Barrovian-type metamorphism in the western domain of the Cordillera Darwin Metamorphic Complex, Fuegian Andes

2021 ◽  
Author(s):  
Mauricio Calderon ◽  
Catalina Zúñiga ◽  
Francisco Hervé ◽  
Thomas Theye ◽  
Gonzalo Galaz ◽  
...  
Keyword(s):  
Geothermal Gradient ◽  
White Mica ◽  
Burial Depth ◽  
Metamorphic Complex ◽  
Constant Composition ◽  
Magmatic Arc ◽  
Garnet Core ◽  
Late Generation ◽  
Si Content ◽  
Two Stages

<p>The Cordillera de Darwin Metamorphic Complex (CDMC) comprise metamorphosed supracrustal rocks and metaplutonic suites which records a unique tectonic evolution among the metamorphic complexes of the southernmost Andes. The pressure (P) and temperature (T) conditions determined in garnet-bearing schists in the Central Domain of the CDMC indicate a clockwise P-T path of metamorphism reaching burial depth as high as 12 kbar at ca. 620°C. This metamorphic event has been related to the closure of a marginal back-arc basin (Rocas Verdes Basin) and collision of an ensialic magmatic arc with the continent in the late Cretaceous. We focus on garnet-biotite schists intercalated within a huge block consisting of repeated sequences of metabasalts and amphibolites (Rocas Verdes Ophiolites), located in the Western Domain of the CDMC, at Seno Martínez. The chemical zonation of small garnet porphyroblasts (diameter of ca. 300 um) record two stages of metamorphism. Garnet is almost almandine in composition with lesser amounts of Ca, Mn and Mg.  The concentric zonation is characterized by relatively lower contents of Fe-Mg and higher contents of Ca-Mn in the core. Garnet bear tiny inclusions of clinozoisite, which is also present as isolated grains in the foliated matrix. Laths of biotite define the main foliation and have a nearly constant composition characterized by X<sub>Fe</sub> of ca. 0.6. Two generations of phengitic white mica are identified on basis of Si content (a.pf.u.) varying between 3.20-3.30 (early generation) and of ca. 3.15 (late generation). To reconstruct the P-T conditions of metamorphism through thermodynamic modeling using the Perple_X software package, the bulk rock and mineral composition were considered. Using compositional isopleths of X<sub>Fe</sub>, X<sub>Mg</sub>, X<sub>Ca</sub> and X<sub>Mn</sub> in zoned garnet, Si content in white mica and X<sub>Fe</sub> in biotite allow the constrain two stages of metamorphism (M1 and M2). The P-T conditions of M1, represented by the composition of the garnet core, are restricted to ca. 8 kbar and 400°C. M2 is restricted to ca. 7.5 kbar at 480°C, determined with the composition of the garnet rim, X<sub>Fe</sub> in biotite and Si content in late phengitic white mica. Our preliminary results indicate that ophiolitic rocks and interleaved garnet-bearing schists were tectonically buried and metamorphosed in a relatively hot subduction interface characterized by a geothermal gradient of ca. 16°C/km, prior to the collision of the ensialic magmatic arc. Acknowledgements. This study was supported by the Fondecyt grant 1161818.</p>

The role of the Shuswap Metamorphic Complex in Cordilleran tectonism: a review

1984 ◽  
Vol 21 (10) ◽  
pp. 1171-1193 ◽  
Author(s):  
Andrew V. Okulitch
Keyword(s):  
Late Paleozoic ◽  
Metamorphic Complex ◽  
Late Mesozoic ◽  
Magmatic Arc ◽  
Tectonic History ◽  
Laramide Orogeny ◽  
Kootenay Lake ◽  
Shuswap Metamorphic Complex ◽  
Transitional Crust ◽  
Two Stages

