中国大陆科学钻探主孔榴辉岩Sm-Nd年龄及其地质意义

南苏鲁中国大陆科学钻探主孔CCSD-MH及地表的榴辉岩Sm—Nd同位素年龄测试结果显示，每件样品中全岩（Wr)与石榴石(Grt)和绿辉石(Omp)点均在一条直线上。除样品B210R186以外，其余5件榴辉岩均给出十分相近的Sm—Nd等时线年龄，位于202．6-219Ma之间，这与榴辉岩围岩——片麻岩锆石边缘记录的近等温减压退变质年龄(200-220Ma)十分接近，表明测试的榴辉岩中石榴石的Sm—Nd同位素体系有可能在近等温减压退变质时重置，并在向角闪岩相退变质过渡时封闭。因此，笔者测定的202．6-219Ma的Sm-Nd全岩-矿物等时线年龄，应代表了南苏鲁榴辉岩在构造折返过程中近等温减压阶段的退变质年龄，而不能代表苏鲁地体的超高压变质年龄。     

内蒙古黑鹰山富铁矿床磷灰石钐-钕同位素年龄及其地质意义

黑鹰山富铁矿床地处北山造山带西伯利亚板块与哈萨克斯坦_北山板块汇聚地带,是中国西北地区规模最大和品位最高的富铁矿床之一,其独特的产出环境和地质特征为国内外地质学界所关注。为了查明该矿床的形成过程,笔者首次对致密块状铁矿体中的6件磷灰石样品和脉状铁矿体中的2件磷灰石样品进行了钐_钕同位素测定。块状矿体的6件样品所获等时线年龄为(32 2 .0±4 .3)Ma,MSWD值为0 .0 9,14 3 Nd/14 4 Nd初始比值为(0 .5 12 30 8±0 .0 0 0 0 0 3) ,εNd(t)为(1.6 6±0 .0 1)。脉状矿体中2件样品的εNd(t)值分别为7.2 0和7.2 6 ,明显高于块状矿体磷灰石样品。依据上述同位素分析数据和特征比值,结合容矿围岩和矿体地质特征,推测黑鹰山富铁矿床的形成与海西早期富碱岩浆流体多期次活动有关,成矿物质主要来自地幔物质占优势比例的壳_幔混源岩浆房。     

Nd and Sr isotopic variations in Chinese eolian deposits during the past 8 Ma: Implications for provenance change

A record of changes in Nd and Sr isotopic composition of the eolian deposits from the central Loess Plateau has been determined for the past 8 Ma. The isotopic records of the silicate fraction of the Quaternary and Tertiary eolian deposits allow interpreting the interplay between the Sr isotopic variations in the eolian deposits and the late Cenozoic tectonic and climatic changes. The results indicate that the temporal variations of Nd and Sr isotopes show remarkable changes around the beginning of the Quaternary. The lower values of the ¹⁴³Nd/¹⁴⁴Nd and the decreasing trend of the ⁸⁷Sr/⁸⁶Sr ratios after 2.58 Ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late Cenozoic uplift induced glacial grinding in the high orogenic belts in central Asia. In this context, the substantial changes in climate and tectonics have modified dust sources significantly, and the Quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the Tertiary Red Clay.     

Sm-Nd and zircon SHRIMP U-Pb dating of Huilanshan mafic granulite in the Dabie Mountains and its zircon trace element geochemistry

Granulites in the Dabie Mountains are mainly ob-served in northern Dabie complex zone. Huangtuling intermediate-acid granulites and Huilanshan mafic granulites in the Luotian dome are two famous out-crops (Fig. 1)[1]. It is important to know the genesis and metamorphic age of these granulites for under-standing tectonic evolution and exhumation history of the Dabie Mountains. Previous geochemical and geo-chronological work[2―8]1) on the Huangtuling granu-lites indicates that their protoli…     

Eclogites and polyphase P–T cycling in the Caledonian Uppermost Allochthon in Troms, northern Norway

