A 180 ka record of environmental change at Erdut (Croatia): a new chronology for the loess–palaeosol sequence and its implications for environmental interpretation

While there are numerous thick loess–palaeosol sequences preserved across the Carpathian Basin, well dated sites that provide terrestrial palaeoenvironmental records extending beyond last glacial–interglacial cycle are scarce. Robust chronologies are essential for correlations of loess with other long-term Quaternary records and to further understanding of the palaeoenvironment and climate of this important region beyond the last 125 ka. Here a new geochronology based on 13 post-infrared infrared stimulated luminescence ages focused on the lower part of the loess–palaeosol sequence at Erdut is presented. The results show that the lower part of the Erdut profile spans the penultimate glacial cycle (MIS 7 to MIS 5). The considerable sediments overlaying the investigated part of the profile suggest that this section spans two glacial cycles, rather than the previously suggested one. The most likely source of the discrepancy is the use of uncorrected infrared stimulated luminescence signal, which can cause age underestimation if not accounted for. This study demonstrates the need to revisit sites such as Erdut, re-date them using updated measurement protocols, and update existing palaeoenvironmental interpretations.     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

Fifty-five-year longevity for the largest member of the family Sparidae: the endemic red steenbras Petrus rupestris from South Africa

A previous study that explored the age and growth of red steenbras Petrus rupestris (Valenciennes, 1830), a large sparid (family Sparidae, seabreams or porgies) endemic to South Africa and reported to approach 2 m in length, provided estimates as a moderately slow-growing species with a maximum age near 30 years. The stock is considered collapsed and a fishing moratorium was imposed in 2012, resulting in this species being assessed as Endangered by the IUCN. One consideration in addressing population status is validation of life-history traits. In this study, estimates of age for red steenbras from thin-sectioned otoliths were reassessed visually in terms of both the original ages and revised estimates using a different age-reading pattern. The revised ages exceeded the original ages by up to 30 years, with a maximum estimated age of 55 years from a well-defined otolith section that provided a basis for the revised age-reading procedure. Bomb radiocarbon (¹⁴C) dating revealed there was an offset in the timing of the ¹⁴C rise on the Agulhas Bank that, when coupled with considerations for regional oceanography, provided support for the revised age-reading pattern and an estimated longevity that exceeds 50 years. These findings were further supported by the fortuitous recapture of a tagged red steenbras that was at liberty for 22 years.     

阿尔金江尕勒萨依榴辉岩和围岩锆石LA-ICP-MS微区原位定年及其地质意义

阿尔金江尕勒萨依榴辉岩及其直接围岩——石榴子石黑云母片麻岩锆石的阴极发光图像、微区原位LA-ICP-MS微量元素分析研究表明,榴辉岩锆石内部结构比较均匀,少数颗粒保留斑杂状残核;位于锆石斑杂状残核测点的重稀土相对富集,Th/U比值多大于0.4,为岩浆锆石的特征;位于锆石边部与内部结构均匀颗粒上的测点显示HREE近平坦型或弱亏损型的稀土配分模式,显示了与石榴石平衡共生的变质锆石特征;而石榴子石黑云母片麻岩的锆石具有核-幔-边结构,核部为碎屑锆石,幔部则为与石榴石平衡共生的变质锆石。LA-ICP-MS微区定年获得榴辉岩的变质年龄为(493±4.3)Ma,其原岩形成年龄为(754±9)Ma;石榴子石黑云母片麻岩的变质年龄为(499±27)Ma。榴辉岩的变质年龄滞后于其原岩的形成年龄约250Ma,并且榴辉岩与其直接围岩副片麻岩的变质年龄几乎完全一致,充分表明该超高压榴辉岩的形成是陆壳深俯冲作用的产物。     

滇西腾冲地区勐连花岗岩体南段LA-ICP-MS 锆石U-Pb定年及其构造意义

高黎贡构造带属于冈底斯地块东缘,滇西高黎贡花岗岩是冈底斯构造活动重要的岩浆记录。对高黎贡构造带的勐连花岗岩体南段的蒲川花岗岩地球化学特征进行的研究表明,蒲川花岗岩主要属于钙碱性-高钾钙碱性花岗岩,并表现出较强的过铝质特点;稀土元素配分模式曲线均表现为向右陡倾的LREE富集模式,具较弱的Eu负异常;花岗岩具后碰撞的特征,形成于主碰撞之后地壳向后碰撞-陆内转换的构造环境。LA-ICP-MS锆石U-Pb定年表明,蒲川花岗岩形成于早白垩世（128.9Ma±2.4Ma）,年龄、地球化学特征与高黎贡构造带北部和中部一致,其形成可能是滇西怒江带碰撞作用的岩浆响应。     

藏东八宿地区泛非期花岗岩锆石SHRIMP U-Pb定年

卡穷细粒黑云母碱长花岗岩出露于藏东八宿县同卡地区,是藏东地区首次发现的泛非期花岗岩.卡穷微陆块呈岩片状夹持于班公湖-怒江缝合带内,卡穷岩群构成卡穷微陆块的主体,卡穷岩群是由花岗岩、花岗片麻岩、黑云斜长片麻岩、大理岩、黑云斜长变粒岩、退变榴辉岩等组成的构造地质体.卡穷细粒黑云母碱长花岗岩获得的锆石SHRIMPU-Pb年龄为507Ma±10Ma,为泛非事件的岩浆活动记录,进一步证实班公湖-怒江板块缝合带以南是泛非期基底,为解决青藏高原南部的构造演化问题提供了新资料.     

