Diabase Intrusions Research Articles

Multiple ages of Nipissing Diabase intrusion: paleomagnetic evidence from the Englehart area, Ontario

Nipissing Diabase sills and baked host sediments of the Coleman Member of the Huronian Supergroup east of Englehart, Ontario, are shown to have a characteristic remanent magnetization direction (called N3) that is steeply up and to the west (D = 268.0°, I = −59.0°, k = 42, α95 = 6.0°). Petrographic study indicates that fresh pyroxene gabbro carries the N3 component at most sill sites. A baked contact test with the Coleman Member suggests that the magnetization is primary. The N3 magnetization direction is unlike either the N1 or N2 magnetization direction reported for Nipissing sills at other localities in the Southern Province. Three distinct ages of Nipissing sill emplacement are proposed. A single Nipissing sill site in the sampling area carries the N1 direction.A northeast-trending diabase dyke crosscuts both the Nipissing sills and Coleman sediments. It carries an N2 direction and has overprinted nearby intrusive and sedimentary rocks (D = 282.0°, I = 61.1°, k = 48, α95 = 5.8°). Several N3 sill sites far from the dyke may also carry a softer N2 overprint. However, the N3 and N2 directions and the direction of the present Earth's magnetic field fall near a great circle, making it difficult to separate the N2 and present-field components in such cases.

Diagenesis of the Upper Proterozoic Siliciclastic Sediments of the Taoudeni Basin (West Africa) and Relation to Diabase Emplacement

ABSTRACT The predominantly siliciclastic Upper Proterozoic sediments of the Taoudeni basin have been buried to depths of 2.5 to 3 km. In a normal geothermal gradient 25°C/km), maximum burial temperatures of the section studied would be no higher than 100°C. However, detailed petrographic and fluid inclusion data of sandstones and shales from three areas in Mauritania and Mall along the western side of the basin indicate two major diagenetic events: an earlier low temperature (< 70°C) quartz cementation of the sandstones and a later high temperature (135-170°C diagenesis that affected both shales and sandstones. These latter temperatures are too high to have occurred simply in response to burial. The sediments are cut by numerous Jurassic diabase intrusions, which crop out es ecially commonly in the south and the northeast. The emplacement of these diabases was related to the opening of the South Atlantic ocean. Contact metamorphism and hydrothermal alteration are visible near intrusive contacts. In western Mall (southern part of basin) where the largest exposed sill in the basin occurs, at 50 to 60 km from any outcropping massive diabase, the late diagenetic paragenesis consists of micas, illite, chlorite, kaolinite, siderite and ankerite. High-temperature diagenesis is also observed in Adrar of Mauritania (northwestern part of basin) where outcropping diabases are extremely rare. There, calcite cement is associated with illite and chlorite. Fluid inclusions indicate formation temperatures of 135°C for the ankerite and 170°C for the calcite. Thus, in spite of a thin sedimentary pile, the Taoudeni basin experienced a high-temperature diagenesis. We propose that this resulted from circulation of hot fluids, generated during the diabase emplacement, over extensive areas within the basin.

Mineral Reactions and Controls on Zeolite-facies Alteration in Sandstone of the Central Transantarctic Mountains, Antarctica

ABSTRACT Sandstone, mudstone and tuff of the Triassic Fremouw and Falla formations display diagenetic and zeolite-facies mineral assemblages that were controlled by parent material composition, fluid chemistry, permeability and temperature. Diagenetic reactions between sediments and ground water at near-surface temperature and pressure resulted in formation of smectite, chlorite, quartz, heulandite, mordenite and analcime cements and grain replacements. Zeolite-facies alterations, which resulted from simple rock-fluid reactions driven by heat from Jurassic diabase intrusions, converted smectite to illite-rich ordered mixed-layer illite/smectite and produced albite, laumontite, prehnite, epidote and chlorite cements and grain replacements. Organic maturation data suggest that, away from local e fects of the intrusions, temperatures may have been as low as 130° to 160°C, whereas stratigraphic evidence suggests maximum pressures of about 750 bars. Chemical patterns in sandstone near intrusions indicate that, although diabase supplied heat to drive rock-fluid reactions, it did not contribute a significant amount of cations to the hydrochemical system. Mineral and chemical patterns, together with hypothesized mineral reactions, suggest that significant mass transfer of Na+, Ca+2 and Si+4 occurred during alteration, whereas Al+3 mobility was restricted to migration from the reaction site to nearby pore space where Al+3 was incorporated into clay and/or zeolite cements.

Geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal Great Valley Group, northern California Coast Ranges

Research Article| November 01, 1988 Geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal Great Valley Group, northern California Coast Ranges GLENN J. MACPHERSON; GLENN J. MACPHERSON 1Department of Mineral Sciences, U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560 Search for other works by this author on: GSW Google Scholar STEPHEN PAUL PHIPPS STEPHEN PAUL PHIPPS 2Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316 Search for other works by this author on: GSW Google Scholar Author and Article Information GLENN J. MACPHERSON 1Department of Mineral Sciences, U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560 STEPHEN PAUL PHIPPS 2Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1988) 100 (11): 1770–1779. https://doi.org/10.1130/0016-7606(1988)100<1770:GAPOMV>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GLENN J. MACPHERSON, STEPHEN PAUL PHIPPS; Geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal Great Valley Group, northern California Coast Ranges. GSA Bulletin 1988;; 100 (11): 1770–1779. doi: https://doi.org/10.1130/0016-7606(1988)100<1770:GAPOMV>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Mysterious Valley formation (MVF) is a 1-km-thick accumulation of chaotic olistostromes, consisting of ophiolitic blocks set in a mudstone and serpentinous mudstone matrix, in the basal Great Valley Group of the northern California Coast Ranges. The MVF overlies serpentinite of the Middle Jurassic Coast Range Ophiolite (CRO).Most igneous blocks from the MVF are mid-ocean-ridge-type tholeiitic basalts (MORB's) with moderate TiO2 contents (1.0%-2.5%) and depletions in light (relative to heavy) rare-earth elements (REE's). Relict clinopyroxenes in these blocks are low-Ti augites. Rare blocks that are light-REE enriched and contain titanaugite probably represent ocean-island-type basalts. Coarse-grained plutonic blocks have not been found; however, abundant blocks of mafic breccia, similar to breccia overlying intact CRO elsewhere in the northern Coast Ranges, contain clasts of ultramafic rock and both cumulus and noncumulus gabbro.Diabase intrusions into the underlying CRO serpentinite are chemically identical to MVF basalts, suggesting a possible relationship between CRO igneous rocks and MVF blocks. Because most MVF basalt blocks are more Ti rich and, in general, more MORB-like than are CRO extrusive basalts, however, the MVF olistostromes are not easily explained as being derived from the uplift and erosion of the ancient CRO. Our chemical data indicate that either (1) MVF basalt blocks were not derived from the CRO; (2) our samples, which are from a geographically limited area, are not representative of the MVF; or (3) the MVF was derived from a more MORB-like part of the CRO that is not well represented in the few analyses presently available from the northern CRO. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