The Shuswap Metamorphic Complex consists of three parts, each with unique stratigraphy and orogenic evolution, separated by major faults of diverse nature and having in common only a post-late Mesozoic tectonic history. The first part, the Monashee Complex, is a possible extension of the Precambrian Shield that contains limited evidence of Mesozoic orogenesis and that was rapidly uplifted during the Cretaceous to Paleogene. The Monashee Décollement, a warped mylonite zone interpreted as a regional thrust fault active through the Middle Jurassic, separates this complex from the second part, which contains rocks correlative with Hadrynian to late Paleozoic strata of the pericratonic prism. The third part, the Okanagan Complex, straddling the 49th Parallel from the Okanagan Valley to Kootenay Lake, contains the probable exhumed roots of a Mesozoic magmatic arc built upon possible North American continental and transitional crust and includes late Paleozoic and early Mesozoic suspect terranes.The Columbian Orogen formed during westward drift of the craton into a continent of accreted elements. Response of the craton, attenuated during at least two episodes of Proterozoic rifting, and its overlying sedimentary prism to underthrusting from the east and simultaneous collision with an accreting collage from the west took place in two stages. First, attenuated crust was telescoped and thickened to its approximate original configuration while westernmost parts of the bordering prism were deformed and metamorphosed (the Jura-Cretaceous Columbian Orogeny that affected the Okanagan Complex and strata above the Monashee Décollement). Second, the thickened crust, the deformed prism, and platformal strata were thrust eastward (the Late Cretaceous – Paleocene Laramide Orogeny that formed the Rocky Mountains Thrust Belt). Waning convergent tectonism led to ascendancy of crustal extension (primarily in the Okanagan Complex) and final uplift of cratonic massifs.

Chapter 23: Alteration, Mineralization, and Age Relationships at the Kışladağ Porphyry Gold Deposit, Turkey

2020 ◽  
pp. 467-495
Author(s):  
T. Baker ◽  
S. Mckinley ◽  
S. Juras ◽  
Y. Oztas ◽  
J. Hunt ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
White Mica ◽  
Western Anatolia ◽  
Low Grade ◽  
Porphyry Deposits ◽  
Magmatic Arc ◽  
Argillic Alteration ◽  
Metamorphic Basement ◽  
Slab Tear ◽  
Roll Back

Abstract The Miocene Kışladağ deposit (~17 Moz), located in western Anatolia, Turkey, is one of the few global examples of Au-only porphyry deposits. It occurs within the West Tethyan magmatic belt that can be divided into Cretaceous, Cu-dominant, subduction-related magmatic arc systems and the more widespread Au-rich Cenozoic magmatic belts. In western Anatolia, Miocene magmatism was postcollisional and was focused in extension-related volcanosedimentary basins that formed in response to slab roll back and a major north-south slab tear. Kışladağ formed within multiple monzonite porphyry stocks and dikes at the contact between Menderes massif metamorphic basement and volcanic rocks of the Beydağı stratovolcano in the Uşak-Güre basin. The mineralized magmatic-hydrothermal system formed rapidly (<400 kyr) between ~14.75 and 14.36 Ma in a shallow (<1 km) volcanic environment. Volcanism continued to at least 14.26 ± 0.09 Ma based on new age data from a latite lava flow at nearby Emiril Tepe. Intrusions 1 and 2 were the earliest (14.73 ± 0.05 and 14.76 ± 0.01 Ma, respectively) and best mineralized phases (average median grades of 0.64 and 0.51 g/t Au, respectively), whereas younger intrusions host progressively less Au (Intrusion 2A: 14.60 ± 0.06 Ma and 0.41 g/t Au; Intrusion 2 NW: 14.45 ± 0.08 Ma and 0.41 g/t Au; Intrusion 3: 14.39 ± 0.06 and 14.36 ± 0.13 Ma and 0.19 g/t Au). A new molybdenite age of 14.60 ± 0.07 Ma is within uncertainty of the previously published molybdenite age (14.49 ± 0.06 Ma), and supports field observations that the bulk of the mineralization formed prior to the emplacement of Intrusion 3. Intrusions 1 and 2 are altered to potassic (biotite-K-feldspar-quartz ± magnetite) and younger but deeper sodic-calcic (feldspar-amphibole-magnetite ± quartz ± carbonate) assemblages, both typically pervasive with disseminated to veinlet-hosted pyrite ± chalcopyrite ± molybdenite and localized quartz-feldspar stockwork veinlets and sodic-calcic breccias. Tourmaline-white mica-quartz-pyrite alteration surrounds the potassic core both within the intrusions and outboard in the volcanic rocks. Tourmaline was most strongly developed on the inner margins of the tourmaline-white mica zone, particularly along the Intrusion 1 volcanic contact where it formed breccias and veins, including Maricunga-style veinlets. Field relationships show that the early magmatic-hydrothermal events were cut by Intrusion 2A, which was then overprinted by Au-bearing argillic (kaolinite-pyrite ± quartz) alteration, followed by Intrusion 3 and late-stage, low-grade to barren argillic and advanced argillic alteration (quartz-pyrite ± alunite ± dickite ± pyrophyllite). Gold deportment changes with each successive hydrothermal event. The early potassic and sodic-calcic alteration controls much of the original Au distribution, with the Au dominantly deposited with feldspar and lesser quartz and pyrite. Tourmaline-white mica and argillic alteration events overprinted and altered the early Au-bearing feldspathic alteration and introduced additional Au that was dominantly associated with pyrite. Analogous Au-only deposits such as Maricunga, Chile, La Colosa, Colombia, and Biely Vrch, Slovakia, are characterized by similar alteration styles and Au deportment. The deportment of Au in these Au-only porphyry deposits differs markedly from that in Au-rich porphyry Cu deposits where Au is typically associated with Cu sulfides.

