Statistical Models of the Seismicity of the Vrancea Region, Romania

A parameterization derived from the Weibull distribution is used to model the seismic activity of the Vrancea region.The analysis of 498 crustal earthquakes with local magnitudes greater than 2.0, and 1377 subcrustal events with local magnitudes greater than 2.5 emphasizes that the shallow sequences show a strong clustering tendency, while the intermediate depth mainshock sequences are modeled by a completely random pattern in space and time. These results are not influenced by the magnitude threshold and the width of the time window.The difference between the seismicity patterns in the crust and in the subcrustal zone correlates with the difference between the stress field within these two regions.     

Seismicity Variations in Depth and Time in the Vrancea (Romania) Subcrustal Region

Seismicity patterns that characterize the seismic regime of the Vrancea intermediate-depth earthquakes are investigated using an earthquake catalogue extending from 1974 to 1998. The analysis is made separately on two characteristic segments of the subducted plate (active zones) which hosted the major earthquakes of 4 March 1977, 30 August 1986 and 30 May 1990. Precursory anomalies preceding the occurrence of the major shock of 1986 (M_w = 7.3) in the lower part of the subducted slab are outlined when analyzing the time variation of the parameter (defined as the ratio of small to moderate events in a given active zone and a given time interval) and of the fractal dimension of the earthquake space distribution. Nothing similar is noticed in the upper part of the Vrancea slab. The analyzed time interval covering 25 years shows that, in contrast to previous studies, the statistical fluctuations of the parameter, computed for a time window of 5 months, appear to be too large to be considered as precursory anomalies. Significant differences among characteristic depth segments are also outlined in the frequency–magnitude distribution and are possibly related to differences in the physical mechanism of the earthquake generation process.     

Stratigraphic and structural characteristics of the Romanian Black Sea shelf

The Western Black Sea basin opened during Cretaceous times by back-arc rifting in association with a north dipping subduction at the rear of the Cretaceous–Early Tertiary Pontide volcanic arc. The sedimentary wedge developed on the shelf of the Romanian Black Sea sector reflects a complex interplay between large scale rifting, uplift of the orogenic flanks, large-scale post-rift subsidence and sea level changes. We examine the detailed structural configuration of this sector for a regional correlation with the adjacent offshore in Ukraine and Bulgaria. The evolution of the western Black Sea basin started in the Albian–Cenomanian times, when two extensional phases with significantly different directions (N–S and subsequently E–W) lead to the formation of a complex interplay between isolated blocks organised in horsts and grabens generally deepening eastwards. Superposition of normal faults footwall blocks from the two extensional episodes generated a deeply subsided area with enhanced accommodation space, i.e., the Histria Depression, and, consequently, recorded a larger thickness of Paleogene sediments in the post-rift stage. (Re)activation of faults and associated folding reflects repeated inversion during the Late Cretaceous–Oligocene times, associated with subsequent periods of non-deposition and/or erosion during moments of basin fill exposure. These periods of inversion recorded in the Black Sea are controlled by coeval orogenic deformations taking place in the Balkans, Pontides and the Crimean thrust belt. Sea level fluctuations during the Neogene and late Alpine tectonics in the neighbouring orogens caused massive sedimentation followed by sediment starvation and/or significant erosion. Large thicknesses of sediments accumulated during the Pontian, presumably associated with an extensional episode deepening the distal parts of the basin and with differential compaction structures. The interpretation of a high-quality seismic dataset combined with published data allowed the correlation of major structural units and lineaments defined onshore towards the Carpathians with the ones deeply buried below the western Black Sea basin sediments. Unit correlations are furthermore used to derive an integrated tectonic image of the western Black Sea area.     

Seismicity and the state of stress from investigations of local earthquakes in the Kumaon Himalaya

Results of investigations of local earthquakes in the region of the Main Central Thrust (MCT) in the Kumaon Himalaya, between and adjacent to the valleys of the Bhagirathi and Yamuna rivers, are presented. Records of over 250 earthquakes were analysed and the following facts emerged:

1. (1) Earthquakes in the Himalayas occur in specific areas and belts. One such belt has been identified in the region under investigation, hypocentral estimates being more reliable for earthquakes occurring in the middle segment approximately 70 km long of this belt, crossing the Yamuna river between the villages of Barkot and Syanachatti.

