Abstract:The Zargoli granite, which extends in a northeast-southwest direction, intrudes into the Eocene-Oligocene regional metamorphic flysch-type sediments in the northwest of Zahedan. This pluton, based on modal and geochemical classification, is composed of biotite granite and biotite granodiorite, was contaminated by country rocks during its emplacement, and is slightly changed to more aluminous. The SiO 2 content of these rocks range from 62.4 to 66 wt% with an alumina saturation index of Shand [molar Al 2 O 3 / … Show more
“…Biostratigraphic data suggest that the Sistan oceanic basin formed in Early Cretaceous time [ Babazadeh and De Wever , ]. Ages of high‐pressure rocks of ~89–78 Ma suggest that subduction of the Sistan Ocean occurred in Late Cretaceous time [ Bröcker et al ., ], but collision‐related granitoids as young as late Oligocene are interpreted to result from collision‐related lithosphere removal [ Rezaei‐Khakhaei et al ., ] and may indicate that shortening continued well into the Cenozoic. Middle Miocene volcanics (14–11 Ma) are only weakly deformed and postdate significant E‐W shortening [ Pang et al ., ].…”
Section: Restoring the Cenozoic Nw India/kabul Block—asia Collisionmentioning
Gondwana breakup since the Jurassic and the northward motion of India toward Eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the Indian and Arabian margins. Here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in NW India and SE Arabia and seismic tomography of the mantle below the NW Indian Ocean. The North Somali and proto-Owen basins formed due to 160-133 Ma N-S extension between India and Somalia. Subsequent convergence destroyed part of this crust, simultaneous with the uplift of the Masirah ophiolites. Most of the preserved crust in the Owen Basin may have formed between 84 and 74 Ma, whereas the Mascarene and the Amirante basins accommodated motion between India and Madagascar/East Africa between 85 and circa 60 Ma and 75 and circa 66 Ma, respectively. Between circa 84 and 45 Ma, oblique Arabia-India convergence culminated in ophiolite obduction onto SE Arabia and NW India and formed the Carlsberg slab in the lower mantle below the NW Indian Ocean. The NNE-SSW oriented slab may explain the anomalous bathymetry in the NW Indian Ocean and may be considered a paleolongitudinal constraint for absolute plate motion. NW India-Asia collision occurred at circa 20 Ma deforming the Sulaiman ranges or at 30 Ma if the Hindu Kush slab north of the Afghan block reflects intra-Asian subduction. Our study highlights that the NW India ophiolites have no relationship with India-Asia motion or collision but result from relative India-Africa/Arabia motions instead.
“…Biostratigraphic data suggest that the Sistan oceanic basin formed in Early Cretaceous time [ Babazadeh and De Wever , ]. Ages of high‐pressure rocks of ~89–78 Ma suggest that subduction of the Sistan Ocean occurred in Late Cretaceous time [ Bröcker et al ., ], but collision‐related granitoids as young as late Oligocene are interpreted to result from collision‐related lithosphere removal [ Rezaei‐Khakhaei et al ., ] and may indicate that shortening continued well into the Cenozoic. Middle Miocene volcanics (14–11 Ma) are only weakly deformed and postdate significant E‐W shortening [ Pang et al ., ].…”
Section: Restoring the Cenozoic Nw India/kabul Block—asia Collisionmentioning
Gondwana breakup since the Jurassic and the northward motion of India toward Eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the Indian and Arabian margins. Here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in NW India and SE Arabia and seismic tomography of the mantle below the NW Indian Ocean. The North Somali and proto-Owen basins formed due to 160-133 Ma N-S extension between India and Somalia. Subsequent convergence destroyed part of this crust, simultaneous with the uplift of the Masirah ophiolites. Most of the preserved crust in the Owen Basin may have formed between 84 and 74 Ma, whereas the Mascarene and the Amirante basins accommodated motion between India and Madagascar/East Africa between 85 and circa 60 Ma and 75 and circa 66 Ma, respectively. Between circa 84 and 45 Ma, oblique Arabia-India convergence culminated in ophiolite obduction onto SE Arabia and NW India and formed the Carlsberg slab in the lower mantle below the NW Indian Ocean. The NNE-SSW oriented slab may explain the anomalous bathymetry in the NW Indian Ocean and may be considered a paleolongitudinal constraint for absolute plate motion. NW India-Asia collision occurred at circa 20 Ma deforming the Sulaiman ranges or at 30 Ma if the Hindu Kush slab north of the Afghan block reflects intra-Asian subduction. Our study highlights that the NW India ophiolites have no relationship with India-Asia motion or collision but result from relative India-Africa/Arabia motions instead.
