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Zircon U-Pb-Hf isotopes, integrated with bulk-rock major, trace element, and isotopic compositions of amphibolites from the Makran ophiolitic mélange complex (OMC), carry implications on the evolution of the Neo-Tethys Ocean. Field and petrographical-geochemical data confirm these amphibolites as products of the metamorphism of a mafic protolith. Zircons from the amphibolites have U-Pb ages of Late Early Permian (273 Ma) to Late Triassic (210 Ma), and their εHf(t) values vary from +6.32 to +15.4. The Makran amphibolites are geochemically similar to transitional- or enriched-MORBs. The 143Nd/144Nd(t) ratios for amphibolites range from 0.51260 to 0.512551, and 87Sr/86Sr(t) from 0.704433 to 0.706244. The Pb-isotope composition of these rocks is radiogenic, ranging from 15.61-15.64 for 207Pb/204Pb(t), 18.98-19.21 for 206Pb/204Pb(t) and 38.88-39.36 for 208Pb/204Pb(t). The isotopic and geochemical signatures of these rocks suggest that they were most likely formed during continental rifting and originated from a relatively enriched mantle source. This is also attested by their high zircon Ce/Ce* ratios. We interpret these amphibolites related to the Permian-Triassic plumes that triggered Gondwana rifting to open the Neo-Tethyan Ocean before metamorphosed, fragmented, and accreted into the Makran accretionary complex probably during Early to Late Cretaceous time. [ABSTRACT FROM AUTHOR]

The Early Cretaceous palaeogeography prior to the India‐Asia collision is still controversial. There are two end‐member models – an integrated passive margin versus an archipelago. Here, we report zircon U–Pb ages, Hf, and whole‐rock Nd isotopes of newly defined Cretaceous mica schists from the Main Central Thrust to constrain the Early Cretaceous palaeogeography of the Himalaya. The mica schists have Early Cretaceous zircons with εHf(t) values of −21.1 to −9.2. The mica schists are characterized by TDMC values of 1.8–2.5 Ga and whole‐rock εNd(0) value of −24.0. These features imply that these zircons generated from partial melting of lower crust as a result of an extension in some older continental crust, which were transported and deposted to form the protolith of the Cretaceous mica schists. Age pattern comparisons indicate that the age populations of the Cretaceous mica schists are significantly distinct from those of other Cretaceous strata in the Himalaya. It is obvious that the protolith of the Cretaceous mica schists were formed in an independent terrane (Arun) in the Neo‐Tethys with significant tectonic separations proventing any inputs from the Tibetan Himalaya, Greater Himalaya, or Indian Craton since 120 Ma. Combined with published U–Pb ages and other geological data, our data supports the archipelago palaeogeography with rifted terranes in the Neo‐Tethys Ocean, shedding light on the multiple amalgamation events along the India‐Asia collision zone. [ABSTRACT FROM AUTHOR]

Detrital age relationship between major lithounits of the orogeny and foreland basin strata can elucidate orogenic events. However, analyses of some selected samples of a certain time interval from a sedimentary basin can lead to misjudgement. We present detrital zircon U–Pb age analyses of some older sedimentary strata of the Tansen Group, a renowned basin for the explanation of the Himalayan Orogeny. Sandstone and tuff samples of the Permian and Cretaceous Periods from the Gondwana sequence of the Lesser Himalaya of eastern Nepal and western Nepal were subjected to U–Pb age analyses, and the results were compared with available younger strata of the same basin along with the major lithotectonic units of the Himalaya. The detrital zircon age population of different units enables us to propose a new stratigraphic framework for the eastern Nepal Gondwana sequence and correlate them with the well‐established Gondwana sequence of the western Nepal Lesser Himalaya. This study reveals that the source region for the Gondwana sequence (Permian to Cretaceous) and post‐Gondwana sequence (Eocene to Miocene) is alternating and casts doubt upon the famous implications for the India and Asia collision and metamorphic core exhumation made from the basin analysis of these sedimentary basins of the southern part of the Himalayan Thrust Fold Belt (HTFB). Furthermore, we argue that these basins cannot be used for the reconstruction of collision and exhumation history of the Himalaya as being used. Alternatively, the results are more consistent with the possibilities of recent unconventional hypotheses of sediment contribution of the Greater Himalaya to the Permian strata of the Lesser Himalaya and the Cretaceous rifting of the Tibetan–Himalayan Microcontinent followed by the accretion of the microcontinent before collision of India and Asia. [ABSTRACT FROM AUTHOR]