Post-Collisional Potassic and Ultrapotassic Magmatism in SW Tibet: Geochemical and Sr-Nd-Pb-O Isotopic Constraints for Mantle Source Characteristics and Petrogenesis
Post-Collisional Potassic and Ultrapotassic Magmatism in SW Tibet: Geochemical and Sr-Nd-Pb-O Isotopic Constraints for Mantle Source Characteristics and Petrogenesis
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DOI：
10.1093/petroj/40.9.1399
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发表时间：
1999-09
影响因子：
3.9
通讯作者：
Christine E. Miller;R. Schuster;U. Klötzli;W. Frank;F. Purtscheller
中科院分区：
文献类型：
--
作者：
Christine E. Miller;R. Schuster;U. Klötzli;W. Frank;F. Purtscheller
给出了青藏高原后碰撞超钾质、硅质型、喜马拉雅期、卡波塔期和高钾钙碱性火山岩的主量元素、微量元素、锶-钕-铅-氧同位素和矿物引入化学数据，拉科拉姆山脉是17-25 Ma Ar/Ar年龄范围内连续胶结的产物。熔岩期间印度与欧亚大陆南缘的超钾质熔体中含有地幔捕虏晶(橄榄石±金红石/莫来石)。过去的50个My(如Klotwijk和Radhakrishnamurty，它们的初始Sr/Sr(0.7172-0.7220)和1981年的Nd/Nd1981)。尽管对该地区进行了大量研究，但PRO(0·51190-0·51200)比值表明，它们来自与高原形成有关的源区和富Rb的低Sm/Nd值的岩石圈源区。最初，周围的山脉仍然存在争议。铅同位素组成(铅/铅=18·41-18·51；铅/三种假说)与西藏地壳增厚和海拔高度有关。在第一类地球化学特征(如Argand，1924；Powell&Conaghan，1975；Ni、Pb和Eu负异常与巴兰扎吉旋回地壳一致)中，如高Th/Ta、低Sr/ND、低Ce/Ce，实际上是整个青藏高原的组成部分。亏损地幔模式年龄范围为1.3~1.9岁，受印度岩石圈俯冲。在第二个阶段(如Ga，而Pb模式测年记录了太古代事件，表明赵和摩根，1985,1987)，增厚是通过流入的方式进行的，因为物源有一个复杂的多阶段演化。相比之下，来自印度的材料。第三阶段，西藏地壳为高钾钙碱性英安岩，流纹岩的富集程度较低，解释为缩短增厚(如杜威初始锶(0·7091-0·7097)和Nd(0·51213-0·51225)iso&Burke，1973年)。第三种模式--话题作文的量化分析。具有垂直平均岩石圈流变性的锆石包裹体的存在，其预蒸发年龄为471±33 Ma，证明了DICTS岩石圈增厚和地壳深熔的额外抬升在其成因中的重要性。交代岩石圈地幔和碰撞后锡林岩石圈的下部熔融对流变薄导致部分整个高原的过程(如England&HouSeman，1988，拉萨地块的岩浆作用可能是(1)1989的结果)。Molnar等人。(1993)认为，突然增加的对流移走下部岩石圈或(2)板块断裂。在约8 Ma时发生了隆升，后
Major and trace element, Sr–Nd–Pb–O isotope and mineral INTRODUCTION chemical data are presented for post-collisional ultrapotassic, silicic The high plateau of Tibet, the Himalaya and the Kapotassic and high-K calc-alkaline volcanic rocks from SW Tibet, rakoram Ranges are the product of the continuing colwith Ar/Ar ages in the range 17–25 Ma. The ultrapotassic lision of India with the southern margin of Eurasia during lavas contain mantle xenocrysts (olivine ± rutile/armalcolite). the past 50 my (e.g. Klootwijk & Radhakrishnamurty, Their initial Sr/Sr (0·7172–0·7220) and Nd/Nd 1981). Despite numerous studies of the region, the pro(0·51190–0·51200) ratios suggest that they originated from cesses responsible for the formation of the plateau and lithospheric sources enriched in Rb with low Sm/Nd ratios. Initial the surrounding mountain ranges are still controversial. Pb isotopic compositions ( Pb/Pb = 18·41–18·51; Pb/ Three hypotheses have been suggested to explain the Pb = 15·68–15·72; Pb/Pb = 39·42–39·60) and crustal thickening and altitude of Tibet. In the first geochemical features such as high Th/Ta, low Sr/Nd, low Ce/ (e.g. Argand, 1924; Powell & Conaghan, 1975; Ni & Pb and negative Eu anomalies are consistent with a recycled crustal Baranzagi, 1983), virtually the entire Tibetan plateau is component. Nd depleted mantle model ages range from 1·3 to 1·9 underthrust by Indian lithosphere. In the second (e.g. Ga, whereas Pb model ages record an Archaean event, suggesting Zhao & Morgan, 1985, 1987), thickening is by inflow of that the source had a complex multi-stage evolution. In contrast, material from India. In the third, the crust of Tibet is the high-K calc-alkaline dacites and rhyolites have less enriched interpreted as having thickened by shortening (e.g. Dewey initial Sr (0·7091–0·7097) and Nd (0·51213–0·51225) iso& Burke, 1973). Quantitative analysis of the third model, topic compositions. The presence of zircon xenocrysts with a Pbassuming a vertically average lithosphere rheology, preevaporation age of 471 ± 33 Ma documents the importance of dicts lithospheric thickening and additional uplift of the crustal anatexis in their genesis. Processes responsible for the partial entire plateau by convective thinning of the lower conmelting of metasomatized lithospheric mantle and post-collisional tinental lithosphere (e.g. England & Houseman, 1988, magmatism in the Lhasa block could be a consequence of (1) 1989). Molnar et al. (1993) argued that a sudden increase convective removal of the lower lithosphere or (2) of slab breakoff. in uplift occurred at ~8 Ma and that the start of post-