Eclogites in the Tromsø area, northern Norway, are intimately associated with meta-supracrustals within the Uppermost Allochthon of the Scandinavian Caledonides (the Tromsø Nappe Complex). The whole sequence, which includes pelitic to semipelitic schists and gneisses, marbles and calc-silicate rocks, quartzofeldspathic gneisses, metabasites and ultramafites, has undergone three main deformational/metamorphic events (D₁/M₁, D₂/M₂ and D₃/M₃). Detailed structural, microtextural and mineral chemical studies have made it possible to construct separate P–T paths for these three events. Chemically zoned late syn- to post-D₁ garnets with inclusions of Bt, Pl and Qtz in Ky-bearing metapelites indicate a prograde evolution from 636°C, 12.48 kbar to c. 720°C, 14–15 kbar. This latter result is in agreement with Grt–Cpx geothermometry and Grt–Cpx–Pl–Qtz geobarometry on eclogites and trondhjemitic to dioritic gneisses. Maximum pressures at c. 675°C probably reached 17–18 kbar based on Cpx–Pl–Qtz inclusions in eclogitic garnets, and Grt–Ky–Pl–Qtz and Jd–Ab–Qtz in trondhjemitic gneisses. Post-D₁/pre-D₂ decompressional breakdown of the high-P assemblages indicates a substantial drop in pressure at this stage. Inclusions and chemical zoning in syn- to post-D₂ garnets from metapelites record a second episode of prograde metamorphism, from 552°C, 7.95 kbar, passing through a maximum pressure of 10.64 kbar at 644°C, with final equilibration at c. 665°C, 9–10 kbar. The corresponding apparently co-facial paragenesis Grt + Cpx + Pl + Qtz in metabasites yields c. 635°C, 8–10 kbar. In the metapelites post-D₃, Grt in apparent equilibrium with Bt, Phe and Pl yield c. 630°C, 9 kbar. The D₁/M₁ and D₂/M₂ episodes are exclusively recorded in the Tromsø Nappe Complex and must thus pre-date the emplacement of this allochthonous unit on top of the underlying Lyngen Nappe, while the D₃/M₃ episode is common for the two units. A previously published Sm–Nd mineral isochron (Grt–Cpx–Am) on a partly retrograded and recrystallized ecologite of 598 ± 107 Ma represents either the timing of formation of the eclogites or the post-eclogite/pre-D₂ decompression stage, while a Rb–Sr whole rock isochron of an apparently post-D₁/pre-D₂ granite of 433 ± 11 Ma is consistent with a K–Ar age of post-D₁/pre-D₂ amphiboles from a retrograded eclogite of 437 ± 16 Ma which most likely record cooling below the 475–500°C isotherm after the M₃ metamorphism.     

The Tertiary collision-related thermal history of the NW Himalaya

Garnet‐whole rock Sm‐Nd data are presented for several samples from the Indian plate in the NW Himalaya. These dates, when combined with the P‐T evolution of the Indian plate rocks, allow a thorough reconstruction of the prograde thermal evolution of this region (including the Nanga Parbat Haramosh Massif) during the early Cenozoic. Combining these data with Rb‐Sr mineral separate ages, enables us to constrain the post‐peak cooling history of this region of the Himalaya. The data presented here indicate that the upper structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, and similar rocks in the Kaghan Valley to the south‐west, were buried to pressures of c. 10 kbar and heated to temperatures of c. 650 °C at 46–41 Ma. The burial of the lower structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, to similar depths but at higher temperatures of c. 700 °C, occurred slightly later at 40–36 Ma, synchronous with the imbrication and exhumation of the amphibolite‐ and eclogite‐grade rocks of the Kaghan Valley. In contrast, the cover rocks of the Nanga Parbat Haramosh Massif were not imbricated or exhumed at this time, remaining buried beneath the Kohistan‐Ladakh Island Arc until the syntaxis‐forming event that occurred in the last 10 Myr. The timing of tectonic events in the north‐western Himalaya differs from that experienced by the rocks of the Central Himalaya in that the earliest stage of burial in the NW Himalaya predates that of the Central Himalaya by c. 6 Myr. This difference may result from the diachronous nature of the Indo‐Asian collision or may simply be a reflection of differing timing at different structural levels.     

