scholarly journals The geology of Tugtutôq and neighbouring islands, South Greenland. Part II. Nordmarkitic syenites and related alkaline rocks

1964 ◽  
Vol 44 ◽  
pp. 1-62
Author(s):  
B.G.J Upton
Keyword(s):  
Magma Chamber ◽  
Parental Magma ◽  
Central Complex ◽  
Central Component ◽  
Surface Complex ◽  
Central Ring ◽  
Quartz Syenite ◽  
Rock Types ◽  
Ring Complex ◽  
Multiple Swarms

Among the Precambrian (Gardar) intrusions in the Tugtutôq area, syenitic rocks are abundantly represented. Quartz-bearing alkalic rocks were first intruded after the emplacement of a number of large gabbro dykes. Although early Gardar nepheline syenites occur on Tugtutôq, no post-gabbro undersaturated syenites occur within the area under discussion. Quartz syenites and their faster cooled equivalents occur either as ENE directed dykes or as ring-dykes and stocks within a late Gardar central complex. The earliest quartz syenite occurs as the central component in a composite sector of one of the large gabbro dykes. This was succeeded by multiple swarms of dykes with alkalic types ranging from 'rhomb porphyry' microsyenite to comendite. Dyke intrusion was virtually at an end by the time of formation of the central ring-complex. The total petrographic range of the oversaturated alkalic rocks extends from ferroaugite-fayalite syenites with relatively calcic feldspar (ca. Or25Ab66An9) to highly acid riebeckite-bearing rock types. The various intrusions are considered to represent magma batches supplied, at irregular intervals, from a deep-seated syenite complex which was crystallising throughout the latter part of the Gardar period. The inferred sub-surface complex is taken to be closely comparable to the Gardar complexes exposed at Nunarssuit and Kungnât, and to have differentiated by process of crystal fractionation. By analogy with the Kungnât complex the parental magma of the underlying magma chamber(s) is believed to have passed through a larvikitic stage. The perthosite stock which forms the latest major intrusion on Tugtutoq is thought to indicate a slight divergence from the general larvikite-nordmarkite-alkali granite differentiation sequence. The magmas of this main differentiation sequence changed in composition along a "thermal valley" dose to that of the synthetic system Or-Ab-SiO2-H2O.

scholarly journals Geology of Tugtutôq and neighbouring islands, South Greenland. Part I

1962 ◽  
Vol 34 ◽  
pp. 1-60
Author(s):  
B.G.J Upton
Keyword(s):  
Large Body ◽  
Central Zone ◽  
Central Component ◽  
Quartz Syenite ◽  
Main Island ◽  
Alkali Granites ◽  
Ring Complex ◽  
Intrusive Activity ◽  
Dyke Swarms ◽  
Marginal Zones

Tugtutôq is an island lying off the SW. coast of Greenland, separated from the mainland by fjords overlying major lines of faulting. The main island, together with numerous smaller islands and skerries, is largely composed of Precambrian granites formed after the close of the Ketilidian orogeny. At a still later date in the Precambrian alkaline rocks were extensively intruded into the south Greenland region and, of these, a large variety are preserved in the Tugtutôq area. Many of the intrusions take the form of ENE.-WSW. trending dykes running parallel to one of the major faulting directions. Tugtutôq lies along a belt in which these dykes are especially concentrated and provides a rewarding field for their investigation. One of the earliest dykes, some 500 m broad, is composite and consists of narrow gabbroic marginal zones and a broad central component of syenite. The syenite centre changes character along its 20 km outcrop from a nepheline-poor 'augite syenite' to a variety of foyaite. 'Giant-dykes' of troctolitic gabbro, up to 800 m across, were intruded after the solidification of the composite dyke. In certain sectors of the dykes the gabbros display primary layering. These gabbro dykes themselves occasionally show composite character and possess a central zone of quartz syenite or of alkalic gabbo akin to the marginal gabbro of the earlier composite dyke. Small bodies of pyroxenite, related to a larger mass cutting the troctolitic gabbros on the mainland, occur on the main island. Subsequent to these ultramafic intrusions dense swarms of small dykes composed of olivine dolerite, quartz microsyenite, alkali microgranite and hybrid variants were injected through the area. Many of these are also composite. The widespread presence of labradorite anorthosite fragments in the dyke rocks prompts the suggestion that a large body of anorthosite underlies the area. At a late stage in the igneous cycle a ring-complex developed across the main dyke belt and this, in striking contrast to the nearby and roughly contemporaneous Ilímaussaq complex, consists only of saturated syenite and alkali granites. The complex comprises some half-dozen ring-intrusions of related syenites and granites followed by a stock of coarse perthositic syenite. Intrusive activity in the area came to a close with eruption of further dyke swarms and occasional sills.

