【摘要】：大火成巖省一般以大面積近同期噴發(fā)的玄武質(zhì)巖石為主,含少量長英質(zhì)巖石,并具有高的地幔潛溫和低的水含量。但出露于青藏高原東南部特提斯喜馬拉雅帶東段的措美大火成巖省,卻具有多樣化的巖石類型,包括玄武巖、輝綠巖墻/巖床、輝長巖侵入體和少量層狀苦橄玢巖、輝石巖、閃長質(zhì)巖墻/巖床和酸性火山巖。這種多樣化的巖石類型使措美大火成巖省成為研究大火成巖省中成分多樣性的原因和準確刻畫巖漿過程的理想研究對象。早期研究主要聚焦在分布范圍、區(qū)域年代學格架、玄武質(zhì)巖石的源區(qū)和成因等方面,并不清楚苦橄玢巖、輝石巖和閃長質(zhì)巖石的原始巖漿成分、熔融條件(包括溫度、壓力和含水性)和巖漿演化過程,直接限制了對措美大火成巖省巖漿成因機制的理解。因此,本論文選取措美大火成巖省東部錯那地區(qū)的苦橄玢巖和相關玄武巖、中部哲古措地區(qū)的輝石巖-輝長巖-閃長質(zhì)侵入雜巖為研究對象,復原原始巖漿成分和熔融條件,分析巖漿演化過程和巖石成因,約束不同巖性之間的成因關聯(lián),為刻畫大火成巖省巖漿成分多樣性的原因提供研究實例。本論文獲得的主要結(jié)論如下:(1)錯那地區(qū)苦橄玢巖的母巖漿的MgO為約20 wt.%,對應的地幔潛溫1550℃。為措美大火成巖省地幔柱成因提供了關鍵性的約束。錯那苦橄玢巖和共生玄武巖具有平行的微量元素分布型式和相似的Nd和Os同位素組成表明兩者來自同一地幔源區(qū)。(2)哲古措地區(qū)發(fā)育有橄欖二輝巖、輝長巖、角閃輝長巖、輝綠巖、閃長巖、石英閃長巖和英云閃長巖巖脈或巖墻,構(gòu)成一套成分連續(xù)且多樣的侵入雜巖。兩件閃長質(zhì)巖石樣品的鋯石U-Pb年齡均為約133 Ma,與措美大火成巖省主要巖漿作用時限一致。根據(jù)其Nd同位素特征共分為兩個系列:輝石巖和組I輝長巖系列和組II輝長質(zhì)巖石和閃長質(zhì)巖石系列。輝石巖和組I輝長巖具有負的εNd(t)值,微量元素和同位素模擬表明兩者為原始巖漿經(jīng)歷地殼混染作用和橄欖石-輝石結(jié)晶分異作用的結(jié)果。組II輝長質(zhì)巖石和閃長質(zhì)巖石具有與措美大火成巖省主體玄武質(zhì)巖石一致的正εNd(t)值,為一套完整的分離結(jié)晶序列。(3)上述巖漿雜巖的單斜輝石-熔體平衡溫壓計和角閃石單礦物溫壓計和濕度計計算結(jié)果表明措美大火成巖省存在多層次的巖漿房。原始巖漿在約20~30 km的下地殼巖漿房發(fā)生橄欖石-輝石結(jié)晶分異和/或地殼混染形成了錯那苦橄玢巖和分異的玄武質(zhì)巖漿以及哲古措輝石巖和組I輝長巖。而分異的玄武質(zhì)巖漿在上地殼約6 km的巖漿房發(fā)生單斜輝石、角閃石、斜長石和榍石的分離結(jié)晶形成哲古措組II輝長質(zhì)巖石和閃長質(zhì)巖石。水含量是玄武質(zhì)巖漿結(jié)晶分異形成中性巖的重要控制因素。
[Abstract]:In the major igneous provinces, Black Tortoise rocks erupting in a large area at the same time mainly contain a small amount of feldspathic rocks and have high mantle potential and low water content. However, the Tom 茅 great igneous province, which is exposed to the eastern segment of the Tethys Himalayan belt in the southeast of the Qinghai-Tibet Plateau, has a variety of rock types, including basalt, diabase dikes / beds, gabbro intrusions and a small amount of layered picrite porphyrite, pyroxenite, and pyroxenite. Diorite dykes / beds and acid volcanic rocks. This diverse rock type makes the province of igneous rocks in Thumei an ideal research object for studying the causes of composition diversity and accurately depicting magmatic processes in the major igneous provinces. Early studies focused on distribution, regional chronological framework, provenance and genesis of Black Tortoise rocks. It was not clear that the primitive magmatic composition, melting conditions (including temperature) of picrite porphyrite, pyroxenite and diorite, Pressure and water-bearing) and magmatic evolution process directly limit the understanding of magmatic genesis mechanism in Tomai great igneous province. Therefore, this paper selects picrite porphyrite and related basalts in Moena area, eastern part of Cumei igneous province, and pyroxenite-gabbro diorite intrusive complex in the central Zegusuo area as the research object, and recovers the original magmatic composition and melting conditions. By analyzing the evolution process of magma and the origin of rocks, the genetic correlation between different lithology is restricted, which provides an example for the study of the reasons for the diversity of magma composition in the great igneous province. The main conclusions obtained in this paper are as follows: (1) the MgO of the parent magma of picrite porphyrite in Sona area is about 20 wt.%, corresponding to the mantle latent temperature of 1550 鈩，

本文編號：2401127