the silicification and formation of an emerald-green copper-bearing chlorite and hematite. For the lower part of the intrusive-extrusive spilite-keratophyre complex association of minerals characteristic of the stage of regional propylitization (T <450°, P = 2 kbar). It includes actinolite, epidote, prehnite, chlorite, albite and quartz, which are combined in the rocks in different proportions. Actinolite is present mostly in the rocks with diabase palimpsest or intersertal structures. Propylites, which are not stored shadowy outlines of pyroxene and plagioclase, are composed mainly of epidote, chlorite, albite, quartz. Most often in hydrothermal-metasomatic minerals association dominated by epidote, regardless of whether these associations are formed at the expense of basic or acid rock. In high-temperature (to actinolite) apodiabase propylites X-ray established the presence of korrensite - ordered mixed-mineral composition of chlorite-montmorillonite. This characteristic is transformed in the contact zones of tuffs and breccias with subvolcanic bodies of quartz keratophyres. In these zones in the strip of tuffs and breccias are observed clusters (4x8 cm), large (up to 0.5 cm), grains of Cu-Fe-sulfides.

The periphery of the grains of Cu-Fe  sulfides successively replaced by hematite and iron hydroxides. The weathering of these rocks are formed zone of wood, painted products altered sulfides in the yellow-orange color. They should be recommended for screening for iron-copper sulfide ores, rich in chromium, nickel, cobalt. A comparison with the localization of massive sulfide ores of the Kuril-Kamchatka and the Japanese island arcs indicates the possibility of  finding Fe-Cu-sulphide ores exhalation-sedimentary origin in volcanic-sedimentary flysch complexes, limiting yields contrasting volcanic series laterally. With regard to the geological situation Peninsula Schmidts proposal to Cu-Fe sullides may relate to sedimentary  tominskoy and toyskoy suites.

Table 1. The average content of oxides (% wt.) Petrogenic elements, siderite and chalcophilic (ppm) of trace elements in rocks spilite-keratophyre complex of Sakhalin and Koryak Range 

Note. 1-4 - quartz keratophyre: 1 - unmodified, 2 - hydrothermal-metasomatic altered without the carbs, 3 - carbonated, 4, 5 – plagiogranites: 4 - igneous, 5 - metasomatic 6 – spilite basalts and diabase (lava), 7 - palagonite hyaloclastite  basic lava, 9, 8 -  propylites: 8 – high temperature, 9 - medium and low temperature: 10 - diabase dyke complex of the central zone, 11 - graywacke.

n - number of samples. Analyses were carried out in a chemical laboratory GIN RAS, Na and K were determined by plasma-spectrochemical analises, V, Cr, Co, Ni, Cu - quantitative spectral methods, analysts A.I. Gusareva and L.V. Ilicheva, other elements - the X-ray fluorescence method (MESA-1044), an analyst Y.I. Pronin.

       Chalcophile elements in volcanic rocks are unevenly distributed (Table 3). The highest copper content are characteristic of basic rocks: basalts, spilites, diabase, high temperature propylites. Contents of Zn, Ga, Pb does not depend on the rocrs type. Exceptis for a significant increase in the role of Zn in the flysch graywacke (see Table. 1).  The formation of acid magma can be assumed as a result of the restructuring of fluid-magmatic system, producing the basic magma, under the influence of strike-slip fault. The dramatic changes in the structure of matter in solid, molten, gellike state under the influence of shear deformation experimentally substantiated by Academician N.S. Enikopolovym [1981]. Getting the acid magma in this case it can be assumed due to the transformation of basic magma fluids (metagenesis). When forming the acidic melt fluids were the source of silica and alkalis, possibly in the form of element-organic compounds. In latemagmatic and postmagmatic stage fluids contributed to the redistribution of major and trace elements (Si, K, Cr Ni, etc.) within intrusive bodies, as well as interaction with host rocks, which led, inter alia, to the formation of hybrid rocks, metasomatic diorite plagiogranites, albite amphibolites and propylites. Relatively high temperature mineral transformations of rocks could provide for the transfer of heat from the thermal study of a large number of intrusive bodies and convection in the fluid flow in a permeable zone.

References:
Enikolopov N.S. Effect of strike-slip fault on the rate of polymerization processes // International. Symp. in Chemical Engineering. physics. Abstracts. M.: 1981. P. 83-86.
Yurkova P.M., Voronin B.I. The rise and transformation of mantle hydrocarbon fluids in connection with the formation of the ophiolite diapir // Genesis of hydrocarbon fluids and deposits. M.: GEOS, 2006. P. 56-67.