Heat Flow Anomalies Research Articles

REHEATFUNQ (REgional HEAT-Flow Uncertainty and aNomaly Quantification) 2.0.1: a model for regional aggregate heat flow distributions and anomaly quantification

Abstract. Surface heat flow is a geophysical variable that is affected by a complex combination of various heat generation and transport processes. The processes act on different lengths scales, from tens of meters to hundreds of kilometers. In general, it is not possible to resolve all processes due to a lack of data or modeling resources, and hence the heat flow data within a region is subject to residual fluctuations. We introduce the REgional HEAT-Flow Uncertainty and aNomaly Quantification (REHEATFUNQ) model, version 2.0.1. At its core, REHEATFUNQ uses a stochastic model for heat flow within a region, considering the aggregate heat flow to be generated by a gamma-distributed random variable. Based on this assumption, REHEATFUNQ uses Bayesian inference to (i) quantify the regional aggregate heat flow distribution (RAHFD) and (ii) estimate the strength of a given heat flow anomaly, for instance as generated by a tectonically active fault. The inference uses a prior distribution conjugate to the gamma distribution for the RAHFDs, and we compute parameters for a uninformed prior distribution from the global heat flow database by Lucazeau (2019). Through the Bayesian inference, our model is the first of its kind to consistently account for the variability in regional heat flow in the inference of spatial signals in heat flow data. Interpretation of these spatial signals and in particular their interpretation in terms of fault characteristics (particularly fault strength) form a long-standing debate within the geophysical community. We describe the components of REHEATFUNQ and perform a series of goodness-of-fit tests and synthetic resilience analyses of the model. While our analysis reveals to some degree a misfit of our idealized empirical model with real-world heat flow, it simultaneously confirms the robustness of REHEATFUNQ to these model simplifications. We conclude with an application of REHEATFUNQ to the San Andreas fault in California. Our analysis finds heat flow data in the Mojave section to be sufficient for an analysis and concludes that stochastic variability can allow for a surprisingly large fault-generated heat flow anomaly to be compatible with the data. This indicates that heat flow alone may not be a suitable quantity to address fault strength of the San Andreas fault.

Deep Fault‐Controlled Fluid Flow Driving Shallow Stratigraphically Constrained Gas Hydrate Formation: Urutī Basin, Hikurangi Margin, New Zealand

AbstractThe Hikurangi Margin east of New Zealand's North Island hosts an extensive gas hydrate province with numerous gas hydrate accumulations related to the faulted structure of the accretionary wedge. One such hydrate feature occurs in a small perched upper‐slope basin known as Urutī Basin. We investigated this hydrate accumulation by combining a long‐offset seismic line (10‐km‐long receiver array) with a grid of high‐resolution seismic lines acquired with a 600‐m‐long hydrophone streamer. The long‐offset data enable quantitative velocity analysis, while the high‐resolution data constrain the three‐dimensional geometry of the hydrate accumulation. The sediments in Urutī Basin dip landward due to ongoing deformation of the accretionary wedge. These strata are clearly imaged in seismic data where they cross a distinct bottom simulating reflection (BSR) that dips counterintuitively in the opposite direction to the regional dip of the seafloor. BSR‐derived heat flow estimates reveal a distinct heat flow anomaly that coincides spatially with the upper extent of a landward‐verging thrust fault. We present a conceptual model of this gas hydrate system that highlights the roles of fault‐controlled fluid flow at depth merging into strata‐controlled fluid flow into the hydrate stability zone. The result is a layer‐constrained accumulation of concentrated gas hydrate in the dipping strata. Our study provides new insight into the interplay between deep faulting, fluid flow and gas hydrate formation within an active accretionary margin.

