北祁连山小柳沟钨矿床中辉钼矿Re-Os年龄测定及其意义

小柳沟是中国在北方最新探明的一个大型钨矿床,本文概要地介绍了该矿床的成矿地质背景和矿床地质特征,用Re-Os同位素方法测试辉钼矿,获得等时线年龄462±13 Ma(2σ),模式年龄436～496 Ma。还证明了成矿发生于板块碰撞期前,成矿物质主要为壳源。     

激光探针等离子体质谱同时测定锆石微区铀—铅年龄及微量元素

建立了一种利用激光探针等离子体质谱技术同时原位测定锆石Ｐｂ－Ｐｂ及Ｐｂ－Ｕ年龄和２５个微量元素的快速分析方法。Ｐ的检出限为１４μｇ／ｇ,Ｓｃ的检出限为３μｇ／ｇ,Ｒｂ、Ｎｂ、Ｂａ稀土元素Ｎｄ、Ｇｄ、Ｄｙ、Ｅｒ及Ｙｂ的检出限为０．１￣０．３μｇ／ｇ,Ｐｂ的检出限０．５μｇ／ｇ,其它稀土元素及Ｓｒ、ｙ、Ｈｆ、Ｔａ、Ｔｈ和Ｕ的检出限为１０￣９０ｎｇ／ｇ。方法对绝大多数微量元素的相对标准偏差为５￣１５％;     

基于贝壳生长轮方法的平端深海偏顶蛤的生长和年龄结构研究

平端深海偏顶蛤(Gigantidasplatifrons)是广泛分布于西太平洋深海热液和冷泉生态系统中的优势种和共有种,也是深海化能生态系统中重要的生境营造种。以南海F冷泉平端深海偏顶蛤为研究对象,基于贝壳日生长轮方法,分析了平端深海偏顶蛤的年龄与生长速率,建立了其年龄与贝壳壳长关系的生长方程。同时,结合获得的生长方程,分析了南海F冷泉采样点(119.285 6°E,22.115 4°N)平端深海偏顶蛤种群的年龄结构。研究结果表明,采样获得的平端深海偏顶蛤种群的最大壳长为11.4 cm,最大寿命为13.5龄。研究区域的贝壳长度分布集中在4～7 cm,占比60%;年龄分布集中在2～4龄,占比49.7%。相关研究结果为进一步开展平端深海偏顶蛤的生长研究提供了基础数据,有助于深入了解冷泉区域的种群动态变化规律。     

Late Eocene–early Miocene provenance evolution of the Crocker Fan in the southern South China Sea

There are many large-scale Cenozoic sedimentary basins with plentiful river deltas, deep-water fans and carbonate platforms in the southern South China Sea. The Crocker Fan was deposited as a typical submarine fan during the late Eocene–early Miocene, and stretches extensively across the entire Sarawak–Sabah of the northern Borneo area. However, systematic analyses are still lacking regarding its sediment composition and potential source suppliers. No consensus has been reached yet on the provenance evolution and sedimentary infilling processes, which seriously impeded the oil-and-gas exploration undertakings. By combining with sedimentary-facies identification, heavy mineral assemblages, elemental geochemistry and detrital zircon U-Pb dating, this paper aims to generalize an integrated analysis on the potential provenance terranes and restore source-to-sink pathways of the Crocker Fan. In general, the Crocker Fan was initially formed over the Cretaceous–lower/middle Eocene Rajang Group by an angular Rajang unconformity. The continual southward subduction of the proto-South China Sea resulted in magmatic activities and subsequent regional deformation and thrusting along the Lupar Line in the northern Borneo. The lowermost Crocker sequence is featured by a thick conglomerate layer sourced from in-situ or adjacent paleo-uplifts. From the late Eocene to the early Miocene, the Crocker Fan was constantly delivered with voluminous detritus from the Malay Peninsula of the western Sundaland. The Zengmu Basin was widely deposited with delta plain and neritic facies sediments, while the Brunei-Sabah Basin, to the farther east, was ubiquitously characterized by turbiditic sequences. The Crocker Fan successions are overall thick layers of modest-grained sandstones, which formed high-quality reservoirs in the southern South China Sea region.     

