浅谈煤各变质类型及变质作用

本文主要介绍煤变质的主要类型,根据受热的主要热源及作用方式和煤质特征等,不同的影响因素划分不同的煤变质作用类型。总结概括为深成变质作用、岩浆热变质作用、动力变质作用和热水变质作用,阐述了煤变质作用的特点。     

辽宁省新宾县徐家堡子韧性变形变质带的特征及变形变质作用

徐家堡子地区以黑云英云闪长质片麻岩（２．４７Ｇａ）为围岩的上壳岩（〉２．９８Ｇａ）包体中,发育几条近东西走向的韧性变形变质带（２．７Ｇａ）。研究表明,该韧性变形变质带在平面和剖面上的均呈舒缓波状,发育糜棱叶理,矿物线理和Ｓ－Ｃ组构。带内的糜棱片麻央矿物成分复且多世代矿物共存,变形前以石榴石,黑云母,斜长石和石英矿物组合为代表,形成温度为５００～５２０℃,压力为０．４ＧＰａ;韧性变形同期以夕线石,石     

临沂煤田煤变质因素的分析

临沂煤田煤变质受多种地质因素的影响,但是,各种煤质指标仍有其变化规律。区域变质作用使煤质达气肥煤阶段,岩浆侵入发生接触变质和气热变质作用,使煤质变为无烟煤和天然焦,煤的变质是上述各种变质作用的有效迭加,在广大区域内,区域变质作用为主,而在局部区域里可能岩浆侵入接触变质等的改造是主要的。     

福建煤变质的因素和类型

从煤岩学角度并结合福建省的地质、构造条件，阐述了影响福建省煤变质的因素和类型，研究表明，福建煤的变质应属多元、叠加的结果。     

阜新煤田东梁勘探区煤变质特征及变质因素的研究

本文利用大量的勘探资料,对东梁勘探区的煤变质特征及变质因素进行了研究,推断在含煤岩系下部2000～2500m处,可能存在一个侵入到下伏榆树沟组地层中的第三系中小型辉绿岩盖:东梁勘探区煤变质作用以远成岩浆变质占主导地位.     

为什么鸡蛋水洗后容易变质

有一次，我见妈妈从超市买回的鸡蛋有些脏，便打算把它们洗一洗再放进冰箱。但是，妈妈说鸡蛋水洗后不易存放，很容易变质。这是为什么呢？     

酸奶变质机理及保鲜研究初探

对酸奶变质原因进行了初步探讨，提出酸奶变质主要由乳酸菌后酵继续产酸所致的观点，同时研究了利用防腐剂、稳定剂等方法提高酸奶品质，延长保存期，并取得了明显的效果     

辽西太古代“建平变质杂岩”的变质作用演化

“建平变质杂岩”是辽宁省西部太古代的最下部的地体,它由连续性很差的表壳岩、TTG岩石及其它深成侵入岩构成。基本岩石类型有镁铁质岩石(包括角闪岩、辉石岩、斜长角闪岩等)、麻粒岩、紫苏花岗岩、片麻岩及少量的超镁铁质岩和磁铁石英岩。常见且主要的矿物相是斜方辉石、单斜辉石、石榴石、角闪石、斜长石和石英。岩相学研究确定了指示变质作用不同阶段的三个变质反应的存在,并且它们与推测的矿物相的转化关系吻合,结合地质温压的限定,本文得出了本区太古代末期的强烈的变质热事件的反时针的P-T-t演化轨迹,并推测出此变质热事件与大量的岩浆增聚密切相关。     

Triassic U-Pb age for zircon from granites in the Tonghua area and its response to the Dabie-Sulu ultrahigh-pressure collisional orogenesis

