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A petrographic, geochemical and geochronological investigation of deformed granitoids from SW Rajasthan : Neoproterozoic age of formation and evidence of Pan-African imprintSolanki, Anika M. 07 December 2011 (has links)
MSc., Faculty of Science, University of the Witwatersrand, 2011 / Granitoid intrusions are numerous in southwestern Rajasthan and are useful because they can provide
geochronological constraints on tectonic activity and geodynamic conditions operating as the time of
intrusion, as well as information about deeper crustal sources. The particularly voluminous Neoproterozoic
felsic magmatism in the Sirohi region of Rajasthan is of particular interest as it may have implications for
supercontinental (Rodinia and Gondwana) geometry.
The Mt. Abu granitoid pluton is located between two major felsic suites, the older (~870-800 Ma) Erinpura
granite and the younger (~751-771 Ma) Malani Igneous Suite (MIS). The Erinpura granite is syn- to lateorogenic
and formed during the Delhi orogeny, while the MIS is classified as alkaline, anorogenic and either
rift- or plume-related. This tectonic setting is contentious, as recent authors have proposed formation
within an Andean-type arc setting. The Mt. Abu granitoid pluton has been mapped as partly Erinpura
(deformed textural variant) and partly younger MIS (undeformed massive pink granite). As the tectonic
settings of the two terranes are not compatible, confusion arises as to the classification of the Mt. Abu
granitoid pluton. Poorly-constrained Rb-Sr age dating place the age of formation anywhere between 735 ±
15 and 800 ± 50 Ma. The older age is taken as evidence that the Mt. Abu intrusion was either a late phase
of the Erinpura granite.
However, U-Pb zircon geochronology clearly indicates that the Mt. Abu felsic pluton is not related to- or
contiguous with- the Erinpura granite suite. The major results from this study indicate that the all textural
variants within the Mt. Abu pluton were formed coevally at ~765 Ma. Samples of massive pink granite,
mafic-foliated granite and augen gneiss from the pluton were dated using U-Pb zircon ID-TIMS at 766.0 ±
4.3 Ma, 763.2 ± 2.7 Ma and 767.7 ± 2.3 Ma, respectively.
The simple Mt. Abu pluton is considered as an enriched intermediate I- to A-type intrusion. They are not
anorogenic A-types, as, although these felsic rocks have high overall alkali and incompatible element
enrichment, no phase in the Mt. Abu pluton contains alkali rich amphibole or pyroxene, nor do REE
diagrams for the most enriched samples show the gull-wing shape typical of highly evolved alkaline phases.
The alkali-enriched magma may be explained by partial melting of a crustal source such as the high-K metaigneous
(andesite) one suggested by Roberts & Clemens (1993), not derivation from a mantle-derived mafic
magma. The fairly restricted composition of Mt. Abu granitoids suggests that partial melting and a degree
of assimilation/mixing may have been the major factors affecting the evolution of this granitoid pluton;
fractional crystallization was not the major control on evolution of these granitoids. Revdar Rd. granitoids
that are similar in outcrop appearance and petrography to Mt. Abu granitoids also conform to Mt. Abu
granitoids geochemically and are classified as part of the Mt. Abu felsic pluton.
Mt. Abu samples from this study have a maximum age range of 760.5-770 Ma, placing the Mt. Abu pluton
within the time limits of the Malani Igneous Suite (MIS) as well as ~750 Ma granitoids from the Seychelles.
Ages of the Sindreth-Punagarh Groups are also similar. These mafic-ultramafic volcanics are thought to be
remnants of an ophiolitic mélange within a back-arc basin setting at ~750-770 Ma. The three Indian
terranes are spatially and temporally contiguous. The same contiguity in space and time has been
demonstrated by robust paleomagnetic data for the Seychelles and MIS. These similarities imply formation
within a common geological event, the proposed Andean-type arc (Ashwal et al., 2002) on the western
outboard of Rodinia. The implications are that peninsular India did not become a coherent entity until after
this Neoproterozoic magmatism; Rodinia was not a static supercontinent that was completely
amalgamated by 750 Ma, as subduction was occurring here simultaneous with rifting elsewhere.
