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1.
Multiple deformation in all the Precambrian metamorphic-migmatitic rocks has been reported from Rajasthan during the last
three decades. But, whereas the Aravalli Group and the Banded Gneissic Complex show similarity in the style and sequence of
structures in all their details, the rocks of the Delhi Group trace a partly independent trend. Isoclinal folds of the first
generation (AF1) in the rocks of the Aravalli Group had gentle westerly plunge prior to later deformations. These folds show reclined, inclined,
and upright attitude as a result of coaxial upright folding (AFla). Superposition of upright folds (AF2) of varying tightness, with axial plane striking N to NNE, has resulted in interference patterns of diverse types in the
scale of maps, and deformation of earlier planar and linear structures in the scale of hand specimens. The structures of the
third generation (AF3) are either open recumbent folds or reclined conjugate folds with axial planes dipping gently towards NE or SW. Structures
of the last phase are upright conjugate folds (AF4) with axial planes striking NNE-SSW and E-W.
The Banded Gneissic Complex (BGC) underlies the Aravalli Group with a conglomerate horizon at the contact, especially in southern
Rajasthan. But, for a major part of central and southern Rajasthan, migmatites representing BGC show a structural style and
sequence identical with those in the Aravalli Group. Migmatization, broadly synkinematic with the AF1 folding, suggests extensive remobilization of the basement. Very rare relict fabric athwart to and overprinted by structures
of AF, generation provide tangible evidence for a basement.
Although the structures of later phases in the rocks of the Delhi Group (DF3 and DF4) match with the late-phase structures in the Aravalli Group (AF3 and AF4), there is a contrast in the structural history of the early stages in the rocks of the two groups. The folds of the first
generation in the Delhi Group (DF1) were recumbent to reclined with gentle plunge towards N to NNE or S to SSW. These were followed by coaxial upright folds
of varying tightness (DF2). Absence of westerly trending AF1 folds in the Delhi Group, and extreme variation in plunge of the AF2 folds in contrast with the fairly constant plunge of the DF2 folds, provide evidence for an angular unconformity between the Aravalli and the Delhi Groups.
Depending on the importance of flattening attendant with and following buckling during AF2 deformation, the lineations of AF1 generation show different patterns. Where the AF1 lineations are distributed in circular cones around AF2 axes because of flexural-slip folding in layered rocks with high viscosity contrast, loci of early lineations indicate that
the initial orientation of the AF1 axes were subhorizontal, trending towards N280°.
The orientation of the axial planes of the earlier folds has controlled the development of the later folds. In sectors where
the AF, axial planes had N-S strike and gentle dips, or E-W strike with gentle to steep dips, nearly E-W horizontal compression
during AF2 deformation resulted in well-developed AF2 folds. By contrast, where the AF, axial planes were striking nearly N-S with steep dips, E-W horizontal compression resulted
in tightening (flattening) of the already isoclinal AF1 folds, and probably boudinage structures in some instances, without the development of any AF2 folds. A similar situation obtains when DF4 deformation is superposed on earlier structures. Where the dominant S-planes were subhorizontal, N-S compression during DF4 deformation resulted in either chevron folds with E-W striking axial plane or conjugate folds with axial plane striking NE
and NW. In zones with S-planes striking E-W and dipping steeply, the N-S compression resulted in flattening of the earlier
folds without development of DF4 folds. 相似文献
2.