EVOLUÇÃO TECTÔNICA DA MARGEM EQUATORIAL BRASILEIRA

Rifting and tectonic evolution along the Equatorial margin of Brazil were highly complex. ln offshore Amapa, an early stage of rifting started ln Permo-Trlaseic time, accompanied by diabase intrusions. Volcanic activity extended eastward to the Maranhao Basin, without leading to continental breakup. ln early Cretaceous time (144-119 Ma) the clockwise rotation of South America relative to Africa, about a pole situated near 39°W and 7°S, caused compression west of Fortaleza, forming the Ferrer-Urbano Santos Arch, and eastward increasing extension east of Fortaleza, leading to the formation of the Potiguar Basin. ln this eastern portion, N-S extension was accompanied by E-W compression as the eastern tip of Brazil was pressed against Africa. The resulting stresses reactivated Precambrian ductile shear zones by transtensional movement, creating several inland half grabens including the Pendencia, Oros, and Rio do Peixe grabens. During Alagoas (Aptian) time, rifting propagated westward along the Equatorial margin and eastward along the Benue trough, both of which became marine seaways. From Albian time on, right lateral transtensional movement created NW trending rhomb grabens along the Equatorial margin. From Campanian through Eocene time, this right lateral movement was repeatedly interrupted by N-S compressional pulses which formed E-W trending folds and thrusts along the Equatorial margin and closed the seaway of the Benue trough. This compression may have been a distant reflex of the continental collision between Africa and Europe.

Evidence for a complex archean deformational history; Southwestern Michipicoten Greenstone Belt, Ontario

The Michipicoten Greenstone Belt extends for about 150 km ENE from the northeastern angle of Lake Superior. In common with many other Archean greenstone belts, it is characterized by generally steep bedding dips and a distribution of major lithologic types suggesting a crudely synclinal structure for the belt as a whole. Detailed mapping and determination of structural sequence demonstrate that the structure is much more complex. The Archean history of the belt includes formation of at least three regionally significant cleavages, kilometer‐scale overturning, extensive shearing, and diabase intrusion. Most well defined, mappable “packages” of sedimentary rocks appear to be bounded by faults. These faults were active relatively early in the structural history of the belt, when extensive overturning also occurred. Steepening of dips, NW‐SE shortening, development of steep NE cleavage, and pervasive shearing all postdate the early faulting and the regional overturning, obscuring much of the detail needed to define the geometry of the earlier structures. The results obtained so far suggest, however, that the Michipicoten Greenstone Belt underwent an early stage of thrusting and associated isoclinal folding, probably in a convergent tectonic environment.

The silver deposits at Cobalt and Gowganda, Ontario. II: An experiment in age determinations employing radiometric and paleomagnetic measurements

U–Pb analyses of primary baddeleyite and vein-related secondary rutile, separated from a Nipissing diabase sill at the Castle mine, Gowganda, yield ages of 2217.5 ± 1.6 and 2217.0 + 6 Ma, respectively. The data allow for the possibility that (i) the vein formed at essentially the same time as diabase intrusion, defined within the limits of the intercept age [Formula: see text], or (ii) the vein could have formed up to 8.1 Ma later than intrusion. Paleomagnetic analyses of the diabase suggest that it is part of the older (N2) phase of this widespread intrusive event. Paleomagnetic analyses of a pre-vein granite dike, intrusive into the diabase, provide a minimum time interval of 20 000 – 50 000 years separating intrusion and vein formation.40Ar–39Ar analyses of silicates obtained from ore veins in the Cobalt camp yield highly disturbed age spectra. Paleomagnetic analyses of altered wall rocks to ore veins in both the Castle mine and the Cobalt camp provide a wide range of apparent ages, inconsistent with the U–Pb data. The 40Ar–39Ar and paleomagnetic data are interpreted as indicating a prolonged history of post-vein disturbances during regional tectonism.

The silver deposits at Cobalt and Gowganda, Ontario. I: Geology, petrography, and whole-rock geochemistry

