摘要
发育于造山带中的蛇绿岩,其剖面下部的地幔橄榄岩部分是造山带地区富集型上地幔的直接标本。其地球化学特点是:主要元素Al_2O_3、TiO_2、CaO、Na_2O、K_2O强烈亏损,而REE,痕量元素和^(87)Sr/^(86)Sr则强烈富集;同时,^(143)Nd/^(144)Nd<0.511836,亦表明它们属于一个富集型的源区。 形成富集型上地幔的主要机制是地幔交代作用,富含不相容元素的低熔岩浆和富Ca-LREE流体与已亏损的地幔橄榄岩发生脉状交代和渗透交代反应,从而造成上地幔中不相容元素的富集。造山带富集型上地幔形成的构造环境是:洋壳从扩张脊向两侧运移并最终拼入造山带这段时间内。富集型上地幔不但存在于大陆区,而且亦存在于造山带地区,它可能是一种全球性的地球内部的化学作用。
The mantle peridotite at the bottom of ophiolitic section in the orogenic zone is direct sample of enriched upper mantle. Its geochemical characteristics are strong depletion of major elemen Al2O3, TiO2, CaO, Na2O and K2O, but are strong enrichment of REE, trace elements and 87Sr/86Sr. Combining with 143Nd/144Nd<0.511836, it shows that the mantle peridotite belongs to a source of incompatile element enrichment pattern.Major mechanism of formation of enriched upper mantle is 'mantle metasomatism'. Low-degree melting magma bearing incompatible elements and fluids of enrichment Ca-LREE react with depleted upper mantle peridotite to create a upper mantle of enrichment incompatible elements through dike and permeable metasomatism.Tectonic environment of formation of enriched upper mantle is oceanic crust displacement from the oceanic mid-ridge to the orogenic zone.Th enriched upper mantle exists not only in the continental aere but in the orogenic zone. It may be a chemical reaction occurred in interior of the whole earth.
出处
《地球学报》
EI
CAS
CSCD
1991年第1期159-166,共8页
Acta Geoscientica Sinica