scholarly journals Solidification of Hypereutectic Thin Wall Ductile Cast Iron

2006 ◽  
Vol 508 ◽  
pp. 63-68 ◽  
Author(s):  
Karl Martin Pedersen ◽  
Niels Tiedje
Keyword(s):  
Nucleation And Growth ◽  
Ductile Cast Iron ◽  
The Other ◽  
Eutectic Solidification ◽  
Thin Wall ◽  
Green Sand ◽  
Metallographic Examination ◽  
Si Content ◽  
Two Stages ◽  
Two Populations

Hypereutectic ductile iron was cast in green sand moulds with four plates with thickness of 1.5, 2, 3 and 4 mm in each mould. Temperatures were measured in the 3 and 4 mm plate. The temperature curves showed that eutectic solidification was divided into two stages: primary and secondary eutectic solidification. The first stage, which was relatively short, had none or very little recalescence. Further under cooling, followed by reheating during recalescence, was necessary to initiate the second part of the eutectic solidification. Both the secondary under cooling and recalescence was larger in the 3 mm plates than in the 4 mm plates. All 1.5 mm plates contained carbides but the other plates solidified without carbides. Metallographic examination showed two populations of graphite nodules. A small group of nodules was larger than rest of the nodules. Color etching revealing the segregation of Si showed a higher Si content in the ferrite around the larger nodules compared to the ferrite around the rest of the nodules. This indicates that solidification took place along the following path: The solidification starts with nucleation and growth of primary graphite nodules. This probably starts during the filling of the mould. The primary nodules act as nuclei for austenite. As austenite easily nucleates on graphite the temperature will be the same for the 3 and 4 mm plate for the first part of the eutectic solidification. This first part of the solidification ends when concentration of carbon around austenite dendrites is too large and new nodules have to nucleate and grow. The larger under cooling for the 3 mm plates compared to the 4 mm indicates that the nucleation of new nodules is governed by kinetics even in very well inoculated melts.

Cenozoic affinity of the Gondwanan rocks of eastern Timor: evidence from geo-thermochronometry

2020 ◽  
Author(s):  
Brendan Duffy ◽  
Brian Lew ◽  
Kevin Boland ◽  
Barry Kohn ◽  
Erin Matchan ◽  
...  
Keyword(s):  
Vitrinite Reflectance ◽  
White Mica ◽  
Indonesian Throughflow ◽  
Metamorphic Complex ◽  
Critical Position ◽  
Basement Faults ◽  
Type Area ◽  
Almost All ◽  
Age Range ◽  
West Timor

<p>Timor occupies a critical position within Wallacea and within the Indonesian throughflow, but its tectonic history remains poorly constrained compared to other parts of the region. Tectonic models typically divide the island into 1) Australian affinity rocks, including a thick sequence of Paleozoic and Mesozoic rocks and metamorphosed equivalents, and 2) Asian affinity rocks, made up of predominantly Cretaceous and Paleogene rocks and their metamorphosed equivalents, known as the Lolotoi Metamorphic Complex (LMC). New field mapping shows that the type-area of the LMC is pre-Permian basement exposed in an erosional window. Much of the previously mapped LMC is actually overlying alkaline Permian basalt. LA-ICPMS U-Pb ages for zircons, apatites and titanites from the LMC type-area are Precambrian and consistent with those from Gondwanan continental slivers that now form the basement of eastern Java and West Sulawesi. Such basement ages are also identified in peaks from inherited zircons from the LMC elsewhere in Timor. Basement faults separating the LMC from Triassic and Jurassic sediments contain white micas yielding Ar-Ar ages of c.38 Ma, which are within the age range of white micas from the Asian affinity Mutis metamorphic complex of West Timor. Zircon and apatite (U-Th)/He thermochronometric data and low vitrinite reflectance values across much of the study area do not support previous models suggesting Cenozoic overthrusting. However, close to the basement fault the thermochronometric data indicate rapid Eocene-Oligocene cooling and like the white mica ages, this is consistent with the thermal history of the Mutis complex of West Timor. On the basis of these data, we revive Barber’s (1978) interpretation that almost all of the pre-Neogene exhumed rocks of eastern Timor, including the Gondwanan rocks, resided in Sundaland during the Cenozoic. This finding has implications for the geodynamics of the Banda Arc, reconstructions of Wallacea, and the Neogene paleogeography of the Indonesian Throughflow.</p>