Heat flow of the Mozambique channel: New data and predicted surface heat flow map

The Mozambique Channel, a complex domain composed of passive margins and oceanic crust affected by younger strike-slip and volcanic activity, is still poorly studied for surface heat flow. We present 33 new marine-type heat flow estimations acquired offshore in 2014–2015 during the MOZ cruises, completed with 4 new heat flow values derived from reappraised old well sites (PAMELA project). Offshore heat flow is generally low to normal and does not display strong variations. As poor data coverage persists in large parts of the area, we performed a heat flow prediction mapping using the similarity method. Based on an extrapolation of old and new data guided by 14 geological and geophysical proxies, we obtain on a 0.1° × 0.1° grid a predicted heat flow and its uncertainty from the statistics of all values at global grid points with similar proxies. We succeeded to obtain good predictability on 70% of pixels and an RMS error <2.3 mW/m2. The proxies selected for the prediction include a map of genetic domains, sediment thickness, topography and bathymetry, crustal ages, Curie point depth, Free air anomaly, distances to volcanoes, tectonic structures and continent-ocean boundaries. The new Mozambique heat flow map shows a predominantly low offshore heat flow of around 50 mW/m2, associated with the Jurassic and early Cretaceous age of the oceanic crust. Several heat flow anomalies standoff to this background heat flow with two main orientations: low heat flow anomalies with a N–S orientation and high anomalies with a mostly NE-SW orientation, which are linked mainly to tectonic structures.

New heat flow data on the South Balearic margin: Evidence of regional fluid circulation system

Crustal heat loss processes in contexts other than mid-ocean ridge flanks are still poorly understood and described in the literature. In this work, we present 54 new surface heat flow measurements recorded along the South Balearic margin and across the Hannibal High area, in the Western Mediterranean Sea, away from spreading centres. The South Balearic margin is a narrow continental margin expressed on the seabed topography by the steep Emile Baudot Escarpment while the Hannibal High area, further south, is a presumed volcanic oceanic crust zone. Recent heat flow studies pointed out the presence of strong local thermal anomalies, imprinted in regional deep basin heat flow increasing from the eastern to the western Algerian basins (70–90 to 100–130 mW/m2). The new data in this study confirm local anomalies around the Emile Baudot seamounts and allow the delineation of some low and high heat zones. We show that (1) a correlation exists between the heat flow variability and the sedimentary cover thickness, and (2) the most pronounced anomaly is a low heat flow zone (30 km wide) observed in the mid-slope South Formentera basin, close to the basaltic basement of the Los Martines volcano. The correlation of heat flow with sedimentary thickness, the lateral extent of the heat flow anomalies, the flux peak magnitudes, and the co-existence of both low and high anomalies suggest the presence of an active fluid circulation system. Based on the arrangement of the anomalies in relation to the basaltic basement seamounts, we consider a syphon-type circulation system in the Formentera basin. Reduced heat flow suggests a recharge zone close to the Los Martines seamount, while local high heat flow located close to a smaller seamount could be a potential zone of fluid discharge. Although different buoyancy-driven circulations could occur in the South Balearic margin, we believe that a syphon-type hydrothermal circulation along permeable basaltic mounds and sealed basement conduits, similar to the off-axis oceanic crust, is best developed in the young marginal basin of the South Balearic margin.

Identification of active faults and tectonic features through heat flow distribution in the Nankai Trough, Japan, based on high-resolution velocity-estimated bottom-simulating reflector depths

Estimates of heat flow can contribute to our understanding of geological structures in plate convergent zones that produce great earthquakes. We applied automated velocity analysis to obtain the accurate seismic profiles needed for precise heat flow estimates using six new seismic profiles acquired during R/V Kaimei KM18-10 voyage in 2018. We calculated heat flow values in the accretionary wedge of the Nankai Trough off the Kii Peninsula, Japan, from the positions of widespread bottom-simulating reflectors (BSRs) in seismic reflection profiles. Calculated conductive heat flow values from the depth of the BSR agree with previous studies where a regional trend is observed from ~ 50 mW/m2 to < 40 mW/m2 60 km landward from the deformation front. This trend is caused by thickening of accretionary sediments and the subduction of the Philippines Sea plate. Segments of profiles are marked by anomalous high heat flow values. Such anomalies represent alterations of the shallow crustal thermal structure caused either by a combination of topographic affects, surface erosion of the seafloor, or by fluid flow that transports heat by advection. We interpret heat flow anomalies (~ 100 mW/m2) as indicators of active faulting, which correspond to low seismic velocity zones along faults. Our results also showed relatively high heat flow at the landward end of several survey lines close to the Kii Peninsula, which we interpret to the possible presence of plutonic rocks that underlie the Kii Peninsula and extend offshore and may be the cause of geothermal springs, steep geothermal gradients, and high heat flow.Graphical abstract

