Stress amplification in the upper crust and the development of normal faulting

Finite element analysis of lithosphere deformation, incorporating failure criteria based on the Modified Griffith Theory for an elastic upper crust and a visco-elastic rheology for the lower crust and lithospheric mantle, demonstrates that normal faulting as a result of comparatively small, horizontal tensile stresses acting throughout the lithosphere can occur by the phenomenon of stress amplification. The use of a simple, Newtonian viscosity or of power law creep for the visco-elastic material does not significantly change the results. The time to failure is dependent upon the magnitude of the applied stress and the effective viscosity of the underlying material. For an applied stress of 20 MPa and a constant viscosity of 10²³ Pa s failure is predicted after 1.19 Ma, with a fault plane hade of about 30°. A decrease of one order of magnitude in the viscosity of the lower crust results in a slightly shorter time to failure whereas an increase of one order of magnitude results in a very much greater failure time.     

The origin of tectonic stress in the lithosphere

The sources of lithospheric stress and their distinctive features are briefly reviewed. It is suggested that there are two main categories of lithospheric stress: renewable stress which persists despite continuing stress relaxation and non-renewable stress which can be dissipated by relief of the initial strain. The two most important types of renewable stress arise from plate boundary forces and from isostatically compensated loads. Non-renewable stress systems include bending stresses, membrane stresses and thermal stresses. An important phenomenon generating large stresses at shallow depth is stress amplification caused by lower lithospheric creep. This applies to renewable stresses but not to the non-renewable type. It is suggested that only renewable stresses contribute significantly to tectonic activity. However, bending and thermal stresses are locally important in subducting lithosphere.     

Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in ¹¹B relative to ¹⁰B (δ¹¹B = −1.2 to +7.7) and ⁷Li relative to ⁶Li (δ⁷Li = −1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (δ¹¹B = −16.6 to −2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle.     

Did hot,high heat-producing granites determine the location of the Oslo Rift?

The Late Carboniferous–Early Permian Oslo Rift formed in apparently cold, stable lithosphere of the Fennoscandian Shield in a tensional stress regime widely documented in Northwest Europe at that time. The Rift formed obliquely to older, crustal structures that display only limited Permian reactivation, and, although numerical modelling suggests that the present-day lithospheric structure would serve to focus tensional stresses in the Oslo region, the assumption that no lithospheric evolution has occurred since the Palaeozoic is by no means obvious. Here, I show that, up to 5 km thick, regional-scale Late- to Post-Sveconorwegian granites in the vicinity of the Oslo Rift, with heat-production rates averaging ca. 5 μW/m³, nearly three times higher than the surrounding Sveconorwegian gneisses, would have increased the temperature in the lower crust and lithospheric mantle by up to 100 °C, resulting in significant thermal weakening of the lithosphere in this area. Given a tensional stress regime, weakening by these high heat-producing element granites would have made the Oslo area a favoured site for passive rifting and may have been a first-order parameter locating rifting to this part of the Fennoscandian Shield. The thermo-rheological effects of such granites must be considered along with other factors in future models of initial rift mechanisms in the Oslo Rift, and probably in other rifts elsewhere.     

Global 1° × 1° thermal model TC1 for the continental lithosphere: Implications for lithosphere secular evolution