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The Mt. Abu pluton has undergone deformation, with much of the pluton having foliated or augen gneiss
textures. The timing of some of the deformation, particularly the augen gneiss and shear zone deformation,
is thought to have occurred during intrusion. The Mt. Abu and Erinpura granitoids have experienced a
common regional metamorphic event, as hornblende (Mt. Abu) and biotite (Erinpura) give 40Ar/39Ar ages of
508.7 ± 4.4 Ma and 515.7 ± 4.5 Ma, respectively. This event may have reactivated older deformatory trends
as well. The temperature of resetting of argon in hornblende coincides with temperatures experienced
during upper-greenschist to lower-amphibolite facies metamorphism. These late Pan-African ages are the
first such ages reported for the Sirohi region and southern part of the Aravalli mountain range. They offer
evidence for the extension of Pan-African amalgamation tectonics (evidence from southern India) into NW
India.
The age of formation of the Erinpura augen gneiss magma is 880.5 ± 2.1 Ma, thus placing the Erinpura
granitoids within the age limits of the Delhi orogeny (~900-800 Ma; Bhushan, 1995). Most deformation
observed here would have been caused by compression during intrusion. The Erinpura granitoids are S-type
granitoids due to their predominantly peraluminous nature, restricted SiO2-content, normative corundum
and the presence of Al-rich muscovite and sillimanite in the mode. Weathered argillaceous
metasedimentary material may also have been incorporated in this magma, while the presence of inherited
cores suggests relatively lower temperatures of formation for these granitoids as compared to the Mt. Abu
granitoids. The age of inheritance (1971 ± 23 Ma) in the Erinpura augen gneiss is taken as the age of the
source component, which coincides with Aravalli SG formation.
The Sumerpur granitoids differ from the Erinpura granitoids in terms of macroscopic and microscopic
texture (undeformed, rarely megaporphyritic) but conform geochemically to the Erinpura granitoid
characteristics and may thus be related to the Erinpura granitoid suite.The Revdar Rd. granitoids that are
similar in macroscopic appearance to Erinpura granitoids also conform geochemically, and may similarly
belong to the Erinpura granite suite. A Revdar Rd. mylonite gneiss with the Erinpura granitoids’
geochemical signature was dated at ~841 Ma, which does not conform to the age of the type-locality
Erinpura augen gneiss dated here, but later intrusion within the same event cannot be ruled out because of
the uncertainty in the age data (~21 Ma). The presence of garnet in one Revdar Rd. (Erinpura-type) sample
implies generation of these granitoids at depth and/or entrainment from the source, similar to the S-type
Erinpura granitoids.
The Ranakpur granitoids differ significantly from both the Erinpura and Mt. Abu intrusives due to their low
SiO2-content and steep REE profiles (garnet present in the source magma); they are thought to have been
generated under higher pressures from a more primitive source. The deeper pressure of generation is
confirmed by the absence of a negative Eu-anomaly. The Ranakpur quartz syenite dated at 848.1 ± 7.1 Ma
is younger by ~30 m.y. than the Erinpura augen gneiss. It is within the same time range as numerous other
granitoids from this region as well as the Revdar Rd. granitoid dated in this study. The prevalence of 830-
840 Ma ages may indicate that a major tectonic event occurred at this time. The Ranakpur quartz syenite
may have been generated near a subduction or collision zone, where thickened crust allows for magma
generation at depth. The deeply developed Nb-anomaly in the spider diagram also implies a larger
subduction component to the magma.
The Swarupganj Rd. monzogranite is interpreted to have formed by high degrees of partial melting from a
depleted crustal source and is dissimilar to other granitoids from this study. More sampling, geochemical
and geochronological work needs to be done in order to characterize this intrusion.
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The Kishengarh nepheline syenite gneiss is situated in the North Delhi Fold Belt and is the oldest sample
dated within this study. The deformation in this sample is due to arc- or continental- collision during a
Grenvillian-type orogeny related to the amalgamation of the Rodinia supercontinent (and peninsular India),
dated by the highly reset zircons at ~990 Ma. This is considered a DARC (deformed alkaline rock and
carbonatite) and represents a suture zone (Leelanandam et al., 2006). The primary age of formation of this
DARC is older than 1365 ± 99 Ma, which is the age of xenocrystic titanites from the sample.
The granitoid rocks from this study area (Sirohi region) range widely in outcrop appearance, petrography
and geochemistry. Granitoids from the Sirohi region dated in this study show a range of meaningful ages
that represent geological events occurring at ~880 Ma, ~844 Ma, ~817 Ma, ~789 Ma, ~765 Ma and ~511
Ma. Granitoid magmatism (age of formation) in this region is predominantly Neoproterozoic, and the
number of events associated with each granitoid intrusion as well as diverse tectonic settings implies a
complexity in the South Delhi Fold Belt that is not matched by the conventional and simplified view of a
progression from collision and orogeny during Grenvillian times (Rodinia formation), through late orogenic
events, to anorogenic, within-plate (rift-related) alkaline magmatism during Rodinia dispersal. Instead, it is
envisaged that convergence and subduction during the formation of Rodinia occurred at ~1 Ga (Kishengarh
nepheline syenite deformation), with a transition to continental-continental collision at ~880-840 Ma
(Erinpura and Ranakpur granitoids). This was then followed by far-field Mt. Abu and MIS magmatism,
related to a renewed period of subduction at ~770 Ma. The last deformatory event to affect this region was
that associated with the formation of Gondwana in the late Pan-African (~510 Ma).
