Geology, Geochemistry and Petrographic Studies of Exposed Rock Units from Zhob and Qila Saifullah Districts of Balochistan

Present research exertion provides the information about the stratigraphy, geological structure, geochemistry and petrographic characteristics of the exposed sedimentary rock units and igneous intrusions around Zhob and Qila Saifullah districts of Balochistan. Sedimentary deposition in this area is attribute to both Pashin basin and Suleiman basin. The litho-stratigraphic sections of Suleiman basin are Spingwar formation and Loralai formation (Allozai Group) of Jurassic age and Goru formation, Parh limestone and Pab sandstone of Cretaceous age, whereas Pashin basin comprises of Nisai formation of Eocene age and Multana formation of 0ligocene - Miocene age. The structural features of the area are comprising of complex, doubly plunging, anticlines and synclines which have been truncated by reverse faults at different places.Geochemical analysis (X-Ray diffraction and X-Ray fluorescence) displays that Igneous Intrusions are comprising of Clay, Mica, Plagioclase and Spinal mineral with abundance of Al203 (11-14% wt.), Si02 (27-34 % wt.), Ca0 (6-17% wt.) and Fe203 (19-32% wt.), whereas sedimentary rocks are rich in Quartz, Calcite and Albite with abundance of Al203 (0-17% wt.), Si02 (1.35-78% wt.), Ca0 (0.92-55% wt.) and Fe203 (0.07-13% wt.). The petrographic studies of the carbonates indicate mudstone to wackstone, carbonate fabric with skeletal grains of Alveolina, Miliolids, Globotrancana, Algae, Stylolites and foraminifera, whereas the sandstone samples are rich in sub rounded to rounded quartz grain, feldspar and mica. Petrographic analysis of igneous intrusion shows muscovite, pyroxene needles, chlorite and opaque minerals. Economically the research area is appropriate for cement factory, glass industry and building stones.

Metamorphism of the Buchan type-area, NE Scotland, and its relation to the adjacent Barrovian domain

The metamorphism of the Buchan block in northeast Scotland, and its relation to the Barrovian domain to its west, have been reassessed from consideration of mineral assemblages, microstructures, phase equilibrium modelling and monazite U-Pb geochronology. Zones of increasing metamorphic grade surround a central low grade domain (biotite zone) and define a northward-opening, U-shaped metamorphic map pattern ascribed to post-metamorphic folding. The eastern and southern Buchan domain show the classic Buchan-type prograde sequence cordierite – andalusite – sillimanite – migmatite/gneiss, representing a metamorphic field gradient of gently increasing pressure between 2.5-3.0 kbar, ∼550 °C and 3.5-4.0 kbar, ∼750 °C. A lower pressure metamorphic field gradient (by less than ∼0.5 kbar) is interpreted for the northeastern Buchan domain. The west Buchan domain shows a prograde sequence of staurolite+andalusite – sillimanite – gneiss/migmatite, representing a metamorphic field gradient higher by ∼1 kbar or less than the classic sequence. Uniquely in the northwestern Buchan domain is a staurolite-cordierite-andalusite domain in which staurolite-bearing schists are interpreted to have been overprinted by cordierite+andalusite assemblages. Monazite U-Pb geochronology of schists and gneisses from the Buchan block, including the Cowhythe and Ellon gneisses, yields ages in the range 470 ±5 Ma, supporting geological evidence that the gneisses are metamorphosed Dalradian strata rather than older basement gneisses. The metamorphic ages are similar to the ages of mafic igneous intrusions in the Buchan block, even though many of the exposed intrusions post-date the regional metamorphic zones. The Buchan metamorphic zones are truncated to the west by the Portsoy-Duchray Hill lineament (PDHL), a ductile shear zone that juxtaposes the Buchan rocks against higher-pressure, lower-temperature (kyanite-bearing) Barrovian schists to the west. A 2-15 km wide corridor of andalusite pseudomorphed by kyanite occurs between the PDHL and the Keith shear zone to its west. Monazite geochronology of the Barrovian rocks west of Portsoy shows little evidence of the c. 470 Ma signature of the Buchan block, instead yielding a dominant cluster of ages at c. 450 Ma and a more poorly defined grouping at c. 490 Ma.Supplementary materials: Analytical methods, thermodynamic modelling; tables S1-S13; figures S1-S5 are available at https://doi.org/10.6084/m9.figshare.c.5536745

