Shuhab D. Khan

Did the Kohistan-Ladakh island arc collide first with India?

The Kohistan-Ladakh block occupies the northwestern corner of the Himalayan mountains and has long been recognized to represent an island arc constructed on ocean floor during Jurassic and Cretaceous times. Because the Kohistan-Ladakh block now lies within the Asian continent, it is important to know how and when it became sandwiched between India and the rest of Asia. We have found from analysis of paleomagnetic data that in Late Cretaceous–early Paleocene times, the Kohistan-Ladakh island arc could not have been far from the equator. India was close to the equator, but the southern margin of Asia was more than 3000 km to the north. Our new U-Pb zircon age results from rocks of the Kohistan-Ladakh block show that calc-alkaline volcanic arc igneous activity ended in the Kohistan-Ladakh arc by 61 Ma. We interpret that cessation to date the collision of Kohistan with India. This new timing is confirmed by evidence that a Southern Hemisphere enriched DUPAL mantle source was involved in the generation of the latest Cretaceous Teru Volcanic Formation rocks of the Kohistan-Ladakh arc. Further confirmation of the collision of the Kohistan arc with India in early Paleocene times comes from evidence of the timing of obduction of ophiolites and from the unconformity of postcollisional sedimentary rocks onto the Indian continental margin in northwestern and western Pakistan. Final incorporation of India, now carrying the Kohistan-Ladakh block in its NW corner, into Asia took place at the Shyok suture. The best evidence for the timing of that suturing ca. 50 Ma comes from two postcollisional granites (ages 47 Ma and 41 Ma) in northern Kohistan, which show in their zircon isotopic compositions evidence of the involvement of ancient Asian continental crust that did not exist under Kohistan before the suture formed. The 50 Ma age for Shyok suturing against the then-active Karakoram Andean arc fits well with the extension of the suture beyond the eastern end of the Kohistan-Ladakh block to join the precisely dated ca. 51 Ma Yarlung–Tsang Po suture between India and the southern (Lhasa block) margin of Tibet, which at that time was also occupied by an Andean arc, the Gangdese arc.

Remote sensing and geochemistry for detecting hydrocarbon microseepages

This work tests the hypothesis that chemical and mineralogical alterations in rocks and soils are related to hydrocarbon microseepages above some of the major oil fields. In this study we used Hyperion hyperspectral imaging sensors to map alterations that appear to be associated with hydrocarbon microseepages in the Patrick Draw area of Wyoming. Our mineralogical, geochemical, and carbon isotope data support the presence of hydrocarbon microseepages. Satellite imagery training classifications defined by areas of hydrocarbon microseepage have resulted in the successful identification of the areal extent of an anomalous area. Geochemical characteristics of samples that define this anomalous area were then compared to the remaining non-anomalous samples using X-ray diffraction (XRD), reflectance spectroscopy, and carbon isotope techniques. XRD analyses demonstrated the increased presence of feldspars in non-anomalous samples compared to anomalous samples. Spectroscopy results demonstrated higher proportions of clays within the anomalous samples compared to non-anomalous samples. The δ 13 C values range from −2.88‰ to as low as −45.32‰, indicating hydrocarbon sources. These methods may provide a foundation upon which further hydrocarbon exploration techniques can develop.

Lidar mapping of faults in Houston, Texas, USA

Over 300 active faults intersect the Earths surface in the Houston metropolitan area on the northern edge of the Gulf of Mexico basin. These surface faults have caused damage to roads, pipelines, and buildings. We used light detection and ranging (lidar) data to more accurately map faults in the Houston area. We developed a grid-refinement algorithm for processing the raw data to generate a 1.5-m–resolution digital elevation model (DEM). The refined grids allowed for better spatial resolution of the scarps and in some cases revealed features that were not noticed on the original DEM. Hillshading proved the best method for identifying faults that were then examined in the field. Most of these faults are part of a larger, regional, down-to-the-basin fault system along the northern Gulf of Mexico; this work complements studies of Houston and Gulf Coast neotectonics.

