本文關(guān)鍵詞：新疆薩爾托海蛇綠巖中高鋁型鉻鐵礦成因　出處：《中國(guó)地質(zhì)科學(xué)院》2015年博士論文　論文類型：學(xué)位論文

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【摘要】：近年在我國(guó)西藏和俄羅斯極地烏拉爾等地的蛇綠巖鉻鐵礦中新發(fā)現(xiàn)了金剛石等深部礦物群,使得對(duì)此前鉻鐵礦的淺部成因理論提出了質(zhì)疑。鉻鐵礦中為什么會(huì)產(chǎn)有金剛石等深部地幔礦物?它們是如何形成的?這些異常礦物在全球不同類型和構(gòu)造背景的蛇綠巖鉻鐵礦和地幔巖中是否普遍存在?其科學(xué)意義何在?新發(fā)現(xiàn)使得蛇綠巖型鉻鐵礦的成因,尤其金剛石等深部礦物的成因和深部地幔作用,成為板塊構(gòu)造面臨的一個(gè)極具挑戰(zhàn)性的新的前沿性科學(xué)問(wèn)題。 本文選擇了新疆達(dá)拉布特蛇綠巖和其中的薩爾托海鉻鐵礦為研究目標(biāo)。薩爾托海鉻鐵礦為高鋁型,產(chǎn)在晚古生代的蛇綠巖中,已發(fā)現(xiàn)金剛石的西藏羅布莎和俄羅斯極烏拉爾鉻鐵礦均為高鉻型,后兩者的蛇綠巖形成時(shí)代分別為中生代和早古生代。說(shuō)明薩爾托海與西藏和俄羅斯的鉻鐵礦不僅礦石類型不同,并且分屬不同的造山帶。因此,探討其中是否含有金剛石等深部礦物及成因,具有重要科學(xué)意義。 本文開(kāi)展了達(dá)拉布特蛇綠巖和薩爾托海鉻鐵礦野外地質(zhì)調(diào)查,室內(nèi)綜合研究和鉻鐵礦人工重砂選礦。研究?jī)?nèi)容包括蛇綠巖和鉻鐵礦的主、微量和鉑族元素,地幔橄欖巖的礦物學(xué)和單礦物微量元素,鉻鐵礦中礦物包裹體分析,鉻鐵礦人工重砂單礦物分選和選出礦物的成分、結(jié)構(gòu)和包裹體分析,以及基性巖類的鋯石U-Pb定年和Hf同位素。主要取得如下進(jìn)展： (1)達(dá)拉布特蛇綠巖形成于弧后擴(kuò)張脊并受俯沖流體/熔體影響。地幔橄欖巖以方輝橄欖巖為主,含少量純橄巖和二輝橄欖巖。方輝橄欖巖中尖晶石Mg#在54-62之間,Cr#在39-48之間,橄欖石Fo值在90-93之間。純橄巖和方輝橄欖巖∑REE都低于球粒隕石,且具有LREE富集的U型稀土元素配分模式。方輝橄欖巖中單斜輝石∑REE介于深海和SSZ地幔橄欖巖中單斜輝石的∑REE之間,高場(chǎng)強(qiáng)元素Ti vs Yb和Ti vs Dy圖解都顯示單斜輝石可能是地幔橄欖巖含水部分熔融的殘余。根據(jù)方輝橄欖巖中共存的橄欖石-尖晶石平衡計(jì)算,獲得方輝橄欖巖的氧逸度在FMQ-0.14至FMQ+0.96之間,具M(jìn)OR到SSZ過(guò)渡的特征,或弧后盆地至島弧過(guò)渡的特征。地幔橄欖巖的單斜輝石、斜方輝石、橄欖石和尖晶石的主量元素成分也具有MOR到SSZ過(guò)渡的特征。尖晶石Cr#vs Mg#以及尖晶石Cr#與共存橄欖石Fo值圖解顯示,方輝橄欖巖為原始地幔20%-25%部分熔融的殘余。蛇綠巖中基性巖類具有N-MORB和E-MORB的特征,表現(xiàn)出高場(chǎng)強(qiáng)元素Nb、Ta、Zr、Hf、Ti虧損,而大離子親石元素U、K、Pb、Sr等富集的特點(diǎn),反映俯沖帶物質(zhì)成分加入,尤其,基性巖鋯石的Hf同位素特征表明有殼源物質(zhì)的加入。 (2)通過(guò)蛇綠巖中基性巖的鋯石U-Pb定年,限制了洋盆演化至少持續(xù)到早石炭世。本研究獲得達(dá)拉布特蛇綠巖帶中木哈塔依蛇綠巖的玄武巖鋯石U-Pb年齡在(393.9±3.0)Ma之間,為達(dá)拉布特蛇綠巖形成的年齡。薩爾托海輝長(zhǎng)巖脈鋯石U-Pb年齡為(359.4±1.0)Ma,達(dá)拉布特輝長(zhǎng)巖脈鋯石U-Pb年齡為(342.0±2.7)Ma,阿克巴斯套輝長(zhǎng)巖脈的鋯石U-Pb年齡為(357.6±2.4)Ma,阿克巴斯套輝石巖脈的鋯石U-Pb年齡為(350.6士4.0)。這些巖脈形成于大洋擴(kuò)張的過(guò)程中由軟流圈地幔部分熔融侵入于地幔橄欖巖中形成,表明大洋擴(kuò)張持續(xù)到早石炭世。 (3)通過(guò)重砂選礦首次在847Kg薩爾托海高鋁鉻鐵礦中發(fā)現(xiàn)了超高壓,強(qiáng)還原性和殼源的20余種礦物。其中包括金剛石、單質(zhì)鉻、自然鐵和單質(zhì)硅等自然元素類；碳化物碳硅石；鐵鎳、鐵鎳鉻合金等金屬合金；方鐵礦、金紅石、赤鐵礦、磁鐵礦、鈦鐵礦、獨(dú)居石、石英和鉻尖晶石等氧化物類；方鉛礦、閃鋅礦、針鎳礦、赫硫鎳礦和毒砂等硫化物類；鎂橄欖石、頑火輝石、透輝石、蛇紋石、鋯石和長(zhǎng)石等硅酸巖類。