Sumit Kumar Ray 《Precambrian Research》1974,1(2):157-164
Axial culminations and depressions of folds are common in regions of superposed deformations involving two sets of folds at high angles to each other. If the intensity of the later folding in these cases exceeds a particular limit, plunge reversal of the early folds gives way to “plunge inversion”. In such instances, segments of early folds rotate through end-on or reclined geometry while being refolded. And instead of plunge reversal at the hinge zones of later folds, the early folds plunge in the same direction in both limbs of the later folds. As a result, an antiform will pass along the axial trend to a synform. A particularly clear instance of plunge inversion has been noted from the “Sawar outlier” comprising a metasedimentary sequence within the older Banded Gneissic Complex in central Rajasthan. In Sawar, the southern segment of a south-southwest-trending synformal early fold has been inverted to attain an antiformal geometry because of superposition of a later fold at high angles to the early fold axes and axial planes. The deformation history of the large-scale folds has been traced and the stratigraphic implications of the plunge inversion discussed. From the movement pattern, it seems justifiable to correlate the metasedimentary sequence of the outlier with the Late Precambrian Delhi Group of parametamorphic rocks. 相似文献
3.
The rocks of the Delhi Supergroup, which occur around Barr-Sendra and Phulad-Deogarh regions in Central Rajasthan, show three
phases of deformational episodes: (i) phase D1—tight-to-long limbed isoclinal fold (F1); phase D2—open, asymmetric fold (F
2) controlling the map pattern of the formational boundaries; and (iii) phase D3—major warps (F3). Interference between nearly coaxial F1 and F2 on northerly axes produced hook-shaped and crescent patterns whereas superimposition of easterly trending F3 on F2 produced dome-and-basin patterns. The thermal peak was achieved during the second phase of deformation when the rocks were
constructively metamorphozed and granites (850−750 m.y.), late synkinematic with respect to second phase of deformation, were
emplaced. The sequence of deformation and the structural pattern of the rocks of the Delhi Supergroup in Central Rajasthan
strikingly resemble those in northeastern Rajasthan. Structurally the characteristics of the Delhi Supergroup as verified
in the entire region from NE to Central Rajasthan are: (a) the same sequence of development of folds, F1, F2 and F3, interspersed with nearly identical phases of recrystallization, (b) hook-shaped interference pattern due to near-coaxial
refolding of F1 by F2, and (c) variation in axial plunge of F2 resulting in culminations and depressions. Lastly, phases of the recrystallization history indicates little time gap between
F1 and F2, and a considerable gap between F2 and F3. 相似文献
4.
Detailed structural and lithological mapping of the Aravalli rocks overlying the Mewar Gneiss in the area east of Udaipur,
Rajasthan, suggests presence of blocks bounded by faults, showing a contrasting structural pattern. The contrast is reflected
in the differential development and in the orientation of AF1, AF2 and AF4 folds in different blocks. In the central Umra
block, the rocks constitute a virtually homoclinal sequence showing one dominant orientation of bedding and axial planar schistosity.
Fold axes, lineations andβ orientations indicate presence of reclined folds of AF1 generation. AF2 folds are either absent or have developed only locally.
The two other blocks which border the Umra block show development of large AF2 synforms and local minor antiforms having N-S
or NNE-SSW trend. The folds interfere with AF4 folds producing irregular domes and basins in the western Kanpur-Kalarwas Block
and minor plunge reversals in Bagdara-Dhamdhar Block. It is argued that the constituents of the different blocks which formed
a collage of rift basins and horsts during sedimentation, responded differentially to deforming forces because of differential
mobility of the underlying basement. 相似文献
5.
Marble, calc-silicate rock, quartzite and mica schist of Precambrian age in the ‘main Raialo syncline’ in the Udaipur district of central Rajasthan, India, have been affected by folding of four main generations (F1–F4), the first two of which are seen in the scale of map to microsection. The very tight to isoclinal F1 folds with long limbs and thickened hinges are generally reclined or inclined, and plunge gently castward or westward where least reoriented. The axial planes of the F1 folds have been involved in upright warps on east-west axes (F1′), nearly coaxial with the F1 folds, in some sectors. These folds have been overprinted by upright F2 folding of varying tightness with the axial planes striking north to northeast, resulting in interference patterns of different types in all scales. A penetrative axial plane foliation related to F1 folding and a crenulation cleavage parallel to the F2 axial pianes are seen in the micaceous rocks. Two sets of conjugate folds and kink bands of smail scale have been superimposed on the F1–F2 folds in thinly foliated rocks. The first of these sets (F3) has its conjugate axial planes dipping gently northeast and southwest, whereas the paired axial planes of the later set (F4) are vertical with north-northwest and east-west strikes. 相似文献
6.
