K-feldspar megacrysts in granites — Phenocrysts, not porphyroblasts

The southern part of the New England Geosyncline is divided by the Peel Fault into two major zones, termed the Tablelands Complex to the east and the Tamworth Belt to the west. Because of stratigraphical similarities the Hastings Block is correlated with the Tamworth Belt. Seven major lithostratigraphic associations are recognized in the Tablelands Complex. The Woolomin Association is a deepwater marine chert‐jasper‐basic volcanic‐dominated sequence in which sandstones are rare. The Sandon Association is a turbidite sequence in which minor chert, jasper, and basic volcanics are present. The Coffs Harbour Association is a deepwater marine turbidite sequence and is distinguished from the Sandon Association by the absence of chert, jasper, and basic volcanics. The Nambucca Association is also deepwater marine in nature and is dominated by diamictites deposited by mass movements. The Silverwood Association contains components of a volcanic arc, and the Dummy Creek Association consists of terrestrial ...

A framework for the palaeozoic geology of the southern part of the New England Geosyncline

How late are K-feldspar megacrysts in granites?

Several mesosocopic structures are consistent with mechanical accumulation of crystals and movement of melt in granite magmas, as well as compaction and shear of crystal-melt aggregates, concentrations of microgranitoid enclaves indented by megacrysts, and concentrations of crystals of the same mineral with different crystallisation histories. Evidence for crystal and enclave accumulation is shown clearly in mafic and silicic layered intrusions (MASLI-type granite plutons), for example, the Kameruka Granodiorite, Bega Batholith, south-eastern Australia.Crystal accumulations with interstitial liquid may become mobile in a magma chamber, owing to instabilities in the host magma caused by seismic and replenishment events or thermal and buoyancy variations. This remobilised material may intrude other parts of the chamber, as well as earlier-formed cumulates and even wall-rocks, as dykes, tubes, troughs and pipes. Marked concentrations of accessory and mafic minerals may also develop in these structures. Interstitial melt may also be extracted from accumulated aggregates, intruding and disrupting the aggregates. Spectacular examples of these various structures are preserved in the Tuolumne Batholith, California. Detailed mechanisms for the formation of many of the structures are not well understood, though the formation of cumulates in vertical layers suggests that sorting and filter pressing during flow and resulting strain of crystal mushes may play important roles.

Mesoscopic structures resulting from crystal accumulation and melt movement in granites

Caesarean section rates are inexorably rising which has led to the possibility of negative impact on m aternal and neonatal health. Present study was aimed to compare the factors associated with caesarean and vaginal births among pregnant women. A retrospective study was con ducted in Obstetrics and Gynaecology Department, Pu njab Institute of Medical Sciences, Jalandhar (Punjab, Iduring the period of April, 2012 to June, 201 2. Details of age group, parity, socioeconomic status, antenatal booking, mode of delivery, obstetric complications, gestational age at delivery, maternal and neonatal outcomes wer e explored. The prevalence of Caesarean Sections (6 5%) was higher over vaginal births (35%). It had higher num ber of Emergency (52.31%) over Elective (47.70%) ca esarean sections. Multiparity (55.38%; p<0.05), high socioe conomic status (18.46%), 21 to 30 yrs of age group (78.46%) and booked status (44.62%) were associated with Cae sarean Sections while primiparity (65.71%) and low socioeconomic status (22.86%) with vaginal births. The commonest reasons for Caesarean Sections were F etal Distress (30.77%) and Repeat Caesarean Sections (29.23%). Ca esarean sections rate is high. High number of referred patients who underwent Emergency sections was the main reason. Trial of vaginal birth after C aesarean Section in approximate cases and confirmation of su spected fetal distress through fetal blood acid bas e study are recommended.

/pdf/available-online-a-t-www-pelagiaresearchlibrary-com-29z9znpv0y.pdf

Available online a t www.pelagiaresearchlibrary.com

Igneous rocks from the Undercliffe Falls-Liston-Maryland area of northern New South Wales vary from metadolerites to granites. The main plutonic rock is the Undercliffe Falls porphyritic adamellite and this intrudes Permian "Boorook" strata which, away from contacts, are little-altered sediments and volcanics. The porphyritic adamellite is intruded by the Stanthorpe adamellite which is displaced by the more acidic Ruby Creek granite. These masses are described by means of new chemical, mineralogical and petrographic data, resulting in the division of the Undercliffe Falls and Stanthorpe masses into a number of varieties. Much of the Undercliffe Falls mass (the normal type) is a porphyritic rock with basic xenoliths which have a preferred orientation developed by a primary platy flow imposed when the intrusion was magmatically emplaced. Contacts are discordant in detail. Large pink K-feldspars, some of which are mantled by plagioclase, are found in the normal type, in its contained xenoliths and in metadolerite country rock. Other varieties of the Undercliffe Falls mass include an even-grained marginal type and a relatively basic phase with white K-feldspar phenocrysts. The younger intrusions are even-grained rocks which were probably emplaced as magmas. Compositionally the Ruby Creek granite falls in the low melting portion of the NaAISi3O8- KAISi3O8-SiO2-H2O-(CaAI2Si2O8) system. The Undercliffe Falls porphyritic adamellite probably formed by chemical hybridization involving gabbroic rock (similar to the wall-rock metadolerite found in the area) and acidic magma. Calculations indicate that the Stanthorpe adamellite is a suitable acid parent and it, together with the Ruby Creek mass, may have been derived by crustal melting.

https://espace.library.uq.edu.au/view/UQ:303082/Dept_Geology_Papers_VI_7.pdf

Some plutonic rocks from a northern part of the New England Batholith

In the Upper Cedar Creek area a gabbro, "diorite", granodiorite, and granite complex is emplaced in the Silurian? Neranleigh-Fernvale Group. This is an orogenic belt, and the post-tectonic sequence is of basic rocks followed by acidic rocks. The gabbro is considered to be derived by the melting of a lower simatic layer. Heat developed by orogenesis and the intrusion of the gabbro, together with the introduction of the elements Na and Ca, caused a replacement of the sediments at depth, giving trondhjemitic rocks which were mobilized and intruded. Later potash metasomatism converted these to granodiorities, and, finally, to true mobilized granites. Contact metamorphism is discussed; especially the metamorphism by the gabbro of unusual slates, giving rise to olivine-bearing hornfelses.

Evan Raymond Phillips

Papers

Some plutonic rocks from a northern part of the New England Batholith

The petrology of the south-western end of the Mt. Samson gabbro-granite complex