2. (2) All but a few epicentres in this middle segment, lie to the southwest of the surface trace of the MCT in a zone with a width of 10–30 km.

3. (3) Most of the earthquakes in this segment occur at depths of less than 10 km below the ground surface, the maximum estimated depth being 32 km.

Using observations of first motion for a composite focal mechanism solution, the nodal planes were observed to be near vertical and the compression axis near horizontal and normal to the local strike of the seismic belt and of the MCT.We conclude that although the Main Central Thrust itself is not seismically active in this region, there is considerable activity immediately to the southwest of it. Furthermore, the mode of faulting as inferred from the records of these earthquakes, is strike slip.     

Distribution of Seismicity and Heat Flow Anomalies in the Barents Sea Region

The contemporary seismicity and heat flow density are indicators of geodynamic processes. A unified seismic catalog is compiled for the European sector of the Arctic region for the period of 1995–2015 with the data on the spatial distribution of heat flow from different databases. The theoretically possible relationships of heat flow values and seismic activity manifestations are discussed for this region, and combined geological and geophysical cross sections of the structure of the lithosphere are made in the latitudinal and meridional directions. The most geodynamically active structures and zones of tectonic stress concentration are distinguished.     

Seismicity and velocity structures along the south-Alpine thrust front of the Venetian Alps (NE-Italy)

In this paper we show the seismicity and velocity structure of a segment of the Alpine retro-belt front along the continental collision margin of the Venetian Alps (NE Italy). Our goal is to gain insight on the buried structures and deep fault geometry in a “silent” area, i.e., an area with poor instrumental seismicity but high potential for future earthquakes, as indicated by historical earthquakes (1695 Me = 6.7 Asolo and 1936 Ms = 5.8 Bosco del Cansiglio). Local earthquakes recorded by a dense temporary seismic network are used to compute 3-D Vp and Vp/Vs tomographic images, yielding well resolved images of the upper crust underneath the south-Alpine front. We show the presence of two main distinct high Vp S-verging thrust units, the innermost coincides with the piedmont hill and the outermost is buried under a thick pile of sediments in the Po plain.Background seismicity and Vp/Vs anomalies, interpreted as cracked fluid-filled volumes, suggest that the NE portion of the outermost blind thrust and its oblique/lateral ramps may be a zone of high fluid pressure prone to future earthquakes.Three-dimensional focal mechanisms show compressive and transpressive solutions, in agreement with the tectonic setting, stress field maps and geodetic observations. The bulk of the microseismicity is clustered in two different areas, both in correspondence of inherited lateral ramps of the thrust system. Tomographic images highlight the influence of the paleogeographic setting in the tectonic style and seismic activity of the region.     

Evidence for variations of mechanical properties in the Friuli seismic area

Tidal strains of the earth were extracted from three horizontal strainmeter records (1979–1986) in the Friuli seismic area by the “filter method”. The areal strain factor, ignoring the tidal loading effects, shows that its time variation is significant: their amplitudes in 1986 are about 50% of those in 1979.

The modifications of mechanical properties, estimated in terms of the local shear and bulk modulus variations, were obtained considering the envelope of the tidal strain signals. The seismic wave velocity determined by the simultaneous inversion of the arrival time data of the local seismometric network displayed comparable changes.

A major change both in the seismic velocities and the elastic parameters started in March 1982, which was about 11 months before an earthquake of magnitude 4.1, the largest event from 1979 to 1986, which occurred within the seismic network on Feb. 10, 1983.     

Rockfall-Dammed Lakes in the Baikal Region: Evidence from the Past and Prospects for the Future

The mountain province of East Siberia, which includes the Baikal Rift system, is a zone of high tectonic and seismic hazard. Earthquakes and coseismic faulting are dangerous not only by themselves but also as far as they initiate rock collapse and downslope movement of unconsolidated deposits, which may block river valleys and produce rockfall-dammed lakes. Within some rifts of the rift system, evidence of past dammed lakes was discovered that arose instantly, in a geological sense, and flooded large areas of forest. In mountains around some rift basins, small living dammed lakes were encountered, as well as traces of catastrophic debris flows that may have accompanied breaching of earlier collapse-produced dams. Analysis of geomorphological setting in the region, especially in the Muya Rift Basin, revealed conditions favourable to hazardous origination of rockfall-dammed lakes. A large dammed lake may come into existence due to the collapse of bedrock over the narrow antecedent valley of Vitim in the Muya Rift. Preliminary estimates based upon data on the Vitim River discharge showed that the lake might form in as short as 27 days, though the rapidity of its formation, and hence the degree of the risk, can vary as a function of the highly variable amount of summer discharge of the river. Rockfall-dammed lakes may also originate in the floors of Chara and Tunka Rift Basins. Due to their rapid formation, lakes will bring about extensive flooding and cause danger to the taiga, railways and constructions in this populated developing area, and will cause degradation of the permafrost.     