The Ag–sulpharsenide vein deposits of northeastern Ontario occur along the north and northeastern margins of the Cobalt Embayment, a large irregular domain of Huronian-age clastic sediments intruded by Nipissing diabase sills and crosscut by regional-scale fault systems. The vein systems are mostly fault controlled, with mineralization always occurring adjacent to or within the diabase sills. Many of the mineralized structures crosscut the sills. All the economically productive deposits occur in close proximity to the Huronian–Archean unconformity where diabase sills and steeply dipping Archean volcanic sequences coincide.The vein systems show remarkable consistencies in their mineralogy, textures, and paragenesis. Their formation involved the precipitation of silicates (mainly quartz, chlorite, actinolite ± K-feldspar) during initial, limited dilation; this was followed by the introduction of significant quantities of carbonate (mainly calcite ± dolomite) during subsequent dilatant episodes. Most of the ore was precipitated during the silicate to carbonate transition. Wall-rock alteration haloes exhibit a silicate to carbonate paragenesis similar to that evident in the veins. Feldspathization is an important consequence of the alteration process, manifesting in the ubiquitous occurrence of albite in Nipissing diabase wall rocks and sporadic occurrences of K-feldspar in Archean basalt wall rocks.The mineralogy and chemistry of the veins and altered wall rocks indicate that CO2, Ca, Na, K, Ag, As, Co, Pb, rare earth elements, and in some cases Hg and Au were among the components introduced with the hydrothermal fluids. This was accompanied by significant net loss of Si, Fe, Mg, Zn, B, Li, and Sc from the wall rocks. The nature of the wall-rock alteration suggests that the mineralizing fluids were of high alkalinity and relatively low [Formula: see text]. They were not derived through lateral secretion but were introduced from a source remote from the immediate environment of ore deposition.Wall-rock alteration postdates the establishment of a low-temperature, regional alteration of the diabases and a chlorite spotting alteration in the Huronian sediments; the latter is a contact metamorphic effect accompanying diabase intrusion. These data indicate that Ag–sulpharsenide vein formation postdated intrusion of the diabases and much (possibly all) of their cooling histories.Collectively, our data discourage the theory that the Nipissing diabase sills acted purely as a heat and (or) fluid source in vein formation. A structural model is proposed in which the diabase sills acted as mechanically favourable sites for fracture generation during regional fault activity. This factor, together with the advent of boiling and (or) degassing of the mineralizing fluids at these specific sites are viewed as possible critical parameters mediating the localization and deposition of Ag–sulpharsenide ore. This model provides a reasonable explanation for the local and regional distribution of the deposits and appears to best satisfy all the geological, petrographic, and geochemical criteria.

Contribuição à geologia do município de Cerquilho, SP

This paper is a contribution to the geology of the Cerquilho county (125 km²), state of Sao Paulo, Brazil, which is located at the center-east of the state, 160km from the city of Sao Paulo. The main purpose of this research was to get geologic and lithologic maps of the area, at a 1:50.000 scale, as a contribution to a better understanding of ground water distribution. Water from wells is urgently needed to the municipality supply. Late Carboniferous to Permian 550m thick Itarare Formation is the main stratigraphic unity in extension and in thickness. Less developed are the Permian Tatui and Irati formations. Latest Jurassic to Earliest Cretaceous tholeitic diabase intrusions, as dyke and sills cut these formations. Along some of the river valleys developed narrow alluvial deposits. The main lithologies of the ltarare Formation are diamictites (some true tillites), sandstones and siltstones. They are highly variable in distribution, interfengering each other vertically and horizontally. Coal seams are distributed mostly in the upper beds of this formation.

Chemical and Physical Properties of Paleozoic Potassium Bentonites from Kinnekulle, Sweden

The < 1-μm fraction of 17 bentonite samples from Kinnekulle, southwest Sweden, were studied by chemical analysis, X-ray powder diffraction, and cation-exchange capacity. The bentonites are interbedded with undeformed, flat-laying Ordovician and Silurian sediments and were formed by the transformation of volcanic ash (dated at about 450 Ma) into smectite, which later converted to mixed-layer illite/smectite (I/S). The reaction, possibly driven by heat from an overlaying diabase intrusion (about 300 Ma), stopped at different stages of conversion, as evidenced by the I/S which ranges in composition from 60 to 10% smectite layers. A 2-m-thick bed shows zonation, with decreasing smectite proportions towards the upper contact. The zonation is not symmetrical towards the lower contact. In thin beds the illite proportion is higher and the regularity of ordering is inversely proportional to the thickness of the bed. K:Sr and K:Rb ratios follow the illite pattern; the ratios are highest at the contact and in thin beds. The inhibiting effect of Ca and Mg on the smectite-to-illite conversion probably was the cause of less-reacted smectite in the center of the thick bed.

