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首页> 外文期刊>Petrology >Variations in the Nd Isotopic Ratios and Canonical Ratios of Concentrations of Incompatible Elements as an Indication of Mixing Sources of Alkali Granitoids and Basites in the Khaldzan-Buregtei Massif and the Khaldzan-Buregtei Rare-Metal Deposit in Western Mongolia
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Variations in the Nd Isotopic Ratios and Canonical Ratios of Concentrations of Incompatible Elements as an Indication of Mixing Sources of Alkali Granitoids and Basites in the Khaldzan-Buregtei Massif and the Khaldzan-Buregtei Rare-Metal Deposit in Western Mongolia

机译：Nd同位素比率和不相容元素浓度的典范比率的变化，指示了蒙古西部哈尔赞-布勒吉地块和哈尔赞-布勒吉地稀有金属矿床的碱性花岗岩和贝氏矿的混合源

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The paper reports data on the Nd isotopic composition and the evaluated composition of the sources of magmatism that produced massifs of alkali and basic rocks of the Khaldzan-Buregtei group. The massifs were emplaced in the terminal Devonian at 392-395 Ma in the Ozernaya zone of western Mongolia. The host rocks of the massifs are ophiolites of the early Caledonian Ozernaya zone, which were dated at 545-522 Ma. The massifs were emplaced in the following succession (listed in order from older to younger): (1) nordmar_kites and dolerites syngenetic with them; (2) alkali granites and syngenetic dolerites; (3) dike ekerites; (4) dike pantellerites; (5) rare-metal granitoids; (6) alkali and intermediate basites and quartz syenites; and (7) miarolitic rare-metal alkali granites. Our data on the Nd isotopic composition [ε_(Nd)(T)] and conventionally used (canoni_cal) ratios of incompatible elements (Nb/U, Zr/Nb, and La/Yb) in rocks from the alkaline massifs and their host ophiolites indicate that all of these rocks were derived mostly from mantle and mantle_crustal enriched sources like OIB, E-MORB, and IAB with a subordinate contribution of N-MORB (DM) and upper continental crustal material. The variations in the ε_(Nd)(T) values in rocks of these massifs suggest multiple mixing of the sources or magmas derived from them when the massifs composing the Khaldzan_Buregtei group were produced. The OIB and E-MORB sources were mixed when the rocks with mantle signatures were formed. The occurrence of nordmarkites, alkali granites, and other rocks whose isotopic and geochemical signatures are intermediate between the values for mantle and crustal sources testifies to the mixing of mantle and crustal magmas. The crustal source itself, which consisted of rocks of the ophiolite complex, was obviously isotopically and geochemically heterogeneous, as also were the magmas derived from it. The model proposed for the genesis of alkali rocks of the Khaldzan_Buregtei massifs implies that the magmas were derived at two major depth levels: (1) mantle, at which the plume source mixed with an E-MORB source, and (2) crustal, at which the ophiolites were melted, and this gave rise to the parental magmas of the nordmarkites and alkali granites. The basites were derived immediately from the mantle. The mantle syenites, pantellerites, and rare-metal granitoids were pro_duced either by the deep crystallization differentiation of basite magma or by the partial melting of the parental basites and the subsequent crystallization differentiation of the generated magmas. Differentiation likely took place in an intermediate chamber at depth levels close to the crustal (ophiolite) level of magma generation. Only such conditions could ensure the intense mixing of mantle and crustal magmas. The principal factor initiating magma generation in the region was the mantle plume that controlled within-plate magmatism in the Altai_Sayan area and the basite magmas related to this plume, which gave rise to small dikes and magmatic bodies in the group of intrusive massifs.
机译：该论文报告了有关Nd同位素组成的数据以及评估了形成哈尔德赞-布雷盖群碱土和基性岩块的岩浆作用源的评估组成。地块位于蒙古西部Ozernaya区泥盆纪终端392-395 Ma。地块的主体岩石是早期喀里多尼亚Ozernaya带的蛇绿岩，其年代为545-522 Ma。地块按以下顺序放置（按从大到小的顺序排列）：（1）与它们同生的北风筝和白云岩; （2）碱花岗岩和同生白云岩; （3）堤形硅藻土; （4）堤pan; （5）稀有金属花岗岩; （6）碱金属和中间的贝氏体以及石英正长岩; （7）微橄榄石稀有碱金属花岗岩。我们关于碱性地块及其基质蛇绿岩中Nd同位素组成[ε_（Nd）（T）]的数据以及不相容元素（Nb / U，Zr / Nb和La / Yb）中不相容元素的常规使用（canoni_cal）比的数据表明所有这些岩石主要来自地幔和富集地幔的资源，如OIB，E-MORB和IAB，其中N-MORB（DM）和上地壳物质是次要的。这些地块的岩石中ε_（Nd）（T）值的变化表明，在产生组成Khaldzan_Buregtei组的地块时，源或岩浆的多种混合存在。当形成具有地幔特征的岩石时，将OIB和E-MORB源混合在一起。同位素和地球化学特征介于地幔和地壳源值之间的降钙锰矿，碱花岗岩和其他岩石的出现证明了地幔和地壳岩浆的混合。地壳源本身由蛇绿岩复合物的岩石组成，在同位素和地球化学上显然是异质的，从中衍生出的岩浆也很明显。提出的Khaldzan_Buregtei地块碱性岩成因模型暗示岩浆是在两个主要深度水平上获得的：（1）地幔，其中羽流源与E-MORB源混合;（2）地壳，位于蛇绿岩被融化，这引起了nordmarkite和碱花岗岩的母岩浆。立刻从地幔中提取出了这些鱼饵。地幔正长岩，pantellerite和稀有金属花岗石是通过深部岩浆岩的深结晶分化或母体深部岩浆的部分熔融以及随后生成的岩浆的结晶体分化而产生的。分化可能发生在中间室，其深度接近岩浆生成的地壳（蛇绿岩）水平。只有这样的条件才能确保地幔和地壳岩浆的强烈混合。引发该地区岩浆形成的主要因素是控制阿尔泰萨彦地区板块内部岩浆活动的地幔柱和与该柱流有关的Basite岩浆，它们在侵入性地块群中产生了小型堤防和岩浆体。

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