Application of the Spatially Smoothed Seismicity and Monte Carlo Methods to Estimate the Seismic Hazard of Eritrea and the Surrounding Region

The region of interest is characterized by incomplete data sets and little information about the tectonic features. Therefore, two methodologies for estimating seismic hazard were used in order to elucidate the robustness of the results: the method of spatially smoothed seismicity introduced by Frankel (1995) and later extended by Lapajne et al. (1997) and a Monte Carlo approach presented by Ebel and Kafka (1999). In the first method, fault-rupture oriented elliptical Gaussian smoothing was performed to estimate future activity rates along the causative structures. Peak ground accelerations were computed for a grid size of 15 km × 415 km assuming the centre of the grids as epicentres, from which the seismic hazard map was produced. The attenuation relationship by Ambraseys et al. (1996) was found suitable for the region under study. PGA values for 10% probability of exceedence in 50 years (return period of 475 years) were computed for each model and a combined seismic hazard map was produced by subjectively assigning weights to each of these models. A worst-case map is also obtained by picking the highest value at each grid point from values of the four hazard maps. The Monte Carlo method is used to estimate seismic hazard, for comparison to the results from our previous approach. Results obtained from both methods are comparable except values in the first set of maps estimate greater hazard in areas of low seismicity. Both maps indicate a higher hazard along the main tectonic features of the east African and Red Sea rift systems. Within Eritrea, the highest PGA exceeded a value 25% of g, located north of Red Sea port of Massawa. In areas around the capital, Asmara, PGA values exceed 10% of g.     

Holocene activity of the Scilla Fault, Southern Calabria: Insights from coastal morphological and structural investigations

Integration of on-land and offshore geomorphological and structural investigations coupled to extensive radiometric dating of co-seismically uplifted Holocene beaches allows characterization of the geometry, kinematics and seismotectonics of the Scilla Fault, which borders the eastern side of the Messina Strait in Calabria, Southern Italy. This region has been struck by destructive historical earthquakes, but knowledge of geologically-based source parameters for active faults is relatively poor, particularly for those running mostly offshore, as the Scilla Fault does. The  30 km-long normal fault may be divided into three segments of  10 km individual length, with the central and southern segments split in at least two strands. The central and northern segments are submerged, and in this area marine geophysical data indicate a youthful morphology and locally evidence for active faulting. The on-land strand of the western segment displaces marine terraces of the last interglacial (124 to 83 ka), but seismic reflection profiles suggest a full Quaternary activity. Structural data collected on bedrock faults exposed along the on-land segment provide evidence for normal slip and  NW-SE extension, which is consistent with focal mechanisms of large earthquakes and GPS velocity fields in the region. Detailed mapping of raised Holocene marine deposits exposed at the coastline straddling of the northern and central segments supplies evidence for two co-seismic displacements at  1.9 and  3.5 ka, and a possible previous event at  5 ka. Co-seismic displacements show a consistent site value and pattern of along-strike variation, suggestive of characteristic-type behaviour for the fault. The  1.5–2.0 m average co-seismic slips during these events document M_e  6.9–7.0 earthquakes with  1.6–1.7 ka recurrence time. Because hanging-wall subsidence cannot be included into slip magnitude computation, these slips reflect footwall uplift, and represent minimum average estimates. The palaeoseismological record based on the palaeo-shorelines suggests that the last rupture on the Scilla Fault during the February 6, 1783 M_w = 5.9–6.3 earthquake was at the expected time but it may have not entirely released the loaded stress since the last great event at  1.9 ka. Comparison of the estimated co-seismic extension rate based on the Holocene shoreline record with available GPS velocities indicates that the Scilla Fault accounts for at least  15–20% of the contemporary geodetic extension across the Messina Strait.     