Alkaline permanganate oxidation of kerogens from Cretaceous black shales thermally altered by diabase intrusions and laboratory simulations

Potassium permanganate oxidative degradations were conducted for kerogens isolated from Cretaceous black shales (DSDP Leg 41, Site 368), thermally altered during the Miocene by diabase intrusions and from unaltered samples heated under laboratory conditions (250–500°C).Degradation products of less altered kerogens are dominated by normal C4–C15 α,ω-dicarboxylic acids, with lesser amounts of n-C16 and n-C18 monocarboxylic acids, and benzene mono-to-tetracarboxylic acids. On the other hand, thermally altered kerogens show benzene di-to-tetracarboxylic acids as dominant degradation products, with lesser or no amounts (variable depending on the degree of thermal alteration) of α,ω-dicarboxylic acids. Essentially no differences between the oxidative degradation products of naturally- and artificially-altered kerogens are observed.As a result of this study, five indices of aromatization (total aromatic acids/kerogen; apparent aromaticity; benzenetetracarboxylic acids/total aromatic acids; benzene-1,2-dicarboxylic acid/benzenedicarboxylic acids; benzene-1,2,3-tricarboxylic acid/benzenetricarboxylic acids) and two indices of aliphatic character (Total aliphatic acids/kerogen; Aliphaticity) are proposed to characterize the degree of thermal alteration of kerogens.Furthermore, a good correlation is observed between apparent aromaticity estimated by the present KMnO4 oxidation method and that from the 13C NMR method (DENNIS et al., 1982).

Cenozoic Diapiric Traps in Eastern China: ABSTRACT

Genetically, there are 2 types of Cenozoic diapiric traps in the oil fields in eastern China. One type is produced by cold diapirism owing to the rise of evaporites and soft mudstone. This type can be divided into 3 patterns. The first pattern is the faulted ridge with 1,000 m (3,300 ft) closure and flanks dipping up to 30°. A complex graben system is developed on the top. The amplitude of the core of the anticline is about 3,000 m (9,800 ft). The Xiangzheng structure in the Shengli oil field and the Wang-cung structure in the Qian-jiang depression are examples. The second pattern is the gentle anticline or dome with 50-300 m (160-985 ft) closure and 3°-10° dip on the flanks. The incompetent strata beneath it are about 1,000 m (3,300 ft) thick. The Tuocun -Shengli structure in the Shengli oil field is an example. The third pattern is a nose-like structure with less than 50 m (160 ft) closure. This pattern is usually located near the zero edge of incompetent strata. The Serniusi structure in the Dagang oil field is an example. Another type of Cenozoic diapiric trap results from hot diapirism associated with the intrusion of gabbro or diabase. Such traps are typically small, round domes. The dip of the flanking strata generally increases with depth as the diapir is approached. A graben system is developed on top of the diapir. The distribution of these traps is related usually to regional fault zones and coincides with the distribution of the magmatism. The Matouzung structure in the Jinhu depression is one of the examples. End_of_Article - Last_Page 520------------

Geologia da folha de Aguaí, SP

The Aguai area comprehends oriental Paraná Basin part and crystalline basement. The Pinhal Complex crystalline rocks (upper precambrian) are characterized by granites and migmatites presenting variated structures and textures. The sedimentary rocks belongs to the Itararé Subgroup (Permian-Carboniferous). Piraçununga Formation (Tertiary) and to alluvial sediments (Quaternary). In the Itararé Subgroupoccur diabase intrusions specially in the central north part of the area. The Itararé Subgroup sediments, sandstones, siltstones, diamictites and shales are disposed deranged in the whale unit. The Cenozóic comprehends Piraçununga Formation (sands and basal conglomerates) and quaternary (alluvial plains) along the main rivers