scholarly journals Paleoproterozoic Multiple Tectonothermal Events in the Longshoushan Area, Western North China Craton and Their Geological Implication: Evidence from Geochemistry, Zircon U–Pb Geochronology and Hf Isotopes

Minerals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 361 ◽  
Author(s):  
Renyu Zeng ◽  
Jianqing Lai ◽  
Xiancheng Mao ◽  
Bin Li ◽  
Jiandong Zhang ◽  
...  
Keyword(s):  
North China Craton ◽  
Tectonic Evolution ◽  
North China ◽  
Regional Metamorphism ◽  
Hf Isotope ◽  
Crustal Growth ◽  
Quartz Syenite ◽  
Isotope Data ◽  
The North ◽  
Rock Types

The Alxa block is located in the southwestern margin of the North China Craton. The Paleoproterozoic tectonic evolution, crustal growth and tectonic affinity of the block remain unknown or controversial. The Longshoushan (LS) area is one of the few areas that outcrop Paleoproterozoic to crystalline basement rocks in the Alxa Block. In this study, we preset whole-rock geochemistry, zircon U–Pb geochronology and Lu–Hf isotope data from metagabbro, metadiorite, quartz syenite, granitic leucosome and pegmatoid leucosome in the LS area. These rocks all are enriched in LREE and LILE, and depleted in HREE and HFSE. Eight new LA-ICP-MS zircon U–Pb ages yielded three magmatic ages of 2044 Ma, 2029 Ma and 1940 Ma, and three metamorphic ages of 1891 Ma, 1848 Ma and 1812 Ma. Lu–Hf analyses reveal that the magmatic zircons and anatectic/metamorphic zircons from all the rock types are characterized by positive εHf(t) (−0.16 to 10.89) and variable εHf(t) (−11.21 to 6.24), respectively. Based on the previous studies and our new data, we conclude that the LS area experienced three magmatic events (2.5–2.45 Ga, ~2.1–2.0 Ga and ~1.95–1.91 Ga) and three regional metamorphism/anataxis events (~1.93–1.89 Ga, ~1.86–1.84 Ga and ~1.81 Ga) in Paleoproterozoic. The age–Hf isotope data establishes two main crustal growth events at ~2.9–2.5 Ga and ~2.2–2.0 Ga in the LS area. These data indicate that the LS area experienced intraplate extensional setting in the middle Paleoproterozoic, and continental subduction, collision and exhumation in the late Paleoproterozoic. Combining the geochronological framework and tectonic evolution, we suggest that the Alxa Block is part of the Khondalite Belt.

Skarn formation between metachalk and agglomerate in the Central Ring Complex, Isle of Arran, Scotland

1987 ◽  
Vol 51 (360) ◽  
pp. 231-246 ◽  
Author(s):  
G. Cressey
Keyword(s):  
Late Stage ◽  
Mineral Assemblage ◽  
Central Ring ◽  
Ring Complex ◽  
Metasomatic Fluid ◽  
Skarn Mineral