Ongoing fragmentation of the subducting Cocos slab, Central America

Abstract Fundamental to plate tectonics is the subduction of cold and mechanically strong oceanic plates. While the subducted plates are conventionally regarded to be impermeable to mantle flow and separate the mantle wedge and the subslab region, isolated openings have been proposed. By combining new shear wave splitting measurements with results from geodynamic modeling and recent seismic tomography and geochemical observations, we show that the upper ~200 km of the Cocos slab in northern Central America is intensively fractured. The slab there is strong enough to produce typical arc volcanoes and Benioff Zone earthquakes but allows mantle flow to traverse from the subslab region to the mantle wedge. Upwelling of hot subslab mantle flow through the slab provides a viable explanation for the behind-the-volcanic-front volcanoes that are geochemically distinct from typical arc volcanoes, and for the puzzling high heat flow, high elevation, and low Bouguer gravity anomalies observed in northern Central America.

Geothermal Heat Flow Anomalies Caused by Thermal Conductivity Contrast

Heat flow measurements are usually made in boreholes considering that the heat flow field is homogeneous and the flux vector is vertical. This is not true in regions where thermal conductivity anomalies exist. In this paper we study configurations which may disturb heat flow density distribution. A numerical method is used to investigate the two-dimensional character of a heat flow field which could be associated with three situations: a layer almost vertical, an inclined layer and a layer situated between two media of different conductivities. Vertical and horizontal heat flow components are calculated along the surface of the earth and through the region of study. The results indicate that the heat flow is greatly disturbed by thermal conductivity anomalies.As medidas de fluxo de calor são usualmente feitas em furos considerando-se que o campo de fluxo térmico é homogêneo e o vetor fluxo é vertical. Isto não é verdade em regiões onde anomalias de fluxo térmico existem. Neste trabalho estudamos as configurações que podem perturbar a distribuição de densidade de fluxo térmico. Um método numérico é usado para investigar o caráter bidimensional do campo de fluxo térmico que pode estar associado com três situações: uma camada quase vertical, uma camada inclinada e uma camada situada entre dois meios com diferentes condutividades. As componentes de fluxo térmico vertical e horizontal são calculadas sobre a superfície da Terra e através da região em estudo. Os resultados indicam que o fluxo térmico é fortemente perturbado por anomalias de condutividade térmica.

Deep genesis of the high heat flow anomaly in the Okinawa Trough

The Okinawa Trough (OT) is characterized by high heat flow anomalies up to 10,000 mW/m2 (especially in the middle area), which is rarely seen in heat flow research all over the world. The genesis of the high heat flow anomaly is probably related to mantle upwelling. However, the deep genesis is yet to be studied. We used heat flow values collected from the Global Heat Flow Database to calibrate the locations of high heat flow anomalies. Gravity data were used to calculate the residual geoid and interlayer geoid anomalies, which can help in characterizing the morphology of mantle upwelling beneath the OT. Earthquake hypocenter distribution maps were presented to show the position of the Philippine Sea Plate beneath the OT. According to P-wave tomography profile and previous research, we discussed the deep genesis of the high heat flow anomaly and proposed a preliminary model to explain the process. We suggest that the deep mantle upwelling, probably from a depth of −1200 km, enters the upper mantle through the front of the subducted Pacific plate. The deep mantle upwelling converges with the molten mantle flow caused by the fluid from the dehydration of the Pacific Plate and the Philippine Sea Plate. Two mantle upwelling branches were revealed to feed the southern OT (SOT) and Changbai Volcano, and the mantle upwelling under the middle OT (MOT) was the second branch from the mantle upwelling branch under the SOT. The MOT should be more influenced by mantle upwelling from deep sources with extremely high temperatures.