Post-Kombolgie metasomatism at Jabiluka, Northern Territory, Australia, and its significance in the formation of high-grade uranium mineralization in lower Proterozoic rocks

Diagenetic lithification of Kombolgie sandstones followed by a metasomatic event which produced veining and replacement. Metasomatism was controlled by brecciation and bedding within the sandstones. The high-grade uranium ores are interpreted to be the product of a low-temperature (100 degrees -200 degrees C) hydrothermal system of ground water which was driven by a regional heating event also manifested by phonolite and/or diabase intrusions. The Kombolgie sandstones were an essential part of the hydrologic system which formed the high-grade orebodies, after lithification of the lower part of the thick clastic section but possibly contemporaneous with diagenetic events in the upper part. The processes operating in the Alligator Rivers uranium field were essentially similar to those in the Athabasca District of northern Saskatchewan, the primary difference probably being that no organic material was remobilized into the overlying sandstone to act as a reductant in the Australian case.--Modified journal abstract.

Oil Migration Examples in Irati Formation, Parana Basin, Brazil: ABSTRACT

The Irati Formation (Late Permian), in the Parana basin, is a source rock with high generating potential. Different geochemical methods have been applied to this study in relation to geological observations, such as, Rock-Eval pyrolysis, optical observations, gas chromatography of C15+ hydrocarbons, and isotopic analysis. The results have shown that this formation contains organic matter belonging to type I and type III predominantly. The T.O.C. contents range from 0.5 to 13% according to the quality of the organic matter. Pyrolysis analysis indicates that the area where the Irati has the highest oil-generating source rock is in the north and south of the Parana basin. In these areas petroleum potential can reach 90 kg HC/t of rock. In the central part of the basin the Irati Formation might reach a depth of about 3,200 m (10,498 ft). The degree of evolution of the organic matter by burial is generally low (immature), reaching the beginning of the oil window in the deepest part of the basin. In many wells diabase intrusions have more or less completely cooked this formation, thus generating or gas, and leaving residual organic matter. The phenomenon of migration into the Irati Formation has been observed in many wells. In certain places, is accumulated in shales embedded between intrusion levels; in other places is accumulated into limestone beds, intercalated in the Irati Formation. It seems safe to assume that the accumulated in the deeper beds resulted from the effect of thermal intrusions and also from the effects of normal burial. Oil migration occurred after diabase intrusions (Late Cretaceous) during the increasing subsidence of the basin. In the Parana basin, the Irati Formation may be compared to a drain with a lateral migration. Vertical migration was hindered by the lack of enough porosity and permeability in the shales above the Irati source rock. Consequently, migration and accumulation of above and below the formation might have resulted from changes in facies of the Irati itself, by faulting, or by fractures due to diabase intrusions. End_of_Article - Last_Page 457------------

Paleomagnetism of the Little Dal lavas, Mackenzie Mountains, Northwest Territories, Canada

