Fazilat Yousefi | The University of New Brunswick (original) (raw)

Papers by Fazilat Yousefi

Geoscience Frontiers, 2024

In recent years, the characteristics, and sources of fertile adakites has received considerable a... more In recent years, the characteristics, and sources of fertile adakites has received considerable attention and most recently the geodynamic environment of subducting oceanic crustal slab break-off after collision has gained more recognition, although their relationship to each other has yet to be explored. The geochemical characteristics imply that adakites, in particular high-silica adakites (HSA), can form by partial melting of subducting hydrothermally altered oceanic crust in convergent plate boundary settings during the terminal stages of subduction, lithosphere thickening, and then failure (all post collisional), while the melting of the mantle wedge during subduction-related dehydration creates more typical calc-alkaline basalt-andesite-dacite-rhyolite series (ADR) to form intraoceanic island arc to intracontinental margin arc systems, before the collisional stage. HSAs are characterized by high-silica (SiO2>67 wt.%), Al2O3>15 wt.%, Sr>300 ppm, Y<20 ppm, Yb<1.8 ppm, and Nb≤10 ppm, and MgO<3 wt.%, with high Sr/Y (>50), and La/Yb (>10). Some specific geochemical features, such as high amounts of Mg# (ave 0.51), Ni (ave 924 ppm), and Cr (ave 36 ppm), in HSAs are typical, in contrast to calc-alkaline arcs, although both groups display similar negative anomalies of Nb, Ta, and Ti in primitive mantle-normalized trace element spider diagram profiles. These unique geochemical features are likely ascribed to the involvement of garnet, hornblende, and titanite either during partial melting of hydrous MORB-like oceanic crust with only minor assimilation and fractional crystallization (AFC) within the mantle and crustal lithosphere during ascent in a transpressional collisional environment. Hypotheses for origin of HSA derivative from melting in convergent margins from young, hot oceanic plates subducting into the mantle is applicable to only some adakitic systems, whereas ‘Adak’ itself is consistent with a slab failure scenario. The difference in geochemical characteristics of adakites compared to ADR, such as relative higher MgO, Cr, Cu, and Ni, are due to interaction of the slab-derived adakitic melts with overlying hot lithospheric mantle, but altered oceanic slabs are also relatively rich in siderophile and other chalcophile elements, as well as sulfates and sulfides. HSA magmas related to slab failure have special geochemical properties, such as Sr/Y>20, Nb/Y>0.4, Ta/Yb>0.3, La/Yb>10, Gd/Yb>2, and Sm/Yb>2.5. Slightly higher Nb+Ta is due to high T melting of rutile. Varieties of Nb/Ta compared to silica are also significant in HSA as a result of slab failure/break-off. High T-P partial melting of the hydrothermally altered oceanic slab produces HSA with quite high activities of H2O, SO2, HCl, with chalcophile metals that remain incompatible at higher fO2 (low fH2); these situations happen in post-collisional settings where the subducting oceanic crust experienced slab failure/break-off due to advective heat addition to the system from upwelling asthenosphere. In such a slab failure system, transpression and transtension play a significant role in the rapid emplacement of a high amount of fertile adakitic magmas through the subduction-modified lithosphere and crust into the upper crust. When oxidized slab melts interact with the subduction-modified lithospheric mantle, the resulting magmas stay oxidized, potentially contributing to the special conditions conducive to formation of porphyry Cu-Au mineralization.