Granitoids indicating moderate to high heat production associated with oceanic subduction system in the NE Tibetan Plateau

Regional heat flow provides a direct surface indication of the thermal state and energy balance of the lithosphere. Heat flux in the Tibetan Plateau remains poorly studied due to the lack of adequate information on heat flow. In this study, we investigated granitoids from the Gonghe-Guide district located in the NE Tibetan Plateau, which have important significance as hot and dry rocks with potential for geothermal resources. Samples from granitoid rocks as well as felsic dikes were collected from this area, and their geochemical data were combined with regional geophysical and drilling core data to evaluate a high-heat-flow anomaly. Our data show that granitoid rocks, including granodiorite, monzogranite, and syenogranite, crystallized at ca. 253−240 Ma, while felsic dikes formed ca. 230 Ma. The former were emplaced during the oceanic subduction process, whereas the latter formed in the syncollisional stage associated with the closure of the paleo-Zongwulong Ocean. Geochemically, these granitoid rocks are metaluminous to slightly peraluminous, with an average differentiation index (DI) value of 80, and they are classified as weakly to moderately fractionated I-type granites. The felsic dikes are peraluminous with high DI values (average of 95), typical of highly fractionated I-type granites. In terms of their high K and especially U and Th abundances, the calculated radioactive heat generation produced by the granodiorite, monzogranite, syenogranite, and felsic dikes is 1.85, 2.91, 6.85, and 3.02 μW/m3, respectively. Their moderate to high heat production generates a local heat-flow anomaly of 14.8−22.2 mW/m2 above the regional value of subduction zones, accounting for 11%−18% of the total regional heat flow. In combination with regional magnetotelluric data, the high-heat-flow anomaly may be attributed to an additional heat-flow contribution from a partial melt layer beneath this region. Furthermore, there is a significant positive correlation between the radioactive heat generation and magmatic fractionation, indicating that the enrichments of heat-producing elements are controlled by fractional crystallization and subsequently source composition. The granitoid rocks with high heat generation correspond to the large-scale intermediate-felsic magmatism during the subduction stage. We propose a model wherein a continuous subduction process during the closure of the paleo-Zongwulong Ocean and protracted cooling and crystallization processes resulted in the enrichment in heat-producing elements.

Thermally-constrained fluid circulation and seismicity in the Lesser Antilles subduction zone

At subduction zones, fluid circulation and elevated pore pressure are key factors controlling the seismogenic behavior along the plate interface by reducing absolute fault strength, increasing the time return of high magnitude co-seismic rupture and favoring aseismic slip. The Lesser Antilles is an end-member subduction zone where the slow subduction of numerous trans-oceanic fracture zones and patches of pervasively fractured, hydrated and serpentinized exhumed mantle rocks increase the water input. Heat-flow variations measured in the trench and the forearc during the Antithesis 1 cruise reveal heat advection by fluid circulation and shed a new light onto the thermal control of seismicity location in the subduction zone.In the Northern Lesser Antilles, heat-flow anomalies, negative in the trench and positive in the forearc, reveal a ventilated fluid circulation with downward percolation of cold fluids at the sediment-starved, pervasively fractured trench and upward discharge of warm fluids through the Tintamarre Fault Zone in the forearc. In contrast, in the Central Lesser Antilles, a positive heat-flow anomaly at the trench and the accretionary wedge is typical of an insulated fluid circulation where warm fluids invade the plate interface flowing updip from the subduction depths up to the trench.The investigated margin segments correspond with a very low number of interplate thrust earthquakes, illustrating the frequent statement that fluids in subduction zones tend to reduce the interplate coupling, favor slow to aseismic slip behavior, and increase the time return of large seismic events. Moreover, the location of intraslab, and supraslab earthquakes at depth beneath the Central Lesser Antilles suggest a close relation to temperature-related dehydration reactions.

