Paleoproterozoic,High-Metamorphic,Metasedimentary Units of Siberian Craton

Sensitive, high-resolution ion microprobe zircon U-Pb ages of Paleoproterozoic, high-grade, metasedimentary rocks from the south-western part of the Siberian Craton are reported. Early Precambrian, high-grade complexes, including garnet-biotite, hypersthene-biotite, and cordierite- bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift. Protoliths of studied gneisses correspond to terrigenous sediments, ranging from greywacke to shale. The paragneiss model Nd ages of 2.4-3.1 Ga indicate Archean-to-Paleoproterozoic source provinces. Zircons from gneisses show corerim textures in cathodoluminescence （CL） image. Round or irregular shaped cores indicate detrital origin. Structureless rims with low Th/U are metamorphic in origin. The three age groups of detrital cores are： 〉2.7, -2.3, and 1.95-2 Ga. The ages of metamorphic rims range from 1.86 to 1.85 Ga; therefore, the sediments were deposited between 1.95 and 1.86 Ga and derived from Archean and Paleoproterozoic source rocks. It should be noted that Paleoproterozoic metasedimentary rocks of the Irkut Block are not unique. High-grade metaterrigenous sediments, with model Nd ages ranging from 2.3 to 2.5 Ga, are widely distributed within the Aldan and Anabar Shields of the Siberian Craton. The same situation is observed in the North China Craton, where metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 to 2.1 Ga （Wan et al., 2006）. All of these sedimentary units were subjected to Late Paleoproterozoic metamorphism. In the Siberian Craton, the Paleoproterozoic sedimentary deposits are possibly marked passive margins of the Early Precambrian crustal blocks, and their high-grade metamorphism was related to the consolidation of the Siberian Craton.

The evolution of refertilized lithospheric mantle beneath the northeastern Siberian craton:Links between mantle metasomatism,thermal state and diamond potential

Although the diamond potential of cratons is linked mainly to thick and depleted Archean lithospheric keels, there are examples of craton-edge locations and circum-cratonic Proterozoic terranes underlain by diamondiferous mantle. Here, we use the results of comprehensive major and trace-element studies of detrital garnets from diamond-rich Late Triassic(Carnian) sedimentary rocks in the northeastern Siberia to constrain the thermal and chemical state of the pre-Triassic mantle and its ability to sustain the diamond storage. The studied detrital mantle-derived garnets are dominated by low-to mediumCr lherzolitic(~45%) and low-Cr megacrystic(~39%) chemistries, with a significant proportion of eclogitic garnets(~11%), and only subordinate contribution from harzburgitic garnets(~5%) with variable CrOcontents(1.2–8.4 wt.%). Low-Cr megacrysts display uniform, “normal” rare-earth element(REE)patterns with no Eu/Eu* anomalies, systematic Zr and Ti enrichment(mainly within 2.5–5), which are evidence of their crystallization from deep metasomatic melts. Lherzolitic(G9) garnets exhibit normal or humped to MREE-depleted sinusoidal REE patterns and elevated Nd/Y(up to 0.33–0.41) and Zr/Y ratios(up to 7.62). Rare low-to high-Cr harzburgitic(G10) garnets have primarily “depleted”, sinusoidal REEpatterns, low Ti, Y and HREE, but vary significantly in Zr-Hf, Ti and MREE-HREE contents, Nd/Y(within 0.1–2.4) and Zr/Y(1.53–19.9) ratios. The observed trends of chemical enrichment from the most depleted,harzburgitic garnets towards lherzolitic(including high-Ti high-Cr G11-type) garnets and megacrysts result from either voluminous high-temperature metasomatism by plume-derived silicate melts or recurrent mobilization of less voluminous kimberlitic or related carbonated mantle melts, rather than the initially primitive, fertile nature of the Proterozoic SCLM. Calculated Ni-in-garnet temperatures(primarily within ~1150–1250 ℃) indicate their derivation from at least ~220 km thick Cr-undersaturated lithosphere at the relevant Devonian to Triassic thermal flow of ~45 m W/m^(2) or cooler. We suggest the existence of rare harzburgitic domains in the primarily lherzolitic diamond-facies SCLM beneath the northeastern Siberian craton at least by Triassic, whereas the abundance of eclogitic garnets, predominance of E-type inclusions in placer diamonds and specific morphologies argue for diamondiferous eclogites occurring within a ~50–65 kbar diamond window of the Olenek province by the same time.

P-T path of metamorphism and U-Pb monazite and zircon age of the Kitoy terrane: Implication for Neoarchean collision in SW Siberian Craton

The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane(SW Siberian Craton).Alumina gneisses of the Kitoy terrane indicate two-staged metamorphic evolution.The first stage of regional metamorphism(M1)occurred at high-amphibolite facies conditions at T=780-800℃ and P=8-9 kbar.The second stage(M2)belongs to MT-HT/LP type of metamorphism with the wide temperature interval 600-750℃ and pressure 2-4 kbar.Two age peaks were established on the basis of U-Pb monazite and zircon dating in garnet-anthophyllite gneisses.Both of them correspond to the Neoarchean age:the age of M1 falls into the interval of ca.2489-2496 Ma,the age of M2-ca.2446-2456 Ma.The high-temperature metamorphism of the Kitoy block and nearly coeval granitoid magmatism can be an evidence for the Neoarchean collision in SW Siberian craton.

Mafic, Ultramafic and Carbonatitic Dykes in the Southern Siberian Craton with Age of ca 1 Ga: Remnants of a New Large Igneous Province?