這些礦物與俄羅斯極地烏拉爾以及西藏羅布莎鉻鐵礦可以對(duì)比,表明了薩爾托海高鋁鉻鐵礦可能和高鉻鉻鐵礦一樣,存在深部地幔成礦階段。 (4)在鉻鐵礦中發(fā)現(xiàn)了大量的含水和無(wú)水的硅酸鹽原生礦物包體。包括透輝石,頑火輝石,鎂橄欖石,鈉-金云母,Na-Cr韭閃石,鈉長(zhǎng)石等。鉻鐵礦選礦發(fā)現(xiàn)的殼源礦物金紅石原巖為變基性巖,鋯石中也存在大量的殼源含水礦物包體。這些礦物的出現(xiàn)暗示了鉻鐵礦在淺部含水上地幔的成礦過(guò)程。計(jì)算所得鉻鐵礦成礦的母巖漿A12O3、TiO2和FeO/MgO與MORB相似,表明成礦與含水的MORB熔體有關(guān)。 (5)提出了薩爾托海深部預(yù)富集和淺部改造成礦的成因模式。俯沖板片進(jìn)入地幔過(guò)渡帶,發(fā)生熔融,形成富Si、Cr、C、Fe、Ni等元素的強(qiáng)還原性流體,并在過(guò)渡帶形成金剛石、碳硅石、單質(zhì)硅、單質(zhì)鉻、單質(zhì)鐵、方鐵礦、Fe-Ni合金等礦物。這些礦物在在擴(kuò)張脊下方向上運(yùn)移過(guò)程中被包裹于過(guò)渡帶頂部或上部(14GPa)的鉻鐵礦中。鉻鐵礦在此階段初步富集,攜帶這些超高壓和強(qiáng)還原性礦物進(jìn)入淺部的大洋巖石圈地幔。板片斷裂使軟流圈地幔上涌并同化俯沖板片,攜帶俯沖帶殼源鋯石和金紅石等物質(zhì),進(jìn)入弧后擴(kuò)張脊中的巖漿房中,形成含水的MORB型巖漿并與地幔橄欖巖發(fā)生大規(guī)模的巖石／熔體反應(yīng),改造之前初步富集的鉻鐵礦,形成薩爾托海高鋁型鉻鐵礦。鉻鐵礦形成時(shí)巖漿為MORB型貧硫和貧PGE巖漿,使得鉻鐵礦中幾乎沒(méi)有原生的鉑族礦物和賤金屬硫化物存在,而在巖漿演化后期,由于硫逸度不斷增加、溫度降低,形成赫硫鎳礦、針鎳礦等賤金屬硫化物和硫釕礦等鉑族礦物賦存于鉻鐵礦的裂隙間或粒間基質(zhì)中。
[Abstract]:In ophiolitic chromitites in China Tibet and Russia, Ural and other places in the new polar diamond found deep mineral group, so this theory causes shallow before chromite questioned. In chromite why diamond producing deep mantle minerals? How are they formed? Whether these abnormalities the mineral is widespread in the global different types and tectonic background of ophiolite and chromite in mantle rocks? What are its scientific significance? The new discovery that causes ophiolitic chromite, especially the deep causes of diamond minerals and deep mantle, as plate tectonics faces a challenging new the frontier of science.
This paper chose Xinjiang DARBUT ophiolite and the Salto sea of chromite as the research target. Salto sea chromite is high aluminum, produced in the late Paleozoic ophiolite in Tibet, has found the diamond LUOBUSHA CHROMITE DEPOSIT IN Ural and Russia are extremely high chromium, the ophiolite formed respectively. The Mesozoic and early Paleozoic. The Salto sea and Tibet and Russia not only chromite ore types are different, and different orogenic belt. Therefore, to investigate whether it contains mineral genesis and deep diamond, has important scientific significance.