This paper reports a new 1° × 1° global thermal model for the continental lithosphere (TC1). Geotherms for continental terranes of different ages (> 3.6 Ga to present) constrained by reliable data on borehole heat flow measurements (Artemieva, I.M., Mooney, W.D. 2001. Thermal structure and evolution of Precambrian lithosphere: a global study. J. Geophys. Res 106, 16387–16414.), are statistically analyzed as a function of age and are used to estimate lithospheric temperatures in continental regions with no or low-quality heat flow data (ca. 60% of the continents). These data are supplemented by cratonic geotherms based on electromagnetic and xenolith data; the latter indicate the existence of Archean cratons with two characteristic thicknesses, ca. 200 and > 250 km. A map of tectono-thermal ages of lithospheric terranes complied for the continents on a 1° × 1° grid and combined with the statistical age relationship of continental geotherms (z = 0.04  t + 93.6, where z is lithospheric thermal thickness in km and t is age in Ma) formed the basis for a new global thermal model of the continental lithosphere (TC1). The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continental upper mantle, with the strongest lateral temperature variations (as large as 800 °C) in the shallow mantle. A map of the depth to a 550 °C isotherm (Curie isotherm for magnetite) in continental upper mantle is presented as a proxy to the thickness of the magnetic crust; the same map provides a rough estimate of elastic thickness of old (> 200 Ma) continental lithosphere, in which flexural rigidity is dominated by olivine rheology of the mantle.Statistical analysis of continental geotherms reveals that thick (> 250 km) lithosphere is restricted solely to young Archean terranes (3.0–2.6 Ga), while in old Archean cratons (3.6–3.0 Ga) lithospheric roots do not extend deeper than 200–220 km. It is proposed that the former were formed by tectonic stacking and underplating during paleocollision of continental nuclei; it is likely that such exceptionally thick lithospheric roots have a limited lateral extent and are restricted to paleoterrane boundaries. This conclusion is supported by an analysis of the growth rate of the lithosphere since the Archean, which does not reveal a peak in lithospheric volume at 2.7–2.6 Ga as expected from growth curves for juvenile crust.A pronounced peak in the rate of lithospheric growth (10–18 km³/year) at 2.1–1.7 Ga (as compared to 5–8 km³/year in the Archean) well correlates with a peak in the growth of juvenile crust and with a consequent global extraction of massif-type anorthosites. It is proposed that large-scale variations in lithospheric thickness at cratonic margins and at paleoterrane boundaries controlled anorogenic magmatism. In particular, mid-Proterozoic anorogenic magmatism at the cratonic margins was caused by edge-driven convection triggered by a fast growth of the lithospheric mantle at 2.1–1.7 Ga. Belts of anorogenic magmatism within cratonic interiors can be caused by a deflection of mantle heat by a locally thickened lithosphere at paleosutures and, thus, can be surface manifestations of exceptionally thick lithospheric roots. The present volume of continental lithosphere as estimated from the new global map of lithospheric thermal thickness is 27.8 (± 7.0) × 10⁹ km³ (excluding submerged terranes with continental crust); preserved continental crust comprises ca. 7.7 × 10⁹ km³. About 50% of the present continental lithosphere existed by 1.8 Ga.     

Geodynamic controls on diamond deposits: Implications for Australian occurrences

Conventional diamond exploration guidelines predict that economic diamond occurrences will be restricted to Archaean cratons, where the lithosphere is thick and cool, and diamond is the stable form of carbon in the lower portions of the lithosphere. However, Australia's current economic diamond deposits are not well predicted by these conventional exploration guidelines. Tomographic images show that Australia's economic diamond deposits lie at step changes in lithospheric thickness within dominantly cratonized Proterozoic provinces with thick (≥ 200 km) lithosphere. The thickest portions of the seismic lithosphere in Australia occur not under the major Archaean cratons, rather the central Proterozoic regions of the continent. We use a numerical code to show that such features are stable, and that the longevity of the diamond stability field is dependent on distance to the continent–ocean boundary, local depth of the chemical boundary layer (CBL), and proximity to changes in CBL depth. We also show that abrupt changes in lithospheric thickness focus lithospheric stress gradients, affecting melt migration paths, and that continental melt production is enhanced in regions adjacent to major cratons. Diamond pipes occur where conditions conducive to diamond stability and deep-seated alkaline volcanism (kimberlite or lamproite) occur simultaneously, and the common confluence of these factors at abrupt changes in lithospheric thickness marks them as potential exploration targets.     

Effects of buoyancy and mechanical layering on collisional deformation of continental lithosphere: Results from physical modeling