AbstractA skarn mineral assemblage occurs at the junction between vent pyroclastics and a xenolithic Cretaceous chalk block which subsided into the collapsed caldera of the Central Ring Complex, Isle of Arran, Scotland. Adjacent to the metachalk marble an andradite garnet exoskarn zone has developed at the expense of the carbonate. An andradite grossular/diopsidic clinopyroxene endoskarn zone has formed in the surrounding agglomerate, and a magnetite exoskarn is present in places between the andradite and garnet/pyroxene zones. The andraditic exoskarn garnets have fluor-hydrogarnet components, indicating that fluorine was present in the metasomatic fluid. From petrographic evidence, three distinct episodes of exoskarn garnet crystallization can be recognized, in which the fluor-hydrogarnet component steadily increased as a function of time, which probably reflects falling temperature. The REE compositions of the exoskarn minerals are regarded as having been largely inherited from the carbonate, and the exoskarn garnets increasingly fractionated HREE with time. The endoskarn and agglomerate have also been epidotized. The REE signatures of epidotes appear to be inherited partially from precursor clinopyroxenes or feldspars, which have been replaced by epidote. Late-stage vein minerals include prehnite, laumontite and K-rich laumontite, and their REE compositions appear to have been derived from the marble, probably via REE fluoro-complexes in the fluid.

Structure and petrogenesis of a mixed-magma ring dyke in the Peruvian Coastal Batholith: eruptions from a zoned magma chamber

1988 ◽  
Vol 79 (2-3) ◽  
pp. 87-104 ◽  
Author(s):  
M. Andrew Bussell
Keyword(s):  
Magma Chamber ◽  
Present Level ◽  
Ring Fault ◽  
Brittle Ductile Transition ◽  
Erosion Level ◽  
Ring Complex ◽  
Ring Structures ◽  
Transient Events ◽  
Flat Roofs ◽  
Ring Dyke

ABSTRACTRing complex granites of the Peruvian Batholith are tabular bodies with flat roofs emplaced by cauldron subsidence. Marginal precursory ring dykes extend upwards above roof level and a typical intrusion is “H”-shaped in cross-section. Advance of magma by repeated subsidence would give a ladder-shaped profile for such intrusions above the brittle-ductile transition. Close relationships exist between intrusion geometry, emplacement process and petrogenetic evolution. Initially a granodioritic magma chamber lay beneath the present erosion level, trapping a rising mass of dioritic magma. Expansion of granodioritic liquid resulted in the injection of microgranite and tuffisite cone sheets accompanied by roof uplift within a ring fault. Next, during subsidence within the ring fault, liquids from deeper levels in the underlying chamber rose by stoping along the outer margin of the fault to form a ring dyke. Prior to intrusion, this liquid was vertically zoned from rhyodacite downwards to diorite and these liquids became partially mixed during emplacement. Finally, granodioritic magma rose to the present level by subsidence of a roof slab bounded by the ring fault. The precursory ring structures preserve evidence of significant but transient events in the underlying chamber. Liquid differentiation may be significant in the evolution of many large plutons.

The petrology and geochemistry of the Creag Dubh composite sill, Whiting Bay, Arran, Scotland

1977 ◽  
Vol 114 (1) ◽  
pp. 1-8 ◽  
Author(s):  
N. W. Rogers ◽  
I. L. Gibson
Keyword(s):  
Trace Elements ◽  
Magma Chamber ◽  
Major And Trace Elements ◽  
Rock Types ◽  
Petrology And Geochemistry

SummaryAnalysis of 17 samples for both major and trace elements reveals that, unlike most other Tertiary composite intrusions, the Creag Dubh sheet possesses silicic margins and a doleritic centre. The two rock types grade together rapidly without chilling at the upper and lower internal contacts. However, there is evidence for mixing of the two magma types prior to or during emplacement with the production of limited amounts of intermediate hybrids. The central dolerite appears to be later than the marginal felsites which in places back-vein the dolerite. The sequence of intrusion is tentatively related to the upward draining of a strongly zoned magma chamber.