Kriging of Ukraine’s deep heat flow map

The article discusses the method of processing the material used to compile a deep heat flow (HF) map on the territory of Ukraine. We are talking specifically about the deep (corrected) HF, since its error (determined by the differences in values at close points) is noticeably less than the observed one and only its values can be used to construct (as a rule, to control) thermal models of the Earth's crust and upper mantle. Despite the unique study of Ukraine on this parameter, which has been going on for almost 60 years, there are still significant fragments of the territory where the HF has not been determined. This is due to the lack of boreholes in such areas suitable for temperature measurements in the required depth interval with the required accuracy. Of course, any method of processing experimental material in areas adjacent to such «white spots» cannot completely replace a full-fledged study of HF within their boundaries. Nevertheless, the available geostatistical methods allow, by processing the existing grid of results, to ensure the construction of a map of the entire study area. In our case, we used the kriging technique. Kriging is a form of generalized linear regression to formulate an optimal spatial estimate in terms of minimum mean square error. The method works best within the shell defined by peripheral data. Within areas with a stable «wavelength» of HF anomalies, it is possible to fill in the gaps in the map without any problems. Naturally, with a noticeable smoothing of the field variations. Most of the processed map fragments belonged to this type. A more complicated situation was encountered at the southwestern contacts of the Kirovograd and Donbas anomalies. It is likely that part of the field structure (local intense anomalies) was not reproduced. Nevertheless, in general, the control carried out showed that the HF error in the assessment points, as a rule, does not exceed the experimental errors. The work done gives completeness to the results of research of the deep heat flow on the territory of Ukraine. It should also be noted that the identified distribution of HF within the former «white spots» reveals reserves of geothermal energy twice as much as the total reserves of combustible minerals in Ukraine.

Heat flow and gravity anomalies in some presumed hidden geothermal prospects in Java

The currently developed geothermal fields in Java are hosted by Quaternary volcanic complexes in the central zone of the island. Those fields have many vigorous thermal manifestations. However, seismic tomography shows the presence of an east-west-trending, low P-wave velocity (Vp) zones along the island. This indicates the presence of some hot, molten mass at depth, and provides the possibility of the existence of subsurface heat energy resource that can be utilized despite the rarity of surface manifestations. We investigate the heat flow and gravity anomalies in the areas lacking thermal manifestations, namely Paguyangan, Candi Umbul-Telomoyo, Pablengan, and Parang Wedang. The first three are associated with Slamet, Telomoyo, and Lawu volcanoes, respectively. Parang Wedang is far from the active Merapi volcano, but close to the Opak Fault – one of the major strike-slip faults of Java. This research is a preliminary effort in exploring those presumed hidden geothermal prospects. The results shows that all the investigated areas have high heat flow anomaly (145 – 160 mW/m2). Their gravity anomaly varies. The highest (>70 mGal) and medium values (12 - 24 mGal) are found in Pablengan, and Candi Umbul-Telomoyo, respectively. The lowest values (< 5 mGal) occur in Parang Wedang.

About geological theory

The author’s advection-polymorphic hypothesis of deep processes in the tectonosphere is based on V.V. Belousov’s system of endogenous regimes, a certain source of energy (radioactive decay in crustal and upper mantle rocks), and the method of energy transfer (advection). Elementary volumes of transported material have been termed «quanta of tectonic action» (QTA) with the diameter of about 50―70 km. The physical reality of such objects is proved. The choice of endogenous regime is related to the type of the preceding thermal model.&#x0D; The mechanism of the tectonosphere’s «heat machine», which relies firmly established facts and quantitatively explains the main events of geological history within the energy conservation law, has been substantiated.&#x0D; For any period, from the Early Archaean to our time, it is possible to numerically justify the pattern of heat and mass transfer, to select the endogenous regimes, and construct a non-stationary heat model and variation in time of the distribution of physical properties of rocks. By using the findings and solving only direct problems, one can determine the geological manifestations of the process and the anomalies of the physical fields. The results are compared with the observed ones (without fitting), and the discrepancies do not exceed the values due to the observation and calculation errors.&#x0D; Pursuant to the advection-polymorphic hypothesis, it became possible for the first time to predict: 1. The emergence of quanta of tectonic action. 2. Stability of parameters (depth and temperature) of magma chambers in the mantle in the history of the Earth. 3. Existence of the global asthenosphere (depth about 700―1000 km). 4. Velocity distribution of longitudinal seismic waves in the upper mantle of regions with all types of endogenous regimes. 5. The difference in the nature of earthquakes at various depths in the focal zones. Successful verification of predictions transfers the hypothesis into the rank of theory.&#x0D; The theory is used to explain the following at the quantitative level: dating of active processes on all platforms of the Earth, temperature distribution in the crust and upper mantle of platforms and active regions, sediment thickness in geosynclines and post-rift depressions, changes in mass flow in geological history, heat flow and gravitational field anomalies.&#x0D; Several applications of the theory to studies of seismicity and UHP-blocks problems and prospecting for mineral deposits (hydrocarbons, hydrothermal sulfide ores, diamonds, and geothermal energy resources) have been considered.