New strike-slip faults and litho-units mapped in Chitral (N. Pakistan) using field and ASTER data yield regionally significant results

Several image‐processing techniques were used to map the Chitral area, northern Pakistan. In this area, the worlds three greatest mountain ranges, the Himalayas, the Karakoram, and the Hindukush blocks, merge together. The area is extremely rugged; local relief is more than 2500 m. Many peaks are higher than 5000 m and Tirch Mir, 12 km north of the mapped area, is 7702 m. ASTER imagery and a digital elevation model developed from the ASTER data are used for decorrelation stretches, principal components analyses, and spectral angle mapper (SAM) classifications. These image‐processing techniques were used to characterize the lithology and structure of the area. This study produced the most current geologic map for fully understanding the interaction between the Kohistan, western Karakoram, and eastern Hindukush blocks along the Shyok Suture and the Tirch Mir Fault. We utilized previously published geologic maps and fieldwork of the area to validate the image classifications. We have discovered two new strike‐slip faults, and recent earthquake activity along the faults indicates that the faults are active. Recognition of these faults has potential tectonic significance, as they may be associated with the Chaman Fault – a major transcurrent fault linking the Indian plate with Pamir. Furthermore, we have discovered an anomalous mineralized zone and further work may uncover new mineral deposits.

Geoinformatic approach to global nepheline syenite and carbonatite distribution: Testing a Wilson cycle model

The association of alkaline igneous rocks and carbonatites (ARCs) with intracontinental rifts has long been recognized. Deformed alkaline rocks (such as nepheline syenites) and carbonatites (DARCs), which form a small subset (<10%) of ARCs and carbonatites, have become a focus of attention since it was recognized that in some places they are associated with suture zones marking locations where oceans have closed. The association of DARCs with sutures can be readily understood in terms of the operation of the Wilson cycle in the opening and the closing of ocean basins. The Wilson cycle hypothesis for the origin of DARCs has been tested for the Proterozoic of both Africa and India. For Africa, an additional hypothesis that we have also tested is that ARCs in intracontinental rifts represent magmas made by partial melting of DARC material in the underlying mantle lithosphere. A limitation of the African and Indian studies is that they are local and regional. Only a worldwide geoinformatic study can fully test the two hypotheses. If one of the hypothesis can be invalidated that will have profound petrogenetic signifi cance. In this study, we describe our ongoing geoinformatic work on the worldwide distribution of ARCs and DARCs, including the databases, techniques, and operating procedures. To illustrate our approach, we report on a local analysis that we have carried out on the ARCs and DARCs of the Kola Peninsula in Arctic Russia.

Lithological mapping of Bela ophiolite with remote-sensing data

Bela ophiolite (BO), the largest ophiolite in Pakistan, is important to our understanding of the western margin of the Indian plate, particularly the collisional history of Indian and Eurasian plates. However, it is located in a remote location and has not been extensively studied. For example, no detailed geological map for this area exists. In this article, remote-sensing data were processed by different techniques that were selected based on reflectance spectroscopy data and compared with a local geological map for the upper unit of BO. False-colour images (Landsat Enhanced Thematic Mapper plus (ETM+) bands 7, 4, 2 in the red, green, blue (RGB)), colour-ratio composite images of Landsat ETM+ data (5/7, 5/1, 5/4 in the RGB), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data (4/5, 6/7, 3/4 in the RGB) and mafic index images are used to discriminate different lithologies. Our results are consistent with published local geological maps. Based on these images and field data, we created a detailed geological map of BO. Two types of basalts are differentiated, and an ultramafic body around 66° 15′ E, 26° 39′ N is recognized for the first time in the lower unit of BO. Integrating all the available data, we suggest that BO formed in two episodes; the upper unit is a classic ophiolite sequence and is younger than the lower unit. First, it was obducted onto the lower unit, and then the two units obducted as one onto the Indian continental edge.