Nonlinear nature of the unavoidable long-lived isotopic, trace and major element contamination of a developing magma chamber

1980 ◽  
Vol 297 (1431) ◽  
pp. 215-227 ◽  
Keyword(s):  
Magma Chamber ◽  
Alternative Explanation ◽  
Incompatible Element ◽  
Sea Water ◽  
Parental Magma ◽  
Final States ◽  
Short Term ◽  
Crustal Rocks ◽  
Pressure Phase ◽  
Nonlinear Nature

Contamination of magmas by crustal materials is a possible alternative explanation of many of the trace element and isotopic features of basalts which have been advanced as evidence of mantle heterogeneity. The space problems associated with the emplacement of large masses of plutonic cumulates in most central volcanoes, and with the formation of the gabbro-dunite portion of the oceanic crust, indicates that at least some digestion of pre-existing crustal rocks has occurred. Contamination is therefore unavoidable. In the ocean basins, contamination is not due directly to incorporation of sea water, but to the digestion of previously erupted basalts which may have been hydrothermally altered by circulating sea water, plus some sediment. In a magma chamber that is periodically replenished with parental magma and periodically tapped to provide lava flows during fractional crystallization, contamination produces changes in the composition of the erupted product which are not, in general, linear between the initial and final states of the system. Moreover, the change in composition produced need not lead towards the composition of the contaminant. Provided that the periodic additions and subtractions of magma are small relative to the size of the magma chamber, the effects of short-term variations in the amount of contamination are smoothed out, while the effects on incompatible element concentrations are persistent long after active contamination has ceased. The effects on major components that enter the crystallizing phases are constrained by the need for the remaining liquid to conform to the relevant low-pressure phase equilibria.

scholarly journals Petro-Mineralogical and Geochemical Study of the Acid Magmatic Rocks of Tusham Ring Complex, NW Peninsular India

2021 ◽  
Author(s):  
Naveen Kumar ◽  
Naresh Kumar
Keyword(s):  
Mineral Chemistry ◽  
Geodynamic Setting ◽  
Present Contribution ◽  
Peninsular India ◽  
Malani Igneous Suite ◽  
Rock Types ◽  
Magmatic Rocks ◽  
Geochemical Study ◽  
Ring Complex ◽  
Field Information

The present contribution reports about the field and petrographical observations which are very important to explain the magmatic evolution and geodynamic setting of Tusham Ring Complex (TRC). TRC is associated with A-type acid volcano-plutonic rock-association which is very common characteristics of Neoproterozoic Malani Igneous Suite (MIS). Based on the geological field information, the investigated rock-types are classified as volcanic phase, plutonic phase and dyke phase. Petrographically, rhyolites show porphyritic, granophyric, glomeroporphyritic, aphyritic, spherulitic and perlitic textures whereas granites show hypidomorphic, granophyric and microgranophyric textures. Based on mineral chemistry and whole-rock geochemistry, the petro-mineralogical results are justified and proposed that the rocks under study belong to A-type affinity, within-plate and anorogenic magmatism. Physiochemical features i.e. F and Cl-rich biotite, pegmatite rim, high mineralized veins, micro-granular enclaves and altered mineralogy indicate rock-fluid interactions which are caused by magmatic origin or secondary metasomatic alteration superimposed on the host rock.

scholarly journals Petrography and Physicomechanical Properties of Rocks from the Ambela Granitic Complex, NW Pakistan

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Mohammad Arif ◽  
S. Wajid Hanif Bukhari ◽  
Noor Muhammad ◽  
Muhammad Sajid
Keyword(s):  
Unconfined Compressive Strength ◽  
Nepheline Syenite ◽  
Construction Material ◽  
Maximum Size ◽  
Physicomechanical Properties ◽  
Quartz Syenite ◽  
Rock Types ◽  
Permissible Range ◽  
Alkali Granites ◽  
Size Contrast

Petrography and physicomechanical properties of alkali granites, alkali quartz syenite, and nepheline syenite from Ambela, NW Pakistan, have been investigated. Whereas the alkali quartz syenite and most of the alkali granites are megaporphyritic, the nepheline syenite and some of the alkali granites are microporphyritic. Their phenocryst shape and size and abundance of groundmass are also different. The values of unconfined compressive strength (UCS) are the lowest and highest for megaporphyritic alkali granite and alkali quartz syenite, respectively. However, all the four rock types are moderately strong. Correspondingly, their specific gravity and water absorption values are within the permissible range for use as construction material. The UCS for the alkali quartz syenite is the highest, most probably because (i) it has roughly equal amounts of phenocryst and groundmass, (ii) it displays maximum size contrast between phenocryst and groundmass, (iii) its phenocrysts are highly irregular, and (iv) it contains substantial amounts of quartz.