Single-grain zircon U-Pb dating was carried out to constrain the emplacement timing of granitic plutons at Chaxinzi, Xiaoweishahe and Longtou in the Tonghua area, south of Jilin Province. The results show that these plutons formed in the Triassic with ages of 203—217 Ma. Geological and geochemical characteristics indicate that the plutons are composed of quartz diorite and granite. The former was derived from partial melting of mafic lower crust, whereas the latter originated from thickened crust with garnet as the residue in the source. It appears that protoliths of these two types of granitits are different although they have the same emplacement age. Considering that these plutons are petrologically different from the coeval granites in the Xingmeng (Xing‘an-Mongolian) to Jihei (Jilin-Heilongjiang) orogenic belt in the north, it is suggested that their formation was related to the Dabie-Sulu ultrahigh-pressure collisional orogenesis since their ages are only 10—20 Ma younger than timing of the ultrahigh-pressure metamorphism, but comparable to that of the first rapid exhumation of the ultra-high-pressure metamorphic rocks and the emplacement of the post-collisional granites.     

Continental subduction channel processes: Plate interface interaction during continental collision

The study of subduction-zone processes is a key to development of the plate tectonic theory. Plate interface interaction is a basic mechanism for the mass and energy exchange between Earth＇s surface and interior. By developing the subduction channel model into continental collision orogens, insights are provided into tectonic processes during continental subduction and its products. The continental crust, composed of felsic to mafic rocks, is detached at different depths from subducting continental lithosphere and then migrates into continental subduction channel. Part of the subcontinental lithospheric mantle wedge, composed of perido- tile, is offscrapped from its bottom. The crustal and mantle fragments of different sizes are transported downwards and upwards inside subduction channels by the corner flow, resulting in varying extents of metamorphism, with heterogeneous deformation and local anatexis. All these metamorphic rocks can be viewed as tectonic melanges due to mechanical mixing of crust- and man- lie-derived rocks in the subduction channels, resulting in different types of metamorphic rocks now exposed in the same orogens. The crust-mantle interaction in the continental subduction channel is realized by reaction of the overlying ancient subcontinental lithospheric mantle wedge peridotite with aqueous fluid and hydrous melt derived from partial melting of subducted continental basement granite and cover sediment. The nature of premetamorphic protoliths dictates the type of collisional orogens, the size of ultrahigh-pressure metamorphic terranes and the duration of ultrahigh-pressure metamorphism.     

Eclogites in the interior of the Tibetan Plateau and their geodynamic implications

Eclogites have been recently reported in the interior of the Tibetan Plateau, including in the central Qiangtang metamorphic belt, in the Basu metamorphic massif of the eastern Bangong-Nujiang suture zone, and at Songdo and Pengco in the eastern Lhasa terrane. Some typical ultrahigh-pressure （UHP） metamorphic phenomena, e.g., garnet exsolution from clinopyroxene, were documented in the Basu and Pengco eclogites. The UHP metamorphism in the interior of the Tibetan Plateau marked by these eclogites generally took place in the Early Mesozoic. Along with exhumation of these eclogites, （post-） collision-related magmatism extensively occurred around the central Qiangtang belt, the eastern Bangong-Nujiang suture zone, and the eastern Lhasa terrane. The occurrence of these Early Mesozoic eclogites manifests an out-of-sequence evolution of the Tethys, and they could be a product of diachronous collision between the eastern Qiangtang terrane and the irregular continental margin of the united western Qiangtang-Lhasa plate, along the linked eastern Bangong-Nujiang-central Qiangtang zone. The collision-related magmatic rocks could have been originated from lithospheric thickening, melting, or detachment due to the collision. The presence of UHP metamorphic rocks in central Qiangtang and Basu implies likely continental deep-subduction, and the denudation of these two metamorphic zones could have served as the source of the Triassic turbidites in the Songpan-Garze complex and the Jurassic turbidites in the western Bangong-Nujiang zone, respectively. However, studies of the eclogites in the interior of the Tibetan Plateau just began, and many principal aspects still remain to be explored, such as their distributions, typical lithologies and minerals, temperature-pressure conditions, timing of formation and exhumation, protoliths and tectonic setting, and relationship with the evolution of the Tethys and large-scale basins in Tibet.     