Long-term burial history and orogenic-scale fluid flow depicted from stable isotopes and stylolite paleopiezometry in the Umbria-Marches arcuate belt (Northern Apennines, Italy).

2020 ◽  
Author(s):  
Nicolas Beaudoin ◽  
Aurélie Labeur ◽  
Olivier Lacombe ◽  
Guilhem Hoareau ◽  
Marta Marchegiano ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Local Maximum ◽  
Geothermal Gradient ◽  
Burial Depth ◽  
Fold Axis ◽  
Clumped Isotopes ◽  
Burial History ◽  
Fluid System ◽  
Calcite Veins ◽  
Absolute Dating

<p>Faults, joints and stylolites are ubiquitous features in fold-and-thrust belts, and have been used for decades to reconstruct the past fluid flow (or plumbing system) at the scale of folded reservoirs/basins. The textural and geochemical study of the minerals filling the fractures makes it possible to unravel the history of fluid flow in an orogen, when combined with a knowledge of the burial history and/or of the paleothermal gradient. In most cases, the latter derives from the former, itself often argued over, limiting the interpretations of past fluid temperatures. Yet, recent methodological developments applied to carbonates and calcite fillings provide new perspectives for a more accurate reconstruction of the temperature, pressure and timing of the fluids that were present in the strata at the time they deformed, at every stage of fold development. Indeed, the temperature at which fluids precipitated can be obtained by Δ<sup>47</sup>CO2 clumped isotopes while the timing of calcite precipitation in veins and faults is given by U-Pb absolute dating. Also, the maximum burial depth of strata before contraction can be estimated using sedimentary stylolite paleopiezometry, hence in a way free of any consideration about the geothermal gradient.<br><br>These techniques were jointly applied at the scale of the Umbria-Marches arcuate belt (UMAR, Northen Apennines, Italy). Mesoscale faults and vein sets were measured and sampled in the Cretaceous-Eocene rocks. Focusing on those fractures that developed during Layer Parallel Shortening (LPS, i.e. oriented NE-SW to E-W) and during folding (i.e. oriented parallel to local fold axis), paleofluid sources, temperatures and timing were reconstructed using U-Pb absolute dating, Δ<sup>47</sup>CO2 clumped isotopes as well as δ<sup>18</sup>O, δ<sup>13</sup>C, and <sup>87/86</sup>Sr signatures of calcite veins. Results show a regional divide in the fluid system, with most of the belt including the foreland recording a fluid system involving basinal brines resulting at various degree from fluid-rock interactions (FRI) between pristine marine fluids (δ<sup>18</sup>O<sub>fluid</sub><span>= 0‰ SMOW) and surrounding limestones (δ<sup>18</sup>O<sub>fluid</sub>= 10‰ SMOW). Precipitation temperatures (35°C to 75°C) appear consistent with the burial history unraveled by sedimentary stylolite roughness paleopiezometry (600 m to 1500m in the range) and estimated geothermal gradient (23°C/km, Caricchi et al., 2004). As the degree of FRI increases forelandward, we propose a lateral, strata-bound, squeegee-type migration of fluids during folding and thrusting. In the western hinterland however, the fluid system rather involves hydrothermal fluids with a higher degree of FRI, the corresponding precipitation temperatures (100°C to 130°C) of which are inconsistent with local maximum burial (1500m). As the Sr radiogenic signatures preclude any deep origin of the fluids, we propose that the fluid system prevailing in the hinterland during LPS reflects the eastward migration of formational fluids originating from the Tuscan basin, located west from the UMAR, where studied Cretaceous rocks were buried under more than 4 km of sediments during the Miocene.</span></p><p><br>Beyond being the first combination of paleofluid geochemistry and burial estimates through paleopiezometry, this fluid flow model illustrates how the large scale structures may control the fluid system at the scale of a mountain belt.</p>

