Modelling the relationship between sexual reproduction and rhizome growth in Posidonia oceanica (L.) Delile

The relationship between flowering and growth performance of Posidonia oceanica (L.) Delile in meadows distributed along the south‐eastern coast of Sicily (Italy) was investigated by means of a statistical model (generalized linear mixed model) combined with the lepidochronological analysis. Over a 28‐year period, 67 floral stalk remains were observed. The highest flowering index was recorded in lepidochronological year 1998 (10.1%) and the Inflorescence Frequency per age showed a clear decrease corresponding to 15‐year‐old shoots. The sexual reproductive event had positive effects on rhizome elongation (cm year^?1) and leaf production (no. leaves year^?1) in the same flowering year, whilst no effect on the rhizome production (mg year^?1) was observed. Rhizome growth variables showed significant negative lagged responses in the two years following flowering. On the whole, we calculated that the effect exerted by flowering, in terms of loss on rhizome elongation and production, was about 27% and 38%, respectively. Although it has been demonstrated that recovery from the stress induced by sexual reproduction is limited to the two years after flowering, the magnitude of the reproductive cost may become quite considerable especially in comparison with the whole lifespan of individual shoots.     

GEOCHRONOMETRY & ISOTOPE GEOLOGY

正20141655 Gao Linzhi(Institute of Geology,CAGS,Beijing 100037,China);Ding Xiaozhong The Revision of the Chentangwu Formation in Neoproterozoic Stratigraphic Column:Constraints on Zircon U-Pb Dating of Tuff from the Mengshan Section in Pujiang County,Zhejiang Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.988-995,5 illus.,1 plate,2 tables,24 refs.)     

西藏南部康马岩体岩石类型及其同位素测年

康马岩体位于西藏南部康马县城北侧 ,其内部可划分出 5种不同的岩石类型 :(1)片麻状黑云二长花岗岩 ;(2 )眼球状黑云二长花岗岩 ;(3)片麻状二云母二长花岗岩 ;(4 )弱片麻状细粒黑云二长花岗岩 ;(5 )变质的暗色辉长辉绿岩。前两类为康马岩体的主体岩石类型 ,侵位时代为加里东早期 (约4 78～ 4 6 1Ma) ;其余均呈脉状产出 ,其中片麻状二云母二长花岗岩与康马岩体主体岩石类型属于同期产物 ,弱片麻状细粒黑云二长花岗岩形成于海西早期 ((339.0± 1.2 )Ma) ,暗色辉长辉绿岩的形成时代目前还不十分清楚。不同类型的岩石其Ar Ar冷却年龄约为 18～ 14Ma。     

Coastal ridge constructive processes at a multi-decadal scale in Barreta Island (southern Portugal)

Multiple ridges across prograding coasts may display variable geometries, commonly expressed through varying elevations. Changes in ridge elevation have been traditionally related to the occurrence of fluctuating progradation rates, which might, in turn, be driven by shifting environmental conditions. Here, we explore the geometry and growth mechanisms of multiple ridges, generated at Barreta Island (Ria Formosa, southern Portugal), as a consequence of the rapid progradation of the island over the last 70 years, following the artificial fixation of the downdrift Faro-Olhão inlet with jetties in 1955. The variability in the morphology of these features was analysed in combination with available wind and wave data, in order to better distinguish growth mechanisms and understand the main parameters determining the final geometry of the observed ridges. The results suggest that (1) most of the identified ridges fall in the beach ridge classification, as they have been mostly built by marine processes, and (2) the parameters derived from, or closely related to wave climate variability (e.g. progradation rates, storm occurrence) can jointly explain most of the observed morphological changes, while aeolian processes played a secondary role. Indeed, ridge geometry appears mainly controlled by progradation rates, with higher ridges associated with lower progradation rates. Progradation rate, in turn, is mostly related to longshore wave power, storminess, and the occurrence storm groups. Yet, the final configuration of ridges can also be affected by runup levels and onshore winds. Therefore, establishing the relation between ridge geometry and wave climate is not a straightforward task, because of the complex processes and interactions that control coastal morphodynamics. © 2019 John Wiley & Sons, Ltd.     