吉林红旗岭铜镍硫化物矿床的成矿时代讨论

通过对红旗岭铜镍硫化物矿床1号含矿超镁铁质岩体和8号不含矿镁铁-超镁铁质岩体进行单矿物40Ar-39Ar法测年,得到与铜镍硫化物矿床相关的角闪石与黑云母结晶年龄分别为250 Ma和225 Ma,这一结果与前人所报道的K-Ar法年龄有明显的差异.结合与热液矿化相关的斜长伟晶岩锆石SHRIMP法年龄216 Ma,认为镁铁-超镁铁质岩形成于250 Ma左右的印支早期,铜镍硫化物矿床的形成时间晚于含矿岩体,大约为225 Ma前后的印支中期.216 Ma前后的岩浆期后热液叠加对成矿具有积极作用.     

Tephra isochrons and chronologies of colonisation

This paper demonstrates the use of tephrochronology in dating the earliest archaeological evidence for the settlement of Iceland. This island was one of the last places on Earth settled by people and there are conflicting ideas about the pace and scale of initial colonisation. Three tephra layers, the Landnám (‘land-taking’) tephra layer (A.D. 877 ± 1), the Eldgjá tephra (A.D. 939) and the recently dated V-Sv tephra (A.D. 938 ± 6) can be found at 58% of 253 securely-dated early settlement sites across the country. The presence of the tephras permits both a countrywide comparison, and a classification of these settlement sites into pre-Landnám, Landnám and post-Landnám. The data summarised here for the first time indicate that it will be possible to reconstruct the tempo and development of the colonisation process in decadal resolution by more systematically utilising the dating potential of tephrochronology.     

SHRIMP U–Pb ages of detrital zircons from the Early Cretaceous Nakdong Formation,South East Korea: Timing of initiation of the Gyeongsang Basin and its provenance

To constrain the depositional age of the lowermost Nakdong Formation in the Early Cretaceous Gyeongsang Basin, SHRIMP U–Pb age determination was carried out on zircon separates. The U–Pb compositions of detrital zircons from the Nakdong Formation yield a wide range of ages from the Archean to the Cretaceous but show a marked contrast in age distribution according to the geographical locations within the basin. The provenance of the southern Nakdong Formation is dominantly the surrounding Yeongnam Massif, which is composed of Paleoproterozoic metamorphic rocks and Triassic to Jurassic plutonic rocks, whereas the central to northern Nakdong Formation records significant sediment derivation from the Okcheon Metamorphic Belt, which is distributed to the northwest, in addition to the contribution from the Yeongnam Massif. It is suggested that the maximum depositional age of the Nakdong Formation is ca 127 Ma, based on its youngest detrital zircon age population. The onset of its deposition at 127 Ma coincided with the tectonic inversion in East Asia from a compressional to an extensional geodynamic setting, probably due to the contemporaneous change in the drift direction of the Izanagi Plate and its subsequent oblique subduction.     

Chronology of late Holocene climatic events in the northern North Atlantic based on AMS 14C dates and tephra markers from the volcano Hekla,Iceland

A combination of AMS¹⁴C dating and tephrochronology has been used to date late Holocene oceanographic events in a 335 cm marine record, covering about 4600 cal. yr with sedimentation rates exceeding 80 cm 1000 yr⁻¹. The core site is located 50 km offshore on the northern Icelandic shelf. Tephra markers from Iceland serve to correlate the marine and terrestrial records. Especially notable is the presence of three geochemically correlated tephra markers from the Icelandic volcano Hekla (Hekla 4, Hekla 3 and Hekla 1104). Benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies. The foraminiferal assemblages reflect a general cooling trend during the last 4600 yr. A marked drop in sea‐surface temperatures is registered at about 3000 cal. yr BP, corresponding to the level of the Hekla 3 tephra. There is faunal indication of temperature amelioration during the Medieval Warm Period and a cooling again during the Little Ice Age. Periods of ice rafting events are indicated by ice rafted debris (IRD) concentrations, e.g. at around 3000 cal. yr BP and during the Little Ice Age. The former event occurred just prior to the deposition of the Hekla 3 tephra marker, the largest Holocene Hekla eruption. A correlation with terrestrial climatic events in Iceland is presented. A standard marine reservoir correction of 400 ¹⁴C yr appears to be reasonable, at least during periods with high influence of water masses from the Irminger Current on the northern Icelandic shelf. An increase to ca. 530 ¹⁴C yr may have occurred, however, when water masses derived from the East Greenland Current were dominant in the area. Copyright © 2000 John Wiley & Sons, Ltd.     