Ram S. Sharma 《Precambrian Research》1977,4(2):133-162
Large-scale structures, textures and mineral assemblages in the Precambrian rocks of the Banded Gneissic Complex and the overlying Delhi Group in north-central Aravalli Mountain reveal a complex deformational-crystallization history. In the basement Gneissic Complex at least three deformational events, D0, D1 and D2, and two separate episodes of metamorphism, M1 and M2, are recognized. The supracrustal Delhi Rocks display only two phases of deformation, D1 and D2, associated with a single protracted period of metamorphism, M2.The first phase of deformation (D1) of the Delhi orogeny (1650-900 m.y.) produced large isoclinal folds that are overturned towards the southeast and have gentle plunges in NE and SW directions. The second phase of deformation (D2) gave rise to tight open folds on the limbs and axial-plane surfaces of the D1 folds. These folds generally plunge towards the N and NNW at 30°–80°. In the Basement Complex one more deformation (D0) of the Pre-Delhi orogeny (> 2000 m.y.) is recorded by the presence of reclined and recumbent folds with W to WNW trending fold axes. The D0 folds were superimposed by D1 and D2 folds during the Delhi orogeny.The three deformational events have been correlated with the crystallization periods of minerals in the rocks and a setting in time is established for this part of the Aravalli range. 相似文献
7.
Structural, stratigraphic and petrologic studies between Amet and Sembal in the Udaipur district of southcentral Rajasthan indicate that all the rocks belonging to the Banded Gneissic Complex, the Aravalli Group and the Raialo Formation have been involved in isoclinal folding on a westerly trend, co-axial refolding, and upright folding on a north to north-northeast trend. There is neither an unconformity nor an overlap between the Aravallis and the Raialos. The conglomerates supposed to mark the erosional unconformity above the Banded Gneissic Complex near Rajnagar is a tectonic mélange of folded and torn quartz veins in mica schist within the Aravalli Group. The Aravalli—Raialo metasediments have been migmatized synkinematically with the first folding to give rise to the Banded Gneissic Complex; the gneissic complex does not have any separate stratigraphic entity. By contrast, there is an undoubted erosional unconformity between the type Aravalli rocks and the underlying Sarara granite to the south. These relations, coupled with the continuity of the Aravalli rocks of Udaipur northward to the metasedimentary rocks of the Sembal—Amet area along the strike, and a comparable structural history, point to granitic rocks of at least two generations in the Early Precambrian of central and southern Rajasthan. Preliminary radiometric dating of rocks of known stratigraphic—structural relationship seems to confirm the presence of granitic rocks of two ages in the Early Precambrian, and of a considerable interval between the deposition of the Aravalli—Raialo rocks and the Delhi rocks. The Udaipur granite, post-dating the first deformation but preceding the upright folding on the northerly trend, provides evidence for granitic activity of a third phase before the deposition of rocks of the Delhi Group. 相似文献
8.
Abstract Two varieties of charnockites are recognized in the Dharwar craton of southern India. The style and sequence of structures in one charnockite variety, and related intermediate to basic granulites, are similar to those in the supracrustal rocks of the Dharwar Supergroup and the adjacent Peninsular Gneiss. This style has isoclinal folds with long limbs and sharp hinges with an axial planar fabric in some instances. Additional evidence of flattening is provided by pinch-and-swell and boudinage structures, with basic granulites forming boudins in the more ductile charnockites/enderbites in the limbs of isoclinal folds. These folds are involved in near-coaxial upright folding resulting in the bending of the axial planes of the isoclinal folds and the associated boudins. All these structures are overprinted by non-coaxial upright folds with axial planes striking nearly N–S. The map pattern of charnockites suggests that this sequence of structures is present not only on a mesoscopic scale, but also on a macroscopic scale. Charnockites of this variety provide, in some instances, evidence of having been migmatized to give rise to hornblende–biotite gneiss and biotite gneiss, which form a part of the Peninsular Gneiss terrane.