The Proterozoic stratigraphic column of the Mackenzie Mountains is dominated by two main successions, the platformal "Mackenzie Mountains Supergroup" beneath, and the Windermere-equivalent Rapitan Group and younger strata, of rift-depression and slope origin, above. The former succession is at least partly older than 770 Ma, the latter younger than 770 Ma. These two main successions are locally separated by an unconformity-bounded succession, the "copper cycle." An important question is whether the copper cycle is more closely related in time and in origin to the older or the younger main succession. Determination of the paleomagnetism of the basaltic lavas locally preserved at the top of the Little Dal Group (top of the Mackenzie Mountains Supergroup) and comparison of their remanence directions with those published for other rocks bearing on the question were thought to be one way of shedding light on this question. Accordingly, paleomagnetic investigation of 10 sites in the Keele River area and six sites in the Thundercloud Range area was undertaken to obtain the remanence direction related to the initial extrusion of the lavas. Coherent directional groupings were only obtained from Little Dal lavas in the Keele River area. Of the three magnetizations found, LD-L (D = 304°, I = 20°, α95 = 7°) is assumed to represent the magnetization acquired on crystallization of the lavas. If this assumption is correct, the significant difference from the direction LD-A (D = 265°, I = 26°, α95 = 4°) reported elsewhere for strata low in the Little Dal Group suggests either that the lavas significantly postdate the group or that significant movement of the North American plate occurred during accumulation of the 2 km or so of platformal strata between the lower Little Dal beds and the lavas. The new results presented here also admit the conclusion that the Little Dal lavas do not represent the same igneous events as diabase intrusions dated at about 770 Ma that cut the lower Little Dal.

Geologia da Folha de Rio Capetinga

A Folha de Rio Capetinga (1:50000) situa-se no nordeste da Bacia. Sedimentar do Paraná (47º00' - 47º15'W e 22º00' - 22º15'S) no Setor Aguaiano da Zona do Moji-Guaçu, da Depressão Periférica Paulista. São encontrados, Super grupo Tubarão: Grupo ltararé (Formação Aquidauana) e Grupo Tatuí; intrusões de diabásio; Formação Piraçununga (esta compondo mais da metade da folha) e sedimentos quaternários. As formações geológicas de Superfície autóctones são representadas pelos regolitos da Formação Aquidauana e do Grupo Tatuí, bem como pelos das intrusões de diabásio, enquanto que as alóctones, pela Formação Piraçununga e sedimentos quaternários

Thermal alteration of Cretaceous black shale by diabase intrusions in the Eastern Atlantic—II. Effects on bitumen and kerogen

The thermal effects of three (one major and two minor) Miocene diabase intrusions on Cretaceous black shales from DSDP site 41–368 have been analyzed. A concentration gradient was observed, especially for the hydrocarbons, decreasing towards the major intrusion and between the three sills. The thermally-altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally-derived pristane over phytane. whereas, the unaltered sediments contained no elemental sulfur, and more phytane than pristane. A maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill. Two classes of molecular markers were present in this bitumen suite. The first was sesqui-, di- and triterpenoids and steranes. which could be correlated with both terrigenous and autochthonous sources. They were geologically mature and showed no significant changes due to the thermal stress. The second class was found in the altered samples, which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds. These compounds were derived from pyrolytic reactions during the thermal event.Kerogen was isolated from all of these samples, but only traces of humic substances were present. The HC, NC, δ13C, δ34S and δD all exhibit the expected effects of thermal stress. The kerogen becomes more aromatized and richer in 13C, 34S and D in the proximity of and between the sills. Maturation trends were also measured by the vitrinite reflectance and electron spin resonance, where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity. The effects of in situ thermal stress on the organic-rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills.

A positive fold test from Nipissing diabase

Positive fold tests are reported on two remanence components resolved from the same Nipissing diabase sills. These tests conclusively indicate that the region south of the Sudbury Basin in the Southern Structural Province has been subjected to two distinct deformational episodes subsequent to the intrusion of the Nipissing diabase. One event precedes (1850–2150 Ma) and one event postdates (1250–1850 Ma) intrusion of the Sudbury irruptive. Some evidence also exists for a third event that may be related to the development of the Sudbury structure, around 1850 Ma. Evidence that the Nipissing was intruded into already folded Huronian sediments confirms previous suggestions of four separate orogenic pulses in the period 2300–1250 Ma.

40 Ar/ 39 Ar ages of diabase intrusions from Newark trend basins in Connecticut and Maryland; initiation of central Atlantic rifting

40 Ar/ 39 Ar ages of diabase intrusions from Newark trend basins in Connecticut and Maryland; initiation of central Atlantic rifting