天水盆地新近纪伸展构造——来自沉积与构造变形方面的证据

天水盆地位于青藏高原东北缘高海拔挤压隆升区与鄂尔多斯低海拔伸展区的过渡部位,新构造活动强烈。然而,新构造活动对天水盆地的影响尚不清楚。通过对盆地的沉积环境、构造沉降、构造变形等方面的研究,结果显示:1盆地由风成堆积、洪积扇、河湖相与湖泊相沉积组成,代表沉积中心的河湖相与湖泊相沿控盆断裂(西秦岭北缘断裂、西和断裂与礼县-罗家堡断裂)分布;2盆地经历了16~14Ma、9.2~7.4Ma和3.6~2.6Ma三次加速沉降期;3控盆断裂在同沉积期为正断层。沉积中心沿断裂分布、快速沉降事件及生长正断层表明,天水盆地至少在中新世晚期受控于走滑伸展构造,记录了青藏高原向北东方向的构造挤出作用。     

Nephelines from the Somma-Vesuvius volcanic complex (Southern Italy): crystal-chemical,structural and genetic investigations

Sixteen nephelines from different geological occurrences were sampled at the type-locality, the Somma-Vesuvius volcanic complex (southern Italy), and investigated for their chemistry and crystal structure obtained by both single-crystal and powder X-ray diffraction. Nepheline-bearing samples are metamorphic or from magmatic ejecta and pumice deposits. The lower K contents characterize the pumice- and some metamorphic-derived nephelines, whereas the higher ones are found in some samples from magmatic nodules. The amount of the anorthite molecule, quite low on average, can be more variable in the metamorphic nephelines. The crystal-structure investigations on Somma-Vesuvius samples compare well with previous studies of natural nephelines. All 16 nepheline samples adopt space group P6₃. The observed lattice parameters vary between 9.9768–9.9946 Å (for a) and 8.3614–8.3777 Å (for c), respectively. Furthermore, chemical analysis revealed that all specimens exhibit an excess of Si relative the ideal Si:Al ratio of 1:1. The analysis of the T-O distances in our samples clearly indicates a distinct ordering process of aluminium and silicon on the tetrahedral sites which is an agreement with Loewenstein’s rule. A linear correlation between the distance of symmetry equivalent split atoms O(1)-O(1)’ and the T(1)-O(1)-T(2) tilt angle was observed. The average <B-O> (B = Na) distances of all crystals are very similar which is consistent with the outcome of the site population refinement indicating full occupancy with sodium. Oriented precession-type sections of reciprocal space indicated the presence of at least the most intense family of satellite peaks, demonstrating that this group of satellite reflections can occur not only in nephelines from pegmatites and ijolites but also in rocks from completely different petrological settings.     

Temporal and spatial variations in density and velocity fields of the waters of Gareloch,Scotland

 Spatial variations in the density and velocity fields have been observed in the Gareloch (Scotland) during surveys in 1987–1988 and 1993–1994. The variation of the density field has been analyzed on a variety of time scales from semidiurnal to seasonal in order to quantify effects caused by the forcing factors of tidal mixing, freshwater input, and wind. Initial results indicate that water density in the loch is controlled (to a major degree) by the freshwater input from runoff from the local catchment area and from freshwater entering on the flood tide from the Clyde Estuary. It is estimated that during winter periods the high freshwater flows from the rivers Leven and Clyde into the Clyde Estuary account for up to 75% of the freshwater creating the density structure in the loch. Analysis of long-term dissolved oxygen data reveals that major bottom water renewals occurred between July and January in the years 1987–1994. Major bottom water dissolved oxygen renewals have a general trend but during the year sporadic renewals can take place due to abnormal dry spells increasing the density of the water entering from the Clyde, or consistently strong winds from the north reducing stratification in the loch and producing better mixed conditions. Velocities vary spatially, with the highest velocities of up to 0.6 m s^–1 being associated with the velocity jet effect at the constriction at the sill of the loch. Observed near-surface mid-loch velocities increased as the vertical density gradients in the upper layers increased. This indicates for the observed conditions that increased stratification in the upper layers inhibits the entrainment rate and hence rate of gain of thickness of the wind-driven surface layer, resulting in increased surface velocities for a given wind speed and direction. The main flow is concentrated in the upper 10 m and velocities below 10 m are low. Observed mean spring tide surface velocities are on average 30% greater than mean neap tide surface velocities. Received: 22 May 1995 · Accepted: 23 August 1995     