We use two suites of lithospheric-scale physical experiments to investigate the manner in which deformation of the continental lithosphere is affected by both (1) variations of lithospheric density (quantified by the net buoyant mass per area in the lithospheric mantle layer, M_B), and (2) the degree of coupling between the crust and lithospheric mantle (characterized by a modified Ampferer ratio, Am). The dynamics of the experiments can be characterized with a Rayleigh–Taylor type ratio, _CLM. Models with a positively buoyant lithospheric mantle layer (M_B > 0 and _CLM > 0) result in distributed root formation and a wide deformation belt. In contrast, models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust (M_B < 0, 0 > _CLM > ≈ − 0.2, and Am > ≈ 10^{− 3}) exhibit localized roots and narrow deformation belts. Syncollisional delamination of the model lithospheric mantle layer and a wide deformation belt is exhibited in models with negatively buoyant lithospheric mantle layers weakly coupled to the crust (M_B < 0, _CLM < 0, and Am < ≈ 10^{− 3}). Syncollisional delamination of the continental lithosphere may initiate due to buoyancy contrasts within the continental plate, instead of resulting from wedging by the opposing plate. Rayleigh–Taylor instabilities dominate the style of deformation in models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust and a slow convergence rate (M_B < 0 and _CLM > ≈ − 0.2). The degree of coupling (Am) between the model crust and lithospheric mantle plays a lesser role in both the style of lower-lithospheric deformation and the width of the crustal deformed zone with increasing density of the lithospheric mantle layer.     

大陆地区构造活动、地热及地壳-上地幔结构之间关系的探讨

随着板块构造学说的兴起和发展,对大洋地区构造活动、地热及地壳-上地幔结构之间的关系已有了较为明确的认识。在大陆地区,由于其构造发展历史的复杂性,对这种关系的认识还远没有大洋区那样系统和清晰。但近二十年来,大陆地区各种地球物理资料的大量积累已为进行这种研究提供了较为坚实的基础。     

Geochemistry of the Cenozoic Potassic Volcanic Rocks in the West Kunlun Mountains and Constraints on Their Sources

The geochemical characteristics of the Cenozoic volcanic rocks from the north Pulu, east Pulu and Dahongliutan regions in the west Kunlun Mountains are somewhat similar as a whole. However, the volcanic rocks from the Dahongliutan region in the south belt are geochemically distinguished from those in the Pulu region (including the north and east Pulu) of the north belt. The volcanic rocks of the Dahongliutan region are characterized by relatively low TiO2 abundance, but more enrichment in alkali, much more enrichment in light rare earth elements and large ion lithosphile elements than those from the Pulu region. Compared with the Pulu region, volcanic rocks from the Dahongliutan region have relatively low 87Sr/86Sr ratios, and high εNd, 207Pb/204Pb and 208Pb/204Pb. Their trace elements and isotopic data suggest that they were derived from lithospheric mantle, consisting of biotite- and hornblende-bearing garnet lherzolite, which had undertaken metasomatism and enrichment. On the primitive mantle-normali     

Normal faulting and flexure in an elastic-perfectly plastic plate

An elastic-perfectly plastic plate model has been developed to analyze the flexure associated with normal faulting. The model consists of a thin layer, which is completely cut by a normal fault, overlying a fluid substratum. For a given applied bending moment at the fault, the relationship between the amount of displacement on the fault and the extent of the failure zone can be calculated. The model is applied to the Wasatch Front region in the eastern Basin and Range Province, USA to determine the correlation of its parameters with geological and geophysical data in the vicinity of a major normal fault, the Wasatch fault, along which there has been 3–4 km of Late Cenozoic uplift. In this region, most seismic activity occurs away from the Wasatch fault in a zone 30 km wide, roughly centered 30 km east of the fault. This activity occurs at depths of 15 km or less. In order to match the observations, the lithospheric layer must have a flexural rigidity of 0.5 to 1.1 · 10²² n-m and a yield stress of 1–2 kb and must have zero applied bending moment at the fault. The effective mechanical thickness of the lithosphere in this region is 20–25 km. These results indicate that the lithosphere in long-term mechanical studies in the eastern Basin and Range is thin and weak. Evaluating these results as compared to the seismic lithospheric thickness and temperature regime of the region produces some interesting correlations with studies in oceanic regions.     

Rheological thickness and strength of the Indian continental lithosphere

The estimates of rheological thickness and total lithospheric strength for the Indian continental lithosphere have been obtained based on the representative rheological properties of upper crust, lower crust and upper mantle, and some of the available heat flow and heat generation data. The rheological thickness, computed at different locations in the Indian shield, shows lateral variation ranging from 79km in the southern part to 65 km in the northern part for a strain rate of 10^-14 s^-1. The total strength of the continental lithosphere is of the order of 10¹³ Nm^-1 for the same value of strain rate and decreases northward. The computations carried out for a range of strain rates show an increase in the rheological thickness and strength of the lithosphere with increasing strain rate. These results would be important in understanding the flexural response of the Indian continental lithosphere to surface and subsurface loading, and response to tectonic forces acting on it.     