“…We do not reconstruct the western margin of the collision zone in Afghanistan and Pakistan because there is a general absence of kinematic data. We note, however, that there is evidence for Cenozoic extrusion of the Afghan Block westward along the conjugate Helmand and Chaman strike‐slip faults [ Tapponnier et al , 1981], and E‐W closure of the Sistan ocean between the Afghan Block and the Lut Block in eastern Iran, which perhaps continued until Oligocene‐Miocene times [ Rezaei‐Kahkhaei et al , 2010] (Figure 2). Given the kinematics of the known major faults and the E‐W compression in eastern Iran, restoring this region would probably indicate some westward lateral escape of the Afghan Block.…”
[1] A long-standing problem in the geological evolution of the India-Asia collision zone is how and where convergence between India and Asia was accommodated since collision. Proposed collision ages vary from 65 to 35 Ma, although most data sets are consistent with collision being underway by 50 Ma. Plate reconstructions show that since 50 Ma ∼2400-3200 km (west to east) of India-Asia convergence occurred, much more than the 450-900 km of documented Himalayan shortening. Current models therefore suggest that most post-50 Ma convergence was accommodated north of the Indus-Yarlung suture zone. We review kinematic data and construct an updated restoration of Cenozoic Asian deformation to test this assumption. We show that geologic studies have documented 600-750 km of N-S Cenozoic shortening across, and north of, the Tibetan Plateau. The Pamir-Hindu Kush region accommodated ∼1050 km of N-S convergence. Geological evidence from Tibet is inconsistent with models that propose 750-1250 km of eastward extrusion of Indochina. Approximately 250 km of Indochinese extrusion from 30 to 20 Ma of Indochina suggested by SE Asia reconstructions can be reconciled by dextral transpression in eastern Tibet. We use our reconstruction to calculate the required size of Greater India as a function of collision age. Even with a 35 Ma collision age, the size of Greater India is 2-3 times larger than Himalayan shortening. For a 50 Ma collision, the size of Greater India from west to east is ∼1350-2600 km, consistent with robust paleomagnetic data from upper Cretaceous-Paleocene Tethyan Himalayan strata. These estimates for the size of Greater India far exceed documented shortening in the Himalaya. We conclude that most of Greater India was consumed by subduction or underthrusting, without leaving a geological record that has been recognized at the surface.
“…It has been suggested that during the initial collision of an orogenic wedge with a continent, major compressional stresses can be transmitted into the continent as a consequence of subduction resistance, giving rise to large-scale intraplate deformations and strike-slip shear zones (Ziegler, van Wees & Cloetingh, 1998; Rezaei-Kahkhaei et al . 2010). Similarly, Triassic collisional orogenesis of the Qinling Orogen produced intensive brittle-ductile shearing deformation and greenschist-facies metamorphism in the WQO (Zhang et al .…”
The Liziyuan goldfield is located along the northern margin of the western part of the Qinling Orogen (WQO). The goldfield consists of five gold-only deposits hosted by metavolcanic rocks, and one polymetallic (Au–Ag–Pb) deposit hosted by the Tianzishan Monzogranite. As the Liziyuan goldfield appears to be spatially and temporally related to the Jiancaowan Porphyry, the study of the deposit provides a crucial insight into the relationship between tectonic-magmatic events and gold metallogenesis in the WQO. In this paper, we present whole-rock major and trace element geochemistry, and in situ zircon U–Pb and Lu–Hf isotopic data from the Tianzishan Monzogranite and Jiancaowan Porphyry. The two granitic plutons are enriched in LILEs and LREEs, depleted in HFSEs and have zircon εHf(t) values between −14.1 and −5.1 for the Tianzishan Monzogranite and between −21.0 and −8.4 for the Jiancaowan Porphyry. These characteristics indicate that the granites are derived from the crust. The Tianzishan Monzogranite has LA-ICP-MS zircon U–Pb ages of 256.1 ± 3.7 to 260.0 ± 2.1 Ma, which suggests that it was emplaced in the WQO during the convergence of the North and South (Yangtze) China cratons in the early stage of the Qinling Orogeny. In contrast, the porphyry has a LA-ICP-MS zircon U–Pb age of 229.2 ± 1.2 Ma, which is younger than the peak collision age, but corresponds to the widespread Late Triassic post-collisional granitic plutons in the WQO. The Tianzishan Monzogranite has somewhat higher Sr contents (196–631 ppm), lower Y (2.23–19.6 ppm) and Yb (0.20–2.01 ppm) contents, and a positive Eu/Eu* averaging 1.15. These characteristics suggest the pluton was derived from partial melting of the thickened crust. In contrast, the relatively higher MgO content (0.85–2.08 wt%) and Mg no. (43.4–58.2) of the Jiancaowan Porphyry indicates that insignificant amounts of subcontinental lithospheric mantle-derived mafic melts were involved in the generation of the magma. The Liziyuan goldfield is hosted by faults in greenschist-facies metamorphic rocks. Fluid inclusion studies suggest that gold was precipitated from CO2-rich, low-salinity and medium temperature fluids. This feature is consistent with the other orogenic gold deposits throughout the world. The field relationships and zircon U–Pb ages of the two granitic plutons suggest that gold mineralization is coeval with or slightly younger than the emplacement of the Jiancaowan Porphyry. Therefore, both the porphyry and deposit formed during the post-collisional stage of the Qinling Orogen.
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