Regional thermal anomalies derived from magnetic spectral analysis and 3D gravity inversion: Implications for potential geothermal sites in Tanzania

Tanzania is one of the several countries intersected by the East African Rift System (EARS) endowed by a geothermal potential that has been explored only to a limited extent. Here we present the first heat flux map over the region based on the Curie point depth (CPD) estimation from aeromagnetic data. We have estimated the base of magnetic sources as a proxy for the CPD from the radially average power spectra of the total magnetic field using the centroid and the de-fractal methods. Our results show that the CPDs range ca. 11 to 43 km and are comparable to, but more detailed than global CPD estimates. The heat flow has then been computed assuming a constant thermal conductivity. In order to evaluate the results against crustal thickness, we have inverted the gravimetric regional field data constrained by the existing Moho depth from seismic receiver functions. Our analysis has revealed high heat flow values (over 100 mW/m2) along the EARS and at the Proterozoic collision boundaries that have been reactivated by the EARS. In general, the high heat flow anomalies coincide with known surface geothermal manifestations and shallow Moho depth in the range ca. 30 to 35 km. A high heat flow anomaly is also found in the central part of the Tanzanian craton, likely related to the mantle plume imaged by seismic tomography. The most interesting areas for geothermal exploration in Tanzania, according to our results, are the EARS triple junction in the Rungwe volcanic province, the north Tanzania divergent zone and the areas of the Proterozoic collision boundaries reactivated by the EARS.

Major tectonic features and geodynamic setting of the Black Sea Basin: Evidence from satellite-derived gravity, heat flow, and seismological data

The origin and development of the Black Sea Basin (BSB) remain controversial. In this study, we determined the main tectonic features of the BSB using satellite gravity, heat flow, and seismological data. Positive gravity anomalies are observed in the arc region due to high-density material, while negative gravity anomalies are seen in the trench region owing to the mass deficiency and sediments. The trench region has a relatively low heat flow anomalies along the Black Sea coasts.The Moho depth increases from 18.11 km in the Eastern Black Sea Basin (EBSB) to 51.83 km in the Eastern Anatolia Plateau (EAP) with an average of 34.13 ± 6.15 km. The lithosphere thickness changed between 78.48 km beneath Anatolia and 120.57 km below the EBSB with an average of 99.17 ± 8.17 km. The low heat flow and Moho temperature values indicate that the lithosphere is strong and cold beneath the BSB. The numerical results, therefore, provide evidence for southward subduction of the Tethys oceanic lithosphere below the Anatolian plate during the late Mesozoic-Cenozoic. Considering all geophysical and geological data, we conclude that the Black Sea Basin represents a relict basin, rather than a back-arc basin.

Maps of deep heat flow and geothermal resources in Ukraine http://gpimo.nas.gov.ua/en/node/1176

