Younger Igneous Rocks Research Articles

The petrology and alteration of tertiary basalts of the coalgate area, Northwest Canterbury

Abstract Basaltic volcanism in the Coalgate area spans a period from lowermost Eocene to Pliocene times. The oldest basalt rocks emplaced are olivine dolerite dykes of probable Paleocene age. The main period of activity commenced in the lower Miocene with hyaloclastic eruptions of olivine-augite basalt with strong alkaline affinities (Burnt Hill Ash and Sand Pit Tuff). Subsequently intrusives, extrusives, and breccias rich in labradorite ,and of high alumina character were emplaced (Bluff Basalt). The youngest igneous rocks in the area are three tholeiitic flows — the Harper Hills Basalt. Alteration of tuffs to iron-rich montmorillonite under freshwater and heavy leaching conditions supports arguments previously advanced for the basaltic nature of the parent material of the Coalgate Bentonite and the processes involved in its montmorillonitisation.

Operation Basement: Buried Precambrian Rocks of Missouri--their Petrography and Structure

The buried Precambrian basement of Missouri is described on the basis of data from 550 drillholes, petrographic analyses of more than 1,000 samples, and geophysical and structural data. Prominent topographic and probable structural highs are identified as (1) the Central Missouri high, (2) the Southeast Missouri high, (3) the Southwest Missouri high, and (4) the Northeast Missouri high. The first two of these underlie the Ozark dome. Basement rocks associated with the Central Missouri high and locally found elsewhere are gneissic granite, gneiss, and schist. These rocks formed at deeper crustal levels, subsequently have been upwarped to the basement surface, and may be part of an earlier orogenic period. They include lenses of infolded metamorphosed sediments, as well as intrusive granite and basic plutonic rocks. It is assumed that the crustal complex is older than late Precambrian igneous rocks exposed in southeast Missouri, and that regionally persistent prominent northwest trends observed on geophysical maps and in Paleozoic structures are related to structural belts of the crustal complex. In western Missouri a northwest-trending basement fault is defined and interpreted as the northern fault of a graben wher supracrustal Precambrian and possibly younger rocks locally are preserved and brought into contact with metamorphic rocks. The association of late Precambrian rhyolitic volcanic and related shallow intrusive rocks is referred to as the St. Francois terrane. These rocks are exposed in southeast Missouri and extend in the subsurface northwestward. They are associated with the Southwest Missouri high and the Northeast Missouri high. Volcanic rocks identified from southwest Missouri may be part of a volcanic terrane extending into southeast Kansas and northeast Oklahoma; rhyolite in northeast Missouri may extend into Illinois. The granitic rocks of the St. Francois terrane are interpreted as postorogenic subvolcanic massifs that are exposed at the basement surface where pre-Paleozoic uplift and erosion removed their supracrustal cover. Northeast-southwest structural trends are believed to be related in part t the evolution of the St. Francois terrane and are superimposed on the older trends. The youngest igneous rocks of the basement complex are dikes and sills of tholeiitic diabase intruded along both sets of pre-existing structural zones. Local accumulations of unmetamorphosed clastic sediments on the basement surface may be Precambrian or younger.

Vertical soil zonality in the Carpathians of Czechoslovakia

The Carpathians in Czechoslovakia form distinct mountain ranges. The major soil-forming rocks are flysch, so-called crystallinicum (granite, gneiss, phyllites) and mesozoic (mainly limestones), and young igneous rocks (andesites). Each of these kinds dominates a region with vertical soil zonality, and each vertical zone is also a zone of ecological conditions for biocoenoses, i.e. ecosystems. Soils of the vertical zones are characterized by different physical, chemical, biochemical, and microbial properties. Over a range from the lowlands to the high mountains, i.e. with rising elevation, the soil properties reveal the following trends: amounts of clay particles diminish and gravel content increases, soil-moisture content increases, temperature decreases, porosity increases, acidity and humus content increase, amounts of available nutrients diminish, C and N contents increase, C/N ratio increases, saturation of the sorption complex decreases, and biological activity decreases.

The Contaminated Gabbro of Easter Saphook near Old Meldrum in Aberdeenshire

In North-East Scotland the igneous rocks have been divided into two series, whose times of intrusion were separated by the movements responsible for the foliation and disposition of the crystalline schists of that area.2 With the older series, intruded prior to or during those movements, this paper is not concerned. The younger, or non-foliated, series supplies rock types ranging from peridotite to granite. Gabbro is the chief rock in the large independent basic masses formed by the younger igneous rocks; to the more important of these masses may be given the names of the Huntly, Insch, Boganloch, Haddo, Arnage, Maud, and Belhelvie Masses. For the most part they lie within Sheets 76, 77, 86, and 87 of the 1 inch Geological Survey Map of Scotland.