Geology of the Almeria-Nijar Basin - Junta de Andalucía

76 Pages·2009·6.34 MB·English

The Almeria-Nijar Basin
Geological Features

Geological Features and Evolution
Juan C. Braga - José M. Martín
The Almería-Níjar Basin has been a small
GEOLOGICAL LOCATION OF THE ALMERIA-NIJAR BASIN
marine sedimentary trough since 15 million
years ago,the time at which emergence of
the relieves occurred,that today constitute the SIERRAS
Sorbas Basin
Sierra Nevada and the Sierra de los Filabres
1.Sierra Nevada
massifs,whose foothills were located at the Tabernas Basin 2 Vera 2.Filabres
coastline. 3.Sierra de Gádor
4.Alhamilla
Vera Basin 5.Cabrera
In this period,however,the Almería Basin was 1 Sorbas 5 6.Sierra de Cabo de Gata
not individualised from the Sorbas and
Tabernas 4
Tabernas basins.In this marine basin, Níjar Carboneras
sediments started to arrive from the Almería
3
dismantling of the emergent relieves through
the fluvial network.Extensive submarine fans
were generated on top of the marine platform, El Ejido 6
while the fully active volcanoes of Cabo de
Gata were rumbling,probably fashioning Almería-Níjar Basin
a tropical volcanic archipelago. Campo de Dalias Basin
It was much later,about 7 million years ago,
when uplift of the Sierra de Gádor and Sierra Neogene-Quaternary sediments Neogene volcanic rocks Betic substratum
Alhamilla caused the individualisation of the
Almería-Níjar Basin,to the south of these same
hills and between the emerged volcanic relieves The Almería-Níjar Basin therefore included all A region that had constituted a marine seafloor
of Cabo de Gata. of the current,low-lying land present between during the last 15 million years in which
Sierra de Gádor,Sierra Alhamilla,Sierra Cabrera a sedimentary record has remained,with
Sierra Cabrera emerged 5 million years ago,and and the coastline,including the volcanic unsurpassed observable characteristics,
it definitively separated the Sorbas and Vera relieves of the Sierra de Cabo de Gata. exceptional for the understanding of evolution in
basins. the Mediterranean Basin at this time,and its
geography,climate and ecology.
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Geological Features and Evolution
SIMPLIFIED GEOLOGICAL MAP OF THE ALMERIA BASIN
According to Zazo and J.L.Goy
Sierra de Alhamilla
Níjar
Sierra de Gádor
Gata
Almería de
Cabo
Cabo de
Roquetas de mar de Gata Sierra
Sª Alhamilla Alquián
Sea level
Sª Alhamilla
Níjar Pozo de Los Frailes
Sea level
Old Quaternary terrain Miocene volcanic Recent Quaternary (Holocene) formations,from 10,000 years ago
(Pleistocene:1.8 Ma to 10,000 yrs) formations (15.7 to 7.9 Ma) to present
Albuferas
Pliocene terrain (5.2 to 1.8 Ma) Ancient basement Fluvial deposits (saltpans) Dunefields
Miocene terrain (23.7 to 5.2 Ma) Alluvial fans Travertines
Littoral barries and/or fringes Deltas
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VOLCANIC EPISODES
Origin of magmatic processes and volcanic features
Juan M. Fernández
MAGMAS AND MAGMATIC ROCKS MELTING OF PRIMARY
MAGMAS
Main cone
Magmas are formed through the partial melting Parasitic cone
and emplacement of rocks at high temperature Lava flow
in the interior of the Earth.They consist of a
Plutonic rocks
mixture of liquid,dissolved gases (water vapour
and carbon dioxide) and minerals. Magma Dykes
chamber
Derived
Magmas that come directly from the partial magma
melting of rocks at depth are called primary
magmas.Sometimes they reach the surface
Partial melting
straight away,however,it is more common that
of the crust
they remain static at different levels within
the mantle and the continental crust,forming
magmatic chambers.In such a situation the CRUST
magmas may partly crystallize,assimilate MANTLE
the country rock and suffer other modifications,
the final result of which is a series of derived
magmas of different compositions.This process
is known as magmatic differentiation.
minerals may crystallise in an ideal manner, matrix a proportion of small minerals of larger
Magmas are generally less dense than the creating rocks with large-sized crystals such as size (phenocrysts) may be present,which had
material within which they are forming,and, granites. crystallised previously in the magma chamber.
therefore,they tend to climb up through the
mantle and continental crust,until they cool and When the magma reaches the surface,it gives At times,during its ascent,the magma is
crystallize,giving place to intrusive rocks. way to volcanic or eruptive activity.The results injected into fissures,forming dykes.These are
are volcanic rocks and so-called volcanic also known as hypabyssal rocks.