The second variety comprises charnockite sensu stricto with an entirely different structural style. This type occurs in the tensional domains of the hinge zones of the later buckle folds, in the necks of foliation boudinage, in shear zones and in release joints parallel to the axial planes of the later folds in the Peninsular Gneiss. Because the non-coaxial later folds are associated with a strain pattern different from, and later than, that of the isoclinal folds of the first generation, it follows that charnockites of the Dharwar craton have evolved in at least two distinct phases, separate both in time and in process. 相似文献
The second variety comprises charnockite sensu stricto with an entirely different structural style. This type occurs in the tensional domains of the hinge zones of the later buckle folds, in the necks of foliation boudinage, in shear zones and in release joints parallel to the axial planes of the later folds in the Peninsular Gneiss. Because the non-coaxial later folds are associated with a strain pattern different from, and later than, that of the isoclinal folds of the first generation, it follows that charnockites of the Dharwar craton have evolved in at least two distinct phases, separate both in time and in process. 相似文献
9.
The Proterozoic basins of India adjoining the Eastern Ghats Granulite Belt (EGGB) in eastern and southern India contain both Mesproterozoic and Neoproterozoic successions. The intracratonic set-up and contractional deformation fo the Neoproterozoc successions in the Paland sub-basin in the northeastern part of Cuddapah basin and similar crustal shortening in contemporaneous successions lying west of the EGGB and Nellore Schist Belt (NSB) are considered in relation to the proposed geodynamic evolution of the the Rodinia and Gondwana supercontinents. Tectonic shortening in the Palnad sub-basin (northeast Cuddapah), partitioned into top-to-westnorthwest thrust shear, flexural folds and cleavage development under overall E-W contraction, suggests foreland style continental shortening within an intracratonic set-up. A thrust sheet containing the Nallamalai rocks and overlying the Kurnool rocks in the northeastern part of Palnad sub-basin exhibits early tight to isoclinal folds and slaty (phylllitic) cleavage, which can be correlated with early Mesoproterozoic deformation structures in the nothern Nallamalai Fold Belt (NFB). NNE-SSW trending folds and cleavage affect the Kurnool Group and overprint earlier structures in the thrust sheet. Thrusting of the Nallamalai rocks and the later structures may have been related to convergence of the Eastern Ghats terrane and the East-Dharwar-Bastar craton during Early Neoproterozoic (Greenvillian) and/or later rejuvenation related to Pan-African amalgamation of East and West Gondwana. 相似文献
10.
The Wadi Hafafit Complex (WHC) is an arcuate belt of orthogneisses, migmatites and other high-grade metamorphic rocks, which marks the boundary between the Central Eastern and the South Eastern Deserts of Egypt. In the WHC, gneissic meta-gabbro outlines macroscopic fold interference patterns characterized by elliptical to irregular culminations cored by gneissic meta-tonalite to meta-trondhjemite. The five main culminations of the WHC have previously been labeled A (most northerly), B, C, D and E (most southerly). A detailed structural investigation of B, C, D and E reveals that these structures are a result of the interference of four macroscopic fold phases, the first three of which may represent a single deformation event. The first folding involved sheath-like fold nappes, which were transported to the N or NW, assisted by translation on gently dipping mylonite zones. The regional gneissosity and mineral extension lineations formed during this folding event. The fold nappes were deformed by mainly open upright small macroscopic and mesocopic folds with approximately NE-trending hinges. As a probable continuation of the latter folding, the sheaths were buckled into large macroscopic folds and monoclines with the same NE-trends. The fourth macroscopic folding resulted from shortening along the NE–SW direction, producing mainly NW–SE-trending upright gently plunging folds. Gravitative uplift is disputed as a component of the deformation history of the WHC. The peculiarities of the fold interference pattern result from the interesting behaviour of sheath folds during their refolding. 相似文献
11.