Evidence for UHP metamorphism of eclogites from the Altun Mountains

Ultrahigh pressure (UHP) metamorphism refers to metamorphism that has occurred at pressures for the stability of coesite. The polycrystalline quartz inclusions showing the characteristic texture within garnets of eclogites indicates the pre-existence of coesites under the peak metamorphic condition. The unusual exsolution textures in ompacites and apatites, and the pressure estimations of phengite-bearing eciogites have been taken to provide further proof of eclogite formation under the UHP conditions.Combined with the fact that coesites have been observed in country rocks of eclogites in North Qaidam Mountains, another UHP metamorphic belt cut by the large-scale strikeslip fault in the AItun-North Qaidam area of China is confirmed.``     

The geological characteristics of oceanic-type UHP metamorphic belts and their tectonic implications: Case studies from Southwest Tianshan and North Qaidam in NW China

The geological characteristics of ultrahigh-pressure （UHP） metamorphic belts formed by deep subduction of oceanic crust are summarized in this paper. Oceanic-type UHP metamorphic belt is characterized by its protolithlc assemblage of typical oceanic crust, the peak metamorphic temperature 〈600℃, P-T path undergoing blueschist facies during prograde and retrograde metamorphic evolution, reepectively, with low geothermal gradient of cold subduction. The further study of oceanic-type UHP metamorphic belt is very significant for constructing metamorphic reaction series of cold subduction zone, for understanding how aqueous fluids were transported into deep mantle and for classifying the types of UHP metamorphism in cold subduction zone. The uplift and exhumation mechanism of oceanic UHP metamorphic rocks is one of the most challenging problems in the study of UHP metamorphism, which is very important for understanding the geodynamic mechanism of solid Earth. As a traveler eubducted into the mantle depth end then uplifted to the surface, oceanic-type UHP metamorphic belts witness the bulk process from the subduction to exhumation and is an ideal target to study the geochemical behavior end cycling of elements in subduction zones. The tectonic evolution of one convergent orogenic belt can be usually divided into two stages of oceanic subduction and followed continental subduction and collision, and the two best-established examples of orogenic belts are Alpa and Himalaya. Therefore, the study of oceanic-type UHP metamorphic belt is the frontier of the current plate tectonic theory. As two case studies, the current status and existing problems of oceanic-type UHP metamorphic belts in Southwest Tianshan and North Qaidam, NW China, are reviewed in this paper.     

Crustal evolution of the Shiwandashan area in South China: Zircon U-Pb-Hf isotopic records from granulite enclaves in Indo-Sinian granites

U-Pb dating coupled with Hf isotope analyses on zircon from metasedimentary granulite enclaves in the Jiuzhou peraluminous granite from the Shiwandashan area in southeastern Guangxi Province, South China are presented in this paper. The results show that the protoliths of these granulite enclaves were mainly composed of Neo-Mesoproterozoic (564–1061 Ma) clastic materials with a peak age at ~822 Ma. These materials were probably derived from the igneous rocks that were emplaced during the Neoproterozoic breakup of Rodinian Supercontinent. Subordinate sediments include the Paleoproterozoic (1778–2227 Ma) and even the Meso-Paleoarchean materials with the oldest U-Pb age at 3551±8 Ma, indicating the existence of ancient crustal rocks in the area and/or its surrounding regions. Younger grains include the early Mesozoic (234±2 Ma) magmatic zircon populations and the late Permian (253±3 Ma) metamorphic zircon populations. Further zircon Hf isotope analyses reveal that their protoliths were complex, containing both recycled crustal rocks and juvenile materials. Combined zircon U-Pb ages and Hf isotope compositions indicate that at ~253 Ma, the Shiwandashan area experienced an intensive thermal event that resulted in the granulite-facies metamorphism; and that crustal remelting occurred at ~234 Ma to form the S-type granitoids during the uplifting stage. The metasedimentary granulite enclaves are resitites of these granitoids.     