Earth Science Research, 2024

Investigating crystal-rich clots hosted in phenocrysts and phenoclasts within Eocene subvolcanic ... more Investigating crystal-rich clots hosted in phenocrysts and phenoclasts within Eocene subvolcanic rocks in Torud-Ahmad Abad, south-southeast of Shahrood (northern part of central Iran zone). These crystal-rich clots and clusters (alias stone inclusions, nanogranitoids, microcrystal clots) are interpreted as crystallized melt inclusions (cMIs) within phenocrysts and phenoclasts, highlighting plagioclase-hosted inclusions. Least-altered hypabyssal igneous rocks are trachy-andesitic, basaltic andesitic, and dacitic porphyries. These porphyries have porphyritic, glomeroporphyritic, granular, and trachytic textures with variable-sized phenocrysts of plagioclase (albite-labradorite), green hornblende (magnesio-hastingsite), and clinopyroxene (diopside-augite), with minor biotite, and Fe-Ti oxides; large plagioclase phenocrysts, exhibiting clear normal oscillatory zoning, were consistently utilized as plagioclase-hosted inclusions due to their abundance in rocks. MIs exhibit complete post-entrapment crystallization (PEC), generally with a slightly finer grain size than the igneous groundmass, i.e. no preserved glassy MI were observed in these phenocrysts, only cMIs. These variably sized, cryptocrystalline to microcrystalline clots in various phenocrysts seem to also represent primary igneous assemblages, manifested as clusters of microphenocrysts; these are referred to as crystal clots. SEM-EDS analyses determined the composition of crystal-rich clots in various plagioclase phenocrysts forming inclusions. The major-element composition of these crystal-rich clots in plagioclase are basalt, basaltic andesite, andesite, trachy-andesite, and trachyte that seem to be melt trapped during plagioclase phenocryst growth; these trapped interface melts then form microphenocryst assemblages that are preserved in phenocrysts, which are trapped when some process interferes with the growth of a phenocryst. These cMIs exhibit compositional variations from their bulk host rock, resulting from entrapment during magma mixing during plagioclase growth

Frontiers in earth science, Jun 3, 2024

The Canadian Journal of Mineralogy and Petrology

The oxidized I-type Eagle Lake Granite stock in southwestern New Brunswick, Canada, is texturally... more The oxidized I-type Eagle Lake Granite stock in southwestern New Brunswick, Canada, is texturally divided into porphyritic and equigranular phases. The porphyritic granite consists of phenocrysts (i.e., plagioclase, K-feldspar, quartz, and biotite) and microcrystalline groundmass with minor magnetite–ilmenite, titanite, apatite, and zircon. The equigranular phase has a similar primary mineral assemblage to the porphyritic phase. Their common magnetite-ilmenite-titanite assemblage reflects co-crystallization (magnetite series) from a magma imparting some redox control. However, these granite phases show minor potassic to propylitic alteration mineral assemblages with very minor sulfides, suggesting localized fluid–rock reaction. The composition of plagioclase varies between albite and oligoclase, and K-feldspar is orthoclase commonly displaying considerable turbidity. The An% versus Al/(Ca+Na+K) data indicate that these feldspars are slightly aluminous, reflecting cryptic alteration....

Journal of Geochemical Exploration

Petrology, 2016

Sahl area, in the south of Shahrood, is a part of the northern portion of the Central Iran Struct... more Sahl area, in the south of Shahrood, is a part of the northern portion of the Central Iran Structural Zone. The area is dominated by a thick sequence of the Paleocene to the middle Eocene volcanic and volcano-sedimentary rocks. Hypabyssal igneous rocks as dome, dike and sill with trachybasaltic andesite and trachyandesite composition intruded the sequence. Various enclaves with amphibolitic, gneissic, hornblenditic, pyroxenitic, tonalitic, gabbroic, tuffaceous sandstone and siltstone nature with different sizes and shapes are present in the rocks studied which can be taken as an evidence of contamination and magma mixing processes. With respect to geochemical characteristics, the studied rocks are belonging to low silica adakites , with calc-alkaline to high potassium calc-alkaline affinity, enriched in LREE and LILE and depleted in HREE and HSFE. Overall, the mentioned adakites resulted from crystallization of melts originated from partial melting of metasomatized or modified mantl...

Journal of Geochemical Exploration, 2017

Journal of Earth Science, 2021

Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt (TAMB), in ... more Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt (TAMB), in the northern part of the Central Iran zone, are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood. These igneous rocks include hypabyssal dacite, trachyte, andesite, trachy-andesite, and basaltic andesite; they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with minor biotite and titanomagnetite; they form domal structures (plugs and stocks), dikes, and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences. Based on isotopic analysis of these intermediate to acidic rocks, initial ratios of 143 Nd/ 144 Nd range from 0.512 775 to 0.512 893 and initial ratios of 87 Sr/ 86 Sr range from 0.703 746 to 0.705 314, with quite positive ε Nd(i) values of +3.69 to +6.00. They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare ...

