西藏措勤晚白垩世英安岩的厘定与地球化学特征   总被引：1，自引：0，他引：1  

王伟  曾令森  刘静  肖萍  高利娥 《地质科学》2013,48(2):484-500

野外地质调查和SHRIMP锆石U/Pb地质年代学研究表明,拉萨地块中带措勤地区发育一套形成于晚白垩世中期的英安岩(88.5±1.2 Ma)。该套火山岩具有岛弧火山岩的地球化学特征,为地壳深部岩浆岩部分熔融形成的Ⅰ型岩浆岩,经历了明显的斜长石分离结晶作用。与同时代的侵入岩相比,该套火山岩为高度演化的岩浆,Rb/Sr比值较高,但Sr/Y比值较低。在拉萨地块内部,广泛发育的90～85 Ma的岩浆作用与新特提斯洋的北向俯冲作用相关。  相似文献   

新疆西准噶尔西南部加里东期成矿斑岩体的发现及意义     

赵文平  张练练  刘松柏  温志刚 《地质科学》2013,48(3):806-814

过去一般认为西准噶尔西南部的侵入岩均为海西中晚期,但近年在玛依勒及巴尔鲁克等构造带发现了一些早古生代侵入岩体,部分岩体显示有铜(金)矿化。本文对其中的占贝勒成矿斑岩体,利用LA-ICP-MS法进行锆石U-Pb同位素测年,结果获得425.3±2.6 Ma的年龄,揭示西准噶尔西南部地区存在有加里东期中酸性侵入岩,进而说明西准噶尔西南部地区存在加里东期斑岩型铜金成矿事件。该研究成果不仅对分析本地区地质构造演化具有重要意义,且对西准地区成矿规律的总结和进一步找矿预测具有重要意义。  相似文献   

Lake George revisited: New evidence for the origin and evolution of a large closed lake,Southern Tablelands,NSW, Australia     

M. Macphail  L. K. Fifield  B. Pillans  M. Davies  G. Hope 《Australian Journal of Earth Sciences》2013,60(7):853-871

Lake George contains the longest continuous sedimentary record of any Australian lake basin, but previous age models are equivocal, particularly for the oldest (pre-Quaternary) part of the record. We have applied a combination of cosmogenic nuclide burial dating, magnetostratigraphy and biostratigraphy to determine the age of the basal (fluvial) unit in the basin, the Gearys Gap Formation. Within the differing resolutions achievable by the three dating techniques, our results show that (i) the Gearys Gap Formation, began accumulating at ca 4 Ma, in the early Pliocene (Zanclean), and (ii) deposition had ceased by ca 3 Ma, in the mid late Pliocene (Piacenzian). Whether the same age control provides an early Pliocene (Zanclean) age for the formation of the lake basin is uncertain. During the Piacenzian, the vegetation at the core site was a wetland community dominated by members of the coral fern family Gleicheniaceae, while the surrounding dryland vegetation was a mix of sclerophyll and temperate rainforest communities, with the latter including trees and shrubs now endemic to New Guinea–New Caledonia and Tasmania. Mean annual rainfall and temperatures are inferred to have been ～2000–3000 mm, although probably not uniformly distributed throughout the year, and within the mesotherm range (>14°C <20°C), respectively. Unresolved issues are: (1) Does the basal gravel unit predate uplift of the Lake George Range and therefore provide evidence that one of the proposed paleo-spillways of Lake George, that above Geary's Gap, has been elevated up to 100–200 m by neotectonic activity over the past 4 million years? (2) Did a shallow to deepwater lake exist elsewhere in the lake basin during the Pliocene?  相似文献   

