Reassembling the Paleogene–Eocene North Atlantic igneous province: New paleomagnetic constraints from the Isle of Mull, Scotland

The paleomagnetic data sets from the British Tertiary Igneous Province (BTIP) have recently been criticized as being unreliable and discordant with data from elsewhere in the North Atlantic Igneous Province (NAIP) [Riisager et al. Earth Planet. Sci. Lett. 201 (2002) 261–276; Riisager et al. Earth Planet. Sci. Lett. 214 (2003) 409–425]. We offer new paleomagnetic data for the extensive lava flow sequence on the Isle of Mull, Scotland, and can confirm the paleomagnetic pole positions emanating from important earlier studies. Our new north paleomagnetic pole position for Eurasia at 59 ± 0.2 Ma has latitude 73.3°N, longitude 166.2°E (dp/dm = 5.2/7.0).A re-evaluation and an inter-comparison of the paleomagnetic database emanating from the NAIP were carried out to test for sub-province consistency. We find a general agreement between the Eurasian part of NAIP (BTIP and Faeroes) and East Greenland data. However a compilation of West Greenland data displays a large and unexplained dispersion. We speculate on if this is related to different sense of block rotation of the Tertiary West Greenland constituents. Combining all data from the NAIP constituents, give a pole position at 75.0°N, 169.9°E (N = 25, K = 84.3, A₉₅ = 3.2) in Eurasian reference frame.     

Optimizing fixed observational assets in a coastal observatory

Proliferation of coastal observatories necessitates an objective approach to managing of observational assets. In this article, we used our experience in the coastal observatory for the Columbia River estuary and plume to identify and address common problems in managing of fixed observational assets, such as salinity, temperature, and water level sensors attached to pilings and moorings. Specifically, we addressed the following problems: assessing the quality of an existing array, adding stations to an existing array, removing stations from an existing array, validating an array design, and targeting of an array toward data assimilation or monitoring.     

Dynamic characteristics and horizontal transports of internal solitons generated at the Columbia River plume front

River plume front-generated internal solitons play an important role in the interaction between the plume and coastal waters. The internal solitons drive a non-harmonic velocity field, resulting in a horizontal transport that carries plume water seaward and redistributes nutrients and sediments. In this study, we present observations of internal solitons generated at the Columbia River plume front that separates the new, tidal plume, older plume and coastal waters. Scale analyses suggest that the plume front-generated internal solitons are highly non-linear waves, and their dynamic properties do not conform to any weakly non-linear theory. Thus, a high-order Korteweg–de Vries (KdV) theory is used to analyze the internal solitons. The comparison between theoretical values and cruise data shows that the high-order KdV model is much better than the weakly non-linear theories for prediction of the soliton dynamic parameters. Based on the model, we develop theoretical and numerical solutions of the soliton-induced upper layer horizontal transport and Lagrangian water parcel transport distance, which shows that the water particle drift, during the internal soliton passage, is as far as 1 km, and demonstrates the role of the internal solitons on the exchange between the plume and ambient coastal water. Energy fluxes caused by the internal solitons are estimated using the high-order KdV theory. The leading soliton fluxes 2.0×10³ W m⁻¹ per unit crest length, and carries energy of 4.2×10⁵ J m⁻¹. The total energy carried by the eight internal solitons is 1.6×10⁶ J m⁻¹, about 70% of the total frontal energy.     

扬子克拉通西缘1.73Ga非造山型花岗斑岩的发现及其地质意义

首次发现扬子克拉通西缘古元古代晚期海孜斜长花岗斑岩岩体.本文报道了其锆石的LA-ICP-MS U-Pb年龄,为1730±15Ma(MSWD=4.0,n=15).岩石具有高SiO2(69.77％～73.83％)、高碱(ALK=5.46～6.65)、低钾(K2O/Na2O=0.02～0.14)含量.里特曼指数1.04～1.65,A/CNK值为1.11～1.25,平均值为1.18(＞1.1),10000 Ga/Al=3.96～7.34(均值为5.18＞2.6),较高的含铁指数[FeO/(FeO+MgO) =0.95～0.99],总体显示了低钾钙碱性过铝质(SP)铁质A型花岗岩的特点.岩石富集Nb、Ta、Zr和Hf等高场强元素,强烈亏损K、Sr和Ba等大离子亲石元素,稀土元素总量∑REE=390.70×10-6～674.91×10-6,LREE/HREE=1.74～3.29(均值2.18),轻稀土分异作用明显,相对富集,表现出强烈的负Eu异常.地球化学特征显示,海孜花岗斑岩岩体为形成于板内伸展构造环境,可能与同期基性岩浆活动的底侵作用相关.海孜花岗岩的年龄和地球化学表明,扬子克拉通西缘存在古元古代晚期与全球性Columbia超级大陆裂解同期的双峰式岩浆岩组合.     