This paper carried out the DARBUT ophiolite and Salto sea chromite ore field geological survey, indoor comprehensive study and chromite artificial placer beneficiation. Research contents include ophiolite and chromite, and trace platinum group elements, mineralogy of mantle peridotite minerals and trace elements, analysis of mineral inclusions in chromite, chromium ore artificial placer mineral separation and select the single mineral composition, structure analysis and inclusions, and zircon U-Pb dating of basic rocks and Hf isotope. The main results are as follows:
(1) DARBUT ophiolite was formed in the back arc spreading ridge subduction and fluid / melt. The mantle peridotite, harzburgite, dunite and containing a small amount of two peridotite. Harzburgite in spinel Mg# at 54-62, Cr# at 39-48, Fo value in the 90-93 of olivine. Dunite and harzburgite are lower than the sigma REE chondrites and U with rare earth element enrichment LREE distribution patterns between REE. Sigma Sigma REE between clinopyroxene and SSZ deep mantle peridotite Clinopyroxenes in harzburgite, vs Yb and high field strength elements Ti Ti vs Dy graphic display of clinopyroxene may be residual partial melting of mantle peridotite water. According to the calculation of the coexistence of harzburgite in olivine - spinel harzburgite, obtain the oxygen fugacity between FMQ-0.14 to FMQ+0.96, with characteristics of MOR to SSZ transition, or to the island arc back arc basin The characteristics of the transition. The mantle peridotite clinopyroxene, orthopyroxene, major element compositions of olivine and spinel has the characteristics of MOR to SSZ transition. The spinel Cr#vs Mg# and spinel Cr# with coexisting olivine Fo graphic display, harzburgite residual 20%-25% primitive mantle partial melting. The characteristics of basic rocks of ophiolite with N-MORB and E-MORB, showed high field strength elements Nb, Ta, Zr, Hf, Ti loss, and large ion lithophile elements U, K, Pb, Sr etc. characteristics, especially the subduction zone components added, Hf isotopic characteristics of mafic zircon showed that adding crustal material.