北秦岭四方台基性-超基性杂岩锆石 LA-ICP-MS年代学研究

四方台杂岩体是北秦岭沿商-丹带出露的基性-超基性杂岩体中最大的一个,出露面积约40 km2,由超基性-基性-中性岩石组成,侵入到丹凤群中。对四方台杂岩体中辉长岩锆石进行LA-ICP-MS微区定年研究,获得岩体的成岩时代为460±29 Ma。获得的32个测点可明显地分为400~500 Ma、700~900 Ma、1 800~2 600 Ma和2 700~2 918 Ma这4个时段,可能分别代表了北秦岭造山带不同地质时期的构造-岩浆事件的时代信息。其中400~500Ma与北秦岭地区表现强烈的加里东运动时限一致,而700~900 Ma则可能与830~740 Ma中国中西部地区响应积极的、造成Rodinia超大陆裂解的地幔柱活动有关。     

Age and significance of voluminous mafic–ultramafic magmatic events in the Murchison Domain,Yilgarn Craton

Mafic–ultramafic rocks in structurally dismembered layered intrusions comprise approximately 40% by volume of greenstones in the Murchison Domain of the Youanmi Terrane, Yilgarn Craton. Mafic–ultramafic rocks in the Murchison Domain may be divided into five components: (i) the ～2810 Ma Meeline Suite, which includes the large Windimurra Igneous Complex; (ii) the 2800 ± 6 Ma Boodanoo Suite, which includes the Narndee Igneous Complex; (iii) the 2792 ± 5 Ma Little Gap Suite; (iv) the ～2750 Ma Gnanagooragoo Igneous Complex; and (v) the 2735–2710 Ma Yalgowra Suite of layered gabbroic sills. The intrusions are typically layered, tabular bodies of gabbroic rock with ultramafic basal units which, in places, are more than 6 km thick and up to 2500 km² in areal extent. However, these are minimum dimensions as the intrusions have been dismembered by younger deformation. In the Windimurra and Narndee Igneous Complexes, discordant features and geochemical fractionation trends indicate multiple pulses of magma. These pulses produced several megacyclic units, each ～200 m thick. The suites are anhydrous except for the Boodanoo Suite, which contains a large volume of hornblende gabbro. They also host significant vanadium mineralisation, and at least minor Ni–Cu–PGE mineralisation. Collectively, the areal distribution, thickness and volume of mafic–ultramafic magma in these complexes is similar to that in the 2.06 Ga Bushveld Igneous Complex, and represents a major addition of mantle-derived magma to Murchison Domain crust over a 100 Ma period. All suites are demonstrably contemporaneous with packages of high-Mg tholeiitic lavas and/or felsic volcanic rocks in greenstone belts. The distribution, ages and compositions of the earlier mafic–ultramafic rocks are most consistent with genesis in a mantle plume setting.     

扬子陆块西缘古元古代基性侵入岩LA-ICP-MS锆石U-Pb年龄和Hf同位素及其地质意义

扬子陆块西缘康滇南北向构造带内发育大量古元古代基性岩脉（墙）,它们对于认识扬子陆块早期的构造演化具有重要意义。对四川会理地区侵入到元古界通安组内的辉长岩进行LA-ICP-MS锆石U-Th-Pb同位素测定,获得的207Pb/206Pb加权平均年龄为1694Ma±16Ma（MSWD=0.9）,代表了该辉长岩的形成和侵位时代,这一结果指示会理地区通安组应为古元古代地层。辉长岩全岩地球化学具有类似于N-MORB的特征。辉长岩锆石初始（176Hf/177Hf）i值为0.281881~0.281982,对应的εHf（t）为6.2~9.8,单阶段亏损地幔Hf模式年龄tDM1为1738~1883Ma,平均值为1803Ma。这些数据表明古元古代辉长岩来源于亏损地幔,指示古元古代晚期扬子西缘之下存在亏损地幔。结合扬子西缘大量古老的碎屑锆石,推测扬子陆块西缘存在太古宙—古元古代的结晶基底。与扬子陆块西缘古元古代晚期基性侵入岩形成有关的幔源岩浆事件明显晚于扬子陆块古元古代碰撞造山及造山后的伸展作用,记录了扬子陆块古元古代晚期一次伸展过程,可能是Columbia超大陆裂解作用在扬子陆块的响应。     

铅同位素地球化学示踪进展

本文论述了铅同位素示在地学中的最新应用和发展。由于它在示踪物质来源,圈定找矿靶区,判别构造环境等方面的优势,是当前最重要的地球化学示踪手段之一和同位素地球化学研究的热点。