12.
The Chengde-Pingquan region is located in the central part of the Yanshan Orogenic Belt (YOB). At Daheishan and Pingquan in the central YOB, thrusts and folds of variable trends are displayed in 2 km-scale fold interference patterns. Detailed field mapping was conducted to decipher the geometry of these two superimposed structures. Map-view geometry and stereonet plots for outcrop-scale folds indicate that the superimposed structures form arrowhead interference pattern where NW-SE-trending F1 folds are refolded by later ENE-WSW F2 folding. After remove the effects of later faulting, restored map-views of the superimposed structures show that when the F1 folds have inclined axial surfaces but with no an overturned limb, an arrowhead interference pattern (here called modified type-2 pattern) can form. Our field data and reinterpretation of the findings of previous studies suggest that five major shortening phases have occurred in the Chengde-Pingquan region. The first two phases, which formed the superimposed folds, occurred earlier than the Late Triassic (D1) and during the Late Triassic to Early Jurassic (D2). These two phases were followed by three deformation phases that are mainly characterized by thrusting and strike-slip faulting, which strongly modified the large-scale fold interference patterns. 相似文献
13.
Dhruba Mukhopadhyay Nandini Chattopadhyay Tapas Bhattacharyya 《Journal of the Geological Society of India》2010,75(1):18-31
The structural geometry of the Anasagar gneiss dome in the axial zone of the South Delhi Fold Belt is controlled by polyphase
folding. It is classified as a thrust-related gneiss dome and not as a metamorphic core complex. Four phases of deformation
have affected both the gneiss and the enveloping supracrustal rocks. D2 and D3 deformations probably represent early and late stages of a progressive deformation episode in a simple shear regime combined
with compression. The contact between the gneiss and the supracrustal rocks is a dislocation plane (thrust) with top-to-east
sense of movement which is consistent with the vergence of the D2 folds. The thrust had a ramp-and-flat geometry at depth. At the present level of exposure it is a footwall flat (that is,
parallel to the gneissosity in the footwall), but it truncates the bedding of the hanging wall at some places and is parallel
at others. The thrusting was probably broadly coeval with the D2 folds and the thrust plane is locally folded by D2. D2 and D3 folds have similar style and orientation as the first and second phases respectively of major folds in the Delhi Supergroup
of the South Delhi Fold Belt and these are mutually correlatable. It is suggested that D1 may be Pre-Delhi in age. Available
geochronological data indicate that the emplacement of the Anasagar gneiss predated the formation of volcanic rocks in the
Delhi Supergroup and also predated the main crust forming event in the fold belt. The Anasagar gneiss and its enveloping supracrustal
rocks are probably older than the Delhi Supergroup. 相似文献
14.
Age determinations mostly by Rb/Sr whole rock isochrons of the Precambrian rocks of Rajasthan in northwest India are summarized
and discussed. On present sampling and subject to its possible bias, the following conclusions can be made. The Untala Granite
believed to be intrusive into the gneissic terrain (bgc) east of Udaipur has the oldest age, 2.95 b.y. yet measured for a granite in Rajasthan. This, coupled with the lead isochron
age of 3.5 b.y. for detrital zircon from the Aravalli schists by Vinogradov and others extends the basement of Rajasthan well
into the Archaean. The time equivalence of thebgc east of Udaipur with the Berach Granite dated only at 2.55 b.y. is not tenable. No satisfactory radiometric age control exists
for the onset and duration of the Aravalli Supergroup, believed to be an early Proterozoic linear belt.
