【摘要】：位于攀西地區(qū)的新街層狀巖體賦含大量釩鈦磁鐵礦,是峨眉山大火成巖省的一部分。巖體下部帶和中部帶以單斜輝石巖為主,并伴生浸染狀釩鈦磁鐵礦礦化;上部帶以輝長(zhǎng)巖為主,賦存厚層的釩鈦磁鐵礦礦體。之前研究認(rèn)為厚層的釩鈦磁鐵礦礦體的形成與粒間不混熔的富Fe熔體有關(guān),但對(duì)富Fe熔體的演化過(guò)程缺乏細(xì)致研究。本文通過(guò)對(duì)新街巖體上部帶的富礦輝長(zhǎng)巖層和上覆淺色輝長(zhǎng)巖中斜長(zhǎng)石環(huán)帶結(jié)構(gòu)和成分的研究,揭示了富Fe熔體的演化過(guò)程。在淺色輝長(zhǎng)巖中保存的巖漿不混熔的直接證據(jù)表現(xiàn)為礦物粒間共軛的富Si交生體和富鈦鐵礦交生體代表的非反應(yīng)結(jié)構(gòu)。本次研究發(fā)現(xiàn),與粒間富Si交生體接觸的斜長(zhǎng)石邊部的FeO和TiO_2含量隨斜長(zhǎng)石牌號(hào)(An)值的降低而降低,而與粒間富鈦鐵礦交生體接觸的斜長(zhǎng)石邊部的FeO和TiO_2含量隨An值的降低而升高,說(shuō)明斜長(zhǎng)石的邊部成分變化記錄了粒間共軛的富Si和富Fe熔體的成分特征。在富礦輝長(zhǎng)巖中,斜長(zhǎng)石可分為初生和新生兩種,初生斜長(zhǎng)石的An值介于57~62,FeO含量為0.34%~0.50%,TiO_2含量為0.06%~0.13%,新生斜長(zhǎng)石具有相對(duì)較高的An值(61~81)和FeO、TiO_2含量,二者的內(nèi)部和邊部還發(fā)育增生斜長(zhǎng)石,其An值(~50)相對(duì)較低;在初生斜長(zhǎng)石邊部可見不連續(xù)的新生斜長(zhǎng)石環(huán)帶和增生斜長(zhǎng)石邊,造成其內(nèi)部成分顯著不均一,并發(fā)育復(fù)雜的環(huán)帶結(jié)構(gòu)。本文認(rèn)為,初生斜長(zhǎng)石是巖漿正常分離結(jié)晶作用的產(chǎn)物。在粒間熔體發(fā)生不混熔后,不混熔的富Fe熔體逐漸向巖漿房下方遷移并結(jié)晶出了一些相對(duì)高An值的新生斜長(zhǎng)石,或沿一些初生斜長(zhǎng)石邊部生長(zhǎng)形成不連續(xù)的高An環(huán)帶。當(dāng)富Fe熔體演化至晚期,由于礦物生長(zhǎng)空間受限,僅在初生和新生斜長(zhǎng)石局部形成了相對(duì)低An值的增生邊、或沿顆粒裂隙進(jìn)入斜長(zhǎng)石內(nèi)部形成增生斜長(zhǎng)石核。
[Abstract]:Xinjie stratified rock body located in Panxi area is a part of Emeishan great igneous province with large amount of vanadium and titanomagnetite. The lower and middle zones of the rock body are dominated by monocline pyroxenite and associated with the mineralization of vanadium-titanomagnetite, while the upper zone is dominated by gabbro with thick layers of vanadium titanomagnetite ore bodies. It is considered that the formation of thick layer vanadium titanomagnetite ore bodies is related to the intergranular immiscible rich Fe melts, but the evolution process of Fe rich melts is not studied in detail. In this paper, the structure and composition of plagioclase ring zone in the upper zone of Xinjie rock body are studied, and the evolution process of rich Fe melt is revealed by studying the structure and composition of plagioclase ring zone in the upper belt of Xinjie rock body and overlying light color gabbro. The direct evidence of the immiscible melting of the magma preserved in the light-colored gabbro is the nonreactive structure represented by the conjugated Si and ilmenite intersecting bodies. It was found that the contents of FeO and TiO_2 in the edge of plagioclase exposed to the intergranular rich Si cross decreased with the decrease of plagioclase (An). However, the content of FeO and TiO_2 in the edge of the plagioclase in contact with the intergranular ilmenite is increased with the decrease of the An value, which indicates that the change of the edge component of the plagioclase records the composition characteristics of the intergranular conjugated Si and Fe rich melts. The plagioclase can be divided into two types: primary and new. The An value of the primary plagioclase is between 57 and 62, and the content of Feo is 0.34 and 0.50. The content of TiO2 is 0.06 and 0.13. The new plagioclase has a relatively high An value (61 / 81) and a higher FeO,TiO_2 content, and a relatively low An value (~ 50) of the plagioclase developed in the interior and the edge of the two plagioclase. At the edge of the primary plagioclase, discontinuous new plagioclase and accretive plagioclase were observed, which resulted in the significant heterogeneity of the internal composition and the development of complex annular structure. It is believed that primary plagioclase is the product of normal separation and crystallization of magma. After the intergranular melt is immiscible, the immiscible rich Fe melts gradually migrate under the magma chamber and crystallize some relatively high An values of new plagioclase, or grow along the edge of some primary plagioclase to form a discontinuous high An ring. When the rich Fe melt evolves to the late stage, due to the limitation of mineral growth space, only a relatively low An proliferative edge is formed in the primary and newborn plagioclase, or an accretionary plagioclase nucleus is formed along the grain fissures into the plagioclase.
【作者單位】： 中國(guó)科學(xué)院廣州地球化學(xué)研究所中國(guó)科學(xué)院礦物學(xué)與成礦學(xué)重點(diǎn)實(shí)驗(yàn)室;廣東省礦物物理與材料研究開發(fā)重點(diǎn)實(shí)驗(yàn)室;中國(guó)科學(xué)院大學(xué);
【基金】：國(guó)家自然科學(xué)基金(41325006、41473037和41502048)聯(lián)合資助
【分類號(hào)】：P575

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