(2) the zircon U-Pb dating of mafic ophiolite, limited oceanic basin evolution continued until at least the Early Carboniferous. This research obtains the DARBUT ophiolite belt in mohurtay ophiolite basalts in zircon U-Pb age (393.9 + 3) Ma, as the dalabut ophiolite formed Salto sea gabbro age. Pulse zircon U-Pb age (359.4 + 1) Ma, U-Pb zircon age of gabbro vein Da Bute (342 + 2.7) Ma, U-Pb zircon age akbastau gabbro vein for (357.6 + 2.4) Ma, akbastau pyroxenite veins zircon U-Pb age (350.6 + 4). These dikes formed in the mantle peridotite formed by partial melting of the asthenosphere mantle intrusion in ocean expansion, that the ocean continues to Early Carboniferous.
(3) the heavy dressing for the first time in 847Kg Salto haigao aluminum chromite found in ultra high pressure, more than 20 kinds of minerals with strong reducibility and crust source. Including diamond, elemental chromium, natural iron and silicon carbide carbon and other natural elements; silica; Fe Ni, Fe Ni Cr alloy and other metal alloys; Party Jin Hongshi, iron ore, hematite, magnetite, ilmenite, monazite, quartz and chrome oxide; galena, sphalerite, millerite, HEAZLEWOODITE and sulfides such as arsenopyrite; magnesium olivine, enstatite, diopside, serpentine, zircon and feldspar silicate rocks. These minerals can be compared with Russia the Ural and Tibet LUOBUSHA chromite, showed Tuohaigao chromite and sal aluminum high chromium chromium ore, there are deep mantle metallogenic stage.
(4) found a large number of hydrous and anhydrous silicate minerals of inclusions in chromite. Including diopside, enstatite, olivine, sodium phlogopite, pargasite Na-Cr, sodium feldspar. Found chromium ore dressing shell source mineral rutile protolith is metabasites, crust derived hydrous minerals a large number of inclusions in zircon. There are also these minerals suggest that the ore-forming process of chromite in the shallow water of the upper mantle. Magma A12O3 calculated chromite mineralization, similar to TiO2 and FeO/MgO and MORB, showed that the MORB melt and water mineralization related.
(5) proposed the Salto sea deep preconcentration and shallow mineralization genesis model. Subduction into the mantle transition zone, melting, forming the rich Si, Cr, C, Fe, Ni and other elements of the strong reduction of fluid, and in the transition zone of the formation of diamond, carbon silica, silicon, single organic chromium, iron and wustite, Fe-Ni alloy and other minerals. These minerals are wrapped in the transition zone at the top or on the upper part of the spreading ridge under the direction of migration in the process (14GPa) in chromite chromite. At this stage the preliminary enrichment, carrying these ultra high pressure and strong reduction of mineral into the shallow oceanic lithosphere the fracture plate. The mantle upwelling of asthenospheric mantle and assimilation of subducted slab subduction zone, carrying crustal zircon and Jin Hongshi etc, the ridge expansion into the magma arc, the formation of MORB type magma water and rock / melt reaction and large-scale transformation of mantle peridotite. Before the preliminary enrichment of chromite, formed Salto haigao aluminium chromite chromite magma formation. MORB and PGE in low sulphur depleted magma, the platinum mineral and base metal sulfides in chromite almost no native existence, and in the late magmatic evolution, because the sulfur fugacity is increasing, the decrease of temperature, the formation of Hector polydymite, millerite base metals such as ruthenium sulfide and sulfur ore platinum mineral occurrence in the chromite fissure or intergranular matrix.

【學(xué)位授予單位】：中國(guó)地質(zhì)科學(xué)院
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：P618.3

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本文編號(hào)：1390556