Goldschmidt2021 abstracts

Bulletin of the Geological Society of Greece

This study investigates for the first time melt inclusions (MI) that are found within fundamental... more This study investigates for the first time melt inclusions (MI) that are found within fundamental minerals of subvolcanic rocks in Torud-Ahmad Abad magmatic belt. The Torud-Ahmad Abad magmatic belt is situated in south-southeast of Shahrood and belongs to the northern part of central Iran structural zone. Melt inclusions represent liquids that were trapped along growth zones (primary) or healed fractures of mineral phases, which crystallized from the silicate liquid as it cooled. Based on SEM analysis of these melt inclusions, their compositions are dacite, andesite and basaltic andesite. Thus, with the use of melt inclusions in the volcanic rocks of Torud-Ahmad Abad magmatic belt, we attempt to show the compositional evolution and origin of magma. The effective factors on magma evolution are magma mixing, fractional crystallization and crustal contamination.

Torud-Ahmad Abad magmatic belt is located 175 km east and southeast of Shahrood in the northern p... more Torud-Ahmad Abad magmatic belt is located 175 km east and southeast of Shahrood in the northern part of the Central Iran Structural Zone and includes a thick sequence of Paleocene to middle Eocene volcanic and volca-nosedimentary rocks. This magmatic belt was formed by numerous hypabyssal igneous adakitic domes constituting basaltic andesite, andesite, trachyandesite, dacite, trachydacite, and dacite. The investigated rocks are mainly composed of pyroxene, amphibole, and plagioclase, with minor biotite and opaque minerals. Mineral chemical analysis reveals that plagioclase composition varies from albite to labradorite, clinopyroxene varies from diopside to augite, and amphibole varies from Mg-hastingsite to Mg-hornblende. Amphibole geothermobarometry suggests crystallization temperatures of 850-1050 °C, at 2-6 kbar and the temperature of 920-970 °C, at a pressure of 3-4.5 kbar, which are conditions in agreement with andesite and dacite formation. Clinopyroxene crystallized at temperatures of 1020-1170 °C, at 2-10 kbar, indicating crys-tallization at crustal depths of maximum 30 km for the studied intrusive rocks in the Torud-Ahmad Abad magmatic belt.

The Torud-Ahmad Abad magmatic belt is located in the south-southeast of Shahrood (East of Semnan ... more The Torud-Ahmad Abad magmatic belt is located in the south-southeast of Shahrood (East of Semnan Province, NE Iran) and lies in the northern part of the Central Iran Structural Zone (CISZ), where a thick sequence of Paleo-cene to middle Eocene volcanic and volcanosedimentary rocks cropped out. This sequence was intruded by numerous dikes, hypabyssal igneous domes and one small gabbrodioritic intrusion, with compositions ranging from trachybasaltic andesite, trachyandesite, dacite, trachyte, gabbro, diorite and syenite. Various enclaves (cogentic and noncogenetic) with different composition, size and shape have been found in these domes and dikes. These enclaves are evidence of magma mixing and crustal contamination. Geochemically, the studied rocks exhibit a calc-alkaline to high potassium calc-alkaline affinity, and are enriched in LREE and LILE and depleted in HREE and HSFE. Other geochemical characteristics, such as a silica content varying between 59-63 wt% and 51-59 wt%, a Na 2 O content N 3 wt%, Al 2 O 3 content N 16 wt%, Yb b 1.8 ppm, and Y b 18 ppm, make it possible to classify these rocks as high silica adakite in the Ahmad Abad region and low silica adakite in the Sahl-Razzeh region or at least, adakitic like rocks. Also, depletion of Nb and Ti, and high enrichment in Rb, Ba, K and Th, imply crustal contamination of the mentioned adakitic domes. The petrographical and geochemical evidence show that the magma forming of the high silica adakites has been originated from partial melting of the subducted oce-anic slab of Neo-Tethys (Sabzevar-Darouneh branch) in amphibolite to eclogite facies and the low silica adakites formed by partial melting of the metasomatized or modified mantle wedge, above the subduction zone. Gabbroic to syenitic rocks are the products of fractional crystallization of basic magma which originated from a nearly non-modified mantle wedge above the subducted oceanic slab. U-Pb dating of the dacitic and andesitic rocks belong to hypabyssal rocks yielded age of 41.4 ± 0.3 Ma, and 35.5 ± 0.2 Ma respectively and consistent to Middle to Late Eocene.