Relationship between metamorphism and structure in the Skiddaw Group, English Lake District

1993 ◽  
Vol 130 (5) ◽  
pp. 631-638 ◽  
Author(s):  
N. J. Fortey ◽  
B. Roberts ◽  
S. R. Hirons
Keyword(s):  
Cross Sections ◽  
Geothermal Gradient ◽  
Geological Structure ◽  
White Mica ◽  
Contact Metamorphism ◽  
Lake District ◽  
Illite Crystallinity ◽  
Directed Movement ◽  
Early Devonian ◽  
English Lake District

AbstractRegional variation of white mica (illite) crystallinity in the Skiddaw Group is set against the structural interpretation of Hughes, Cooper & Stone (1993, this issue) in which early- or pre-Ludlow deformation and slaty cleavage development (S1) were succeeded by southward thrusting and an associated development of S1 and S1 crenulation cleavages, possibly during early Devonian times. Kubier index (KI) values are plotted in relation to geological structure for a major part of the Skiddaw Group, and cross-sections constructed. The pattern is interpreted in terms of three processes: (1) diagenetic to low anchizonal burial metamorphism under a relatively high geothermal gradient during the late-arc stage (early to mid-Silurian) which preceded the orogenic phase and formation of S1; (2) upper anchizonal to epizonal metamorphism due to tectonic thickening and slaty cleavage development during the early to pre-Ludlow orogenic phase following closure of Iapetus; (3) late-tectonic uplift of already metamorphosed rocks by southward-directed movement on the Loweswater, Gasgale Gill and Causey Pike Thrusts possibly during early Devonian time. An analogous interpretation is made for the Skiddaw area, though with the addition of major post-S1 contact metamorphism.

Pristine metasomatic melt preserved in mantle rocks of the Bohemian Massif

2021 ◽  
Author(s):  
Alessia Borghini ◽  
Silvio Ferrero ◽  
Patrick J. O'Brien ◽  
Bernd Wunder ◽  
Oscar Laurent
Keyword(s):  
Trace Elements ◽  
Continental Crust ◽  
Bohemian Massif ◽  
Melt Inclusions ◽  
Mafic Rock ◽  
Major Elements ◽  
White Mica ◽  
Garnet Core ◽  
Melt Composition

<p>Melt inclusions of very unusual nature occur in garnets of eclogites of the Granulitgebirge, Bohemian Massif. This is one of the first direct characterization of a preserved metasomatic melt responsible for the formation of eclogites enclosed in garnet peridotites. The inclusions are micrometric, from glassy to fully crystalized as nanogranitoids and randomly distributed in the garnet core. Nanogranitoids contain kumdykolite/albite, phlogopite, osumilite and kokchetavite with a variable amount of quartz, pyroxene, carbonate and rare white mica. The melt has a granitic composition rather than basaltic or tonalitic/trondhjemitic as would be expected from the partial melting of ultramafic or mafic rocks and it is as well hydrous and peraluminous. The trace elements composition is also unusual for melts in mantle rocks with elements typical of continental crust (Cs, Li, B, Pb and Rb) and subduction zone (Th and U). Similar signatures, i.e. continental crust and subduction, are visible also in the whole rock trace elements in the form of high amounts of LILE and U. The eclogite major elements composition is similar to a Ca- and Fe - rich mafic rock akin more to the crust than to the mantle.</p><p>The peculiar melt composition and the lack of a clear residue of a melting reaction in the eclogites suggest that this melt is external, i.e. metasomatic. It infiltered the peridotites during subduction of the continental crust at mantle depth and aided the transformation of basic layers, already in the peridotite, to eclogite. In addition, similar trace elements patterns to the melt reported here can be found in the so-called durbachite -ultrapotassic melanosyenite present in the high-grade Variscan basement- and in the garnet peridotites and garnet pyroxenites of the T-7 borehole. In both case metasomatism was suggested but the agent was just inferred based on the geochemical signature. All these occurrences suggest that mantle contaminated by melts from deeply subducted continental crust is widespread beneath the Bohemian Massif.</p>

scholarly journals Stratigraphic and provenance analysis of Triassic rock units between 28-29° S, northern Chile: implications on the tectonic and paleogeographic evolution of the southwestern margin of Gondwana