A technique for processing the material used to map the deep heat flow (HF) on the territory of Ukraine and constructing a map of geothermal resources on its basis is considered. We are talking about the deep (corrected) HF, since its error (determined by the differences in values at close points) is noticeably smaller than in the observed one, and only its values can be used to build thermal models of the earth's crust and upper mantle and solve the indicated applied problem. Due to the unique study of Ukraine in this parameter, which has been going on for almost 60 years, there are still significant fragments of the territory where the HF has not been determined. This is due to the lack of boreholes in such areas suitable for temperature measurements in the required depth interval with the required accuracy. Of course, any means of processing the experimental material in the territories adjacent to such white spots cannot completely replace a full-fledged study of HF within them. Nevertheless, the existing methods of geostatistics allow, by processing the available network of results, to ensure the construction of a map of the entire study area. In our case, the kriging technique was applied. The method works best inside a wrapper defined by peripheral data. In areas with a stable «wavelength» of HF anomalies, it is possible to fill in the gaps of the map without any problems. Naturally, with a noticeable smoothing of field variations. Most of the processed fragments of the map belonged to this type. A new edition of the description of the distribution of Ukraine's geoenergy resources is considered. We used a map of the deep heat flow processed by the kriging method and the construction of maps by region with the calculation of thermal conductivity at depths of up to 6 km at their contacts. This allowed to fill in the gaps in the network of experimental data and clarify the position and intensity of parameter anomalies in the southern part of the Carpathians, the north-eastern slope of the shield, in the Donbass and improve the overall assessment of geoenergy resources (up to 1.1 trillion tons of reference fuel). Geothermal energy from the deepest possible extraction interval (5.5—6.0 km) is about 26 times larger than the reserves of all fossil fuels in Ukraine.

Density contrast, deep structure, rheology and metallogeny of the crust and upper mantle of the Verkhoyano-Kolymsky region

Research subject. The Verkhoyano-Kolymsky areal of ore mineralization in the Far East of Russia.Data and methods. We used the state metallogenic map of Russia, Sc. 1: 2 500 000 (2000) and the gravity map of Russia Sc. 1: 2 500 000 (2001). Modeling was conducted by studying the deep structure of the earth’s crust and upper mantle from the anomalies of the density contrast of geological media in the intervals between the centers of density inhomogeneities and the surfaces of equivalent spheres.Results. 3D-distributions of density contrast (µz-parameter) in the crust and upper mantle of the Verkhoyano-Kolymsky region related to the rheological properties of geological media were analyzed. In the gravity models designed without attraction of external information, the structures of thrust, splitting, stretching, as well as the structures of central type (CTS) of the plume nature, were identified. In the regional stretching zone, at the border of lithospheric segments, the revealed Indigiro-Kolymsky and Verkhoyansk CTSs were described in 3D space. These structures are characterized by a mushroom-like upwelling of the asthenosphere, associated with heat flow anomalies. The identified structures differ in terms of asthenosphere depth, age and ore mineralization. The location of ore clusters and regions in the zones of CTS obeys concentric ore-magmatic zoning, typical for this type of structures. The central (trunk-like) zone of Indigiro-Kolymsky CTS features mainly high-temperature gold-quarts mineralization. On the periphery, along with gold areas, there are tin-tungsten, tin and complex ore mineralization areas. The majority of gold fields with low-temperature gold-sulfide, tin and polymetallic mineralization are attributed to the flanks of Indigiro-Kolymsky CTS. In the Verkhoyanska CTS, the majority of ore regions are characterized by multi-formation ore mineralization. In the central part of this structure, areas with mainly low-temperature tin, mercury-antimony and gold-silver ore mineralization are located. On the flanks, gold mineralization is either absent or subsidiary.Conclusions. As a result of a simple procedure, implying generalization of multiple decisions of the elementary inverse problem of gravity potential, main features of the deep structure of the Verkhyano-Kolima region were defined. In the regional stretch zone, at the boundary of lithospheric segments, the Indigiro-Kolimskaya and Verkhoyanskaya CTSs of the plume nature that control the location of ore deposits were identified and described in 3D space.

Transport of Heat by Hydrothermal Circulation in a Young Rift Setting: Observations From the Auka and JaichMaa Ja'ag' Vent Field in the Pescadero Basin, Southern Gulf of California