Small-volume melts of lithospheric mantle during continental collision: Late Cenozoic lavas of Mahabad,NW Iran

Basanites and alkali basalts from Mahabad in the West Azerbaijan province of Iran are part of a widespread series of Late Miocene–Quaternary mantle-derived magmas erupted within the Turkish–Iranian orogenic plateau, itself part of the active Arabia–Eurasia collision zone. New elemental and Sr–Nd isotopic results are combined with geophysical and geological constraints to suggest that these lavas formed predominantly by small degrees of partial melting of the thick (≫100 km) Eurasian lithospheric mantle within the garnet facies. Samples are highly enriched in large ion lithophile elements (LILE) and the light rare earth elements (LREE), up to 600 times chondritic values. They mostly possess negative primitive mantle-normalised Rb, K, Nb–Ta, Zr–Hf and Ti anomalies, with an overall signature that indicates a mantle source metasomatised by fluids or melts derived from crust during continental collision or the Tethyan oceanic subduction that preceded it. Sr–Nd isotopic values are similar to other Quaternary centres in NW Iran; ⁸⁷Sr/⁸⁶Sr is slightly depleted with respect to Bulk Silicate Earth, at ∼0.7045, and ¹⁴³Nd/¹⁴⁴Nd is slightly enriched, at ∼0.5127. Crustal contamination does not appear to be an important process in the chemistry of these samples. Possible triggers for melting may include: breakdown of hydrous phases during lithospheric thickening; hydration of the mantle lithosphere by underthrusting of the Arabian passive margin; small-scale sub-lithospheric convection due to a significant thickness gradient in the Zagros lithosphere. Such processes may account for small-volume syn-collisional mantle-derived magmatism elsewhere in regions of thick lithosphere where recent slab break-off or lithospheric delamination cannot be proven.     

Asymmetric dynamics at subduction zones derived from plate kinematic constraints

The lithospheric sinking along subduction zones is part of the mantle convection. Therefore, computing the volume of lithosphere recycled within the mantle by subducting slabs quantifies the equivalent amount of mantle that should be displaced, for the mass conservation criterion. The rate of subduction is constrained by the convergence rate between upper and lower plates and the motion of the subduction hinge H that may either converge or diverge relative to the upper plate. Here, starting from the analysis of the slab hinge kinematics, we evaluate the subduction rate at 31 subduction zones worldwide, useful to compute volumes of sinking lithosphere into the mantle. Our results show that ∼190 km³/yr and ∼88 km³/yr of lithospheric slabs are currently subducting below H-divergent and H-convergent subduction zones, respectively. We also propose supporting numerical models providing asymmetric volumes of the subducted lithosphere, using the subduction rate instead of plate convergence, as boundary condition. Furthermore, H-divergent subduction zones appear to be coincident with subductions having “westward”-directed slabs, whereas H-convergent subduction zones are mostly compatible with those that have “eastward-to-northeastward”-directed slabs. On the basis of this geographical polarity, our lithospheric volume estimation gives ∼214 km³/yr and ∼88 km³/yr of subducting lithosphere, respectively. This entails that W-directed subduction zones contribute more than twice in lithospheric sinking into the mantle with respect to E-to-NE-directed ones. In accordance with the conservation of mass principle, this volumetric asymmetry in the mantle suggests a displacement of ∼120 km³/yr of mantle material from west to east, providing a constraint for global asymmetric mantle convection.     

