The ophiolitic Mélange of Nain located in the
north of Nain city with a north-south trend. It is one of the
Mesozoic ophiolites of Central-East Iran Microplate (CEIM).
This ophiolite includes of pelagic limestones,
basalts and pillow lavas, plagiogranites, gabbros, pyroxenite,
and mantle peridotites. The metamorphic rocks found in this
ophiolite, are marble, schist, quartzite, banded metachert,
skarn, amphibolitic rocks, spilite, metagabbro, serpentinite,
rodingite, and listvenite. These metamorphic rocks are seen in a
matrix of serpentinite.
The most important metamorphic rocks, which
considered in this research, are amphibolites and skarns.
On the contrary, the previous concepts, these
metamorphic rocks are not exotic blocks coming from other areas.
In fact, they have formed during the metamorphism of the oceanic
crust and its overlying sediments.
This ophiolite has undergone several metamorphic
events since it has formed. Three of the most important ones are
the first regional metamorphism (M1), contact metamorphism (M2)
and the second regional metamorphism (M3).
Amphibolitic rocks (amphibolite and amphibolitic
dikes) formed by the regional metamorphism (M1), from basic
rocks (basalts, pillow lavas, diabasic dikes) generated during
the first rifting in Jurassic. Based on the geothermobarometric
studies, it was at about the middle of the amphibolite to the
first of granulite facies.
Limestone covering these amphibolitic rocks,
turned into skarn and during a contact metamorphism (M2) which
caused by intrusion of tonalitic dikes in some parts. This
metamorphism has occurred in albite-epidote hornfelse to
pyroxene hornfelse facies.
Then a retrograde metamorphism (M3) affected the skarns and amphibolites. So new foliation and new minerals (like
prehnite, epidote and chlorite) formed in skarns and
amphibolites, respectively. It was about greenschist facies.
Presence of amphibolitic enclaves in skarn bodies
indicates the formation of amphibolites before the skarns.
Therefore, the occurrence of contact metamorphism (M2) was after
the first regional metamorphism (M1). In addition, the second
regional metamorphism (M3) has occurred after the contact
metamorphism (M2), based on the foliation in skarns.
Field studies show that the sedimentary parts
covering the amphibolites are different from those that are on
the spilitized pillow lavas. In addition, the geochemical
analysis demonstrated that there is a distinction between
amphibolitic dikes and sheeted dikes of Nain ophiolitic mélange.
Presence of amphibolites and amphibolitic dikes together with
spilitized pillow lavas and sheeted dikes in this ophiolite
shows that rifting in this area might be happened for two times.
Therefore, two phase of rifting realized in this area. The first
one, which occurred in Jurassic, caused the formation of
basaltic protolith of amphibolitic rocks, and the second one in
upper Cretaceous, caused the formation of sheeted dikes and
spilitized pillow lavas.
According to the chemical composition of primary
igneous clinopyroxenes in amphibolitic rocks, these rocks have
an IAT affinity and somehow are similar to MORB. However,
application of NAA as whole rock analysis method confirmed a
MORB origin for these rocks. In addition, these geochemical
analyses indicate a depleted mantle as the origin of basaltic
protolith of amphibolitic rocks.
آشنایی با رشته سنگ شناسی، سرفصل دروس دانشگاهی و نحوه پذیرش
مباحثه
علمی در زمينه سنگ شناسي و علوم وابسته توسط پژوهشگران و کاربران
تصاوير
مربوط به
کاني ها و سنگ
ها که توسط کاربران براي پايگاه ارسال شده اند
در
زمینه سنگ شناسی و علوم وابسته در ایران و سایر نقاط جهان
مجله
هاي علمي - پژوهشي و
ISI فعال در زمينه سنگ شناسي
در
زمینه سنگ شناسی و علوم وابسته در ایران و سایر نقاط جهان
در
زمینه
زمين شناسي،
سنگ شناسی و علوم وابسته در ایران