scholarly journals The Late-Paleoarchean Ultra-Depleted Commondale Komatiites: Earth's Hottest Lavas and Consequences for Eruption

2019 ◽  
Vol 60 (8) ◽  
pp. 1575-1620 ◽  
Author(s):  
Allan H Wilson
Keyword(s):  
High Temperature ◽  
Marginal Zone ◽  
Parental Magma ◽  
Mantle Peridotite ◽  
Rock Types ◽  
Low Viscosity ◽  
Incompatible Elements ◽  
Olivine Cumulates ◽  
Rare Category ◽  
Initial Source

Abstract The c.3·3 Ga Commondale komatiites located south of the Barberton greenstone belt in the Kaapvaal Craton are different from other komatiites, possessing compositional and textural features unique to this occurrence. Unlike almost all other known komatiite occurrences, they are not associated with komatiitic basalts or basalts. The komatiite flows are 0·5–25 m thick and are made up of a marginal zone of spinifex-textured and fine-grained aphyric rocks (low-Mg group) and an inner zone of olivine cumulates (high-Mg group), arranged in such a way to give highly symmetrical compositional profiles for many flows. Olivine is the dominant phase in all rocks, but orthopyroxene occurs as spinifex and elongate laths in the marginal zone. Clinopyroxene and plagioclase are entirely absent. The olivine cumulates formed from Mg-rich magma (36·1% MgO, 6·8% FeO) which caused inflation of the thicker flows. The maximum observed olivine composition in cores (Fo 96·6) is the highest recorded for any komatiite worldwide. The high-Mg magma would have erupted at a temperature close to 1670°C, the highest inferred temperature for an anhydrous terrestrial lava. The marginal zone is enriched in incompatible elements compared with the inner zone and formed by fractionation of the parental melt. However, all rock-types in the marginal zone are depleted in FeO (some as low as 3·5%) which could not have been derived by any primary magmatic process. The marginal zone rocks were modified by assimilation and/or alteration by seawater (or brine) components causing migration of iron and strong enrichment of sodium (up to 1·6 wt % Na2O) and chlorine (up to 2400 ppm). Zirconium has an identical distribution to sodium, with both elements greatly enriched above what would result from fractional crystallization, and may result from speciation of these elements at high temperature followed by post-crystallization alteration. Rare earth elements, Y and Nb have contents commensurate with fractionation of the primitive parental magma. Dendritic-textured olivine-rich rocks with orthopyroxene spinifex spatially and compositionally transitional between the marginal zone and the olivine cumulates resulted from interaction of the high temperature parental magma in the centre of the flows with the fractionated melt at the flow margins. A further manifestation of this association is the development of highly regular fine-scale (5–15 cm) layering (up to 45 layers) of alternating olivine cumulate and spinifex near the base of thick flows. This is overlain by olivine cumulates in which the melt/crystal-mush became arranged into a 3-dimensional network controlled by re-distribution of the trapped melt manifest by a spectacular knobbly texture in outcrop. Over 200 flow units are recognized and detailed chemical and mineralogical studies were carried out on drill cores intersecting 375 m of stratigraphy. The parental magma was highly depleted (in ppm Nb 0·017, Zr 1·18, total REE 1·7 and Gd/YbN=0·3, La/YbN=0·038) and although generally regarded to fall into the rare category of Al-enriched komatiites (AEKs), it is considered that these lavas are a unique class of their own of ultra-depleted komatiites. Relative to other AEKs the Commondale komatiites are both enriched in Al as well as being markedly depleted in Ti (390 ppm), giving rise to the extremely high Al2O3/TiO2 (81). The high temperature and low viscosity of the magma resulted in emplacement processes previously unrecognized in komatiites. The primary melt was derived by melting of mantle peridotite in equilibrium with olivine and orthopyroxene. The initial source was depleted in incompatible elements by small degrees of melting (3–4%) followed by high degrees of partial melting (70%) of the subsequent refractory source at 5 GPa (∼150 km).

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