Heron’s original Delhi Supergroup has recorded acid magmatism widely separate in space and time. The earliest activity between
1700 and 1500 m.y. is recorded mainly in the Alwar basin in northeastern Rajasthan while the younger activity between 850
and 750 m.y. is represented by the ‘Erinpura type’ granites in the central and southern Aravalli sector. This younger event
not only has let its thermal overprinting on the older Alwar rocks but also marks the onset of emplacement of the Malani Igneous
suite in the trans-Aravalli terrain. This raises the new possibility that the Delhi rocks of Heron represent atleast two chronologically
independent sequences with varying geographical extent. The trans-Aravalli terrain is most probably floored by partly reworked,
crystalline basement and developed along linear rift zones which acted as loci for high heat flow and igneous activity since
about 800 m.y. ago. 相似文献
15.
P. K. Gangopadhyay 《Journal of Earth System Science》1995,104(3):523-537
The Dating rocks and Darjeeling gneisses, which constitute the Sikkim dome in eastern Himalaya, as well as the Gondwana and
Buxa rocks of ‘Rangit Window’, disclose strikingly similar sequences of deformation and metamorphism. The structures in all
the rocks belong to two generations.
The structures of early generation are long-limbed, tight near-isoclinal folds which are often intrafolial and rootless. These
intrafolial folds are associated with co-planar tight folds with variably oriented axes and sheath folds with arcuate hinges.
Penetrative axial plane cleavage and mineral lineation are related structures; transposition of bedding is remarkable. This
early phase of deformation (D
1) is accompanied by constructive metamorphism. The structures of later generation are open, asymmetrical or polyclinal; a
crenulation cleavage or discrete fracture may occur. The structures of early generation are distorted by folds of later generation
and recrystallized minerals are cataclastically deformed. Recrystallization is meagre or absent during the later phase of
deformation (D
2).
The present discussion is on structures of early generation and strain environment during theD
1 phase of deformation. The concentration of intrafolial folds in the vicinity of ductile shear zones and decollement or detachment
surface (often described as ‘thrust’) may be considered in this context. The rocks of Darjeeling-Sikkim Himalaya display minor
structures other than intrafolial folds and variably oriented co-planar folds. The state of finite strain in the rocks, as
observed from features like flattened grains and pebbles, ptygmatic folds and boudinaged folds indicate combination of flattening
and constrictional type strain. The significance of the intrafolial folds in the same rocks is discussed to probe the environment
of strain during progressive deformation (D
1). 相似文献
16.
福建宁化溪源锌矿床的地质特征及其成因探讨 总被引：3，自引：0，他引：3
位于闽西北的溪源锌矿床产在中变质的中-上元古界黄潭组中段第二层和第四层中,呈层状,沿走向、倾向变化较稳定。矿层与围岩存在着过渡的关系。矿区内中-上元古界黄潭组至少经历了两期叠加的褶皱构造变形,早期为紧闭等斜向形,构成矿区的主体构造,总体为近东西向,向南西倾伏;晚期为直立褶皱,褶皱轴主要为北东—北北西向。矿区的断裂和岩脉均形成于成矿后,对含矿层位起破坏作用。矿床成因类型为沉积一变质型,属于同生型层控矿床。中-上元古界黄潭组中段含矿层位的透辉石岩等钙镁质岩是锌矿矿源层。区域变质产生的热液交代矿源层及其围岩,造成矿质分配、富集成矿。后期岩浆热液的改造叠加了铍矿化,并导致锌矿的再次富集,但仅限于局部,意义不大。 相似文献
17.