从华北克拉通中、西部结构的区域差异性探讨克拉通破坏

详细的深部结构信息是深入认识华北克拉通显生宙改造和破坏的重要依据。基于密集流动地震台阵和固定台网记录的远震P波和S波接收函数资料,获得了跨越华北克拉通东、中、西部的3条剖面的岩石圈和上地幔结构图像,揭示了克拉通不同区域深部结构特征的显著差异。与东部普遍减薄的岩石圈(60～100km)相比,中、西部表现出厚、薄岩石圈共存的强烈横向非均匀性,既在稳定的鄂尔多斯盆地之下保留着厚达200km的岩石圈,又在新生代银川—河套和陕西—山西裂陷区存在厚度<100km的薄岩石圈,差异最大的厚、薄岩石圈仅相距约200km。岩石圈厚度在东、中部边界附近的约100km横向范围内显示出20～40km的迅速增加。岩石圈厚度的快速变化与地表地形从东向西的突然改变以及南北重力梯度带的位置大致吻合,并对应于地壳结构、地幔转换带厚度和660km间断面结构的快速变化。这种从地表到上地幔底部深、浅结构的耦合变化特征表明,东西两侧区域在显生宙可能经历了不同的岩石圈构造演化和深部地幔动力学过程。克拉通东部薄的地壳、岩石圈和厚的地幔转换带以及复杂的660km间断面结构可能与中生代以来太平洋板块深俯冲及其相关过程对这一地区岩石圈的改造和破坏有关;而中、西部存在显著减薄的岩石圈这一观测结果,并结合岩石、地球化学资料表明,克拉通岩石圈改造和减薄不仅发生在东部,而且可能影响了包括中、西部在内的更广泛的区域。岩石圈薄于100km的中、西部裂陷区可能与先前存在于岩石圈中的局部构造薄弱带相联系。这些古老岩石圈薄弱带可能经历了后期构造事件的多次改造,并在新生代印度—欧亚陆陆碰撞过程中被进一步弱化、减薄,最终造成地表裂陷。另一方面,中、西部总体较厚的地壳、岩石圈以及正常偏薄的地幔转换带表明,同太平洋深俯冲对东部的作用相比,包括印度—欧亚大陆碰撞在内的多期热-构造事件对该地区的构造演化影响相对较弱,不足以大范围改造和破坏高强度的克拉通岩石圈地幔根,从而造成了该地区现今岩石圈结构的高度横向不均匀。     

Sheet silicates of the Lawler Peak granite,Arizona: chemistry,structural variations,and exsolution

Coarse-grained muscovite, biotite, and chlorite from the Lawler Peak granite, Yavapai County, Arizona, have been studied with electron microprobe analysis, powder X-ray diffraction, transmission electron microscopy (TEM), electron diffraction, and analytical TEM methods. All three sheet silicates exhibit multiple polytypes and an abundance of stacking faults and dislocations. Chlorite formed by subsolidus replacement of biotite. Muscovite also may have formed by replacement of biotite and other minerals, but there is no clear microstructural evidence to support either a primary or secondary origin for the coarse-grained muscovite. X-ray and electron diffraction reveal that the muscovite consists of two separate phases, which give rise to splitting of diffraction maxima. TEM experiments suggest that the two components resulted from exsolution, which produced two symmetry-related sets of irrationally oriented lamellae with a wavelength averaging about 10 nm. Exsolution occurred in both 1M and 2M₁ muscovite. Although the lamellae are too small to analyze directly, the muscovite bulk composition and structural data are consistent with the separation of celadonitic and muscovite components.     

Theoretical investigations of the spin Hamiltonian parameters and local angular variations for the trigonal V3+ centers in alum compounds

The spin Hamiltonian parameters (zero-field splittings D, g factors g _// and g _⊥) for V³⁺ in the alum compounds are theoretically studied using the perturbation formulas for these parameters for a 3d² ion in the trigonally distorted octahedra. The contributions from the dynamical Jahn–Teller effect, the configuration interactions and the ligand orbital and spin–orbit coupling interactions are considered from the cluster approach in a uniform way. The angles in the deformed octahedra around V³⁺ ions are increased by 1.1°–2.7°, as compared with those ones for the host. The theoretical spin Hamiltonian parameters based on the above angular variations and the related effects show good agreement with the experimental data, which reveal that these effects (especially the Jahn–Teller effect) can bring forward significant influences on the spin Hamiltonian parameters, and should be taken into account in electron paramagnetic resonance (EPR) analysis. The contributions from the configuration interactions and the ligand orbital and spin–orbit coupling interactions are quantitatively involved from the cluster approach in a uniform way. The results are discussed.     