2020 ◽  
Vol 47 (2) ◽  
pp. 207
Author(s):  
Esteban Salazar ◽  
Paulina Vásquez ◽  
Daniela Vallejos ◽  
Christian Creixell ◽  
Verónica Oliveros ◽  
...  
Keyword(s):  
System Development ◽  
Volcanic Rocks ◽  
Northern Chile ◽  
Provenance Analysis ◽  
Forearc Basin ◽  
Magmatic Arc ◽  
Base Level ◽  
Southwestern Margin ◽  
Forearc Basins ◽  
Two Stages

Triassic rock units of northern Chile (28-29° S) record the transition, both in time and space, between two major orogenies that affected the southwestern margin of South America, the Gondwanian and Andean orogenies. The geodynamic configuration of the margin during this transition is still a matter of debate, particularly whether subduction was interrupted or continued under different parameters in between the orogenies. In order to evaluate these hypotheses by understanding the paleogeographic evolution of the margin, this work synthesizes recent stratigraphical, structural and geochronological data from northern Chile (28-29° S), along with detrital zircon analysis and detritus characterization of the two main siliciclastic Triassic basins present in the area. A detailed study of the evolution of the San Félix and the Canto del Agua basins, their source areas, and exhumation processes of the margin recognizes two stages of intra-arc/forearc basins system development separated by a Carnian unconformity. The first stage (Lopingian-uppermost Middle Triassic) develops an eastern intra-arc basin, which is represented by the volcaniclastic rocks included in the Guanaco Sonso Formation and the roots of the volcanic arc represented by Chollay Plutonic Complex, bounded to the east by a Pennsylvanian-Cisuralian basement block. The forearc basin for this stage is constituted by two graben depocenter, separated by a topographic high, of marine to transitional depositional environment and proximal sediment sources. The eastern graben is filled by conglomerates and turbiditic rocks grouped in Members M1 to M4 of the San Félix Formation, and the western graben, by sedimentary and volcanic rocks of the lower section of the Canto del Agua Formation. The second stage (Norian-Rhaetian) involves an eastern intra-arc basin, represented by the volcanic rocks of the La Totora Formation that seals the exhumed roots of the magmatic arc developed in the previous stage, and a marine to transitional forearc basin to the west, represented by the sedimentary rocks of M5 member of the San Félix Formation and the upper section of the Canto del Agua Formation. These two successions show basal fluvial conglomerates unconformably overlying Anisian prodelta deposits of the first stage, recording a major base level drop of the forearc basin.

Gas hydrate stability zone in Muri coalfield, Qinghai Province, China

2021 ◽  
pp. 1-6
Author(s):  
Jing LI ◽  
Zheng YAO ◽  
Hongbo ZHAO ◽  
Zewei WANG
Keyword(s):  
Phase Equilibrium ◽  
Gas Hydrate ◽  
Regional Distribution ◽  
Geothermal Gradient ◽  
Mining Area ◽  
Burial Depth ◽  
Stability Zone ◽  
Hydrate Phase ◽  
Gas Component ◽  
Hydrate Stability

ABSTRACT The gas hydrate stability zone (GHSZ) is the essential condition for gas hydrate accumulation, which is controlled by three main factors: gas component, geothermal gradient and permafrost thickness. Based on the gas component of hydrate samples from drilling in Muri coalfield, the gas hydrate phase equilibrium curve was calculated using Sloan's natural gas hydrate phase equilibrium procedure (CSMHYD) program. Through temperature data processing of coalfield boreholes, some important data such as thickness of permafrost and geothermal gradient were obtained. The GHSZ parameters of a single borehole were calculated by programming based on the above basic data. The average thickness of GHSZ of 85 boreholes in Muri coalfield amounted to approximately 1000 m, indicating very broad space for gas hydrate occurrence. The isogram of GHSZ bottom depth drawn from single borehole data in Muri coalfield demonstrated the regional distribution characteristics of GHSZ, and identified three favourable areas of gas hydrate occurrence where the bottom of GHSZ had a burial depth >1500 m – namely, the southern part of Juhugeng Mining Area, the middle part of Duosuogongma Mining Area and the eastern part of Xuehuoli Mining Area.

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