Brittle and ductile deformation of alternating layers of Devonian sandstone and mudstone at Cape Liptrap, Victoria, Australia, resulted in upright folds with associated fold accommodation faults and multiple fracture sets. Structures were mapped at the Fold Stack locality at Cape Liptrap using high-resolution aerial photographs acquired by a digital camera mounted on an unmanned aerial vehicle (UAV). Subsequent photogrammetric modelling resulted in georeferenced spatial datasets (point cloud, digital elevation model and orthophotograph) with sub-cm resolution and cm accuracy, which were used to extract brittle and ductile structure orientation data. An extensive dataset of bedding measurements derived from the dense point cloud was used to compute a 3D implicit structural trend model to visualise along-strike changes of Devonian (Tabberabberan) folds at the Fold Stack locality and to estimate bulk shortening strain. This model and newly collected data indicate that first generation shallowly south-southwest plunging upright folds were gently refolded about a steeply plunging/subvertical fold axis during a Devonian low-strain north–south shortening event. This also led to the local tightening of first generation folds and possibly strike-slip movement along regional scale faults. In order to distinguish fractures associated with Devonian compression from those that formed during Cretaceous extension and later inversion, we compared the five fracture sets defined at Cape Liptrap to previously mapped joints and faults within the overlying sedimentary cover rocks of the Cretaceous Strzelecki Group (Gippsland Basin), which crop out nearby. An east-southeast trending fracture set that is not evident in the Strzelecki Group can be linked to the formation of Devonian folds. Additionally, hinge line traces extracted from the Fold Stack dataset are aligned parallel to a dominant fracture set within the overlying cover sediments. This suggests that basement structures (folds and coeval parallel faults) have an important influence on fault and joint orientations within Cretaceous cover rocks. 相似文献
18.
J. W. Pickett with contribution by J. S. Jell G. Seddon P. Telford & A. J. Wright 《Australian Journal of Earth Sciences》2013,60(4):457-466
In the Precambrian rocks west and southwest of the Mount Isa Fault three significant fold generations are recognized. Within individual successions, units containing an early phase of deformation are juxtaposed by a late fault against a sequence that does not share these earlier events. Many of the large‐scale structures in the Judenan Beds are first‐generation folds, whereas west of the Judenan Beds the area is dominated by second‐generation folds. These two sets of folds are tentatively correlated and are referred to as the Judenan Folds. An earlier set of pre‐Judenan folding is only found in the units west of the Judenan Beds. One phase of the Sybella Granite is also associated with the Judenan folding. Later small‐scale folds associated with a crenulation cleavage are, however, of little regional importance and are commonly found only in zones of highly deformed rocks. 相似文献
19.
对于朝鲜平南盆地沉积盖层内发育的倒转褶皱,过去一般认为是直立褶皱的次级从属褶皱。通过对平南盆地内倒转褶皱发育区详细的地质调查,结合煤炭开发过程中获得的地质及钻探资料,提出平南盆地内叠加褶皱的主要识别标志为：地质平面图上呈现不同类型的两组褶皱脊线的交叉;倒转褶皱的轴面被直立褶皱改造弯曲;直立褶皱的两翼发育的倒转褶皱表现为两组牵引褶皱。查明了平南盆地存在3个阶段的褶皱构造：第一阶段为东西向的倒转褶皱,形成于印支期;第二阶段褶皱为东西向的直立褶皱,形成于早燕山期;第三阶段褶皱为北北东向的直立褶皱,形成于晚燕山期。 相似文献
20.
NILANJAN DASGUPTA TARITWAN PAL JOYDEEP SEN TAMOGHNO GHOSH 《Journal of Earth System Science》2011,120(4):617-626
The study involves the characterization of pegmatoidal granite, southeast of Beawar, Ajmer district, Rajasthan. Earlier researchers
had described this granite as part of the BGC, basement to the Bhim Group of the Delhi Super Group rocks. However, the present
study indicates that it is younger than the rocks of Bhim Group of South Delhi Fold Belt, into which it is intrusive. The
intrusion is structurally controlled and the outcrop pattern is phacolithic. The granite had intruded post-D2 deformation of the Delhi orogeny along the axial planes of D2 folds. The intrusion has also resulted in the formation of a contact aureole about the calc gneisses. 相似文献