秦岭环斑花岗岩的年代学研究及其意义

本文对秦岭环斑花岗岩带进行了系统的测年工作,通过对实测Ｕ－Ｐｂ,Ｒｂ－Ｓｒ,＾４０Ａｒ／＾３９Ａｒ年龄测定结果研究,认为２１０－２１７Ｍａ是秦岭造山带主造山阶段结束的时间,为秦岭主造山期结束提供了确切的语气具有重要的科学意义。     

陕西小秦岭地区太华群的锆石U-Pb年龄和 Hf同位素组成

本文对陕西华山岩体南侧一个太华群黑云斜长片麻岩进行了地球化学、锆石U-Pb年龄和Hf同位素分析.地球化学分析显示其原岩为中酸性钙碱性花岗质岩石,稀土含量较低( ∑REE =83.13×10-6),但富集Pb和LILE元素(如Rb、Ba).锆石的176Hf/177Hf比值变化于0.281258～0.281404,具明显负的εHf(t)值(-6.86～- 11.23).锆石的Hf同位素模式年龄(2.96 ～3.24Ga)表明原岩是由中太古代地壳演化而来.对比显示小秦岭太华群黑云斜长片麻岩与鲁山地区的太华群具有相似的中太古代地壳源区,但它们的形成时代可能不同.锆石内部结构、Th/U比值以及定年结果显示小秦岭地区的太华群在～1.91Ga经历了一期重要的变质热事件,该事件与Columbia超大陆拼合时的全球性碰撞造山事件相关联.小秦岭太华群为华北克拉通块体南缘的地质单元,但各地区太华群在原岩组成、形成时代和变质时代上具有不同的特征,太华群应是一个杂岩体,至少可以解体为新太古代和古元古代两部分.     

河套地区全新世黄河古河道的分布及期次划分

黄河古河道的分布及其年代学框架的建立对于探讨黄河迁移规律、重建古气候演化历史具有重要意义。通过Landsat8遥感影像解译、1∶5万野外地质地貌调查、钻孔资料分析,结合剖面实测基本判定了色尔腾山以南至现代黄河以北河套平原区黄河埋藏古河道的分布,,采用OSL与14C测年较精确地确定了黄河古河道的年代。依据年代学研究结果,将全新世黄河古河道划分为三期:Ⅰ期古河道,分南北两支,南支分布在复兴镇西北部,埋深2~6 m,北支分布于呼勒斯太中南部,埋深8.2~9 m,时代为9.93~7.4 ka B.P.;Ⅱ期古河道,河道主体分布在色尔腾山山前,呈北西─南东向,埋藏于现今乌加河古河道下部4~11m处,南北最宽处约1.5km。塔尔湖区存在同一期的古河道,埋深7~9 m,以东西向展布为主,时代为7.4~4.1 ka B.P.;Ⅲ期古河道,呼勒斯太中部、塔尔湖中南部及复兴南部都曾发育,但河道主体为塔尔湖区的古河道,埋深2~9 m,时代为4.1~1.2 ka B.P.。黄河古河道分布及时代确定有助于更深入地研究黄河在河套段演化历史,为河套地区的水利建设和农业生产提供参考和借鉴。     

西藏安多早侏罗世火山岩岩石成因及对班公湖-怒江特提斯洋俯冲消减的制约

拉萨地块广泛分布着中生代的岩浆活动,研究它们对于认识特提斯洋的演化过程有着重要的启示。本文报道安多地区新识别出的早侏罗世岛弧型火山岩LA-ICP-MS锆石U-Pb年龄、锆石原位Hf同位素、全岩主微量元素分析和Sr-Nd同位素结果。英安岩206Pb/238U年龄为180.7±4.7Ma(MSWD=0.22,n=10),指示其形成时代为早侏罗世。这些火山岩的SiO_2含量为62.50%~76.15%,MgO含量为0.33%~3.05%,Fe_2O_3T含量为2.35%~6.69%;所有样品都显示轻稀土元素相对富集,具有铕的弱负异常,具有富集大离子亲石元素、亏损高场强元素的地球化学特征;同时这些火山岩锆石原位εHf(t)值均为正值(+15.1~+17.1);全岩Sr-Nd同位素εNd(t)值也均为正值(+7.1~+13.2),指示这些火山岩很可能是特提斯洋俯冲消减过程中新生下地壳部分熔融的产物。结合区域地质资料,认为安多火山岩不可能是龙木错-双湖古特提斯洋或雅鲁藏布江新特提斯洋俯冲消减的产物,而是班公湖-怒江特提斯洋俯冲消减的产物,区域上很可能与改则北、日土地区的侏罗纪侵入岩一起构成了班公湖-怒江特提斯洋北侧的岩浆弧带。由此本文认为安多早侏罗世岛弧型火山岩是班公湖-怒江特提斯洋北向俯冲消减的产物,从而为班公湖-怒江特提斯洋的俯冲消减过程提供了直接的火山岩证据。