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Fracture study of the Paleozoic bedrock in a portion of east-central IndianaPentecost, David C. 03 June 2011 (has links)
Regional fracture patterns were determined from 2,419 fracture measurements collected from 11 quarries in a portion of East-Central Indiana. When the entire study area was considered, three orthogonal fracture systems were evident. The master system appeared at every station andhad fracture sets striking from N17W to N6W and N85E to N68E. The secondary systems were more inconsistent in respect to their appearance from quarry to quarry and had fracture sets striking approximately N45W and N48E, and N75W and N20E, respectively. The fractures were vertical or nearly so and were interpreted as being extensional in nature.The regional fracture patterns became apparent after data from several quarry walls, including fractures of varying persistence and intensity, were considered in combined plots for each data collection site.Suggested major mechanisms of fracturing include: 1) warping of the Cincinnati Arch, 2) the propagation of pre-existing joints in the basement rock upward into younger material, 3) the release of older residual stresses by the production of positive structural relief with associated erosional unloading, and 4) recent compressive stresses caused by the same mechanism that drives sea-floor spreading.Ball State UniversityMuncie, IN 47306
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An analysis of fracture systems, lithologic character and kinematic history of Paleozoic rock formations in a portion of southeastern IndianaKeene, David G. January 1989 (has links)
This is an analysis of fractures occurring within the Paloezoic sedimentary rocks in a portion of southeastern Indiana. Fifteen hundred seventy-two fractures were used in analysis of distribution, orientation, pervasiveness, persistence, and intensity. The data collected is representative of eight counties and seventeen different collection sites.All fracture data were given an associated numerical value identifying each variable used for analysis and recorded into computer data files. A computer program was used for statistical analysis and construction of equal area nets which graphically displayed the distribution of variables. The compilation of the fracture data allowed for close interpretative analyses of variables and correlation of the orientation and distribution of the fractures within the study area.This study revealed that two orthogonal fracture systems exist in southeastern Indiana. The fracture set containing the largest percentage of those measured is oriented N11W with its compliment oriented N73W. The orientation of the second largest fracture set is N8E with its compliment oriented N82°W.The effects of the tectonic history as well as contemporary stress on the area are discussed relative to their effects on the overall distribution of fracture sets.Evidence is presented to substantiate a reactivation of the Cincinnati Arch as indicated in the Devonian-Mississippian lithologic units from data collected in the southeastern portion of the study area. Fracture data correlating to these units displays a rotation of the major fracture set maxima 90w. This data is supported by radiometric dates from the Belfast member of the Brassfield Limestone in which Laskouski, et.al., correlated a reactivation of the arch.Also within this study are lithologic descriptions of all the Paleozoic formations used for data collection. These descriptions were developed over a three year period from extensive field observation.A map of the study area is presented displaying the distribution and orientation of the fractures recorded at each data collection site. / Department of Geology
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Diagenesis and deep-water depositional environments of lower Paleozoic continental margin sediments in the Québec City area, CanadaOgunyomi, Olugbenga January 1980 (has links)
Deep-water clastic sediments of the lower Paleozoic continental margin in the Quebec City area are piled up in imbricated thrust sheets and nappes constituting the External Domain of the Northern Appalachians. The youngest sediments (Middle Ordovician Citadelle and Quebec City Formations) occu
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The stratigraphy and structure of the type-area of the Chilliwack group, : southwestern British ColumbiaMonger, James William Heron January 1966 (has links)
The stratigraphy and structure of Upper Palaeozoic and Mesozoic sedimentary
and volcanic rocks, and of amphibolitic rocks of unknown age, were studied in an area of about 140 square miles in the Cascade Mountains of southwestern British Columbia.
The amphibolitic rocks are probably of diverse origins; their stratigraphic relationship to the other rocks is not known, although they may, in part, be equivalent to pre-Devonian rocks in northwestern Washington.