AbstractHeat flow measurements collected throughout the Auka and JaichMaa Ja'ag' hydrothermal vent fields in the central graben of the Southern Pescadero Basin, southern Gulf of California, indicate upflow of hydrothermal fluids associated with rifting dissipate heat in excess of 10 W/m2 around faults that have a few kilometers in length. Paradoxically, longer faults do not show signs of venting. Heat flow anomalies slowly decay to background values of ∼2 W/m2 at distances of ∼1 km from these faults following an inverse square‐root distance law. We develop a near‐fault model of heat transport in steady state for the Auka vent field based on the fundamental Green's function solution of the heat equation. The model includes the effects of circulation in fracture networks, and the lateral seepage of geothermal brines to surrounding hemipelagic sediments. We use an optimal fitting method to estimate the reservoir depth, permeability, and circulation rate. Independently derived constraints for the model, indicate the heat source is at a depth of ∼5.7 km; from the model, permeability and flow rates in the fracture system are ∼10−14 m2 and 10−6 m/s, respectively, and ∼10−16 m2 and 10−8 m/s in the basin aquitards, respectively. Model results point to the importance of fault scaling laws in controlling sediment‐hosted vent fields and slow circulation throughout low permeability sediments in controlling the brine's chemistry. Although the fault model seems appropriate and straightforward for the Pescadero vents, it does seem to be the exception to the other known sediment‐hosted vent fields in the Pacific.

Permian geothermal units in the Sichuan Basin: Implications for the thermal effect of the Emeishan mantle plume

The Emeishan mantle plume is supposed to play an important role in the Permian thermal regime and source rock hydrocarbon generation evolution in the Sichuan Basin, Southwest China. In this paper, we provide new valuable insights into the spatial thermal effect of the Emeishan mantle plume to the Sichuan basin and maturity evolution of the Paleozoic source rocks. Cambrian core samples from four wells were selected for zircon fission track and zircon (U–Th)/He analysis in order to determine their thermal histories. Then the thermal histories of typical wells throughout the basin were obtained based on the above result and previous studies. According to the peak heat flow value (q), four Permian geothermal units were classified: a stratospheric heat flow unit (q ≥ 90 mW/m2), a high heat flow unit (80 ≤ q < 90 mW/m2), a medium heat flow unit (70 ≤ q < 80 mW/m2), and a normal heat flow unit (q < 70 mW/m2). The interpretation of the abnormal Permian heat flow indicates that the enormous heat flow anomalies with values of >20 mW/m2 occurred in the stratospheric and high heat flow units was mainly caused by the mantle plume, while the weak Permian thermal perturbation with heat flow anomalies of <15 mW/m2 in other two units was more likely associated with crustal thinning. The thermal effect of the Emeishan mantle plume may be contained within the stratospheric and high heat flow units. By comparing the maturation histories of the Paleozoic source rock, we identified the thermal effect on the maturity evolution. The thermal perturbation had no obvious impact on the maturity evolution of the Lower Permian and Lower Silurian Longmaxi Formation. Only the Lower Cambrian Qiongzhusi Formation within high geothermal unit suffered significant thermal effect of the mantle plume and matured rapidly during the end of the Early Permian.

Depth to the bottom of the magnetic layer, crustal thickness, and heat flow in Africa: Inferences from gravity and magnetic data

Data from the Earth Gravitational Model (EGM2008) and the Earth Magnetic Anomaly Grid (EMAG2) were used to develop a continental scale crustal thickness model for Africa, and to estimate the depth to the bottom of the magnetic layer (DBML) and the geothermal gradient and heat flow. The results are: (1) the estimated DBML from the magnetic data varies from ~23.0 to ~37.2 km. The shallowest DBML values are located in the northern, eastern, and western parts of the continent, whereas the deepest values are observed in the central and southern regions. (2) The estimated crustal thickness based on gravity data varies from ~29.9 km in the northern and western parts of Africa to ~48.0 km in its southern regions, with an average thickness of 35.1 km for the whole continent. (3) The estimated heat flow varies between high values of 46–59 mW/m2, observed in the northern, eastern, and western regions to low values of ~< 41 mW/m2, observed in the central and southern parts of the continent. (4) The geothermal gradient values vary between 14.5 and 23.6 °C/km (5) The East African rift zone is underlain by shallow DBML characterized by high heat flow values that vary between 42 and 59 mW/m2 (6) The heat flow anomalies in Egypt and Libya may be associated with the zone of the Pelusium megashear system, and it shows heat flow values that vary between 36.3 and 59.0 mW/m2. The current study has taken advantage of the availability of the EGM2008 and EMAG2 datasets to map crustal thickness variations and DBML beneath the continental landmass of Africa.