中国大陆岩石圈厚度分布研究

利用不同物理性质所估计的岩石圈厚度可能具有不同的地球动力学意义。大陆岩石圈等效弹性厚度往往只与岩石圈内部的某些岩层相关,因此它可能不代表一般意义上的岩石圈厚度。地震学岩石圈厚度虽然有较高的精度,但依赖于人为地对岩石圈的定义;并且其具有的短时间尺度效应决定了它与长时间尺度的岩石圈概念不一致。热学岩石圈厚度体现了长时间尺度上的岩石圈热学作用,因此其厚度定义的标准是较合理的。地震-热学岩石圈厚度研究利用地震波速反演得到的温度数据按照热学岩石圈标准来对岩石圈厚度进行研究,具有地震学和热学岩石圈厚度两者的优点,是较合理的对岩石圈厚度的估计。中国大陆地震-热学岩石圈厚度分布有如下特点:(1)中国东部岩石圈较薄,厚度约100 km,其中包括中国东北、中朝克拉通、扬子克拉通东部和华南造山带;(2)青藏高原和塔里木克拉通以南地区的厚度变化较大,厚度约在160~220 km;(3)三大克拉通的岩石圈厚度有较大区别,扬子克拉通的核心最厚达约170 km,塔里木克拉通的核心厚度约140 km,中朝克拉通的厚度约100 km;(4)昆仑秦岭造山带的岩石圈上地幔内部较复杂,可能有大面积的部分熔融;(5)整个大陆岩石圈厚度分布并没有显示出与地壳年龄的线性相关关系,却表现出了与大地构造格局的直接关系。受板块碰撞强烈影响的地区,岩石圈较厚;受大洋俯冲带影响较强的地区,岩石圈较薄。     

On the role of heat flow, lithosphere thickness and lithosphere density on gravitational potential stresses

Gravitational potential stresses (GPSt) are known to play a first-order role in the state of stress of the Earth's lithosphere. Previous studies focussed mainly on crust elevation and structure and little attention has been paid to modelling GPSt using realistic lithospheric structures. The aim of the present contribution is to quantify gravitational potential energies and stresses associated with stable lithospheric domains. In order to model realistic lithosphere structures, a wide variety of data are considered: surface heat flow, chemical depletion of mantle lithosphere, crustal thickness and elevation. A numerical method is presented which involves classical steady-state heat equations to derive lithosphere thickness, geotherm and density distribution, but additionally requires the studied lithosphere to be isostatically compensated at its base. The impact of varying surface and crustal heat flow, topography, Moho depth and crust density on the signs and magnitudes of predicted GPSt is systematically explored. In clear contrast with what is assumed in most previous studies, modelling results show that the density structure of the mantle lithosphere has a significant impact on the value of the predicted GPSt, in particular in the case of thick lithospheres. Using independent information from the literature, the method was applied to get insights in the state of stress of continental domains with contrasting tectono-thermal ages. The modelling results suggest that in the absence of tectonic stresses Phanerozoic and Proterozoic lithospheres are spontaneously submitted to compression whereas Archean lithospheres are in a neutral to slightly tensile stress state. These findings are in general in good agreement with global stress measurements and observed geoid undulations.     

Secular evolution of the lithosphere beneath the eastern North China Craton: evidence from Mesozoic basalts and high-Mg andesites

Geochemical and isotopic data from Mesozoic lavas from the Jianguo, Niutoushan, Wulahada, and Guancaishan volcanic fields on the northern margin of the North China Craton provide evidence for secular lithospheric evolution of the region. Jianguo lavas are alkaline basalts with LILE- and LREE-enrichment ((La/Yb)_N=12.2-13.2) and MORB-like Sr-Nd-Pb isotopic ratios ((⁸⁷Sr/⁸⁶Sr)_i<0.704; ε_Nd=3.9-4.8; (²⁰⁶Pb/²⁰⁴Pb)_i≈18). Niutoushan basalts are similar but show evidence of olivine fractionation. Wulahada lavas are high-Mg andesites (Mg#∼67) with EM1 Sr-Nd-Pb isotopic signatures. Geochemical data suggest that the basalts originated from MORB-type asthenosphere whereas the high-Mg andesites were derived an EM1 mantle source, i.e., a refractory lithospheric mantle modified by a previously subducted slab. The result, combined with the available data of the Mesozoic basalts from the southern portion of the NCC (Zhang et al., 2002), manifests a vast secular evolution of the lithospheric mantle beneath the eastern NCC from the Paleozoic refractory continental lithosphere to this Mesozoic modified lithosphere. Compared with the cratonic margin, the lithospheric mantle beneath the center of the craton was less extensively modified, implying the secular evolution was related to the subduction processes surrounding the NCC. Therefore, we suggest that the interaction of the slab-derived silicic melt with the old refractory lithospheric mantle converted the Paleozoic cratonic lithospheric mantle into the late Mesozoic fertile mantle, which was also different from the Cenozoic counterpart. A geodynamic model is proposed to illustrate such a secular lithosphere evolution.     