小兴安岭-张广才岭地区晚古生代至中生代花岗岩的成因及其地质意义

中国东北地区显生宙花岗岩的成因一直是中亚造山带东段研究的热点之一,尤其是小兴安岭-张广才岭地区的花岗岩其成因及形成的大地构造背景一直存在较大争议。本文新获得小兴安岭-张广才岭铁力和依兰地区的二长花岗岩LA-ICP-MS锆石U-Pb年龄分别为188±1 Ma和257±3 Ma。地球化学数据显示,两地区的二长花岗岩均为Ⅰ型花岗岩并且富集大离子亲石元素(Th和U等)和轻稀土元素,亏损高场强元素(Nb和Ta等)和重稀土元素具有弧岩浆岩的地球化学特征。锆石Hf同位素数据显示,铁力地区二长花岗岩的岩浆源区可能来自于中新元古代的下地壳部分熔融。综合前人在小兴安岭-张广才岭地区已发表的花岗岩类岩石的地质年代学和地球化学数据,初步推测小兴安岭-张广才岭地区在晚古生代至中生代期间处于活动大陆边缘环境。同时,小兴安岭-张广才岭地区晚古生代至中生代的岩浆岩具有自东向西形成时代逐渐变年轻的趋势,这可能是由于东侧的牡丹江洋在晚古生代至中生代期间俯冲角度逐渐变缓造成的。     

滇西北剑川盆地新近系地层时代的新认识及构造意义

地处板块接触地带的滇西北剑川地区是研究新构造运动的重要场所。剑川盆地保留有较为完整的新生代地层,在1:250000地质图上,新生界自下而上为古新统勐野井组、始新统宝相寺组、渐新统金丝厂组、中新统双河组和上新统剑川组;其中双河组为一套含可采煤层的砂泥岩夹泥灰岩沉积,剑川组为一套火山-沉积岩组。近期的研究揭示双河组和剑川组均属始新世,但发表的年龄相互包含,并没有清楚的把两者分开。本文采用Ar-Ar和锆石U-Pb方法测试了双河组和剑川组顶、底凝灰岩的年龄,辅以岩体、岩脉的年龄,重新厘定了两个组的顶、底年龄。剑川组顶部凝灰岩锆石SHRIMP U-Pb年龄为34 Ma±;底部凝灰岩黑云母Ar-Ar坪年龄为36 Ma±,与底部侵入岩脉的锆石SHRIMP U-Pb年龄一致;中上部侵入岩脉的黑云母Ar-Ar坪年龄在34~36 Ma之间。同时,老君山岩体、玉召块岩体和沙帽山岩体的锆石SHRIMP U-Pb年龄在34~35 Ma之间。剑川火山-沉积岩组的年龄集中在34~36 Ma之间,属始新世晚期。剑川双河煤矿矿部至三家村及五家村一带,双河组之下新发现一套凝灰岩,其黑云母Ar-Ar坪年龄和锆石SHRIMP U-Pb年龄均为37 Ma±,表明双河组的起始年代不超过37 Ma;双河组形成于36~37 Ma之间,也属始新世晚期。新的结果表明剑川盆地始新统地层应包括宝相寺组、金丝厂组、双河组和剑川组,缺失渐新统沉积。结合其他盆地的年龄数据,表明剑川乃至整个云南地区在渐新世期间为褶皱隆起期。