南秦岭西乡群孙家河组锆石SHRIMP U-Pb年龄及其构造地质意义   总被引：1，自引：0，他引：1       下载免费PDF全文

崔建堂  王峰  段建国  赵陕兰  崔海涛  崔海曼 《沉积与特提斯地质》2013,(4):1-5

对南秦岭西乡群孙家河组英安质火山熔岩进行了锆石SHRIMP U-Pb年龄和岩石化学、稀土元素、微量元素等方面的研究。获得的锆石年龄为814.8±5.2Ma,属于晚青白口世。该年龄为研究南秦岭扬子陆块过渡基底的形成时代提供了有力的佐证,并为研究扬子陆块Rodinia超大陆汇聚时限及秦岭造山带的构造演化提供了新证据。  相似文献   

The origin of the Maozu carbonate-hosted Pb–Zn deposit,southwest China: Constrained by C–O–S–Pb isotopic compositions and Sm–Nd isotopic age     

《Journal of Asian Earth Sciences》2013

The Maozu Pb–Zn deposit, located on the western margin of the Yangtze Block, southwest China, is a typical carbonate-hosted deposit in the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province with Pb + Zn reserves of about 2.0 million tonnes grading 4.15 wt.% Pb and 7.25 wt.% Zn. Its ore bodies are hosted in Sinian (635–541 Ma) Dengying Formation dolostone and show stratiform, vein and irregular textures. Ores are composed of sphalerite, galena, pyrite, calcite, dolomite, quartz and fluorite with massive, banded, disseminated and veined structures. The C–O–Sm–Nd isotopic compositions of hydrothermal calcites and S–Pb isotopic compositions of sulfides were analyzed to constrain the origin of the Maozu deposit. δ¹³C_PDB and δ¹⁸O_SMOW values of hydrothermal calcites range from −3.7‰ to −2.0‰ and +13.8‰ to +17.5‰, respectively, and plot near the marine carbonate rocks field in a plot of δ¹³C_PDB vs. δ¹⁸O_SMOW, with a negative correlation. It suggests that CO₂ in the hydrothermal fluids was mainly originated from marine carbonate rocks, with limited influence from sedimentary organic matter. δ³⁴S_CDT values of sulfides range from +9.9‰ to +19.2‰, similar to that of Cambrian to Triassic seawater sulfate (+15‰ to +35‰) and evaporate (+15‰ to +30‰) in the Cambrian to Triassic sedimentary strata. It suggests that reduced sulfur was derived from evaporate in sedimentary strata by thermo chemical sulfate reduction. Sulfides have low radiogenic Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.129–18.375, ²⁰⁷Pb/²⁰⁴Pb = 15.640–15.686 and ²⁰⁸Pb/²⁰⁴Pb = 38.220–38.577) that plot in the field between upper crust and the orogenic belt evolution curve in the plot of ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb, and similar to that of age corrected Proterozoic basement rocks (Dongchuan and Kunyang Groups). This indicates that ore-forming metals were mainly derived from basement rocks. Hydrothermal calcite yields a Sm–Nd isotopic age of 196 ± 13 Ma, possibly reflecting the timing of Pb–Zn mineralization in the SYG province, younger than the Permian Emeishan mantle plume (∼260 Ma). All data combined suggests that hydrothermal fluids circulated through basement rocks where they picked up metals and migrated to surface, mixed with reduced sulfur-bearing fluids and precipitated metals. Ore genesis of the Maozu deposit is different from known magmatic–hydrothermal, Sedimentary Exhalative or Mississippi Valley-types, which maybe represent a unique ore deposit type, named as the SYG-type.  相似文献   

Further evidence for a relatively high sea level during the penultimate interglacial: open-system U-series ages from La Marina (Alicante,East Spain)     