InSAR observation of the strike-slip faults in the northwest Himalayan frontal thrust system

The Indo-Asian collision formed a series of north-dipping Cenozoic thrust faults in the Himalayan region, some of which are still active. The frontal thrust system in the northwest Himalayas has signifi cant lateral variation, with the appearance of a reentrant along the thrust front. In the transfer zone of the structural reentrant, strike-slip faults dominate the deformation. To better understand the activities of the strike-slip faults in the northwest Himalayan frontal thrust system, interferometric synthetic aperture radar (InSAR) was used to measure the slip rate and direction. Radar image pairs with long time intervals are preferred to monitor the cumulative displacement caused by a low slip rate along the faults. The measurement across the Kalabagh fault zone indicates that ongoing slip rates are lower than those previously measured by conventional methods. The activities along the Kalabagh fault have segmental characteristics. Current deformation at the north segment mainly concentrates on the splay faults east of the Kalabagh fault. The southward decrease of displacement in the eastern fault block suggests that active deformation is mostly accumulated within the Potwar Plateau‐Salt Range thrust wedge instead of at the thrust front. This work indicates that the Kalabagh fault zone linking the thrust fronts of the Salt Range and the Surghar Range plays an important role in accommodating the deformation in the Himalayan frontal thrust system caused by the Indo-Asian convergence.

Newly discovered mud volcanoes in the Coastal Belt of Makran, Pakistan—tectonic implications

The Makran accretionary wedge has a much larger number of mud volcanoes then those reported earlier. Using high-resolution satellite images, over 70 active mud volcanoes were identified. These mud volcanoes occur within a well-defined zone; we call it the Makran zone of active mud volcanoes (MZAMV), which is parallel to the regional trend of the accretionary wedge. Mud volcanoes within the zone occur as clusters, which form linear belts parallel to the regional thrusts associated with anticlines. The MZAMV zone also includes the offshore mud volcanoes occurring in the shallow shelf area, including the recurrently emerging mud islands. Several occurrences of thick deposits of old mud volcanoes (Pleistocene or even older) are also present within this zone, which also display recognizable features that are characteristic of the fossil mud volcanoes. We propose that the MZAMV developed and evolved in response to the continued compression within the Makran accretionary wedge, which in turn, is a response of the subduction process. Mud diapirism has been an ongoing phenomena since Pleistocene or even earlier. The events of enhanced mud extrusion in mud volcanoes and/or emergence of island(s) have relevance with seismic phenomena and, therefore, may be closely monitored.

Grenville Province and Monteregian carbonatite and nepheline syenite distribution related to rifting, collision, and plume passage

Stimulated by the recognition of a rifted continental margin to pre-Grenville Laurentia, we interpret the deformed alkaline igneous rocks and carbonatites (DARCs) adjacent to that margin in the Bancroft domain of Ontario, Canada, to be rocks initially erupted as alkaline rocks and carbonatites (ARCs) in an intra-continental rift. When an ocean began to form, rupturing Laurentia on the site of that rift, the newly formed Laurentian rifted continental margin contained ARCs that had erupted into the intra-continental rift. Later in a Wilson cycle of ocean opening and closing, those ARCs became DARCs during a collision that sutured the Grenville province composite arc belt and Bancroft domain rocks against the margin of Laurentia on the Central Meta-sedimentary Belt boundary thrust zone. Using this interpretation we show that DARCs of the down-dip Bancroft domain suture zone in the mantle at a depth of ~100 km are likely sources of the Early Cretaceous ARC rocks in the Monteregian province.

Geomorphometric features and tectonic activities in sub-Himalayan thrust belt, Pakistan, from satellite data

The sub-Himalayan thrust belt is an active thrust wedge which progresses southward over the north-dipping Indian plate. The north-south compression resulted in severe deformation of sedimentary rocks in this belt. Distinct thrust geometries and topography have evolved under the interaction between tectonic and erosional environments. To better understand the relationship between tectonics and topography, A Digital Elevation Model (DEM) derived from Shuttle Radar Topography Mission (SRTM) data was used to extract the geomorphic and drainage features. Based on comprehensive analyses of topographic relief, drainage density, and drainage patterns, nine topographic units were identified. The thrust wedge was divided into three physiographic assemblages with apparent lateral variations. These units match up with the interpreted main structures from the Landsat Enhanced Thematic Mapper Plus (ETM+) images and published geological maps. The relationship between geomorphometric features and tectonics indicates that structural activities primarily control the topography in the sub-Himalayan thrust belt. Topographic features are indicative of tectonics in the young tectonic regions with low elevation.