Magmas that solidify slowly underneath the features.Cooling is very rapid,so that the rocks
terrestrial surface form bodies of intrusive do not crystallise well,forming a vitreous
rocks.Cooling happens very slowly,so that the matrix or a very fine crystal size.Within this
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Origin of magmatic processes and volcanic features
MAGMAS AND PLATE TECTONICS The origin of magma is related to the dynamics The origin of Cabo de Gata volcanism is
of the lithospheric plate margins:The majority of complex,and under discussion at present.
Although there are a great variety of types basaltic magmas originate through partial
and compositions of magmas,the three most melting of the mantle in divergent plate In whatever case,it is related with the orogenic
important generic types are the basaltic group boundaries (mid-oceanic ridges).Andesitic and process of crustal thickening in this area,
(or basic,50% of silica),the siliceous group siliceous magmas are generated in subduction the Alborán domain,due to the collision of the
(or acid,65 to 70% of silica),and the andesitic zones by partial melting of both the oceanic plate African and European plates;and afterwards
group (or intermediate) such as those of Cabo and the continental crust. their thinning through phenomena of
de Gata. extensional or transtensional character.
OCEANIC CRUST CONTINENTAL CRUST
Island arc Trench Mid-oceanic ridge Trench Rift valley
Plateau
basalts
Continental
crust
Oceanic
crust Upper mantle Lithospheric
(asthenosphere) mantle
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Origin of magmatic processes and volcanic features
ACTIVITY AND VOLCANIC FEATURES BASALTIC MAGMAS
The type of eruption and the products resulting
PYROCLASTIC CONE OR CINDER CONE Lava flows STRATOCONE
from volcanic activity depend,above all,on two
important aspects:the viscosity of the lava, Pyroclastic
levels
which determines fluidity,and the gas content
of the lava.
Basaltic magmas,poor in silica,are fluid.At the
surface they flow rapidly,forming lava flows
that at times travel great distances (this type of
volcanism is known as effusive).If the basaltic
lava is rich in gas,it is released with ease by ACIDIC MAGMAS
means of intermittent explosions,creating
pyroclastic types of cone (also known as cinder
DOMES OF SILICEOUS MAGMA
cones).The alternation of lava flows and
pyroclastic episodes fashions another type of
volcanic edifice known as the Stratocone
volcano.
Acidic magmas,on the other hand,rich in
silica,are much more viscous.Upon exiting
onto the surface,they cannot flow easily,and
form accumulations around the eruptive Pelean Dome Cumulate Dome Crypto-dome
mouth (domes),or flow very slowly forming
lava flows over short distances (this type of
volcanism is called extrusive).
SOME TYPES OF DOME
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Origin of magmatic processes and volcanic structures
EXPLOSIVE VOLCANISM IGNIMBRITES collapses into the vacated space,forming an
PYROCLASTIC FLOWS enormous depression called a caldera.Some
calderas can be more than 25 kilometres in
The high viscosity of lavas from acidic magmas Ash diameter and several kilometres deep.When,after
cloud
means that on occasions gases cannot be the formation of a caldera,the magmatic chamber
easily liberated,accumulating as bubbles,and Eruptive Column receives new supplies from deeper zones,the
increasing their internal pressure until they are Volcanic interior of the caldera can return to a state of
ash fall
unleashed in enormous explosive phenomena uplift,a phenomenon known as resurgence.
Nuee Ardente
that violently erupt huge volumes of Pyroclastic flow The calderas are one of the most dynamically
semi-molten rock into the atmosphere. active volcanic features and are frequently
The so-called pyroclastic flows are generated associated with earthquakes,thermal activity,
by this means,their solidification then geysers,hydrothermal waters etc.
produces rocks known as pyroclastics.