赣东北蛇绿岩的离子探针锆石U－Pb年龄及其构造意义

离子探针锆石Ｕ－Ｐｂ年龄分析结果表明，赣东北蛇绿岩套的高度分异岩浆的结晶年龄为９６８±２３Ｍａ。重新计算的蛇绿岩Ｓｍ－Ｎｄ等时线年龄９５５±４４Ｍａ，与锆石Ｕ－Ｐｂ年龄在误差范围内一致。１５个样品的εＮｄ（Ｔ）值（Ｔ＝９７０Ｍａ）为＋４．３－＋６．７，表明蛇绿岩来源于强亏损地幔源。少数样品的Ｓｍ－Ｎｄ体系可能受到后期变质、变形或蚀变作用的影响。结合已发表的４０Ａｒ－３９Ａｒ年龄资料，可以初步确定赣东北晚元古代碰撞带发育的时限为０．９７－０．８０Ｇａ。     

钐钕分离的化学方法及其在同位素地质年龄中的应用

本文主要介绍了分离Sm-Nd的3种化学方法,其中有适合分离高含量Sm,Nd的了酮-疏氰酸铵纸色层法;适合分离一般含量Sm,Nd的P_(204)柱色层法;适合低含量Sm,Nd的加压离子交换法。同时介绍应用Sm-Nd法得出的我国第一条Sm-Nd等时线,测出了冀东早太古代岩石Sm-Nd同位素地质年龄。     

娘娘山碱性火山-侵入岩特征及成岩定量模拟

本文通过对铜井娘娘山旋回中生代火山-侵入岩系岩石化学、微量、稀土元素以及铷锶、钐钕等同位素详细研究,认为这套岩石具高碱、硅不饱和、强烈富集不相容元素和轻稀土特征。岩石的~(87)Sr/~(86)Sr初始比值为0.7070—0.7073,∈_(Nd)值为-3.4—3.3,利用二元混合模式计算得出蓝方石响岩和霓辉正长岩源区物质成分相当41%、42%上部陆壳和59%、58%亏损地幔组成的混合物,源区物质经6.4%、6.6%部分熔融形成初始岩浆,表明娘娘山旋回碱性火山-侵入岩系是壳幔混合物经部分熔融后所形成的产物。     

Nd isotopic stratigraphy of Paleoproterozoic to late Paleozoic sedimentary strata of the southwestern Yangtze Block and implications for its tectonic evolution

ABSTRACT

A systematic Sm-Nd isotopic study is reported for Paleoproterozoic to Late Paleozoic strata from the Dongchuan area in the southwestern Yangtze Block. The results, combined with the available detrital zircon U-Pb ages and Hf isotope data, constrain the provenances of these sedimentary rocks and further identify three important tectono-magmatic activities. Most of the Paleo-Mesoproterozoic samples (Dongchuan Group) display a wide T_DM2 range of 1.92–2.52 Ga with corresponding ε_Nd(t) values of +4.0 to ?3.5, suggesting Paleoproterozoic-dominated provenances mixed with mantle-derived materials. This corresponds to the ~1.7–1.5 Ga mafic magmatic activities commonly occurred in the southwestern Yangtze Block, which are related to the early breakup of the Columbia supercontinent. The obvious vale of T_DM2 and apex of ε_Nd(t) occurred in the Neoproterozoic strata (~0.8 Ga) of the southwestern margin over the whole Yangtze Block. This is consistent with the widely recognized mantle-derived magmatism around the Yangtze Block related to the breakup of Rodinia. However, the decreases in Nd model ages are different among various regions, indicating that the Neoproterozoic mantle inputs are more profound in the southwestern and central Yangtze Block than the southeastern Yangtze and the Jiangnan orogenic belt. The late Ediacaran to early Cambrian strata from the southwestern Yangtze exhibit a decrease in T_DM2 (from 2.00 to 1.67 Ga) and increase in ε_Nd(t) (from ?9.0 to ?5.2). This is in accordance with the coeval juvenile crustal materials discovered in the northwestern Yangtze, which were probably derived from the assembly of the Gondwana continent. Thus, a Gondwanan affinity is suggested for the southwestern Yangtze Block. Overall, the Nd isotopic studies of the Paleoproterozoic to Late Paleozoic sedimentary strata from the southwestern Yangtze Block identified three major episodes of magmatic activities, late Paleoproterozoic (~1.7 Ga), Neoproterozoic (~0.8 Ga) and late Neoproterozoic-early Cambrian (~0.55 Ga) in the context of Columbia, Rodinia and the subsequent Gondwana supercontinents.