海南公爱地区抱板群花岗片麻岩的年代学、地球化学及其构造意义

海南岛地处华南陆块南缘,紧邻印支陆块,大地构造位置独特,其地质特征一直备受关注。厘定该地区中元古代岩石的成因对恢复华南中元古代构造演化具有重要意义。海南岛西部公爱地区花岗质岩石与围岩抱板群变沉积岩呈侵入接触关系,绝大部分岩石片麻状构造发育、韧性剪切标志明显。这些岩石高SiO_2、K_2O、Al_2O_3、Rb、U,贫CaO、MgO、FeO~T、TiO_2,铝饱和指数A/CNK1.1,具S型花岗岩特点,稀土元素配分模式类似于抱板群变沉积岩,全岩ε_(Nd)(t)=-2.02~-2.38,Nd同位素二阶段亏损模式年龄(t_(DM2)~(Nd))为2.2~2.3 Ga,锆石Hf同位素ε_(Hf)(t)=-5.4~4.0,Hf同位素二阶段亏损模式年龄t_(DM2)~(Hf)=1.71~2.53 Ga。对四个代表性花岗片麻岩样品进行LA-ICP-MS锆石U-Pb定年,其~(207)Pb/~(206)Pb加权平均年龄为1444±15 Ma、1439±19 Ma、1433±31 Ma和1450±23 Ma,属中元古代。综合区域研究资料认为,海南岛西部公爱地区中元古代花岗质岩石的熔融源区为类似抱板群变沉积岩组分,推测其产出于大陆边缘构造背景,是哥伦比亚超大陆边缘的增生产物。     

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.     

滇中禄丰地区中元古代早期球颗玄武岩的锆石U-Pb年龄、地球化学特征及其大地构造意义

在1∶5万区域地质调查的基础上,在禄丰地区东川群黑山组新发现了球颗玄武岩及凝灰岩夹层。采用LA-ICP-MS技术测得球颗玄武岩和凝灰质板岩中锆石U-Pb加权平均年龄分别为1678±10 Ma和1572±19 Ma,表明黑山组沉积时代为中元古代早期;其中球颗玄武岩SiO_2含量介于40.83%～52.56%,δEu正异常,大离子亲石元素Rb、Ba和高场强元素Nb、Ta、Th等强不相容元素相对富集,全岩地球化学显示为大陆板内低钛拉斑海相玄武岩,形成于伸展的构造环境,可能为Columbia超大陆裂解的产物。本次的发现,为准确地标定东川群时代、层序及大地构造属性提供新的参考依据,也为重塑整个滇中前寒武纪地层格架提供时代约束。     

Impact of katabatic winds on the environment of Neanderthals during the Middle Palaeolithic in westernmost Europe

Compilation of the offshore and onshore altitudinal limits of the loess deposits of western France and southern England shows that they were deposited by low-level wind fields. These relate to (i) the deflation of silt-rich sediment extracted from the outwash plains of the not far distant British–Irish Ice Sheet and from the palaeo-rivers of the Channel, and (ii) the existence of north and north-western palaeo-winds deduced from particle size analysis and heavy mineral distribution, and suggest (iii) that loess particles were transported by strong katabatic winds blowing from the northern ice-covered regions towards Brittany and Normandy. Comparison between the main orientation of Neanderthal shelters and the direction of the katabatic winds shows that they were perpendicular to each other. The dominant orientation of the shelters was apparently ruled by these winds. A small-scale study concentrating on the penultimate glaciation shows that in contrast to Brittany and Normandy where loess deposits accumulated on north-facing cliffs, in England the same particles were deposited on the leeside of the hills. The existence of deflation zones, violently swept by Marine Isotope Stage 6 katabatic winds south of the British–Irish ice sheet, was probably at the origin of the restricted number of Neanderthals at that time in England. © 2021 John Wiley & Sons, Ltd.     

Late Quaternary solifluction sheets in the British uplands

Solifluction sheets are large-scale and extensive valley-floor and valley-side landforms developed widely in the British Isles from mass-wasting of glacial and periglacial sediments during late-glacial times. We describe their geographical distribution and review the processes that have led to their development. We use data from the Cheviot Hills, the one site in the British Isles where sedimentology and optically stimulated luminescence dating have been combined, to assess their age and nature of deposition. We also present data from central Wales where a new mapping and resistivity survey has reconstructed the nature of valley-side solifluction sheets. We explore the relative lack of recent research on these landforms and argue that solifluction sheets represent a clear example of how upland geomorphological systems have responded to late-glacial climate change. We end by identifying a number of areas where research on these enigmatic features could be focussed, including better understanding of their distribution, sedimentology and age.     

Tree‐ring records unveil long‐term influence of the Pacific Decadal Oscillation on snowpack dynamics in the Stikine River basin,northern British Columbia

Long hydroclimate records are essential elements for the assessment and management of changing freshwater resources. These records are especially important in transboundary watersheds where international cooperation is required in the joint planning and management process of shared basins. Dendrochronological techniques were used to develop a multicentury record of April 1 snow water equivalent (SWE) for the Stikine River basin in northern British Columbia, Canada, from moisture‐sensitive white spruce (Picea glauca) tree rings. Explaining 43% of the instrumental SWE variability, to our knowledge, this research represents the first attempt to develop long‐term snowpack reconstructions in northern British Columbia. The results indicated that 15 extreme low April 1 SWE events occurred from 1789 to the beginning of the instrumental record in 1974. The reconstruction record also shows that the occurrence of hydrological extremes in the Stikine River basin is characterized by persistent below‐average periods in SWE consistent with phase shifts of the Pacific Decadal Oscillation (PDO). Spectral analyses indicate a very distinct in‐phase (positive) relationship between the multidecadal frequencies of variability (~40 years) extracted from the SWE tree‐ring reconstruction and other reconstructed winter and spring PDO indices. Comparison of the reconstructed SWE record with other tree‐ring‐derived PDO proxy records shows coherence at multidecadal frequencies of variability. The research has significant implications for regional watershed management by highlighting the hydrological response of the Stikine River basin to prior climate changes.