Impact of igneous intrusion and associated ground deformation on the stratigraphic record

The geomorphology and sediment systems of volcanic areas can be influenced by uplift (forced folding) related to subsurface migration and accumulation of magma. Seismic geomorphological analysis presents a unique tool to study how surface morphology and subsurface magma dynamics relate, given seismic reflection data can image buried landscapes and underlying intrusions in 3D at resolutions of only a few metres-to-decametres. However, differential compaction of the sedimentary sequence above incompressible igneous intrusions during burial modifies palaeosurface morphology. Here we use 3D seismic reflection data from offshore NW Australia to explore how the stratigraphic record of igneous intrusion and associated ground deformation can be unravelled. We focus on a forced fold that formed in the Early Cretaceous to accommodate intrusion of magma, but which was later amplified by burial-related differential compaction of the host sedimentary sequence. We show how: (1) marine channels and clinoforms may be deflected by syn-depositional intrusion-induced forced folds; and (2) differential compaction can locally change clinoform depth post-deposition, potentially leading to erroneous interpretation of shoreline trajectories. Our results demonstrate seismic geomorphological analysis can help us better understand how magma emplacement translates into ground deformation, and how this shapes the landform of volcanic regions.

Implications of Tectonic Anomalies From Potential Field Data in Some Parts of Southeast Nigeria.

Tectonic structures controlling mineralization in some parts of Southeast Nigeria were evaluated using airborne potential field data. High and low frequency filters and depth determination tools were adopted to evaluate short and long wavelength anomalies, resolve the spatial spreading of igneous intrusions, depths to geologic sources and basin topography. The high frequency results exhibited high concentration of short wavelength anomalies in the Obudu Plateau and Ikom-Mamfe Rift. The underlying main tectonics of the area elucidated by the low frequency results caused the widespread occurrences of short wavelength geologic structures that are revealed by the high frequency maps. The study area is characterized by comparatively thin (~13.0 to <3000 m) sedimentation. The observed thin thickness is as a result of the massive Precambrian basement outcrops in some locations in the Obudu Plateau and the proliferation of igneous intrusions within this part of the Lower Benue Trough. The 2-D models showed the undulating nature of the underlying basin topography, the location of intrusions, domal structures and related normal faults. The locations and neighbourhood of intrusions and/or short wavelength structures are viable sites for lead-zinc-barite, brine and metallogenic minerals.

Analysis of deformation bands associated with the Trachyte Mesa intrusion, Henry Mountains, Utah: implications for reservoir connectivity and fluid flow around sill intrusions

Shallow-level igneous intrusions are a common feature of many sedimentary basins, and there is increased recognition of the syn-emplacement deformation structures in the host rock that help to accommodate this magma addition. However, the sub-seismic structure and reservoir-scale implications of igneous intrusions remain poorly understood. The Trachyte Mesa intrusion is a small (∼1.5 km2), NE–SW trending satellite intrusion to the Oligocene-age Mount Hillers intrusive complex in the Henry Mountains, Utah. It is emplaced within the highly porous, aeolian Entrada Sandstone Formation (Jurassic), producing a network of conjugate sets of NE–SW striking deformation bands trending parallel to the intrusion margins. The network was characterized by defining a series of nodes and branches, from which the topology, frequency, intensity, spacing, characteristic length, and dimensionless intensity of the deformation band traces and branches were determined. These quantitative geometric and topological measures were supplemented by petrological, porosity and microstructural analyses. Results show a marked increase in deformation band intensity and significant porosity reduction with increasing proximity to the intrusion. The deformation bands are likely to impede fluid flow, forming barriers and baffles within the Entrada reservoir unit. A corresponding increase in Y- and X-nodes highlights the significant increase in deformation band connectivity, which in turn will significantly reduce the permeability of the sandstone. This study indicates that fluid flow in deformed host rocks around igneous bodies may vary significantly from that in the undeformed host rock. A better understanding of the variability of deformation structures, and their association with intrusion geometry, will have important implications for industries where fluid flow within naturally fractured reservoirs adds value (e.g. hydrocarbon reservoir deliverability, hydrology, geothermal energy and carbon sequestration).