印度与欧亚两大陆块碰撞时间的厘定:来自锆石SHRIMP U-Pb年龄的证据

通麦地区片麻岩中锆石SHRIMP定年结果表明:①变质锫石和变质复合锆石的新壳U-Pb年龄为42 Ma,属于中始新世.相当于陆陆碰撞的峰期时间,而印度和欧亚两个大陆开始碰撞的时间略早于42 Ma;②变质复合锫石中的老核(继承锆石),有2个点U-Pb年龄为201 Ma,相当于早侏罗世早期,表明通麦片麻岩是沉积岩变质的,其沉积岩的时代不会早于三叠纪;③文章最后对锆石成因类型及意义、片麻岩的时代和印度与欧亚两大陆碰撞的时间等问题进行了讨论.     

Evidence for structural repetition in the greenstones of the Kalgoorlie district,Western Australia

Regional mapping and air-photographic interpretation of an area of about 20 000 km² centred on Kalgoorlie provided compelling evidence that some previously published polycyclic stratigraphies cannot be substantiated. Large areas of rocks formerly proposed as younger cycles represent repetition, mainly by faulting, of a somewhat simpler stratigraphic sequence. The main lines of support are: (1) the similarity of older and younger mafic-ultramafic successions, (2) the tendency of ‘younger’ sequences to merge with ‘older’ ones when traced along strike, and (3) the abundant evidence of faulting along critical contacts. The subtle concordant nature of some of the faulting is consistent with an origin by thrusting at an early stage in the tectonic history, especially where repeat sequences are folded around major upright structures. Later reactivation of sheared contacts, and initiation of new ones during upright folding and faulting, and transcurrent shearing, is believed to have widely occurred. Gravitational gliding is proposed as a possible mechanism for thrust generation, this being consistent with evidence of earlier instability in the sedimentation style of turbidites, debris flows and olistostromes, however, conclusive evidence of a mechanism is lacking due to incomplete field evidence. The repetition is viewed as a rearrangement of recognisable elements of the local stratigraphy, rather than the result of a major collisional event at a plate margin. This tends to favour an intracratonic rather than an oceanic setting for the local greenstones, though the characteristic geological features of modern continental rifts have not been observed.     

Observations of Li isotopic variations in the Trinity Ophiolite: Evidence for isotopic fractionation by diffusion during mantle melting

The Trinity peridotite (northern CA) contains numerous lithologic sequences consisting of dunite to harzburgite to spinel lherzolite to plagioclase lherzolite. Previous workers have documented geochemical gradients in these sequences consistent with melt-rock reaction processes occurring around dunites, interpreted to reflect conduits for melt ascent. We have undertaken a study of Li isotope compositions of clinopyroxene and some olivine within these sequences using ion probe techniques to test the hypothesis that the geochemical gradients are related to diffusive fluxing of alkali elements into or away from the melt conduit.Results show large variations in ⁷Li/⁶Li occurring in a consistent pattern across three transects from dunite to plagioclase lherzolite within the Trinity peridotite. Specifically, measurements of average δ⁷Li for single thin sections along the traverse reveal a low in δ⁷Li in the harzburgite adjacent to the dunite returning to higher values farther from the dunite with a typical offset of ∼10 per mil in the low δ⁷Li trough. This pattern is consistent with a process whereby Li isotopes are fractionated during diffusion through a melt either from the dunite conduit to the surrounding peridotite, or from the surrounding peridotite into the dunite conduit. The patterns in ⁷Li/⁶Li occur over a length scale similar to the decrease in REE concentration in these same samples. Explaining both the trace element and Li isotopic gradients requires a combined process of alkali diffusion and melt extraction.We develop a numerical model and examine several scenarios of the combined diffusion-extraction process. Using experimentally constrained values for the change in Li diffusion coefficient with isotope mass, large changes in δ⁷Li as a function of distance can be created in year to decade timescales. The addition of the melt extraction term allows larger Li concentration gradients to be developed and thus produces larger isotopic fractionations than diffusion only models. The extraction aspect of the model can also account for the observed decrease in rare earth element concentrations across the transects.