CAJ | 학술논문

达机翁蛇绿岩位于雅鲁藏布江缝合带的西段北亚带,该蛇绿岩主要由地幔橄榄岩、玄武岩以及硅质岩组成,其中地幔橄榄岩以方辉橄榄岩为主,同时含有少量的纯橄榄岩,纯橄岩主要呈不规则透镜状或团块状分布于方辉橄榄岩中。在达机翁地幔橄榄岩中产出有3种不同类型的铬铁矿,分别为块状,豆状以及浸染状铬铁矿。文章主要对达机翁地幔橄榄岩的方辉橄榄岩及豆荚状铬铁矿进行了研究,结合岩石的主量元素和铂族元素,对地幔橄榄岩和豆荚状铬铁矿的成因以及雅鲁藏布江缝合带的找矿远景进行了探讨。达机翁地幔橄榄岩具有较高的MgO含量以及较低的Al2O3和CaO等含量,这种亏损的全岩成分指示了达机翁地幔橄榄岩经历了较高的部分熔融作用,同时方辉橄榄岩的PGEs的总量为23.68×10?9~31.02×10?9,高于原始地幔的值, Pd和Cu 2个元素的含量较为分散明显偏离部分熔融曲线,指示了达机翁方辉橄榄岩可能遭受了熔体的改造,在熔体?岩石反应的过程中,导致了富含PPGE的硫化物的加入。达机翁豆荚状铬铁矿为高Cr型铬铁矿,具有IPGE和Rh明显富集以及Pt, Pd明显亏损的特征,不同类型的铬铁矿之间具有一致的PGEs的分配模式。雅鲁藏布江缝合带内大量分布的超镁铁岩体在岩石组合、地球化学特征、成因以及形成时代等方面,均具有相似性,是中国铬铁矿找矿的有利远景区。
체궤옹사록암위우아로장포강봉합대적서단북아대,해사록암주요유지만감람암、현무암이급규질암조성,기중지만감람암이방휘감람암위주,동시함유소량적순감람암,순감암주요정불규칙투경상혹단괴상분포우방휘감람암중。재체궤옹지만감람암중산출유3충불동류형적락철광,분별위괴상,두상이급침염상락철광。문장주요대체궤옹지만감람암적방휘감람암급두협상락철광진행료연구,결합암석적주량원소화박족원소,대지만감람암화두협상락철광적성인이급아로장포강봉합대적조광원경진행료탐토。체궤옹지만감람암구유교고적MgO함량이급교저적Al2O3화CaO등함량,저충우손적전암성분지시료체궤옹지만감람암경력료교고적부분용융작용,동시방휘감람암적PGEs적총량위23.68×10?9~31.02×10?9,고우원시지만적치, Pd화Cu 2개원소적함량교위분산명현편리부분용융곡선,지시료체궤옹방휘감람암가능조수료용체적개조,재용체?암석반응적과정중,도치료부함PPGE적류화물적가입。체궤옹두협상락철광위고Cr형락철광,구유IPGE화Rh명현부집이급Pt, Pd명현우손적특정,불동류형적락철광지간구유일치적PGEs적분배모식。아로장포강봉합대내대량분포적초미철암체재암석조합、지구화학특정、성인이급형성시대등방면,균구유상사성,시중국락철광조광적유리원경구。
Located in the northern subbelt of the western Yarlung Zangbo ophiolite zone, Dajiweng ophiolite is mainly composed of peridotite, basalt and silicious rocks. The peridotite is dominated by harzburgite with minor dunite. Dunite occurs as patches in the peridotites. Podiform chromitite can be found in the harzburgite with dunitic envelope. According to the texture and mineralogy of the chromitite, Dajiweng podiform chromitite can be divided into three types, namely massive chromitite, disseminated chromitite and nodular chromitite. This paper mainly reports the research on the harzburgite and podiform chromitite and makes a discussion on the petrogenesis of the peridotite, the origin of the chromitite and chromitite prospect in the Yarlung Zangbo suture zone combined with the major and platinum group elements. Dajiweng harzburgite has a depleted whole rock composition with higher MgO content and lower Al2O3, CaO content than the primitive mantle, indicating that Dajiweng peridotite has experienced a high degree of partial melting. Dajiweng harzburgite has higher PGEs content (23.68 × 10?9-31.02 × 10?9) than primitive mantle. The Cu and Pd content of Dajiweng harzburgite strongly deviates from the modeled partial melting curves, which is a symbol of melt-rock reaction. During the process of melt-rock reaction, sulfides were enriched with PPGEs and these materials were added to the Dajiweng harzburgite. In the primitive mantle-normalized PGE patterns of podiform chromitite, Dajiweng chromitite shows obvious enrichment of IPGE and Rh, and depletion of Pt and Pd. Podiform chromitites of different types have consistent primitive mantle-normalized PGE patterns. Ultramafic rock in the Yarlung Zangbo ophiolite belt shows remarkable similarities in such aspects as rock assemblage, rock geochemistry, formation age and petrogenesis, suggesting that the Yarlung-Zangbo ophiolite is a promising prospecting area for chromitite.