They can be of different types:
BRECCIAS AND AGGLOMERATES FORMATION OF A VOLCANIC CALDERA
Ignimbrites
Nuee
A mixture of very hot gas,ash and rock Pyroclastic flow Ardente
fragments is launched from the volcano in an Dome
eruptive column.The density of the mixture,
greater than that of air,means that it falls
rapidly,smothering the underlying hillside in
the form of a covering flow comprising a
1
glowing cloud of gas.They create rocks rich
in ash and pumice. CALDERAS
Lithic Breccias or Agglomerates The largest and most explosive volcanic eruptions
2
The flow forms from the rupture,explosive or throw out tens and hundreds of cubic kilometres
otherwise,of the summit of the volcano. of magma onto the earth's surface.When too
Rock fragments that made up the actual dome high a volume of magma is extruded from a
3
dominate in this case. magmatic chamber,the earth subsides or
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The Cabo de Gata Volcanic Complex
Juan M. Fernández
GEOLOGICAL CONTEXT AND AGE grown out of the sea sufficiently enough to in various cycles.The better-known and
reach the surface,forming islands of volcanic conserved volcanic features are the most recent,
The Cabo de Gata volcanic complex is the origin fringed by marine sedimentary platforms. produced between 9 and 7.5 million years ago.
largest-sized element of all the volcanic
manifestations in SE Spain.It continues to The age of the Cabo de Gata volcanic complex is The base of the volcanic complex outcrops at
expand beneath the Alboran Sea,and has been known through the study of fossils present in various points (Serrata de Níjar and Carboneras)
brought into its present position by the sedimentary rocks associated with the volcanic and is formed of Betic basement rocks
operation of the Carboneras-Serrata Fault.The elements and from dating with isotopes (mostly (carbonate rocks and phyllites of the Malaguide
greater part of volcanism in the Alboran basin is Potassium/Argon) in the volcanic rocks.Volcanic and Alpujarride complexes) and some marines
actually submerged.The volcanic structures of activity developed in a broad period that extends sediments (marls) from the Lower-Middle
Cabo de Gata also indicate signs of having been from around 14-15 to around 7.5 million years Miocene.Towards the top,the volcanic activity is
generated,by and large, beneath the sea.Some ago (that is to say,Middle and Upper Miocene). fossilised by marine sedimentary deposits of the
of the oldest volcanic structures could have During this interval the volcanic activity occurred terminal Miocene (Messinian reefs).
THE CABO DE GATA VOLCANIC COMPLEX WITHIN THE CONTEXT OF THE ALBORAN SEA SUBMARINE VOLCANISM
Calderas
Sª de Los Filabres
Volcaniclastic
Mediterranean Sedimentary deposits
Sorbas Sea levels
Sª Nevada Sorbas (Alboran Sea)
Basin Sea level
Níjar
Sª de Gádor SAª BlAmalsheianrímaillaSerrata de Níjar Las Negras Polarca
Ridge
Almería
AlbBoertaicn B BasaeAsmidner ant CBhaenlkla CarAlbmoenríear aCs aFnayuolPtnB oalnlukx CaGbaot ade S.Jose Islet GeRniodvgeeses PlatforHmydrothermal Magmatic Chambers
Neogene Basins Sabinal Bank Systems
Volcanic Rocks ESmubemrgeerdg ed
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The Cabo de Gata Volcanic Complex
RELIEF FEATURES OF THE CABO DE GATA VOLCANIC COMPLEX
A
Nijar-Almeria Serrata de Sierra de
Basin Nijar Cabo de Gata
PlioQuaternary
Carboneras
Miocene
Volcanic Complex
Basement
Carboneras Fault Carboneras Fault C Mesa Roldán
Agua Amarga
La Serrata de Nijaris a zone of volcanic origin,associated with the Carboneras
Fault.The rocks,concealed beneath the sedimentary filling of the Campo de A
Níjar,have been uplifted and project outwards at the surface of La Serrata
because they are caught up between different fractures in the fault zone. Serrata de Níjar Las Negras
D
Rodalquilar
B Rodalquilar Caldera
Del Garbanzal Dome-Flow
Miocene sediments
B Los lobos
LA ISLETA
Ancient massive rocks White ignimbrites E Los Frailes
Caldera
El Cerro de Garbanzalis a unique volcanic structure,almost circular in plan, San José
formed by the extrusion of a massive dome-flow.The geometry of this type of
structure is known in some places as fortified domes or 'tortas'.Quite eroded,
it is preserved as a ceiling above marine sedimentary remains. Barronal
Cabo de Gata
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