On the regional variation of heat flow, geotherms, and lithospheric thickness

Geotherm families in which surface heat flow is the principal independent variable have been constructed for continental and oceanic lithospheres. The continental model is characterized by geotherms in which surface heat flow is in equilibrium with heat flowing into the lithosphere at its base plus heat generated by radioactive decay within the lithosphere. The model accommodates the regional variation of the surface heat flow with proportional variations in the radioactivity of the surficial enriched zone and in the deeper heat flow. The proportionality is dictated by a new and general linear relationship between reduced heat flow and mean heat flow for a region ( ), which enables both q^* and the mean heat production of the enriched zone to be estimated from knowledge of the mean surface heat flow of a province. The oceanic model is characterized by the transient cooling of a semi-infinite medium with an initial temperature gradient and some near-surface radiogenic heat production. The model yields a heat flow in satisfactory agreement with observations in the oldest ocean basins. The depth at which both the oceanic and continental geotherms reach ~0.85 of the melting temperature is shown to be a consistent estimator of the depth to the top of the low-velocity channel, or the thickness of the high-velocity lid overlying the channel. We identify the lid as synonymous with the lithosphere, and produce a global map of lithospheric thickness based on the regional variation of surface heat flow. The lithosphere is less than 100 km thick over most of the globe, but thickens appreciably and becomes more viscous beneath the Precambrian shields and platforms, regions of low heat flow. These characteristics of shields are consistent with recently reported models of the driving mechanisms of the plate system, which require greater retarding forces beneath plates with large continental areas.     

CO_2 degassing and melting of metasomatized mantle lithosphere during rifting-Numerical study

:Reactivation of metasomatized mantle lithosphere may occur during continental extension,which is an important component of plate tectonics.The lower most part of the metasomatized domains in the subcontinental mantle lithosphere can be locally enriched in CO2.Therefore,partial melting of these metasomatized domains may play a crucial role in the global carbon cycle.However,little is known about this process and up until now few numerical constraints are available.Here we address this knowledge gap and use a 2-D high resolution petrological-thermomechanical model to assess lithospheric rifting.CO2 degassing and melting.We test 4 lithospheric thicknesses:90,110,130 and 200 km with a 10 km thick metasomatized layer at the base using CO2 of 2 wt.%in the bulk composition.The carbonate enriched layer is stable below^3 GPa(>110 km)for a temperature of 1300℃;therefore,we only observe degassing patterns for lithospheric models that are 130 km and 200 km thick.The metasomatized layer for the 130 km thick lithosphere mostly comprises carbonatite melting,whereas in the 200 km thick scenario propagation of melt development from kimberlites to carbonatites occurs as the metasomatic mantle is exhumed during extension.The numerical models fit well into natural rifting zones of the European Cenozoic Rift System for young(shallow)and of the North Atlantic Rift for old(thick)lithosphere.     

大陆岩石圈有效弹性厚度与有关地球物理参数的关系--以泉州-黑水地学断面为例

大陆岩石圈有效弹性厚度(Te)是反映岩石圈综合强度的参数,它反映了岩石圈的整体特征。分析岩石圈有效样性厚度与反映深部地质特征的有关地球物理参数之间的关系,对研究控制Te的因素、各因素之间的关系以及探索大陆构造与大陆动力学等具有重要意义。泉州一黑水地学断面Te与地壳厚度、热岩石圈厚度、均衡重力异常、磁性构造层底面深度、上地幔低速层顶界面深度、上地幔低阻层顶面深度之间的关系研究表明：Te与大地热流关系密切的“热”地球物理参数磁性构造层底面深度、热岩石圈厚度相关性好;与地壳厚度有一定的相关性;上地幔低速层顶界面深度和上地幔低阻层顶面深度与大陆岩石圈Te相关性均较差。     

NUMERICAL MODELLING OF LITHOSPHERE EVOLUTION IN THE NORTH CHINA CRATON:THERMAL THINNING VERSUS TECTONIC EXTENSION THINNING

The boundary between lithosphere and asthenosphere essentially represents a thermal boundary (the solidus).Temperature variation across this boundary can lead to the change of lithosphere thickness.In the case of elevated temperatures in a lithospheric layer above 1 200℃,partial melting will begin and the result of that is a thinned lithosphere.The other mechanism that can also thin lithosphere is extension.