Virtual absence of igneous complexes with ages between1.8 Ga and 0.8 Ga in southern part of the Siberian Craton allowed to Galdkochub et al.(2010)to formulate a hypothesis of long magmatic quiescence.Most reliable

Age and Geochemical Characteristics of Major Mafic Dyke Swarms in the Southern Part of the Siberian Craton

Several generations of mafic dyke swarms of different ages and geochemical characteristics cut Precambrian rocks of the southern part of the Siberian craton(Irkutsk Promontory).Each generation of dykes is related to a

Proterozoic Dyke Swarms of the Siberian Craton and Their Geodynamic Implications

We present a summary of late Paleoproterozoic to Neoproterozoic mafic magmatism in the Siberian craton which allows us distinguish following main pulses of mafic dyke emplacement:1)1860–1850 Ma mafic dykes are localized within the

Palaeoproterozoic High-metamorphic Metasedimentary Units of Siberian Craton

In this paper,I report SHRIMP zircon U-Pb ages of Paleoproterozoic high-grade metasedimentary rocks from southwestern part of the Siberian Craton.Early Precambrian high-grade complex including garnet -biotite,hypersthene-biotite and cordierite-bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift.Protoliths of studied

西伯利亚克拉通东南缘1.84Ga构造热事件——俄罗斯斯塔诺夫南带南缘混合岩化黑云斜长片麻岩锆石U-Pb年龄和Hf同位素记录

对俄罗斯远东腾达(Tydna)斯塔诺夫南带南缘混合岩化黑云斜长片麻岩中锆石进行了U-Pb年龄测定和Hf同位素测试,获得其锆石核部年龄主要为≥2.57、~2.39、~2.33和~2.20 Ga,锆石增生边年龄为1.84 Ga,可靠的最年轻碎屑锆石年龄为~2.20 Ga,表明其原岩沉积时代为古元古代,而不是以往认为的太古宙,混合岩化事件年龄为1.84 Ga。锆石核部εHf(t)值为2.7^-16.2,Hf同位素地壳模式年龄为3.7~2.8 Ga;锆石增生边的εHf(t)值为-7.5^-18.6,峰值为-15,Hf同位素地壳模式年龄为3.6~2.9 Ga。锆石的εHf(t)值基本为负值说明这些岩石主要来自于地壳岩石的部分熔融;Hf同位素两阶段模式年龄的峰值在~3.4 Ga,表明它们可能主要来源于阿尔丹地盾下地壳物质的部分熔融。这些年龄资料将为西伯利亚克拉通东南缘地质构造演化提供重要的年代学制约。

地幔柱活动对克拉通岩石圈地幔的影响:西伯利亚克拉通地幔橄榄岩包体Sr-Nd-Hf同位素制约

利用单矿物溶液法分析了Obnazhennaya金伯利岩中橄榄岩包体单矿物的Sr-Nd-Hf同位素组成,并且与Udachnaya金伯利岩中橄榄岩包体单矿物的Sr-Nd-Hf同位素组成进行了对比。结果显示,Obnazhennaya金伯利岩中橄榄岩包体单斜辉石具有亏损的Sr同位素组成和富集的Nd、Hf同位素组成。橄榄岩包体石榴子石的Sr-Nd-Hf同位素组成表现出原始的特征,没有受到交代作用的影响。通过对比Udachnaya和Obnazhennaya金伯利岩中地幔包体的特征和单斜辉石的二元混合模拟发现,Udachnaya金伯利岩中的地幔包体的Sr-Nd-Hf同位素组成更偏向于金伯利岩的特征,而与之相反,Obnazhennaya金伯利岩中的地幔包体的Sr-Nd-Hf同位素组成则位于金伯利岩和地幔柱溢流玄武岩之间,且更加偏向于溢流玄武岩的同位素特征。因此,地幔柱活动对西伯利亚克拉通岩石圈产生了影响,改变了其岩石圈地幔的同位素组成。

远震数据显示贝加尔裂谷带北穆伊斯克(Severomuysk)段地壳和上地幔的精细结构

通过贝加尔裂谷系统北穆伊斯克(Severomuysk)段的密集地震台站线性网络获得的远距离强震记录,并利用P波接收函数技术,揭示了地壳和上地幔顶部的复杂分层块状结构。横波速度的分布表明构成北穆伊斯克地壳的地块具有不同性质。这些地块的西部聚散和地壳下部的分层证实了该地区隆起的堆积-碰撞起源。位于西伯利亚克拉通变薄的倾斜边缘上的北穆伊斯克段解释了该地区地壳碰撞效应的强度。2015年地震的震中深度与Muyakan凹陷地壳上部的明显速度差异存在令人信服的相关性。

西伯利亚软玉

软玉是西伯利亚地区主要的宝石品种。软玉矿床集中在西伯利亚克拉通南部 :西萨彦、东萨彦、Djida和 Vitim。大多数软玉矿床与纯橄岩 -二辉岩建造中的超基性岩有关。Vitim矿床有两种成因类型 :超基性岩的蛇纹石化作用及白云质大理岩与花岗岩接触带的碳酸盐化作用。超基性岩型软玉多为亮绿色 ,常有磁铁矿、铬铁矿和硫化物浸染。产于大理岩和花岗岩接触带的浅色软玉 ,透明度高 ,无金属矿物浸染。详细介绍了西伯利亚软玉的特征 (颜色、化学组成及组构 )。