Petrogenesis of the Late Cretaceous Tholeiitic Volcanism and Oceanic Island Arc Affinity of the Chagai Arc, Western Pakistan

• Published in: Acta geologica Sinica (Beijing) Vol. 91; no. 4; pp. 1248 - 1263
• Main Authors: SIDDIQUI, Rehanul Haq, JAN, M. Qasim, KHAN, Mohammad Asif, KAKAR, M. Ishaq, FODEN, John D.
• Format: Journal Article
• Language: English
• Published: Richmond Wiley Subscription Services, Inc 01-08-2017; Baluchistan University of Information Technology, Engineering and Management Sciences, Quetta, Pakistan%National Centre of Excellence in Geology, University of Peshawar, Peshawar, & COMSTECH, Islamabad,Pakistan%Karakoram International University, Gilgit, Pakistan%Centre of Excellence in Mineralogy, University of Baluchistan, Quetta, Pakistan%Department of Earth Sciences, University of Adelaide, SA 5005, Australia
• Edition: English ed.
• Subjects: Anomalies; Barium; Basalt; Chagai arc; Chert; Convergence; Convergence zones; Cretaceous; Depletion; Island arcs; Late Cretaceous; Lava; Lava flows; Limestone; Magma; Mantle; Niobium; Oceanic islands; Ophiolites; Outcrops; Petrogenesis; Sandstone; Sedimentary rocks; Shale; Strontium; Strontium isotopes; Subduction; Subduction zones; Tantalum; tholeiitic volcanics; Volcanic activity; Volcanism; western Pakistan; Zirconium; 亲和力; 大洋岛弧; 巴基斯坦; 拉斑玄武岩; 晚白垩世; 火山群; 玄武安山岩; 西部; Pakistan; tholeiitic volcanics; Chagai arc; western Pakistan; Late Cretaceous
• ISSN: 1000-9515; 1755-6724
• DOI: 10.1111/1755-6724.13358

The Late Cretaceous Chagai arc outcrops in western Pakistan, southern Afghanistan and eastern Iran. It is in the Tethyan convergence zone, formed by northward subduction of the Arabian oceanic plate beneath the Afghan block. The oldest unit of the Chagai arc is the Late Cretaceous Sinjrani Volcanic Group. This is composed of porphyritic lava flows and volcaniclastic rocks, and subordinate shale, sandstone, limestone and chert. The flows are fractionated low-K tholeiitic basalts, basaltic- andesites, and andesites. Relative enrichment in their LILE and depletion in HFSE, and negative Nb and Ta and positive K, Ba and Sr anomalies point to a subduction-related origin. Compared to MORB, the least fractionated Chagai basalts have low Na2O, Fe2O3^T, CaO, Ti, Zr, Y and ^87Sr/^86Sr. Rather than an Andean setting, these results suggest derivation from a highly depleted mantle in an intraoceanic arc formed by Late Cretaceous convergence in the Ceno-Tethys. The segmented subduction zone formed between Gondwana and a collage of small continental blocks （Iran, Afghan, Karakoram, Lhasa and Burma） was accompanied by a chain of oceanic island arcs and suprasubduction ophiolites including Semail, Zagros, Chagai-Raskoh, Kandahar, Muslim Bagh, Waziristan and Kohistan-Ladakh, Nidar, Nagaland and Manipur. These complexes accreted to the southern margin of Eurasia in the Late Cretaceous.