Upper Palaeozoic rocks comprise the Chilliwack Group. The base is not exposed. Oldest rocks are volcanic arenites and argillites which are overlain by an argillaceous limestone, about 100 feet thick, in which Early Pennsylvanian (Morrowan) fusulinids occur. Apparently conformably overlying the limestone is a succession of argillites, coarse volcanic arenites, minor conglomerate and local tuff, which contains both marine and terrestrial fossils and ranges in thickness from 450 to 800 feet. A cherty limestone, generally about 300 feet thick, in which there is an Early Permian (Leonardian) fusulinid fauna, is conformable upon the clastic sequence. Altered lavas and tuffs are in part laterally equivalent to this Permian limestone, and, in part, overlie it; these volcanic rocks range in thickness from 700 to 2,000 feet.
Disconformably above the Permian volcanic rocks are argillites and volcanic arenites of the Cultus Formation. This formation is apparently about 4,000 feet thick, contains Late Triassic, Early and Late Jurassic fossils and no stratigraphic breaks have been recognized within it.
All of these rocks underwent two phases of deformation between Late Jurassic and Miocene time. The first phase, correlated with mid-Cretaceous deformation in northwestern Washington, was the most severe., and thrusts and major, northeast-trending recumbent folds were formed. These structures subsequently were folded and faulted along a northwest trend, possibly in response to differential uplift of the Cascade Mountains. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
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Diagenesis and deep-water depositional environments of lower Paleozoic continental margin sediments in the Québec City area, CanadaOgunyomi, Olugbenga January 1980 (has links)
No description available.
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Geology and geochronology of the Avawatz Mountains, San Bernardino County, CaliforniaSpencer, Jon Eric January 1981 (has links)
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1981. / Microfiche copy available in Archives and Science / Includes bibliographies. / by Jon Eric Spencer. / Ph.D.
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A geologic investigation of contact metamorphic deposits in the Coyote Mountains, Pima County, ArizonaCarrigan, Francis John, 1941- January 1971 (has links)
No description available.
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Stratigraphic and structural framework of Himalayan foothills, northern PakistanPogue, Kevin R. 03 December 1993 (has links)
The oldest sedimentary and metasedimentary rocks exposed
in the Himalayan foothills of Pakistan record a gradual transition
seaward from the evaporites of the Salt Range Formation to pelitic
sediments deposited in deeper water to the north. The Upper
Proterozoic Tanawal Formation was derived from erosion of a
northern highland produced during the early stages of Late
Proterozoic to early Ordovician tectonism. Early Paleozoic tectonism
is indicated by an angular unconformity at the base of the Paleozoic
section, the intrusion of the Mansehra Granite, and the local
removal of Cambrian strata. Paleozoic shallow-marine strata are
preserved in half-grabens created during extensional tectonism
that began during the Carboniferous and climaxed with rifting
during the Permian. Paleozoic rocks were largely or completely
eroded from northwest-trending highlands on the landward side of
the rift shoulder. Thermal subsidence of the rifted margin resulted
in transgression of the highlands and deposition of a Mesozoic
section dominated by carbonates. Compressional tectonism related
to the impending collision with Asia commenced in the Late
Cretaceous. Rocks north of the Panjal-Khairabad fault were
deformed and metamorphosed during Eocene subduction of
northern India beneath the Kohistan arc terrane. Following their
uplift and exhumation, rocks metamorphosed beneath Kohistan
were thrust southward over unmetamorphosed rocks along the
Panjal and Khairabad faults which are inferred to be connected
beneath alluvium of the Haripur basin. Contrasts in stratigraphy
and metamorphism on either side of the Panjal-Khairabad fault
indicate that shortening on this structure exceeds that of any other
fault in the foothills region. The migration of deformation towards
the foreland produced south- or southeast-vergent folds and thrust
faults in strata south of the Panjal-Khairabad fault and reactivated
Late Cretaceous structures such as the Hissartang fault. The
Hissartang fault is the westward continuation of the Nathia Gali
fault, a major structure that thrusts Proterozoic rocks in the axis of
a Late Paleozoic rift highland southward over Mesozoic strata.
Fundamental differences in stratigraphy, metamorphism, and
relative displacement preclude straightforward correlation of faults
and tectonic subdivisions of the central Himalaya of India and
Nepal with the northwestern Himalaya of Pakistan. / Graduation date: 1994
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Paleozoic tectonic evolution of the Chinese Altai Orogen: contraints from geochemical and geochronologic studies ofmafic rocksWong, Po-wan, Kenny., 王步雲. January 2010 (has links)
published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy
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