Zircon U-Pb SHRIMP dating of the Yematan batholith in Dulan,North Qaidam,NW China

The Yematan batholith crops out over 120 km^2 in the North Qaidam ultrahigh pressure (UHP) metamorphic belt. It consists of granodiorite, monzogranite and biotite granite and forms an irregular intrusion into Neoproterozoic gneiss that has undergone Caledonian UHP metamorphism. Zircons from the Yematan granodiorite yield a SHRIMP U-Pb age of 397 3 Ma. These granitic rocks have geochemical characteristics intermediate between I- and S-type granites, and are post-collisional. We suggest that the Yematan granitic rocks were formed during the last exhumation event of the North Qaidam UHP belt.     

Granitic magmatism related to early Paleozoic continental collision in North Qinling

Zircon U-Pb dating of early Paleozoic granitoids in North Qinling yields three age peaks of ~500, -452 and -420 Ma. They can be temporally correlated with high-pressure to ultrahigh-pressure metamorphism at ca. 500 Ma, retrograde granulite-facies meta- morphisms at ca. 450 Ma and amphibolite-facies metamorphism at ca. 420 Ma, respectively. The first episode of granitic magma- tism is considered to have resulted from continental collision, whereas the second and third episodes of magmatism are attributed to crustal uplifting. Combined with the regional geological setting and new results from high-pressure and ultrahigh-pressure metamorphic rocks, the ca. 500 Ma magmatism is interpreted as the result of partial melting of sedimentary rocks in accretionary wedge between the south Qinling microcontinent and the north Qinling belt including the southern margin of the North China Craton. The ca. 450 Ma intensive magmatism is ascribed to dehydration melting of deeply subducted continental crust at thick- ened conditions in response to slab breakoff, and the final magmatism in ca. 420 Ma is interpreted as the product of partial melt- ing during the tectonic transition from contraction to extension.     

A perspective view on ultrahigh-pressure metamorphism and continental collision in the Dabie-Sulu orogenic belt

The study of continental deep-subduction has been one of the forefront and core subjects to advance the plate tectonics theory in the twenty-first century. The Dabie-Sulu orogenic belt in China crops out the largest lithotectonic unit containing ultrahigh-pressure metamorphic rocks in the world. Much of our understanding of the world＇s most enigmatic processes in continental deep-subduction zones has been deduced from various records in the Dabie-Sulu rocks. By taking these rocks as the natural laboratory, earth scientists have made seminal contributions to understanding of ultrahigh-pressure metamorphism and continental collision. This paper outlines twelve aspects of outstanding progress, including spatial distribution of the UHP metamorphic rocks, timing of the UHP metamorphism, timescale of the UHP metamorphism, the protolith nature of deeply subducted continental crust, subduction erosion and crustal detachment during continental collision, the possible depths of continental subduction, fluid activity in the continental deep-subduction zone, partial melting during continental collision, element mobility in continental deep-subduction zone, recycling of subducted continental crust, geodynamic mechanism of postcollisional magmatism, and lithospheric architecture of collision orogen. Some intriguing questions and directions are also proposed for future studies.     

西昆仑山南缘上三叠统变质岩系及构造变形特征

西昆仑山南侧沿北西向分布的变质复理石海相碎屑岩系,其时代主要属晚三叠世,是巴颜喀喇山群的西延部分。它的东段和西段岩石变质程度、构造样式和变形机制的不同,是同一构造带中不同构造层次构造的反映。东段属下部构造层次,西段属深部构造层次和深熔花岗岩。它们形成于晚三叠世昆仑地块南缘的陆缘盆地,印支期褶皱变质,燕山期和喜山期的挤压、抬升和剥蚀,使东西两段出露了于不同深度构造层次形成的构造。