《Geodinamica Acta》2013,26(6):409-426

The elevation and timing of high sea stands during Oxygen Isotope Stage (OIS) 7 are not as well constrained as those of OIS 5e. Conflicting values are reported from Mediterranean coastlines, and fossil dating is inaccurate because of ubiquitous open U-series systems. New morphostratigraphic data from La Marina (eastern Spain) supported by open-system U-series coral ages shed light on the maximum sea level during OIS 7. Fossil corals (Cladocora caespitosa) underlying an OIS 5e marine unit yielded U-series ages from 178 ± 10 to 208 ± 11 ka (±2s; n=7) with an outlier at 240 ± 18 ka. Mean open-system limit ages of 170 ± 10 (minimum age after correction for 234Th -230Th uptake) and 237 ± 20 ka (maximum age after correction for 238U - 234U uptake) were calculated to have a probable age closer to the minimum value, for an assignment of OIS 7a or 7c. The occurrence of a warm-water “Senegalese” fauna (Strombus bubonius) in OIS5e and OIS 7 marine units confirms the arrival of tropical species to the Mediterranean before the last interglacial period. Morpho-sedimentological and neotectonic studies suggest that the maximum paleo-sea level during OIS 7c or 7a was a few meters below that of OIS 5e.  相似文献   

Late Variscan “Basin and Range” magmatism and tectonics in the Central Alps: evidence from U-Pb geochronology     

Urs Schaltegger  Fernando Corfu 《Geodinamica Acta》2013,26(2):82-98

Abstract

Towards the end of the Variscan orogeny, volcano-sedimentary basins were formed within the mountain hell. U-Pb age determinations on zircons of volcanic and plutonic rocks from intramontane basins of the Central Alps allows us to define the age of two volcano-sedimentary units: The former one was dated older than 333 Ma (probably Visean), the younger one was deposited in a short time span between 303 and 298 Ma (Stephanien). The latter contains tuffs (303 ± 4 Ma), ignimbrites and microgranites (299 ± 2 Ma) and intrusive rhyolites (300 ± 2 Ma) that are all coeval within analytical precision. Granitoid rocks intruded into the volcano-sedimentary rocks at 333 ± 2 Ma, 310 ± 3 Ma and 298 ± 2 Ma. An angular unconformity between the older and the younger units in the Tö di area (Aar massif) indicates uplift and erosion between 310 and 303 Ma.

Our results suggest the existence of two periods of late Variscan extension (or transtension) in the Alpine realm, both combined with magmatic activity. The extensional event of Stephaniun age is characterized by a short duration of only a few million years, between 303 and 298 Ma, comprising tectonic activity, volcanism and plutonism. The plutonic rocks are characterized by a dominant lithospheric mantle component, which was contaminated by different amounts of crostai material and might have been increasingly influenced by aslhcnos-pherie mantle melts in the course of crostai thinning. The ealc-alkaline geochemical characteristics of the granites may be explained as an inherited source feature.

The overall tectonic style and the mode of magmatism resembles the situation of the Basin-and-Kange Province (eastern USA). Consequently there is no need to invoke a late-Variscan Andean-type subduction to explain the geochemical composition of the magmatic rocks. We conclude that late-orogenic extension is an important tectonic stage of the Variscan orogeny, which lasted for some 50 million years. The extension led to thinning of the crust and upwelling of hot mantle, causing high heat flow, intrusion of mantle melts and formation of huge volumes of acid melts.  相似文献   

