INTRODUCTION AND METHODS. In the Municipality of Bandeirantes' quarry, basalt lava flows of the Serra Geral Group are exposed along with features such ...
FLOW DIRECTION OF PAHOEHOE BASALTS AND THEIR INTERACTION WITH SALT LAKE SEDIMENTS, SERRA GERAL GROUP - BANDEIRANTES, STATE OF PARANÁ. Lucas Albanese Valore¹, Otavio Augusto Boni Licht² ¹Universidade Federal do Paraná – UFPR; ²MINEROPAR – Serviço Geológico do Paraná
INTRODUCTION AND METHODS In the Municipality of Bandeirantes' quarry, basalt lava flows of the Serra Geral Group are exposed along with features such as sharp contacts, interaction with sediments and peperites. The quarry has an eliptical shape (320 m x 170 m), N10°-15°E oriented, with its center point at 23°6'34.70"S; 50°24'42.46"W. The volcanic rocks set Figure 1: Location of study area, State of Paraná, Brazil. Red color indicates the
comprises three lithological units A, B and C, being the lowermost divided into subunits A1 and A2 , regarding the different flow directions that were observed in lobes of this unit.
RESULTS
city of Bandeirantes.
All units show typical pahoehoe flow morphology. The base of the unit A hasn’t
In the quarry's Northeastern sector, it flows to 294,4° ± 05,2°, in the Southwestern
been observed, being impossible to measure its thickness. After a neighboring
to 226,9° ± 17,8°° and in the Northwestern to 038,0° ± 08,5°. Thus, unit A was
quarry located 480m SE, at the altitude of 495m, it is possible to estimate the
divided into A1, which flowed mainly to NW (secondly to SW) and A2, which flowed
thickness of Unit B at 9 m. In this quarry, Unit B is overlaid by another flow (Unit C).
to NE. It is still unclear whether these units are two different lobes of the same flow
Mining activity directed at the massive core of the middle flow (unit B) (mostly in
or are two separate and practically contemporary flows. In the SW sector, subunit
the Northern and Southwestern sectors) exposed the top ropy surface of the lower
A1 shows brecciated lobes cut by quartz veins and irregular masses of zeolites
subunit (A). The top vesicular zone shows empty vesicles or with minor silica
(green apophyllite, white stilbite and chabazite), quartz and carbonates, showing
fillings in the Northern sector, whilst well developed amygdales in the Southern. To
typical hydraulic fracturing features. The breccia's matrix is sandy-silty and
characterize the flow direction of Unit A, as well as its local variations, 164 GPS
supports angular to sub-angular amygdaloidal clasts of the same basalt flow. In
located points had the azimuth of each ropy structure’s average bisector measured
thin section, the matrix is mainly composed by quartz, muscovite, clays and Fe
with a compass. Statistical handling of the azimuth measures showed that the
oxides, as well as sideromelane shards with cuspate edges and vesicular surfaces.
general flow direction (median of the azimuths) of the unit is not constant. G
A
294° N = 103
038° N = 44
F
226° N= 14 B
D
C
E
Figure 2: A) ropy surfaces of the A2 unit, showing NE trends in flow direction. B) Apophyllite in the hydrothermal veins of the peperite. C) features of in situ, coarse hydraulic fragmentation, typical of flow peperites. D e E) Same in situ fragmentation features, with clastic veins and dykes inside the upper flow unit (B unit), thermal contact halos (red halos in boundaries between flow and sediments). F) ropy surfaces of the A1 (northwestern sector) unit, showing W trends in flow direction. G) photomicrograph of the silty-clayey matrix of the peperitem lithic (basaltic) framework seen in the bottom.
CONCLUSIONS Because of its features, it is possible to conclude that this set was formed by the
wind transportation and sedimentation in water bodies - has been observed and
interaction of basic lava with bottom sediments of a salt lake. The lake must have
described in various breccia beds and intertrappean sandstones of the Serra
been formed on the uneven surface of the volcanic landscape, although the water
Geral Group in the North of the State of Paraná. Not only that, this outcrop is an
could be meteoric, underground or volcanic. The shards must have originated
exceptional
from a previous hydrovolcanic event and deposited in the lake before the peperite
transformation into a specific site for geodiversity must be taken into account by
formation. This depositional process of mixed character - that is, pyroclastic fall,
the respective organizations.
and rare exposure of the products of such processes, and
its