辽东半岛东北部宽甸地区南辽河群沉积时限的确定及其构造意义   总被引：13，自引：7，他引：6  

孟恩  刘福来  刘平华  刘超辉  施建荣  孔庆波  廉涛 《岩石学报》2013,29(7):2465-2480

辽东半岛东北部宽甸地区出露大面积南辽河群变质表壳岩系,本文通过对其中黑云石英片岩、含电气石浅粒岩和花岗质片麻岩进行精确的锆石LA-ICP-MSU-Pb定年及微区痕量元素分析,并结合锆石阴极发光(CL)图像研究来制约其原岩形成时代和变质时代,进而探讨胶-辽-吉活动带的大地构造属性。Cl图像显示锆石可以分为三类,第一类无核边结构,呈灰黑色均质特征;第二类发育核边结构,核部不发育或具弱生长环带,第三类锆石整体或者核部发育明显生长环带或具条痕状吸收特点,而后两类多数发育灰色均质边,与第一类特征一致。微区痕量元素分析结果显示,灰色均质锆石或边部具有高U(731.2×10-6～1383×10-6)、低Th(51.09～85.15×10-6)和Th/U(0.06～0.07)等特征,为变质成因;第二类锆石核部具有较高Th(97.68～219.7×10-6)和Th/U(0.21～0.27),为岩浆成因;第三类具有高Th(249.6×10-6～469.4×10-6)和Th/U(0.60～0.74),为岩浆成因。定年结果显示,所有测点均位于谐和线上或附近,三类锆石207Pb/206Pb年龄分别介于1878～1903Ma,2011～2043Ma和2082～3285Ma,前两者峰期年龄分别为1885Ma和2035Ma,表明该区南辽河群的原岩形成于～2035Ma之后,而峰期变质作用应发生在～1885Ma,其沉积作用应发生于2035～1885Ma之间;第三类锆石年龄区域上与古元古代辽吉花岗岩、火山岩及古老结晶基底年龄相吻合,暗示它们为南辽河群提供重要物源。结合前人有关辽吉花岗岩及区域构造变形、变质作用等资料,本文研究认为辽东半岛东北部宽甸地区南辽河群应形成于伸展的构造环境。  相似文献   

浙江东南印支晚期的构造伸展事件：来自诸暨大爽岩体的证据   总被引：1，自引：0，他引：1  

徐岩  胡艳华  顾明光  卢成忠 《岩石学报》2013,29(9):3131-3141

出露于浙江省东南部的大爽岩体为黑云母二长花岗岩,LA-ICP-MS锆石U-Pb年代学研究表明该岩体形成于227±2Ma,属印支晚期岩浆作用的产物。地球化学分析显示该岩石低Na2O、富K2O,A/CNK=1.26~1.49(大于1.1),为强过铝质、钾玄质系列花岗岩;岩石稀土总量较高,富Sr(Sr=874.6×10-6~1158×10-6),贫Yb(Yb=3.00×10-6~3.92×10-6),富轻稀土而亏损重稀土,具轻微的负铕异常(δEu=0.68~0.70);相对富集Rb、Th等大离子亲石元素,而亏损Nb、Ta等高场强元素;Sr-Nd同位素分析表明岩石具有较高的初始锶比值(I Sr=0.710718~0.711008)和较低εNd(t)值(εNd(t)=-10.9~-11.1),上述地球化学特征指示该岩体岩浆源区为古老的地壳物质。综合分析认为大爽岩体是古老地壳部分减压熔融的产物,受控于印支造山后的伸展应力作用。  相似文献   

江西相山铀矿田如意亭剖面火山岩的年代学格架及其地质意义   总被引：10，自引：5，他引：5  

杨水源  蒋少涌  赵葵东  姜耀辉  凌洪飞  陈培荣 《岩石学报》2013,29(12):4362-4372

江西相山铀矿田如意亭剖面最底部的熔结凝灰岩代表了相山火山-侵入活动的开始时间,本文首次报导了该熔结凝灰岩的LA-ICP-MS锆石U-Pb定年结果,得出其形成年龄为137.3±0.9Ma,表明相山火山-侵入活动开始于早白垩世。此外,对如意亭剖面的两个流纹英安岩样品的锆石U-Pb定年结果分别是136.8±2.5Ma和136.4±1.5Ma,对采自如意亭剖面的流纹英安斑岩的锆石U-Pb定年结果是135.0±2.0Ma,对采自如意亭剖面的碎斑熔岩的定年结果是134.1±1.6Ma,这些定年结果结合前人已有的研究,得出相山火山-侵入杂岩的形成时代集中在135Ma左右（137~132Ma）,再次证实了相山火山-侵入活动始于早白垩世,是一次集中且短暂的火山-侵入活动。本文对如意亭剖面的定年结果证实相山地区打鼓顶组和鹅湖岭组的火山岩地层应属于早白垩世。然而赣杭构造带上原先所划分的打鼓顶组与鹅湖岭组火山岩形成的时间与武夷山北坡冷水坑盆地中火山岩系并不相同,因此,打鼓顶组与鹅湖岭组地层在区域上应予重新厘定。  相似文献